The Red Notebook

The following brief news item seems to lend support to a hunch I have had for some years:

New Scientist: Bird song goes out of fashion too

… Behavioural ecologists have long known that some songbirds develop local dialects, and that individual birds respond more strongly to their own dialect than to a foreign one. Less is known about how, or how quickly, such differences arise.

To study how a dialect changes over time, Elizabeth Derryberry, a behavioural ecologist at Duke University in Durham, North Carolina, compared recordings of male white-crowned sparrows’ song from 1979 […] and 2003. The modern song, she found, was slower and lower in pitch.

This difference mattered to the birds… [Derryberry] found that females solicit more copulations and males showed more aggressive territorial behaviour to the contemporary song than to the older ones… The result shows that meaningful differences in song styles can arise within just a few years, and thus that mating barriers can be erected quickly, says Derryberry.

I have long suspected that sexual selection might be more important in species-creation than it is generally given credit for. Sexual selection tends to play second fiddle to natural selection in discussions about speciation. In fact, I would argue that sexual selection is simply a sub-category of natural selection—albeit a very important sub-category.

It seems to me that differing sexual preferences amongst potential mates creates evolutionary niches without the need for haphazard geographical isolation. This must greatly increase the opportunities for speciation. In fact, my hunch is that sexual selection could prove to be more important than traditional natural selection in terms of speciation.

See also: Guppy love under the microscope (old weblog)

The Natural History museum has a fascinating news story about sexual arms races in diving beetles.

Apparently, every time male diving beetles evolve better suction cups on their feet to hold on to females during mating, the females evolve countermeasures to decrease the effectiveness of the suction cups. This is because the optimal time, length or the number of matings is not the same for males and females.

Who says romance is dead?

I have to admit, I’ve never had much time for sociobiology or its close relative, evolutionary psychology. It’s not that I think there’s anything wrong with seeking evolutionary explanations for social behaviour—how could I, when Darwin himself predicted similar studies:

In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.

The problem I have with sociobiology is the same problem I have with psychology in general, and sociology in particular: it tries so hard to be recognised as a rigorous, scientific discipline, but any armchair hypothesist can come up with a sociobiological explanation for pretty much any behaviour they care to think about. And because sociobiology often provides simple (and, in some cases, over-simple or obvious) explanations for quirky human behaviour, any crackpot theory emanating from a university department with an -ology suffix is pretty much guaranteed plenty of media coverage—especially if it involves sex: the punters (and lazy science correspondents) just love it!

I appreciate this is being totally unfair to serious sociobiologists. In my defence, however, I would add that most serious sociobiological studies I have read about left me thinking that’s all very interesting, but so what?

There was a typical example of it this week. Sociobiologists in Norway published a serious academic paper entitled Why do blue-eyed men prefer women with the same eye color? It’s all good stuff, and received plenty of press coverage. Their hypothesis (supported by, as far as I can tell, a well-designed experiment) is that blue-eyed men tend to be attracted to blue-eyed women because blue eyes are the product of recessive alleles; so choosing a mate with blue eyes means that any offspring they have with her must also have blue eyes. So blue-eyed men who have children with blue-eyed women can be slightly more confident—possibly only subconsciously—that their blue-eyed children are their own (and, conversely, will know for certain that any brown-eyed children are not theirs). On the other hand, brown-eyed men, whose eye colour is based on dominant alleles, can end up having children with eyes of either colour, so there is no genetic reason for them to have a preference for any particular eye-colour when selecting a mate.

Does this tell us anything particularly important about what it is to be human? Is eye colour now, or has it ever been, a major factor in mate selection for males with blue eyes? Does it come anywhere near more traditional visible sexual factors? Somehow I doubt it. The sociobiologists carrying out the study are not suggesting that whatever genetic benefits there might be are sufficiently strong to make it a positive evolutionary advantage to have blue eyes (in which case, there would presumably be selective pressure for there to be all sorts of other eye colours associated with recessive alleles); they are simply saying that, given that there is a visible (possibly non-adaptive) trait that is associated with recessive alleles, males who happen to have that trait appear to have a slight preference for females who also happen to have it.

Which is all very interesting, but so what?

In fact, I’m not entirely convinced that this study establishes categorically that there is a clear genetic reason for blue-eyed men’s preference for blue-eyed women. I can certainly imagine alternative, cultural explanations for such preferences—although they wouldn’t be nearly as neat (or newsworthy) as the sociobiological interpretation, and I don’t have an armchair to hand at the moment.

In science, even self-evident truths need to be put to the test. There was an interesting story in the Telegraph last week, which described how scientists have tried to show that the long necks of giraffes are adaptations to give them an advantage over shorter animals when grazing trees. Bleeding obvious, you might think, but it has also been suggested that giraffes’ long necks might be a result of sexual selection. Although the scientists concede that their experiment is not definitive, they conclude that giraffes browse at high levels in the leaf canopy out of preference (to avoid competition with shorter browsers), rather than simply because their necks happen to be long.

A small victory for common sense, then.

My first lesson in giraffe evolution occurred when I was about six years old. My primary school teacher explained to the class how giraffes tried to stretch their necks to reach the higher leaves and, over time, all giraffes ended up with longer necks. Little did I realise at the time that I was being taught a Lamarckian version of evolution. I’m sure this was not a deliberate mistake on my teacher’s behalf: she probably thought she was introducing us to Darwinian thinking.

Come to think of it, that was the only lesson I ever received in evolution at either primary or secondary school. English school biology in my day was all about the organs of species, not their origins. I wonder if it has changed much.