Interview with Sarah Kraak (continued)

Conducted October 2007 to April 2008 by Paul Cooijmans

[Back to the first page of this interview]


The fish you have studied is called Aidablennius sphynx. However, it was named differently before. Why, when and by whom was its name changed? And why are there two references to Egypt in it: Aida (a Verdi opera that plays in Egypt) and sphynx (the lion sculpture near the Great Pyramid)? Incidentally, it is remarkable that when searching for images of this fish in a popular Internet search engine, your own photo tends to appear on the first results page.


The science of taxonomy and especially the rules for the naming of species are very obscure (there is the International Commission on Zoological Nomenclature and its International Code on Zoological Nomenclature). I guess only the insiders - these are the handful of scientists who study the taxonomy of a particular group of species - will ever understand why scientific names change. I was once involved in the study of the taxonomy of a group of snails (Littorina spec.). There was a host of scientific articles arguing why one species should be split up into several or why several species should be lumped into one. This is often based on anatomical characteristics, habitat, and geographic range of the species, and paradigm shifts between lumping and splitting. But the real can of worms here is that the naming is according to a system of "the first name ever given to the species gets priority". So one is not allowed to give a new name to exactly the same entity as was named otherwise before. Wars are fought over these issues. But this is not my type of thing. With my blenny I was not at all involved in the study of taxonomy (which I find totally uninteresting) so I never sought to find out why the species was renamed. I guess the reason is only interesting for insiders. It may be more interesting for outsiders that there are the two references to Egypt in the name.

In Verdi's opera, Aida waited in a cave for her lover, a king who was sentenced to death by being buried alive in a cave underground. In the blenny, the male waits for his lover in a cave...

Incidentally, a search on the Internet ( indicates that aida does not refer to Verdi's opera (I had not expected it to refer to that in the first place...). Apparently, its etymology is from the Greek aida or aides, referring to the Hades, the gods of hell. I don't know why the name of the fish refers to hell - the fish is beautiful and butterfly-like. Blennius is from the Greek blennios, meaning mucus. This is easy to explain. The fish family of which the English name is "blennies" and the scientific name is "Blenniidae" is called "slijmvissen" in Dutch and "Schleimfische" in German (this would be "slime fish" in English). These fish are called slime fish because they don't have their skin covered with hard scales as most fish do, but only with a layer of slime/mucus. I haven't been able to find out why the fish's species name is sphynx.


Do you think the fish you have handled are capable of suffering? And if so, do you feel the suffering caused to some individuals while studying them is acceptable in fundamental research without direct practical applications?


The short answers are: Yes, I think they are capable of suffering, and no, I don't feel that this suffering is acceptable. So I live with the burden of being guilty of having caused unjustified suffering. This does not feel pleasant but I live with it. And I would do the same thing again. It belongs to one of the tragedies of life: knowingly committing 'crimes' or 'sins' without any intention to stop. It is an almost unbearably painful feeling.

There is a medicine to alleviate that pain, 'though: I can argue and reason for hours and hours and give numerous justifications for my behaviour. They would sound reasonable and they would probably be accepted by most people - after all, my 'crime' of causing suffering in fish while doing science is entirely legal. But the fact remains that I myself don't find them really acceptable, and therefore also the pain remains.

Most of my work did not involve killing fish. Nor did it involve intrusive operations. I guess the suffering I caused was really minor. Often the fish would live in an aquarium, which might have been boring to them. On the other hand, the situation is of course quite comfortable, without the risk of predation and always having enough to eat.

I remember one time looking into an aquarium (not of one of my own experiments, by the way!) with a single male stickleback in it. The aquarium contained nothing else, no shelter, no plants. The male fish was in breeding condition, which had been induced and was maintained by two lab conditions, namely the water temperature and the day length. Under these circumstances male sticklebacks usually search for plant or other material for nest building, and subsequently attract females to mate with. This male was - it seemed desperately - searching for nesting material, which it couldn't find because the aquarium was completely empty. I inferred "desperation" because the male was picking up minute pieces of debris and handling them as he would nesting material, but without the slightest success towards the completion of a nest. He was just making all the necessary movements.

I then realized that this fish was programmed, as a result of evolution by natural selection, to DO JUST THAT ONE THING under these circumstances: build a nest. The fish must have been very frustrated being so strongly driven to do something without the right basic material whereby his actions were not rewarded with a satisfactory result (= a nest). I call that suffering. Of course the animal does (probably) not have any conscious faculties to be aware of its frustrations. But, I believe the faculty of suffering must have evolved because it is adaptive. An animal should be programmed such that it has a powerful avoidance response to situations that are averse to its survival and reproduction. For example, a bacterium (= an organism without the slightest thing such as a brain or nervous system) displays an automatic response to move away from higher concentrations of toxic substances because by that response it avoids those substances. The sensitivity towards such substances must "feel" to the bacterium like "suffering" in order to make the response urgent as needed. The same is true for a male stickleback who is urged against all challenges (e.g. the risk of predation or starvation, not being able to find proper nesting material nearby) to do what it takes to build a nest: if it does not succeed it "suffers" in order to urge him on. Therefore, I strongly believe that animals in captivity should be allowed to do what they are naturally urged to do, otherwise they suffer. Sometimes, all it needs to prevent suffering is, for example, to expose the stickleback to different temperatures and/or day lengths, such that the animal is not driven to build a nest and does not have to be frustrated by failure. Or, of course, one can provide the animal with some material to build a nest; sewing threads will suffice.

Sometimes the work involved killing fish. When I had to kill sticklebacks together with my husband (who is a biologist and an artist - I met him through field work on sticklebacks) we used to "pray" for the fish just before the act of killing.

[Beat] [There is also pink - painting by the artist and husband Beat]

The handling of the fish was another thing. Sometimes, for example for measuring, it was necessary to hold the fish for an amount of time (up to a minute) out of the water. I imagine this to feel as unpleasant as it would be for me to be held for a minute with my head under water. At the same time I would have to constrain the fish in a certain position, for example along a centimetre ruler. Or I would have to sting a needle into the fish for injection of a colour dye under the skin (comparable with setting tattoos). These, however, are short term sufferings. Personally I myself can handle short suffering much better than continuing suffering. I can deal with short pain; so why can't my fish?

Recently I read something really thought-provoking on the subject of suffering in the brilliant book Breaking the spell by the brilliant philosopher Daniel Dennett. Apparently, anesthesiologists sometimes use amnestics to wipe out postsurgical memories of pain experienced by insufficiently anesthetized patients during surgery. After having read that I was wondering, thinking: does suffering not matter if one does not remember it afterwards? Imagine you are suffering hellish pains - but afterwards you have no conscious memory of those whatsoever. Then there is nothing to be upset about anymore, no reason to feel bad - is there? I was thinking, is this what animals experience? Can animals suffer in the moment - but have no conscious memory of it afterwards? In that case, do they really suffer? On the other hand, for sure pain, stress, and frustration have a lasting effect on animals (including humans) even if they can't remember anything consciously. The body does have a memory of these events, just not a conscious one. These effects are mediated through changes in the physiology, e.g. levels of corticosteroids. As a biology student I learned from Professor Jaap Koolhaas (University of Groningen) that a rat will never be the same rat after having experienced losing a fight. Another interesting fact I just learned from the Dutch newspaper for biologists Bionieuws (15 March 2008): If caterpillars learn to associate a specific odour with an electrical shock, the individual will still avoid that odour as an adult butterfly after metamorphosis. Thus, I believe that animals could become nervous wrecks after painful experiences, even if they have no conscious memories of those.

Then, there is the other side of the equation. Is the imposture of suffering compensated by the importance of the scientific research? In applied research the reasoning is so much simpler than in pure (fundamental) research. One can argue, for example, that it is ethical to let one hundred monkeys suffer in an experiment that will finally lead to the cure of a certain type of cancer. But can one argue that it is ethical to let even one stickleback suffer in an experiment that gives insight into the nature of nature? Some people argue that the fundamental insight might at a later stage in time lead to knowledge needed for applications. But what if it isn't? Or what if it is, but if that is not the motivation that drives me? What if it only serves to still my curiosity about the nature of nature? Stilling the hunger for understanding and insight is a natural desire, after all. Some of us would be suffering if we were frustrated in our attempts to still part of that hunger. But how can we balance the equation? In what units do we have to measure the suffering? And how many people should be able to enjoy the fruits of my studies to offset the costs of suffering of the fish? Is my pleasure alone enough? Or do I have to be sure that my studies were enjoyed by a minimum number of people?

Well, I don't know and nobody really knows. I do what I do. And many people agree with what I do. And most people don't think I should be in prison for what I do. And I am happy that I don't have to decide on that.

Actually, I do not like to prescribe what one (we, humans) should or should not do. I just hope that scientists and other intelligent experts will go on providing relevant information on suffering and that animal liberation action groups will also go on making their point. With increasing awareness - by input from both camps - we will have to accept dynamic norms and values: what is acceptable today may not be acceptable tomorrow. (Note: I am not a relativist. I only think that I have not yet found absolute truth nor absolute goodness.)

By the way, I find the suffering of a gazelle being killed by a lion also unacceptable, as I find the suffering of a starving lion not succeeding in catching a gazelle. But, as you may counter, lions and gazelles are not moral agents, whereas I am.


At some point you stopped doing behavioural research and began working in fish stock assessments. Was this a satisfactory change? And what is your view on fundamental research; that is, research aimed at gaining insight, understanding and knowledge, rather than at applications?


That happened in the year 2002, when I was 40 years old. The change was far from satisfactory. Instead, it was very traumatic indeed.

At the practical level it was extremely annoying that the quality standards of applied science were so much lower than those for fundamental science. Inside I was screaming of shock at what I saw in terms of the quality level that was judged as acceptable by everybody around me in my new job. As if science with an applied purpose has to be only cheap, efficient, and commercially viable, whereas fundamental science is a hobby, a vocation, a passion, a way of life. For the latter no quality standards are good enough.

But it was far more traumatic on the level of the soul. I had invested my identity and my life purpose in fundamental research.

When I was an adolescent I had been going through deep quests for the meaning of life. I found no justification for living (this, incidentally, by no means implied that I did not like living - I just did not think there was any rational justification for it, and that seemed all that mattered). Furthermore, I judged no occupation worthwhile or ultimately justifiable. All occupations that involve the production of goods or services were not living up to my standards for justification. How could it be justifiable to produce stuff for the maintenance of life, if life itself was not justifiable?

I can recommend any intelligent adolescent finding oneself in my position to read some of the philosopher Arthur Schopenhauer's writings. Arthur Schopenhauer Arthur Schopenhauer is the best remedy against depression and nihilistic thought. And that is because he will not try to ease your pains with sweet little lies, fairy tales, and illusions. He will just mercilessly bring you further down into nihilism. He is the greatest nihilist of all. He will argue brilliantly that life is no good, that suicide is the only choice that makes rational sense, that in life there is only suffering, and that after reaching one goal of ridding oneself of suffering the next road of suffering will commence, and so on and so forth.

Anyway, the adolescent me read Schopenhauer and enjoyed him being "on my side". And then, hidden between his lamentations I found the little gem that saved my life. (Incidentally, recently I discovered another secret gem in Schopenhauer, the nihilist of all nihilists.)

The gem I found in Schopenhauer's writings when I was an adolescent I reproduce below in German and in Dutch translation. I have no English translation. [English translation included below by interviewer.]


Es werde musiziert oder philosophiert, gemalt oder gedichtet - ein Werk des Genies ist kein Ding zum Nutzen. Unnütz zu sein, gehört zum Charakter der Werke des Genies: es ist ihr Adelsbrief. Alle übrigen Menschenwerke sind da zu Erhaltung oder Erleichterung unserer Existenz; bloss die hier in Rede stehenden nicht: sie allein sind ihrer selbst wegen da und sind in diesem Sinn als die Blüte oder der reine Ertrag des Daseins anzusehn. Deshalb geht beim Genuss derselben uns das Herz auf: denn wir tauchen dabei aus dem schweren Erdenäther der Bedürftigkeit auf.]


Of het nu om musiceren gaat of om filosoferen, om schilderen of om dichten - een werk van het genie is niet iets dat ergens toe dient. Nutteloosheid is karakteristiek voor de werken van het genie, het is er de adelbrief van. Alle overige werken van de mensenhand zijn er voor de instandhouding of vergemakkelijking van onze existentie, alleen die speciale waarvan hier sprake is zijn dat niet. Het zijn de enige producten die er uitsluitend omwille van zichzelf zijn en in deze zin zijn ze op te vatten als de bloesem of als de zuivere opbrengst van ons bestaan. Bij het genieten ervan gaat dan ons hart open, want dan duiken we op uit de aardse dampen van onze behoeftigheid.]


Whether music or philosophy, painting or poetry - a work of genius is not a thing for use. To be useless, belongs to the character of works of genius: it is their patent of nobility. All other works of humankind are there for the preservation or facilitation of our existence; only those raised here are not: they alone are there because of themselves and can in that sense be considered the blossom or the pure yield of our existence. Therefore in enjoyment thereof our hearts open up: for with that we emerge from the heavy earthly vapour of destitution.]

From Die Welt als Wille und Vorstellung II, Kap. 31 (III, 444). Dutch translation from De wereld een hel. [English translation by Paul Cooijmans.] Bold letter format is my own emphasis.

The secret now seemed to be that the best occupation to devote one's life to is exactly the opposite of trying to be useful and productive. The only extra, the only net benefit, blossom, yield, or harvest that life has to offer is doing exactly those things that are not useful or directed towards maintaining life: Art. Art, in the broad sense, also includes philosophy for the sake of philosophy and science for the sake of science. l' Art pour l'art.

Doing this - art or science - is also an act of rebellion against life, but not a destructive one such as suicide! Biologically speaking, life is always and only concerned with maintaining and multiplying itself in an endless chain - all traits of living organisms attest to that. We, as free human beings, are the only ones who can choose to step out of this natural necessity and do useless things.

Are we...? On the other hand nature itself, of course, displays lots of seemingly useless traits, such as peacock's tails and peahen's preferences thereof (or the bower bird's bower and the female's preference thereof), that have arisen by the process of sexual selection, also known as signal selection. Art is perhaps one of those useless natural traits.

Earlier in this interview I spoke of one of the books that influenced me most (The selfish gene by Richard Dawkins). The book that is at the top of that list, however, is De wereld een hel (this translates as 'The world a hell'), an anthology of writings by Arthur Schopenhauer. That book really spoke to my heart and found a mirror.

The insight I gained from that book fitted so well with the only thing I had always been: a scientist. My whole life is and has always been - as you phrase it - "aimed at gaining insight, understanding and knowledge, rather than at applications". No more and no less it is what I live for.

One thing I have to admit: I would rather have been an artist than a scientist. Being an artist seems to me even higher and more evolved. But my talents and personality clearly made me go for science. That is what I am. Art is for my next life. Or maybe not.

So, yes, I am bitter about that involuntary change in my life. And, science for science and l'art pour l'art represent the only added value of life.


Your work involves assigning fish quota. Do you think this is necessary; would any fish species actually die out if you allowed unlimited fishing?


The answer certainly is, yes, of course species would die out if we would hunt them with no limits. It has happened in the past. And not just with fish. It is commonly thought that various big mammals have gone extinct when early humans became efficient hunters. There is a nice popular science book by the Australian zoologist Tim Flannery called The future eaters in which the author tells the story of the impact that humankind has had on wildlife, told from an ecology point of view in which humans are part of the ecosystem as ecological agents. According to this book not only big mammals died out as a consequence of hunting, but also bird and fish species that lived on or near islands were hunted down to extinction soon after these islands had become colonized by humans. And these stories are about "primitive" human hunters. Nowadays fishing involves high tech and is operated with enormous fishing power.

The latest feat in fishing history is the well-known collapse of the cod stock off the eastern coast of Canada. Although the species is not extinct biologically, it became commercially extinct in the early 1990s as a result of over-fishing. Despite a fishing moratorium that has been in place ever since the stock's collapse, the population never recovered. This is thought to be due to irreversible changes in the ecosystem following the decline of the cod population.

What does it mean when I say that a species is not biologically extinct but commercially extinct? This means that individuals of the species still survive, but at much lower numbers and densities than before, and that exploitation of the stock by fisheries is not viable because the catch rate (catch per unit of effort) is too low.

As an intermezzo I have to comment briefly on my use of the term irreversible. The Dutch scientist Martin Scheffer has argued that ecological systems can have two stable states. A system can gradually change and then "pop" into the other stable state, after which it cannot come back to the original state just by bringing back the original conditions. The conditions have to be changed back much further than merely to those present at the time when the system "popped" into the alternative state in order to let it "pop" back into the original state. And that may just not be feasible. In that sense the change of the ecosystem after the collapse of the cod stock is deemed irreversible.

[Changes are sometimes irreversible]

All in all, the famous Canadian fisheries scientist Daniel Pauly documented that the percentage of fish stocks that are overexploited and threatened with collapse has increased from 0% in 1950 to more than 60% in 2000 (with more than 25% of the stocks having crashed) (Ambio Vol. 36, No. 4, June 2007).

The problem with over-fishing seems to reside in what is called The Tragedy of the Commons. In fisheries management it is overly clear that this tragedy is in operation. The Tragedy of the Commons states that whenever several individuals make use of a common resource, each individual is tempted to use more than his share. In this context a "share" could mean the share of such a size that if all individuals would take that share the resource would be exploited sustainably. If an individual takes more than his share, the resource is overexploited and may give lower average yields. But for each individual it pays more if he himself is the one who takes more than his share than if someone else does. This is because although in both cases the individual will suffer from the lower average yield, in the first case he gets more than in the latter. Because each individual may expect that the others will take more than their share, he is tempted to do so himself. And almost all people give in to the temptation in such a case (otherwise one would be the "sucker"; the latter is a common term in a related Games Theory problem The Prisoner's Dilemma: the sucker's payoff).

What I personally find the real tragedy, is that humankind has been clever enough to invent the technology to increase, e.g., fish catch efficiency such that we are able to wipe out entire fish stocks - or fly to the moon for that matter - but has so far been unable, unfortunately, to counter The Tragedy of the Commons. And this is so despite the fact that research is being done investigating under what conditions humans are more inclined to be "nice" (= cooperative, social). My belief is that if governments would decide on policies that create these conditions, the world would be a nicer place, where, for example, resources would be exploited more rationally and hence sustainably, or where people would be less inclined to cheat. And all this is possible, without having to change human nature! We would just take human nature as it is: selfish and social (= cooperative, altruistic, committed), depending on the conditions.

What kind of conditions should be created? I am not a social scientist, but I believe the work of Elinor Ostrom is important in this context. I know something about Game Theory (e.g. The Tragedy of the Commons and The Prisoner's Dilemma) and how it operates in biology, for example in evolutionary theories of animal behaviour. What I know suggests that if individuals interact repeatedly with familiar other individuals (as opposed to strangers) they are more inclined to be "nice". For example, employers could thus create loyal employees by retaining them for long periods instead of considering workers a replaceable work force. I am actually surprised that such ideas are not more applied, by policy makers such as governments or employers.

For fisheries management I and my colleagues are working on it. For the time being it seems necessary to enforce quota.


Are there specific problems you have encountered in your career or social life, resulting from the fact you are a woman working as an exact scientist? And why do you think there are so relatively few women in exact science?


In some aspects my brain appears to be working in ways that are thought to be more typically male. looking feminine enough These are especially the qualities I use professionally: my mind is analytical, logical, systematic, more focused on contents than on form - but also creative and original [Sarah thinking]. Moreover, I am not a very "mothering" or caring type of person - I prefer to let myself be cared for! But in other respects my mind has feminine qualities as well, and I am feminine enough in my looks.

Although it is very hard to pinpoint to any problems caused by how people treated me, the state of affairs described above may have caused some confusion, not in the least to myself. Starting with the latter, when I was a child I was vaguely aware that how my mind worked was not very girlish - I mean as is expected from a girl. Especially during my puberty this caused some friction. As a heterosexual girl it was quite important to present my feminine sides, but I also wanted to compete with the boys in the intellectual realm. In a way this has been the case ever since.

It sounds too dramatic to say that I feel like a male mind in a female body. In fact, to me there seems to be nothing problematic about me, about the combination of my mind with all its various aspects and the gender of my physical appearance. This is who I am, and to me all aspects feel quite integrated as one whole. It is only with respect to expectations from the outside world that there seems to be friction. The discrepancy between part of my mind and the rest of me only exists with reference to the standards of the outside world.

As I said, I can imagine that the people around me are confused. People I meet may respond to the fact that I look like a woman and hence treat me as a woman and just ignore the masculinity of how my mind works. In such a case I may feel unrecognized and unappreciated. Others may disapprove of it, the same traits being acceptable in a man but not in a woman. "A man who argues rationally is clever, a woman doing the same is hard and cold"; such observations have often been made by students of women's studies and feminists. Yet others may feel threatened by it. Men may feel threatened because they experience me as a competitor, yet they don't know how to compete with a woman. Women may feel threatened by it for other reasons.

Moreover, to all of us, also to me, gender is a very salient feature of human beings. It is almost impossible not to react to gender when meeting a person. Recently I noticed that I react differently to female than to male bus drivers, physicians, shop sellers, etc. Therefore I find it almost unimaginable that throughout my career I have been treated similarly as men are treated.

All in all, I have often felt I had to prove harder than men that I am "one of the guys" ("guys" here referring to exact scientists). Below you refer to one of my favourite books, Gödel, Escher, Bach by Douglas Hofstadter (incidentally, Hofstadter doesn't like the word "guys" being used for females...). The book contains intellectual conversations between fictive characters such as Achilles, Mr Tortoise, and Mr Crab, which are all male (except for the ant colony Aunt Hillary). In my internal world I always felt to be one of them, but in relation to the outside world I almost never felt recognized as such.

In the world of fundamental science I felt more treated as "one of the guys" than in my present job's institute. In the latter I more often feel unrecognized, unappreciated, that people disapprove of my masculinity, and that they feel threatened by it. But as I said, it is hard to pinpoint to any problems specifically caused by that. I also think, but I cannot prove it, that my career has been less successful than it could have been otherwise because of the mentioned discrepancy.

Another thing is of course that I was confronted with the question "do I want babies, a career, or both, and if the latter, how?" whereas men with my qualities are not. In that respect I would have liked to be a man who is married to a lovely housewife caring for my kids while I go off doing interesting things professionally. I almost found such a wife... but not.

Then you ask why there are so relatively few women in exact science. First of all I would like to say that there are most probably biological and social reasons. It is often said that men and women differ with respect to their faculties in an innate way. While I haven't personally read any primary scientific literature on this (that provides convincing evidence, e.g. rules out early socialization), I believe that this may be the case. Indeed, as a biologist and researcher of sex determination, sex differences, and sexual behaviour, I am fully aware of the existence of innate differences between men and women. I just haven't personally seen any scientific evidence of whether or why any sex differences in, e.g., ambition to reach the top, affinity with abstract thinking versus interest in social interaction, intelligence, etc., would be innate.

In any case I believe that social factors play a role as well. One of them is that there aren't enough role models for us. When I was a young student there was only one female professor at the faculty of biology. She was an unmarried woman and she looked like the stereotype of one. Not someone you would like to be. In contrast, I often saw men who were role models for how I would like to be. Even recently I saw a television interview with Carl Popper, a philosopher of science, and I thought I would like to be like him. Also in newspapers or other media, the standard scientist seems to be a "he" having a wife.

The issue is quite complex. I read in the Dutch gratis newspaper Spits (late 2007) that the proportion of women among lawyers and solicitors is increasing. At the same time fewer and fewer men are attracted to go to law school, apparently because the social status of these professions is diminishing since so many women practice them! I think the same has happened with the profession of family doctors (GPs): in the past the profession had very high status, but since more and more women have begun to practice it, its status has dropped down. From this I conclude that causality in these matters is complex.

Another social factor that I think may be relevant is the existence of "old-boys networks" and the non-existence of "old-girls networks". Because I am a woman, I am not in such an "old-boys network", so I don't really know what they are and how they function. I only know that there is a lot of talk about them, stating that in these networks men help each other to get influential positions. Recently I talked to an old friend and colleague, who is a female scientist. I have known her for about 25 years now; we met as students. We both admitted that we don't really know what the mysterious "old-boys networks" are, and that we do not have the equivalent "old-girls networks", and that we have no idea how we should proceed to set one up. Also we are too rare to have a network. Anyway, I am afraid that men are not really aware of how they benefit from their networks because they take them for granted, and thus they don't recognize that we don't have these benefits.

Another possible social factor is that men as well as women (!) tell (other) women that we don't need to be so ambitious, that we don't need to want to get to the top. Recently I was in a therapy group for women who got burnt-out in their job. The female therapists kept on telling us that we should be nice to ourselves and that we should not put such high demands on ourselves, that we don't have to be perfect. I was wondering what burnt-out men get told by male therapists. I felt that my ambitions were not recognized. Or is it really unhealthy to have ambitions?

Anyway, even if genetic differences in personality traits exist between men and women, it is often overlooked that although men and women may differ on average there may be a strong overlap. Take body height. Men are on average taller than women. However, the two respective normal distributions of body height of men and women overlap widely. Pick any random Dutch person that is 1.75 meters tall. From this information only it is impossible to say whether the person is a man or a woman. Also, there are many women taller than many men, and there are many men shorter than many women. The same is true for running speed. Men run faster than women on average. But there are many women running faster than many men. And, the same is true for IQ or other psychometric measures as well. Society just has to accept and accommodate for the existence of women with extraordinarily high IQs and give them equal opportunities to men with similar IQs.

Whether through socialization or through biological differences, it is a fact that many women who are in principle suitable for a career in the exact sciences step out or accept a less successful career when they give priority to raising babies; it may just be too difficult for many to work in exact science alongside being a mother. This would rarely play a role for men, although they may step out for different reasons.

I have to admit that when I was occupied answering this question, something curious happened. Before working on this interview I had never actually considered the question - why there are so relatively few women in exact science - at a very serious level. I had held some diffuse private thoughts about it, but I was not convinced enough about anything - owing to lack of factual knowledge - to even call my thoughts "opinions". I would certainly never have written them down for a public without further investigation. I would at most have presented some arguments for discussion among friends. Being a scientist by nature, I find it impossible to maintain any opinion without considering the facts and ordering them in a consistent argumentation, or otherwise build at least an argumentation pending the facts.

Your interview challenged me to dive into the subject and present at least some non-trivial food for thought. First I started to build an argumentation, and then I tried to acquire some information, e.g. on IQ distributions of men and women. During this process - you may remember that I had some private correspondence with you in an attempt to get some facts from you - I found out more and more that the subject is a can of worms. There are no final facts that come in simple packages. The answer to the question should deal with the abilities and personality traits that make a person suitable for the exact sciences, the distribution of these abilities and traits among men and women, and to what extent differences in these abilities and traits are innate or shaped by socialization. These are many questions to which there are no easy answers. Having had a brief look at the extensive scientific literature on the subject it seemed to me that I would only be able to give an informed opinion that would be of any value to you and your readers - above the level of twaddle - if I would undertake a serious scientific query. That would take several months of full time work.

Fortunately for me, and I hope that this is also acceptable for you, I came across a web site where someone who I trust entirely - because he is a scientist, and even a scientist whose style corresponds to mine - had to answer the very same question! This person, Steven Pinker, a researcher of the origin of language, had apparently been challenged to answer the same question: why there are so relatively few women in exact science. From his answer it appeared to me that he had done the scientific query I would have found necessary to give any comment of value. I read his answer and agreed with almost everything he expressed. I sincerely feel that there is nothing of value that I could add to his thoughtful exposition without studying the subject myself for months (which has no priority for me). Therefore, rather than summarizing his lengthy, well-informed, and balanced answer, I refer you to the web site where he expressed his view: His exposition would be my answer to your question if I had taken the time to investigate it. A better answer I cannot give, or at any rate not an answer that would have taken me a shorter time than a couple of months to research.

Incidentally, as you will see, Steven Pinker was asked to express his opinion in a debate. The web site contains a transcript of the entire debate, also of the view of the woman, Elizabeth Spelke, opposing him. While knowing nothing on the subject myself I have to grant that Spelke probably also presented a lot of factual knowledge in favour of her case. However, in fact I did not really see how her arguments opposed those of Steven Pinker, which were in my opinion all-encompassing. Secondly, her arguments and her style of argumentation were less convincing to me. Despite my lack of knowledge on the subject I do have the ability to judge other people's reasoning. Thus, in the end you are getting a bit more of an informed opinion from me than the cowardly "find out your own opinion from the literature". My answer based on my expert judgement of scientific reasoning is: "I recommend to go for what Steven Pinker has to say about it on that web site".

One more thing I have to say on this. In so far as social aspects are relevant, we do not have to accept them as static. If society "decides" to shift patterns of socialization, the "natural" tendencies of men and women to end up in the exact sciences may change. An example would be that universities decide to favour women in case the male and female applicants for tenure positions in the exact sciences are of similar quality. The increase of the proportion of women in science thus achieved may in turn influence the ambitions and propensities of the next generation of girls - to the extent that these are influenced by socialization rather than biology. Politics will have to decide whether such a shift would be desirable.


Do you have scientists in your family background?


Yes, both my mother and my father are.

My mother is a biologist as well. When I was a kid she did research on sex determination in frogs and toads, on the taxonomy of a gastropod family, and on the evolution of our species Homo sapiens. She is also in love with the seashore.

My mother and I collaborated on a research project between 1988 and 1993; this collaboration has been one of the most beautiful episodes in our relation, and is a very special one in the history of mother-daughter relations. When I had finished my study for what is the equivalent of a MSc degree my mother approached me with some ideas she had about the evolution of sex determination in vertebrates. She had been working on sex determination in the past, from the developmental point of view. Through the stories I had been telling her during my studies she learned about the evolutionary point of view, i.e. about adaptive strategies that are favoured by natural selection. Combining these views and the view by the controversial scientist Ursula Mittwoch, she had come up with the rudiments of an hypothesis on the evolution of sex determination. She came to me to check with me whether her ideas made any sense. I immediately became very enthusiastic about her ideas and recognized that they were truly innovative.

In the years that followed we continued working on the hypothesis - we had so much fun! My days were normally filled with working on my Ph.D. research of course. But in weekends I often went to visit my mother and in the evenings we sometimes phoned for hours. During those visits the floor of my mother's living room was full of paperwork. Our work consisted of first thinking it all through: did the idea really make any sense, could we phrase it in a more formal way, how did it fit with current thinking, and were there any empirical studies whose observations supported the hypothesis? We did a lot of reading, a lot of discussing, a lot of arguing and reasoning. We were a good team. My mother was absolutely fabulous in finding articles that seemed relevant, from many different sub-disciplines, and sometimes from very obscure sources. She was the truly innovative one with the open mind, combining all possibly relevant facts and ideas, but sometimes a bit uncritically. My role was the critical and scrutinizing one; I was also open-minded, i.e. willing to depart from established thinking, but very strictly adhering to honest reason and logics, to proper deduction. I was the more formal one. I played the advocate of the devil.

In the second phase we started to write it all down. I remember endless phone calls between me and my mother, debating every word and every comma, according to our respective role - me being the critical one again, not wanting to jump to conclusions we could not justify or corroborate. We had so much fun. We were anarchists. The work we did was not embedded in any research program of any research group at a university. This was the work of only the two of us. I started to ask feedback from famous evolutionary scientists I met in the grapevines at conferences. Some of them were politely positively interested, but our work was also too much out of the ordinary, too much non-establishment, to raise much interest. Finally we submitted the work for publication to a scientific journal. Neither of us had much experience with that. We just did it. Our manuscript was refereed by a scientist who was the established researcher of sex determination. In our view our hypothesis was largely compatible with his ideas, but we knew that our hypothesis required shifting his views totally around in a new way and looking at everything in a different way. Of course he rejected our work. We understood: after all, we were overthrowing the views he had invested in for years and years. We appealed to the editor of the journal, asking that our manuscript be reviewed by someone else. We did not get in. Later we got our work published in another scientific journal in 1993, although not such a highly ranking one [1].

Remarkably, in the years that followed publication we earned quite a lot of interest in our work. The paper got cited by some big shots. I got shortlisted for good positions at universities because of it. And I will never forget that the late great evolutionary biologist John Maynard Smith, after reading our paper, said to his promising genius protégé Eors Szatmary, in the presence of everybody in the grapevines of a conference (of the European Society of Evolutionary Biology, 1995, Edinburgh), "Eors, this is a great idea, why did you not come up with it?". I subsequently constructed a simulation model, together with Ido Pen and Franjo Weissing, to check whether the hypothesized evolutionary processes would actually occur under realistic assumptions. A few years later I was asked to write a chapter about these ideas in a scientific book on sex ratios [2]. Still later I was asked to lecture at conferences and public seminars about the subject.

As far as maternal effects go (this is a biological term for non-genetic but fitness-increasing provisions from mother to offspring): I got exceptionally much from my mother, an advance in my career [my mother and I, 2005].

My father was a scientist too. A very different one from my mother. While my mother is an exact scientist, my father was a linguist. He was really very erudite. He knew everything about everything, and if there was something he did not know he had the ability to make something up such that it seemed even more true. He could talk about almost any topic very convincingly. He can be characterized by the term "intellectual snob", a phrase he once came up with, although not to refer to himself, but which suits him very much. Although he was typically interested in language, literature, history, and philosophy, he also developed an interest in evolutionary biology. I have always suspected that he envied me and my mother, knowing that what we were doing was the real stuff, real science. Thus it could also happen that, as I said before, while my mother introduced me to Dawkins' book The selfish gene, it was my father who gave me my own copy of that book. My father also gave me books on human evolution, whereas this was a topic I would typically discuss with my mother. My father also incorporated evolutionary biology into his theories on the origins of human language faculties - to his credit. My father's intelligence was one of fast comprehension and overview, and also open-mindedness [my father, 2005].


Your favourite book is Gödel, Escher, Bach by Douglas R. Hofstadter. How has this inspired or influenced you in becoming a scientist?


You are right saying that this is my favourite book, along with the other two books I mentioned (Dawkins' The selfish gene and Schopenhauer's De wereld een hel) plus a fourth book which I will mention just below. These are the books I would take with me if I were never to come back. However, I don't think Hofstadter's Gödel, Escher, Bach has inspired me or influenced me in becoming a scientist. It certainly inspired me to love the music of Bach.

My fourth favourite book is a children's book by the late Dutch author of children's books Paul Biegel, entitled De tuinen van Dorr. It is a beautiful, tragic, complicated love story (with a happy ending of course). I would love to come and read it to you. German and English translations exist as well (respectively Die Gärten von Dorr and The gardens of Dorr). For a long time I had in mind to write a note to the author to tell him how much this book means to me even in my adult life. I had already looked up his address on internet. But I did not send such a note and a few years ago the author died.

I also like to say here that I have corresponded intensively with Douglas Hofstadter through e-mail and letters during the first half of the year 1997, just when he was finishing his book Le Ton beau de Marot. We also exchanged music tapes, photographs, and video recordings - and he sent me his book. Incidentally, this correspondence started at the time when my collaboration mentioned above with Ido and Franjo on simulations of sex determination started; in that collaboration I felt as a couple of friends ("one of the guys") such as Mr. T and Mr. C, the characters from Gödel, Escher, Bach.

I had always felt, since I started reading Gödel, Escher, Bach in about 1983, that I really knew Douglas Hofstadter as a person, from between the lines of his books. I felt like being on the same wavelength or being in resonance (as he would like to say; he likes metaphors referring to music). I wrote something like a fan mail to him in January 1997. And somehow I had touched the right string with him (a musical metaphor again): to my surprise he wrote back! Some time later we found ourselves exchanging very long and very personal e-mails every day; and that went on for a couple of months. It also became quite romantic. We spent hours and hours of writing per day (he actually wrote mainly during the night). It is too private to tell here why and how it ended, but it did.

I felt a very deep friendship for him, and for all I know that was mutual. Moreover, I felt that I really knew him and understood him - not so much intellectually, but as a person - understood who he is. And, indeed, he is a - literally - extraordinary person. I cherish the brief encounter forever.


The main conclusion of your Ph.D. study is, put simply, that Aidablennius sphynx females choose mates based on the number of eggs already present in the nests guarded by their potential mates. They choose mates with many eggs, and you argue this behaviour is adaptive because with a high number of eggs it is less likely that the female's eggs will be eaten by the guarding male, who has to eat a number of eggs daily to keep fit. By choosing males with many eggs, a female will have more eggs surviving and therefore more progeny and greater "fitness".

Implicit in this argumentation appears to be the assumption that this choosing behaviour is encoded in the genes of the fish. For otherwise, the trait of choosing mates with many eggs would not be passed on to the female's offspring, and there would be no natural selection to begin with. This genetic nature of behaviour is so obvious to evolutionary biologists that it is hardly, if at all, mentioned explicitly in scientific literature such as you have written. Traits are discussed in terms of selection pressures, genetic drift, and evolutionary stability, without any need to explicitly refer to or justify that the traits MUST be genetically encoded for all this to make sense.

But have you also considered how this is in the case of humans; for instance, do you acknowledge that human behaviour has an important genetic component? Or do you side with those who claim that behaviour comes forth mainly from social environment and upbringing?


According to evolutionary biologists every trait is determined by genes and the environment. An organism develops from a zygote (a fertilized egg cell) containing genes and some maternal material in an environment that supports the proper development. Only genes are not enough: a frog zygote will never become a frog if it finds itself in outer space, or if you try to implant it in a human womb for that matter. Only environment is also not enough: a zygote will never become a human being if you try to implant it in a human womb but it contains frog genes. What I have just said here seems self-evident. But I want to make things clear from the start because people often use erroneous views in their arguments in the debate of nature versus nurture.

In this very trivial sense intelligence, for example, is thus caused by genes as well as by the environment. On the one hand intelligence needs a substrate, such as big brains. Brains consist of neuron cells. Cells, of course, can only develop when they contain genes. Our genes specify that some of our cells become neurons. Our genes also specify to what kind of chemicals these neurons will respond. Intelligence depends on genes in terms of a chain of chemical causes and effects. On the other hand intelligence depends on the environment. The human species is characterized by a long period of learning in which neural connections are made and modified; we are not born with the reasoning abilities we use as an adult. This can be more easily illustrated with the example of language. Human beings are genetically predisposed to acquire language, but for the acquisition of a particular language itself we depend totally on the environment, on the spoken and also written language we experience. No particular vocabulary nor any particular grammar are hardwired in our brains. It is the same with intelligence: the potency for intelligence may be innate but its expression needs an environment.

Another, eye-opening, example is provided by the disorder phenylketonuria. Phenylketonuria is a genetic disorder characterized by a defect in the enzyme phenylalanine hydroxylase. This enzyme is necessary to metabolize the amino acid phenylalanine to the amino acid tyrosine. When the enzyme does not work properly, phenylalanine accumulates and is converted into phenylpyruvate. Left untreated, this condition can cause problems with brain development, leading to progressive mental retardation and seizures. However, it can be controlled by diet. A diet low in phenylalanine and high in tyrosine can be a very effective treatment. This condition is often cited as the ultimate example of a disorder caused by a defective gene. However, if you bring the patient in an environment low in phenylalanine and high in tyrosine the person will not suffer whatsoever! Thus the disorder can also be said to be entirely caused by the environment.

The important issue when considering whether a trait can respond to natural or artificial selection is, therefore, not whether the trait "has an important genetic component" or "comes forth mainly from [the] environment", as you phrase it. That question is rather meaningless, or, at least, it is hard to see what it could mean. Instead, the question to ask is to what extent the variation present in the trait is caused by genetic variation as opposed to variation in the environment. The variance found in a trait can be seen as split up into a component caused by environmental variation, a component caused by additive genetic variation, and a component caused by non-additive genetic variation. These components can be determined empirically from observations or experiments. The response to selection - i.e. the degree to which the average "value" of the trait will change from generation to generation as a result of selection - depends on the fraction of the total variation that is caused by additive genetic variation. This quantity is what evolutionary biologists call the heritability of a trait. The heritability can thus be calculated from these components of variation. Heritabilities are numbers between 0 and 1 (inclusive), but rarely approach 1.

Note that most traits are considered to be so-called "quantitative traits", the expression of which may be influenced by many different genes and environmental factors, often additively. A typical quantitative trait is growth, and intelligence is likely to be one as well.

The heritability of a trait is not a fixed property of the trait. First of all, it will change as a response to selection: strong directional selection tends to reduce the heritability. This is because selection will bring the favoured genes to fixation, meaning that all individuals in the population will eventually possess all of the genes for the favoured ("value" of the) trait. The genetic variation is then exhausted and, until mutation brings in new genetic variation, any remaining variation found among individuals will be caused by environmental variation. Further selection will then not yield any response in terms of a shift in the trait "value" between generations. Secondly, the heritability depends on the range of environments it is measured in. Of course, the broader that range, the higher the environmental component of the trait's variance and thus the lower the heritability. In the extreme example of phenylketonuria, if the environment in which the heritability of this condition is measured excludes situations where the diet is low in phenylalanine and high in tyrosine, the heritability will be 100%: all variation found in the expression of the trait is caused by genetic variation. If, on the other hand, one includes the environment with the special diet, then some variation in the expression of the trait is caused by environmental variation and the heritability is smaller. Hence, whether a trait responds to selection also depends on the range of environments the population under consideration experiences at the moment.

These basic principles are actually very explicitly written down in the basic scientific literature, namely in the textbooks that serve students of quantitative genetics and evolutionary biology in their first year of study.

I will translate your question into the following alternative question: "Do you believe that differences in human behaviour are to a significant extent caused by genetic differences?" We also need to specify the range of environments under consideration. Do we only consider behaviour expressed in Western society as opposed to all contemporary societies including e.g. indigenous societies in the Amazon and Papua New Guinea? Do we consider behaviour of the present day, or do we include human behaviour in the Middle Ages or prehistoric times? I take your question as considering Western society during our own lifetime. This specification is important, because even if I believe that many human behavioural traits have been shaped by selection in the course of our evolution, it could be the case that the genetic variation in some of these traits is presently exhausted due to fixation (i.e. everybody has the trait). Moreover, as explained, considering a wider range of environments (such as indigenous or medieval) will automatically lower the relative extent to which the differences have genetic causes. Conversely, if we would consider a narrower range of environments, e.g. the environment of well-educated atheists in Western Europe, the heritability of some traits will automatically increase as the extent to which individual differences can be attributed to the environment will decrease.

My answer to the question is positive: Yes, I certainly believe that many differences in human behaviour have a partly genetic basis. The first ground for my belief is that I know of a multitude of pieces of evidence from the primary scientific literature for a genetic contribution to differences in animal behaviour. With some reservations relating to the idiosyncrasies of human nature (e.g. elaborate learning period, flexibility, complex social interactions) I extrapolate these findings to our species in a general sense.

Secondly, I know for some specific human behaviours that evidence has been found for a genetic contribution to the differences. Even yesterday I read in the Dutch newspaper for biologists Bionieuws (22 December 2007) about an experiment which suggests that generosity is influenced by the AVPR1-gene (the argin vasopressin receptor 1 gene). Generosity was measured in a test situation where a test person was asked to distribute money between oneself and an anonymous person one would never meet. Apparently most people give away money in such test situations, and in this experiment people with the a-variant of the gene were one and a half times more generous than the others. The a-variant induces people to have more vasopressin receptors in their brain. Vasopressin is a hormone involved in social bonding.

A couple of months ago I read in the German magazine Der Spiegel that differences in behavioural responses to ethical issues and also criminal behaviours have been shown to be correlated with genetic differences. Furthermore, I have read various times about IQ differences having a partly genetic basis (in addition to influences from culture and the social environment). And of course homosexuality has been shown to have a partly genetic basis (with added influences from the intra-uterine environment and social environment of upbringing). I am sure I must have read about many more examples, but I don't remember any details.

The examples of human behaviour I just mentioned I have read about in the non-scientific literature. Of course I also have some examples I have read about in the primary (scientific) literature. For example, studies on mate preferences by Claus Wedekind have shown that women find the smell sexually attractive of men having a MHC (Major Histocompatibility Complex) complementary to their own. The MHC is involved in the immune responses against alien substances such as diseases. A mating between individuals with complementary MHCs produces offspring with a wider range of possible immune responses than a mating between similar individuals does. The immuno-effective properties of the MHC are idiosyncratic (differ per individual) and are determined genetically. Therefore, the differing sexual preferences based on MHC have a genetic basis. Note that such preferences are also idiosyncratic and therefore do not result in directional selection.


You must have been thinking a lot about evolution, natural selection and adaptation. How do you look at eugenics; that is, at improving human stock in terms of intelligence, character and physical health through selective breeding and possible prenatal scanning and abortion? Implicit in this are questions like: Do you agree that the named human faculties have a considerable genetic component; do you agree that improving them is objectively good and desirable; and do you agree that, for example, Western populations are deteriorating genetically, and that this is something to worry about and act against? Basic information on eugenics is provided at


I prefer to start answering the question(s) before reading the article you provided, and then later add views to my answer if necessary after reading the article.

Let me first answer the implicit questions you made explicit. Again I have to slightly modify the first question and my answer is: Yes, I think that differences in the named human faculties quite likely have a significant component caused by genetic variation. However, I have no idea how considerable this component is, and thus I have no estimates of the heritabilities in contemporary Western society. Without the heritabilities I cannot say how easily these human faculties would respond to selection, in this case artificial selection. (Note that if you would look up estimates - if there are any - of the heritabilities of these faculties in the primary scientific literature, it would be fairly easy to calculate their responses to selection.)

Then you ask whether I agree that improving these faculties is objectively good and desirable. To this I answer: Yes, in principle I agree. However, there are some very big problems with this answer.

First of all, any programme for such improvement should be based on much more scientific knowledge than we currently have. Otherwise we run the risk of getting irreversible but undesirable effects of our efforts. Desirable traits may be genetically or physiologically linked to undesirable traits. It might be the case, for example, that high intelligence is linked to low levels of empathy. In evolutionary biology we often find trade-offs between traits that are important for fitness. Increasing one fitness component through selection, e.g. reproductive investment, will often decrease another fitness component, e.g. longevity, as a so-called "correlated response". In other words, selecting for one trait may inadvertently select at the same time for another, undesired, trait. Physiological trade-offs may be mediated through mechanisms such as testosterone-based suppression of the immune response. You talk very generally about human faculties to be improved. However, I believe we need an enormous amount of very specific knowledge of what precisely these faculties are - what "character", what "health"? these are not simple, one-dimensional, traits - how their physiology is, with which traits they have trade-offs, and with which traits they are genetically correlated, etc. If humankind would seriously decide on a programme of genetic improvement, it would have to be preceded by a concerted world-wide research agenda involving hundreds of researchers spanning a decade or more specifically devoted to these and other questions.

The even bigger problem is that it would be very hard to reach agreement about what constitutes an improvement. Here we arrive at the philosophical or ethical question of what is good, what is desirable. I am afraid it will be impossible to reach consensus on this. Do we want to have honest people or cunning people? Do we want to have intelligent or empathic people? Do we want to have generous people or do we want to have "the winner takes it all"-type of people? Do we want to have happy people or do we want an efficient society? And for whom do we want improvement? Do all people have to benefit from the improvements or only a small elite? Even if the answer to the latter question is that all people have to benefit, how would you avoid even mild versions of the nightmare-scenario that a small elite breeds slaves with low intelligence and low dominance to do the work? The elite could argue that it is good for human society to have that arrangement. But why should we favour the "interests" of society over the interests of individuals? If I were to choose I would tentatively say I would like to have happy people and I would mind less about everything else. The ability to experience happiness may have genetic correlates ( - I haven't checked out the site!).

Finally you ask whether I agree that Western populations are deteriorating genetically. No, I don't agree with that, and I find it quite hard to imagine what you could mean.

I wonder on what grounds you base your belief that this is the case. Since I don't think that there is enough genetic material available sampled from historic or prehistoric populations to compare, I think that it is presently not possible to know whether such a deterioration is happening. One can speculate that the process is probably or likely taking place, but we cannot know whether it is actually occurring. The simple reason for this is that the required science as well as the techniques for measuring the genetic makeup of populations have only been available to us since barely one generation time. We can compare the genetic makeup of current populations with the genetic makeup of populations that lived thirty or forty years ago, but not of populations farther removed from us in time. This time span is too short to conclude from any observed difference whether it is random fluctuation or constitutes a real trend.

Deteriorating implies some standard along which we can measure good and bad or positive and negative or more and less, and with that we are back at the problem discussed above.

Populations are usually well adapted genetically to the conditions they live in, meaning that the individuals have the traits that are needed to survive and reproduce optimally in the situation they find themselves in. If a trait is no longer needed under the conditions the population currently experiences, the trait often gets lost in the course of evolution. But is this deterioration? Did cave-dwelling animals deteriorate genetically when they lost their eyes? Did worms living as parasites in the bowels of other animals deteriorate when they lost their own intestinal system? Did vertebrates deteriorate when they lost their gills (and got lungs instead)? Did hominids deteriorate when they lost their fur? Or when their sensitivity to smell decreased? Or when they started to walk on two instead of four legs? Would you say that humans are deteriorating genetically if, as a consequence of the use of optical instruments such as glasses and contact lenses, natural selection on good eyesight relaxes and the average eyesight is getting worse? It could be opposed that under the contemporary conditions individuals that are genetically predisposed to invest in other (important) qualities rather than in eyesight are genetically superior.

In other words, it can be questioned to what extent eyes, intestines, or furs are "good". I don't think it can be argued that they are "good" in any absolute or inherent sense; I think they are only "good" with reference to their functionality. They become "neutral" or even "bad" under conditions where they are useless.

Recently I read in Breaking the spell, the book by Dennett I mentioned before, a nice and original view on domesticated sheep. According to this view domesticability is a trait that enhances sheep fitness. Due to having this trait domestic sheep acquired a shepherd as an evolutionary adaptation. Having a shepherd who helps avoiding predation and finding food, the domestic sheep does not need to be as intelligent as its wild ancestors were who had to avoid predation and find food themselves. And yet, despite its lower intelligence but thanks to its domesticability resulting in the acquisition of a shepherd, the domestic sheep is clearly superior in terms of biological fitness: it outnumbers its wild sisters and brothers by orders of magnitude! Apparently domesticability is a much more important trait for survival and reproduction than intelligence is. Did the sheep deteriorate? If yes, to whose standard? In any case not to the standards of biological fitness. In biology there is no "good" and "bad". The only thing one can say is that genes which, by whatever means, enhance their own replication will outnumber alternative genes. These genes code as often for "ugly", "stupid", "inefficient", "bad" (etcetera) traits as not.

Western populations have low fitness. With this I mean that currently they produce lower numbers of offspring surviving into adulthood than some Asian or African populations do. However, this is a very recent development - since about two or three generations ago - and it can, therefore, not yet have had any consequences in terms of changed gene frequencies. We also don't know whether genetic differences underlie the behavioural patterns leading to smaller family size. But even if genetic fitness of Western populations is deteriorating, so what? For evolution numbers of progeny are important. But not to me. To you? Why? I find happiness more important. I prefer living in world with one billion happy people to living in a world with 10 billion unhappy people.

Biologists may understand under the term "genetic deterioration" or "genetic erosion" the process that genetic variation gets lost. This often happens when effective population size is low. The loss of genetic variation can be seen as something "bad" because it would result in the population being less able to adapt to changing conditions. However, such a process is not currently happening in Western society. On the contrary, with global mobility and the mixing of people from different ethnic origins genetic variation probably increases in the Western population. Also the relaxation of selection pressures against formerly fatal genetic defects will tend to increase variation in the contemporary Western population (i.e. in the past people with such defects would not pass on their genes; in present society with medical care these genes are preserved).

I don't understand why you phrased your question about the genetic deterioration of Western populations with the words "for example". Do you think many other populations are also genetically deteriorating and that the Western populations are just a subset of them? This makes it even harder for me to understand what you mean with your question.

Anyway, for obvious reasons I cannot answer your question whether we should worry about and act against this supposed deterioration. Note that even without worries about deterioration I could still agree on the desirability and possibility of improving human faculties.

I have now answered your explicit implicit questions. With that, I think I also have answered your main question. Let me now read the information you provided and let you know my response to that. Perhaps it will then also become clearer to me what you mean.

I read the article, and I don't have much to add to what I wrote above.

Of course I understand now what you could mean with your question on deterioration. However, in the article the supposed evidence for a genetic deterioration in intelligence is very indirect and not presented sufficiently clearly to judge it. According to evolutionary biologists the response to selection (as defined above) is a function of the selection differential (i.e. the difference in the number of offspring surviving to adulthood between individuals differing in the trait under consideration) and of the heritability of the trait (as defined above). It is not clear from the article whether the heritability (which is certainly < 1) was taken into account in their calculation of the effect per generation.

Disregarding whether I agree or not with the actual case for eugenics, I find the paper quite unpleasant. It is tendentiously and aggressively written, resembling a narrow-minded crusade instead of carefully examining the issue. This is a style I don't like very much - I rather like to ask questions and look at an issue from all possible sides and only suggest possible answers (compare to the style of Pinker on the issue of women being underrepresented in the exact sciences discussed above). Furthermore, the paper is not very scientifically written. It is full of unproven statements, assumptions (which are not shared by me), and conclusions that do not follow from the argumentation. One of the most conspicuous irritations I felt while reading this paper is that after again and again having argued her case based on evidence from correlations, the author suddenly ridicules the use of correlational evidence when used by "the other camp". This disqualifies the author for me. In scientific circles arguments based on correlations have a lower status as compared to, e.g., experimental evidence, but they are not ridiculed. Good examples of careful, ongoing scientific discussions of whether evolutionary changes are taking place on a contemporary time scale - in this case in fishes as a consequence of fishing - are provided by Kraak [3] and by Heino et al. [4]

The paper on eugenics does not convince me of anything.

When reading such an article I find myself being a biologist to the core - and I enjoy it. My starting points, values, and basic views (of life, the universe, and everything) are so totally different from what I taste in that article. This can be illustrated by my puzzlement about the word "dysgenic". We biologist don't use that word. In biology there is no "good" and "bad". The evolution of life takes many roundabout routes, some outrageously inefficient or utterly nonsensical - but awe-inspiring. The use of sex in reproduction, for example, is particularly clumsy, dangerous, costly (etcetera). Yet, it gave rise to almost everything we find beautiful in nature (e.g. flowers, colourful bird feathers, bird song, species diversity). But sex really is irrational - "dysgenic". And then, given that sex exists, the almost ubiquitous sex ratio of close to 1 : 1 (females : males) is prodigiously wasteful: usually one male would suffice to fertilize hundreds of females. Irrational and "dysgenic". Yet, the mechanism of natural selection provides the iron logics for the 1 : 1 sex ratio (as convincingly put forward in 1930 by the great statistician and evolutionary biologist of the first half of the previous century R. A. Fisher). Another example of a "dysgenic" phenomenon is the use by plants of insects to fertilize their mates. What a fanciful and roundabout way! - couldn't that be done more efficiently and rationally? Life on earth is ever-lastingly fascinating, but who are we to judge what course its evolution should take? Skip the flowers and be rational? Or let there be flowers...

The grand scheme of things in biology does not know "right" or "wrong", "good" or "bad". Evolution does not go anywhere. Let's look for example at the concepts of r-species and K-species. Species deploying an extreme r-strategy opportunistically produce extremely large numbers of offspring as soon as possible and without much of investment; they use the "wasteful and sloppy" strategy. On the other side of the spectrum, species with the K-strategy invest in development and even learning, and produce relatively few individual offspring in which they invest a lot; these are often very specialized. Both strategies seem equally successful in the history of life on earth, although you may find the K-strategists more sophisticated (perhaps because humans belong to those species deploying the most extreme K-strategy).

One time you told me that you thought evolution has a direction, towards increased complexity, sophistication, or intelligence. I think this was a mistaken thought and the apparent direction is caused by randomly-directed processes only: life forms as often evolve in the direction of the loss of complex adaptations as in the direction of gaining them (leaving aside the problems of defining "complexity"). Compare with the process of diffusion. Imagine that a colourful substance such as ink is released at one end of a water basin. Despite the fact that the ink particles only move around in random directions (by the so-called "Brownian" motions), an outside observer may think that the ink is progressively moving to the other side of the basin. Note that the ink was released not in the middle, but at the extreme end of the basin. The analogy is that life on earth has started by necessity at one extreme end, namely at the end of least complexity. Then, if each evolutionary step is random with respect to whether it goes in the direction of more or less complexity, the process will yield more and more complex life forms, in addition to the simple ones! Hence, the null hypothesis to explain the progressive arrival of complexity in life on earth is actually random evolution, without any direction towards more complexity, sophistication, or intelligence.

Despite the above characterization of myself as convinced that nature is indifferent about "right" or "wrong", I do have a strong sense of morality and a deeply rooted and very strong longing for the "good". This longing drives my actions and especially the judgment of my actions, and it determines my basic feeling of unhappiness. Morally speaking I believe "right" and "wrong" are very real. Is the word "dysgenic" a moral term rather than a biological one? Biological fitness and moral value are entirely different issues, and I got a bit confused as to what we are discussing here.

I always dream that the world could be made a better place by increasing traits such as altruism, generosity, and cooperation (rather than intelligence; think of all the intelligent people in history with evil intentions or whose actions had evil consequences; to me intelligence seems neither desirable nor undesirable, but neutral). I believe that egoism, selfishness, lust for power, greed, spite, mistrust, and the ensuing break of cooperation and the inability to give and forgive constitute the source of most of our misery, not the lack of intelligence. My ideas about improving these qualities are based on the common view that natural selection gave rise to genetic predispositions to behave altruistically under specific environmental conditions. If we would create these conditions often enough, the pleasant behaviour would arise automatically.

What kind of conditions should be created? As I said before, the scientific work of Elinor Ostrom seems to be important in this context, as well as the scientific work of Nowak and Sigmund [5]. The Game Theory's Prisoner's Dilemma is often considered a simplified model for social interactions where the temptation exists to behave selfishly because it yields high direct payoff. The dilemma arises because if both interacting individuals behave selfishly both lose the benefits, while if both would behave nicely and cooperate they would gain, 'though less than the selfish individual would if he succeeded to parasitize on the nice behaviour of the other. The loser of the game is the one who behaves nicely but falls victim of the selfish parasite. In the Iterated Prisoner's Dilemma, where the same individuals meet repeatedly, the winning strategy seems to be Tit for Tat and variations thereof. This roughly means that when individuals meet repeatedly it is advantageous for each of them to be nice to the other because this will increase the chance that next time the other will be nice back. In this case the individual net gain is higher than when the individual defects resulting in not being treated nicely. The advantage of being nice is even bigger if onlookers observe the nice behaviour, increasing their tendency to treat the altruist nicely when interacting with her. All of this suggests that if individuals interact with familiar individuals (as opposed to strangers) they are more inclined to be nice. Politics should therefore give priority to creating these conditions - conditions of dealing between familiar individuals. I could even imagine that those conditions that favour the expression of the altruistic side of our nature already present, would in addition favour genes that code for more altruistic behaviour, that way creating a positive feedback loop.

As a last remark I would like to say that if your motive is to make the world a better place I do not recommend looking at eugenics. Even if the case for eugenics would actually be a valid one, it is, unfortunately, a subject that, owing to its taboo-nature, attracts a lot of suspicious types such as ill fanatics with insincere agendas. The subject is a dangerous can of worms. Because of that I would recommend to invest in one of the many other ways to make the world a better place. I grant that it might be a pity to forego the possibilities that eugenics has to offer, but as long as there is so much other work to do to save humankind, I would recommend to take on these other challenges first.


You have appeared in the National Science Quiz of 2005 on Netherlandic television (A web page with video of the quiz is at Did you feel in place as a scientist in that situation?


Unfortunately not very much. I would love to be on television as a scientist - as what I believe to be a real scientist. Science is more difficult than many people know. It should not be equated to a lot of encyclopaedic knowledge or presented as a handful of fun facts and curious phenomena and experiments.

You should know that the questions of the National Science Quiz are generally distributed to the Dutch public a couple of weeks before the television show is broadcast. During that period the public can think about the questions and discuss them with friends and colleagues at length. People can submit their answers before a closing date for the competition. Then, at Christmas Eve, the show is broadcast which has been recorded a few days before the questions would become public. However, in that show the contestants (of which I was one in the year 2005) are confronted with the questions for the first time and have at most twenty seconds to come up with the answer.

That is not science. Scientists don't come up with answers in twenty seconds. This quiz was about general factual knowledge and a little bit about reasoning and calculating faculties. Of course most scientists do have a lot of knowledge and scientists certainly need these faculties. But, for example, my own knowledge tends to be rather specialist, and my reasoning and calculating faculties are, despite being very good, slower than needed for such a quiz. I would have liked more time for thinking things over, turning them around in my mind, discussing them (with myself or others), considering the alternatives, etc. As you know, it took me two months before I submitted the answers to one of your IQ tests, the Test of the Beheaded Man, which tested my reasoning abilities (and for which you awarded me an IQ of 154).

But it was great fun. And it made me aware that I like to talk about my work on television.


How do you define sex - the being male or female - in an animal or human? Is there an ultimate definition, either in biology or in society?


I cannot imagine what you mean with an "ultimate definition". Definitions are by definition (Smile) something we choose, something arbitrary, a convention. In my very first class of philosophy we did an interesting exercise. We had to come up with the definition of a spoon! After having stated our first coarse definition we found out that we could imagine objects that we would still like to call spoons but that did not fall under our definition, and, vice versa, we could come up with objects that we definitely would not call spoons but yet they fell under the definition. Subsequently we refined our definition, so that we could distinguish spoons from spades, for example, not just based on shape, but also on function. But new examples always came to mind that violated the boundaries of our definition. You can try it yourself. The lesson I learned from that exercise was that any definition becomes problematic at the margins. That's why we should abandon the notion of ultimate definitions but just use operational definitions. The classification of things is not a truth of nature but only a preference in the human mind. Sex, or gender, is no exception - whatever your definition is, you will always find examples of beings that seem to be female but yet fall under your definition of male or the other way round or that seem to be neither or both.

Hence, everybody may choose a definition to their purpose. However, it is important to be clear about one's definition because it is handy if it is shared by the people one communicates with. Moreover, some definitions are more useful, operational, than others.

I sometimes like to provoke people's concepts and clichés of male and female gender. For example, a couple of weeks ago I participated in a group of about eight women and eight men. I was the only woman not wearing earrings and none of the men were wearing earrings. I concluded that, based on earrings, I must be a man. Similarly, when I almost bumped into a lamppost in the street while I was typing a text message on my mobile phone and someone commented that women were supposed to be good in multitasking, I replied that this shows that I am in fact a man. And why not? If I would have more masculine traits then feminine traits, then what's the point of calling me a woman?

In the seventies my mother published an article in response to the practice that for sports events such as the Olympic Games participants registering for the female competition had to have the root of their hair checked for the presence of the Barr body (the second X-chromosome) in order to prove that they were really women. My mother stated in her paper that although the law requires that each human being is either man or woman, there is actually no good definition of the sexes. She gives four criteria to decide on a person's sex or gender: 1. the external body morphology; 2. the internal gonads (ovaries or testes); 3. the sex chromosomes (XX or XY); and 4. the subjective experience. These four criteria are not always unambiguous and do not necessarily point in the same direction, in which case it may not be possible to make an objective decision at birth to which sex to allocate the infant. Naturally, this has resulted in the existence of people with mixed sexual characteristics suffering from the fact that at birth a decision has been made that does not fit with how the person experiences self at a later age.

I read in the Dutch newspaper Het Parool of 4 April 2007 that a sixty-year-old Dutch person lost the juridical battle to be officially acknowledged as sexless or genderless. In the same article I read that the Nepalese authorities were the first in the world to give a double sex or gender to a "man" who behaves and dresses like a "woman"; in his official documents under sex it reads "both".

Many people spontaneously react saying that of course the presence of a Y-chromosome and an X-chromosome as opposed to two X-chromosomes should decide the matter. My reaction to that is: of course not! Scientifically, the claim of a causal relation between sex and chromosomes should follow from the empirical facts, not the other way round. First we saw men and women, based on the anatomy. Later we found that most men have one Y- and one X-chromosome and most women have two X-chromosomes. This finding led to the scientific hypothesis that (something located on one of) these chromosomes cause(s) embryos to become male or female. If one finds an exception, e.g., a man without a Y-chromosome, science must then of course conclude that the supposed causality is not absolute instead of saying that the person is not a man. Science must then search further for the causative factor(s) for maleness. Such a factor is apparently strongly, but not absolutely, correlated to the Y-chromosome, as for example the SRY-gene or maybe a set of several genes.

A human being (or any other mammal) can possess a Y-chromosome that lacks the SRY-gene, and be just as female as any other female. Conversely, someone without the Y-chromosome but in the possession of a (e.g. translocated) SRY-gene can be as a normal man. An entirely different phenomenon is the case with persons with a normal Y-chromosome but lacking testosterone-receptors. Such a being would develop embryonal testes, but subsequently all processes leading to masculinisation would fail. No sperm will ever be produced. The person will look like an absolutely normal female, an even very feminine female for that matter, owing to the total breakdown of any testosterone-effects. Such a woman would possibly never know that she is not a "normal" woman, except for the fact that she is not fertile and has no menstrual cycles. Perhaps she would visit a doctor because she does not get pregnant. Perhaps it would then be found out that she does not have ovaries, but undeveloped and non-functional (internal) testes instead. Maybe you could argue calling such a woman a "sex-reversed genetic man". But the woman with a Y-chromosome without the SRY-gene I personally would not like to call a "genetic man".

The definition commonly used in biology I take from Michael Jennions and Hanna Kokko [6]:

"Individuals that produce smaller gametes (sperm or pollen) are males and those producing larger gametes (eggs or ovules) are females. Consequently, a seahorse that allows a conspecific [i.e an individual of the same species] to insert gametes into its brood pouch, where they are subsequently fertilized and then protected while they develop into young fish, is described as a male despite its effective 'pregnancy'. This definition works for all anisogamous species because gamete size typically has a very clear bimodal distribution across a population. This is true even for species in which an individual can produce different types of gametes. Hermaphroditic plants, for example, produce seeds and pollen but no intermediate-sized gametes, so we can still speak about male and female functions in hermaphrodites. [...] It is important to note that the definition of males and females is a convention that creates a fixed reference point for studying trait covariation. Consider Drosophila bifurca [a fruitfly] that produces giant sperm so that gamete sizes of males and females differ by less than an order of magnitude [...]. This is a tiny difference compared to, say, humans where the difference in volume is 4 or 5 orders of magnitude. If sperm of D. bifurca ever evolved to be larger than eggs, the sex currently producing sperm will become the female sex! This would not violate any natural law [...]."

Thus, this definition is not what you would call an "ultimate definition", because, as the authors point out, we may run into problems in some instances. We may prefer a definition stating that the sex producing motile gametes (sperms), whatever their size, is the male sex, and the sex producing motionless gametes (eggs) is the female sex. But I am sure with this definition other problems will ensue. Again: I think definitions and classifications are constructs of the human mind, and not something that can be found in nature.

Another problem may arise with the definition of sex or gender with reference to the gametes the individual produces. There are of course human beings who for some reason (genetic or not) have disrupted gamete production and happen to be infertile. Is such a person then neither man nor woman? Even if she looks like a woman or he looks like a man? Just because he or she does not produce any gametes?

My message is: do not try to define sex or gender and classify people into one of the sexes. It may cause trouble and even suffering. We should look at individual people and see all their relevant characteristics. Some women may have many masculine traits and some men may have many feminine traits. Some people may be a mixture of the two sexes. Let them be. [7]

I end with a quote of the feminist Florynce Kennedy: "There are very few jobs that actually require a penis or vagina. All other jobs should be open to everybody."


When taking your doctoral degree you defended a number of theses, some of which unrelated or at best remotely related to your dissertation's topic (female mate choice in Aidablennius sphynx). For instance, one thesis dealt with the contempt of intellectuals for "soap" television series. Are such remote theses common in taking one's doctoral degree? And did you have interesting discussions or receive remarkable comments when defending them?


Yes, it is very common to attach such remote theses to the dissertation, at least in the Netherlands. The most remarkable or funny ones are published in certain newspapers. Nevertheless, it is very rare that the candidate is asked to defend them in the public defence of the dissertation; I have never witnessed it at the public defences I have attended. I guess the fun of it is to offer some insight into your private opinions about matters to your colleagues and friends. In my case I am sure they triggered fun discussions between friends or colleagues and myself, but unfortunately I do not remember any that are worth relating here.

Aidablennius sphynx - by Hedwig Dekker (aged 10), 1994
Aidablennius sphynx - by Hedwig Dekker (aged 10), 1994


  1. Kraak, S. B. M. & de Looze, E. M. A. 1993. A new hypothesis on the evolution of sex determination in vertebrates; big females ZW, big males XY. Netherlands Journal of Zoology 43, 260-273. Back to text.
  2. Kraak & Pen, I. 2002. Sex determining mechanisms in vertebrates. Chapter 7. In: Hardy, I.C.W. (ed.) Sex Ratios: Concepts and Research Methods. Cambridge University Press, Cambridge. Back to text.
  3. Kraak, S. B. M. 2007. Does the probabilistic maturation reaction norm approach disentangle phenotypic plasticity from genetic change? Marine Ecology Progress Series, 335, 295-300. Back to text.
  4. Heino, M. et al. 2008. Evolution of growth in Gulf of St Lawrence cod? Proceedings of the Royal Society B, 275, 1111-1112, doi:10.1098/rspb.2007.1429. Back to text.
  5. Nowak, M. A. & Sigmund, K. 2005. Evolution of indirect reciprocity. Nature 437, 1291-1298, doi:10.1038/nature04131. Back to text.
  6. Kokko, H. & Jennions, M. 2009. Sexual Selection. Chapter 20. In: Westneat, D. F. & Fox, C. W. (eds.) Evolutionary Behavioral Ecology. Oxford University Press, in preparation due 2009. Back to text.
  7. Note by Paul Cooijmans: Please observe that while the good Dr Kraak urges us not to try to define sex or gender and not to classify people into one of the sexes, and while she carefully circumvents unneeded sex-specific pronouns almost everywhere, she does use the word "her" to refer to the altruist in "The Prisoner's Dilemma", and the words "his", "himself", and "he" for the egoists in "The Tragedy of the Commons", thus, in a subtle biologist's vein, defining the female sex as altruist and the male sex as egoist. So we did get the definition asked for in the present question after all! Back to text.