Alle gedrag is evolutionair bepaald Bioloog Robert trivers 16-11-95
Robert Trivers became well known for his publications on, among other things, parental investment and sexual selection, parent-offspring conflict, and reciprocal altruism. The following interview took place during the conference on 'Biological Perspectives in the Social Sciences' at the Gruter Institute, Darthmouth College, Hanover, USA, August 1995.
Thirty years ago or so your life was turned around by evolutionary theory. How did this happen?
I was a history major in college, after having been in mathematics. Of course I heard of Darwin, but I had never had any biology. I had never watched animals or paid any attention to them growing up as a child. I remember people at the university used to make fun of me, because they would show me a picture of a rhinoceros and I might guess it was a hippopotamus, -I didn't even know my animals! I believed, like many people then, that human behaviour had very little in common with animal behaviour, -with of course no knowledge of this subject at all.
When I was 22 years old, I was asked to write children's books on animal behaviour, and I became exposed to facts about animals. I remember being struck by a very good movie-footage on adult-offspring interactions in baboons. The adults indulged in something that looked like parental discipline of young baboons that were beating up other youngsters. It reminded me very much of parental discipline in our own species, the big difference being that the baboons said nothing while disciplining their youngsters, while we of course fill the airways with words. So that immediately suggested that parental discipline did not require language, and if it didn't require language, you needed an explanation that applied to both baboons and humans at the same time. And that led naturally into evolutionary logic, because it is only evolutionary logic that is going to provide us with an explanation that works for many different species.
Death and destruction constitute important selection-pressures in nature. How can natural selection nevertheless be a creative process?
It is not so easy to give a simple answer to that question. The selective elimination of individuals within a species results in a more and more non-random sample of individuals that are surviving and that do breed with each other. Once again in the next generation the non-random elimination of some individuals rather than others, leaves an increasingly unusual sample of genes or individuals that are still there. So that over time you can see natural selection as a creative process, not by focusing on the eliminated individuals, but on those that were not eliminated, and understanding that they are increasingly unusual. This is how natural selection creates novel forms.
Speed and strength are important adaptive traits. Then why are not all living organisms fast and strong?
Well, all traits in principle have a drawback and negative features which in some settings outweigh the positive ones. Strength for example is costly in protein necessary to built and maintain muscle-mass. So the expensiveness of strength can easily outweigh its benefits in various situations. No trait is adaptive in all environments.
A very general question: What are organisms designed to do from an evolutionary point of view, and why?
Well, the answers are intimately connected. We believe all creatures have evolved here on earth according to the principle of natural selection, which says that the genes of the individual producing the most surviving offspring, increase in frequency the most in the next generation, because the genes are found in the offspring. This process of always selecting in every generation the hereditary traits that are associated with high reproductive success, presumably results in creatures which today unconsciously attempt to maximize their reproductive interests.
You are reported to have said: "All you need to know is Darwin and Hamilton". What did you mean?
The only change in our conception of natural selection since Darwin is the result of Hamilton's work. All you need to know to understand the underlying evolutionary principle of natural selection, is Darwin for giving us the concept of fitness or reproductive success -number of surviving offspring- and Hamilton who extended this to effects on other relatives. He noted that we are not only related to our children, we are also related to our brothers and sisters, more distantly our cousins and so on. So Hamilton came up with a slightly more general formulation which says that we are not trying to maximize the number of surviving offspring per se; no, we are trying to maximize the number of surviving copies of our own genes, whether found in offspring or found in other relatives, each category weighted by how closely related we are, or, as we call it, degree of relatedness.
You introduced the term 'reproductive success' to replace 'fitness'. Why?
I very much dislike the tendency in academia in general to proliferate unnecessary terms, and yet I am someone who has done that. Prior to 1970, I don't think the term reproductive success was much used, but instead the term fitness was used. I did not like the term fitness because of its connotation of being physically fit. It suggested that you could tell who was fit before you found out who left many surviving genes. Over the preceding hundred years, ever since Darwin, fitness was used in this dual sense, and people slipped back and forth between fitness meaning simply reproductive success, or something that could be judged separately, like physically fit. So I coined the term reproductive success simply because it was more accurate. It caught on, and yet Hamilton who preceded me had already chosen 'inclusive fitness', and nobody, including me, uses 'inclusive reproductive success'. So we have parallel language usage. I do like the term reproductive success though, and I have no doubt that in teaching students it is beneficial to use that term, and not to use the term fitness.
In your book Social Evolution you describe social differences between seals breeding on land or on ice, different sex-ratio's between ants that do or don't 'hold slaves', and many other examples from the animal kingdom. Why should studying these phenomena be relevant to social scientists who are interested in human behaviour?
It is very important what the form of the argument is linking other creatures to humans. One thing we are trying to do is understand general theories that apply to our own species but also apply to other species, and it is often easier to test the general theory in some other species than in our own. That often makes studying distantly related creatures valuable to understanding ourselves, not because we act like them, not because we necessarily share any behaviours in common, but because we are both subject to the same principles. And to test and refine the principles themselves, it is valuable to get away from humans.
To give you an example, when I first worked on parent-offspring conflict, Richard Alexander said: "Well and good. There is parent-offspring conflict in theory. But if you go to nature you will find that the parent always wins. The outcome is always exactly what the parent wants". Now for our own species, no way to measure the relevant parameters sufficiently precisely so as to test that notion. The cost of an additional day of nursing an offspring? Very hard to measure. The benefit of a given day of nursing to the offspring? Difficult to measure. Remember cost and benefit must be expressed in terms of reproductive success. However, you could go to those ants you were mentioning, and you could prove back in the seventies that regarding some parameters in an ant nest, the offspring wins, and the mother looses. Now you can not generalize from that result to say: "Oh well, in humans the offspring always wins". Nonsense! In ants the mother is facing tens of thousands of daughters simultaneously. But the demonstration that offspring are capable of expressing their own interests counter to their parent's best interests, destroyed a certain line of reasoning regarding the general principle.
Are there aspects of social behaviour of any species for which evolutionary theory is irrelevant?
I cannot imagine there are. I am a little timid about work on humans recently, because I have not concentrated on that for some time, and because people care so much about the application to humans, get emotional about it. I would prefer to speak from a position of strength, and not from a position of weakness or ignorance. You know, the questions often get subtle and complex, and if you are not on top of every nuance and detail....
A polemical statement: Most social scientists are either anti-Darwinist, or only have misconceptions about evolutionary theory. For that reason they are trailing some 140 years. Do you agree?
Well in this country, that is the US, I feel that this is a fairly accurate picture, but I don't know about social scientists the world around. Here most social scientists, as part of their training, learn reasons why biology is irrelevant. For instance, anthropologists learn that culture is critical and not shared by any other creature, so forget about all the rest of the creatures. By the way, the most distressing feature of this to me is the failure to educate the students in some biology. I harp on this educational thing, because until that has changed, you are continuing to turn out a generation of people who will be ill prepared to understand and accept biological work being done in their area.
Let's say you are a forty year old psychology professor, and you come on Darwin, and you come on Hamilton and some recent work in evolutionary psychology, and you say: "My God, that looks exiting and fun". Now if you have never had a course in biology, there is so much work staring you in the face before you feel you can be expert in this area so as to use it, that there will be a very strong tendency for you to do the opposite: Figure out reasons why evolutionary theory is not relevant and not so important. So this failure to educate the graduate students in a little bit of biology is a very regressive feature of the educational system, and it slows down the movement of biology into the social sciences.
The social sciences are divided in all these subsections that do not get properly integrated and related to each other. You know, twenty years ago I had the future exactly wrong. I didn't imagine the work we were doing taking over biology to the degree that is has. I instead imagined that the social sciences would be reformulated around this work. I confidently predicted that in twenty years, in other words right now, you would not be able to walk down the hall of a psychology or a sociology or an anthropology department, without hearing people arguing with each other "Yes but why would natural selection favour that?". This has not happened.
The parallel fact in biology has been extremely gratifying, for instance completely reorganizing the work on animal behaviour, and I was surprised by it. But biology is a unified science with a central paradigm coming out of Darwin, so it is much easier for ideas to rapidly diffuse within biology.