Saturday, February 18, 2006

Books: "Evolution's Rainbow" by Joan Roughgarden

I see that Joan Roughgarden has a new paper in Science this week: Reproductive Social Behavior: Cooperative Games to Replace Sexual Selection

Theories about sexual selection can be traced back to Darwin in 1871. He proposed that males fertilize as many females as possible with inexpensive sperm, whereas females, with a limited supply of large eggs, select the genetically highest quality males to endow their offspring with superior capabilities. Since its proposal, problems with this narrative have continued to accumulate, and it is our view that sexual selection theory needs to be replaced. We suggest an approach that relies on the exchange of direct ecological benefits among cooperating animals without reference to genetic benefits. This approach can be expressed mathematically in a branch of game theory that pertains to bargaining and side payments.

This is bound to provoke strong responses in the evolutionary community, just as her last book did. A few years ago I read Evolution's Rainbow and it sure is controversial. The trick is not to accept or reject her book 100%. There is too much stuff in there, some clearly correct, some pretty clearly wrong (or at least far too exagerated), some thought-provoking even if the jury is still out, to just dismiss the book wholesale.

The strongest parts are in the beginning - first six chapters or so - where she describes a lot of examples (and I mean a LOT!) of alternative sex-roles in the animal kingdom and I really like her re-definition of 'gender' as it pertains to non-human animals: "Gender is the appearance, behavior, and life history of a sexed body". In other words, it is not true that all animals have sexes, but only humans have genders. This also means that "gender, unlike gamete size, is not limited to two".

Next three chapters are the most provocative, as she strongly dismisses the whole edifice of sexual selection. Proceed with care.

Chapters 10 through 14 are, again, masterful explanations of basic biology, the role of genes in development, sex determination and differentiation, and the ontogeny of sex, gender, and sexual orientation. I see nothing controversial there, and these chapters provide a great resource - all the stuff in one place - for people interested in this topic. As a transgender herself, she clearly studied this issue with passion for years, and as much that means she has an axe to grind, it is a good axe and her scholarship on this is impeccable.

Afterwards she dives into topics she is not such an expert on - psychology, biotechnology and sociology and she makes one cringe on many occasions. Chapter 20 is a dissection of all the places in the Bible that are used by Regressives to argue against gay marriage. While Biblical scholars are certain not to like her interpretations, in my opinion she skillfully debunks the myth that Bible says anything at all about homosexuality. Progressives should read this chapter in order to get the ammunition neccessary to debunk the anti-gay Bible-thumpers.

But, back to sexual selection. Last summer she published an article - The Myth of Sexual Selection - that succinctly reviews her stance against the theory of sexual selection. I strongly suggest you click on that link and read the whole thing and I would like to hear your reactions to it.

Among else, she writes:
"Clearly, the idea that males and females conform to rigid gender profiles still dominates sex role discussions. According to this model, passionate males with cheap sperm pursue coy females with expensive eggs. Females look for males with the best genes, whereas males want to fertilize as many females as possible. Genetically superior males distinguish themselves as the winners of male-male combat, as with jousting elk, or by having the most expensive and beautiful ornaments, as among peacocks. These male and female profiles, together with the cheap sperm/expensive egg rationale, comprise what biologists call "sexual-selection theory." Throughout nature, it would seem, delicate discerning damsels welcome horny handsome warriors to bed.

This is rubbish."
This is Evolutionary Psychology she is debunking, not evolutionary biology. Straw-man!

This is interesting:
"Sexual selection theory also teaches that because eggs are larger and more expensive to produce, females must conserve this resource by playing hard to get. Conversely, because sperm are small and easy to manufacture, males can spread them around with little loss on investment. But in fact, sperm are not cheap. The relevant comparison is not between individual sperm and egg, but between ejaculate and egg. An ejaculate often has a million sperm whereas an individual egg is often a million times as large as an individual sperm, making the mating investment of both male and female about the same. As a result, in many species a mating for a male may be just as costly as for a female, even when there is no male investment in raising the offspring."
Now the alternative she proposes:
"Sexual selection views mating as solely for conception. But the point of mating is not usually to make babies; it usually serves a social function. Mating occurs too often relative to number of offspring produced to be solely for conception. The intimacy of sex strengthens relationships between adults, defuses social tensions, and helps keep groups together, as in our closest living relative the bonobo. Strong social bonds help ensure males and females will work well as a team to protect and raise young.

Same-gender sex can promote friendships as well, helping to explain why homosexual sex has been observed in more than 300 species of vertebrates as a regular component of social interactions."

I actually like this. I just don't think it is an alternative to anything.
"I suggest that we replace sexual-selection theory with a new approach that I call social selection theory. I argue that reproductive social behavior, including mate choice and family organization, can be completely explained by focusing solely on the direct ecological benefits each individual obtains from the interactions it has with others. Indirect genetic benefits can be ignored; they don't realistically factor into mating decisions at all.

Social selection theory proposes that every animal has a time budget for its social interactions. Each animal interacts with others in ways that improve the number of offspring he or she can successfully rear. Animals may pursue their most beneficial course by acting independently or by acting together in teams, but usually in teams. From a group's many instantaneous decisions as to whom to associate with and what actions to perform with one another, a unique social system emerges for each species in each ecological situation."
Good. But, I do not see the two ideas as mutually exclusive at all. One can certainly have both sexual selection and social selection operating, even in the same species. Why not?

Now comes the axe she grinds:
"To a naturalist, the failure of sexual- selection to describe and explain animal behavior is reason enough to reject it at this time. But the stakes are even higher. Sexual selection is not innocent. It promotes a view of nature as violent and deceitful, emphasizing male-male combat and war between the sexes. It licenses male promiscuity. It views female choice of mates as a broom to clean the gene pool of males with bad genes. It persecutes diverse expressions of gender identity and sexuality. Social scientists and the popular media uncritically reproduce its myths."
Again, that is an attack on Evolutionary Psychology, not on sexual selection theory per se. Also, see how she rejects it for its social implications, then goes on to argue the opposite:
"To be clear, the scientific truth, or lack of it, of sexual selection is logically independent of its social implications. Yet, the ethical wrongs issuing from sexual selection's narrative require holding it to the highest standards of scientific rigor. It fails. After 130 years, sexual selection is still not confirmed and I suggest it never will be.

Once scientists start looking through the lens of social-selection, animal behaviors become much easier to understand, and many of the apparent contradictions fall away. Instead of trying to shore up Darwin's sinking theory of sexual selection, we should be improving our understanding of gender and sexuality, because friendship, love, and sex are important."
So, yes. Simplistic gender roles as espoused by Evolutionary Psychology are bunk. Social selection theory is just fine - Frans de Waal probably likes the idea. But I do not see any reason to ditch sexual selection as an explanation for a lot of what is going on in nature. I do not agree that sexual selection is not confirmed. Even the first arguments, those of Darwin in Descent of Man are pretty strong, not to mention all of the research that followed from it over the last century and a half.

A few years ago I did an almost exactly same experiment in two very different species: the Japanese quail and the crayfish. The results from the crayfish experiment were consistent with sexual selection and not with social selection theory. The data from quail were not consistent with sexual selection but were nicely explained by Roughgarden's social selection theory (sorry, no details, both studies are unpublished yet).

So, do not dismiss sexual selection yet, but don't dismiss Joan Roughgarden's ideas, either. Read the book - it will make you think in some very different ways. While you should keep your skeptical antennae on alert while reaidng it, it will also set your thinking free to go in directions you may not have anticipated before.

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