Thursday, February 12, 2009

Wednesday, February 11, 2009

Special issue of Nature on evolution

This week's Nature is a special issue on evolution. You can access it through the library website (electronic journals). There are a couple of news articles looking at recent research on the evolution of human culture, a debate on whether scientists should research the link between race and IQ, a fanciful article asking what would've happened if Darwin's publisher had asked him to rewrite the Origin as a popular book about pigeons, an article about how Darwin's anti-slavery views shaped his scientific ones, reprints of the poetry of Darwin's great-great-granddaughter, and a bunch of review articles on various evolutionary topics by various famous evolutionary biologists.

Chapter VII

Permit a humble supplicant to pose a question to the biologists of this outfit. In regards to warning calls, it was said the caller announcing his location to the predator by making noise isn't too much of a disadvantage. I would agree. Even if it is a disadvantage, it probably isn't so much of a disadvantage that the trait would be deselected. Callers rarely are killed as a result of their behaviour. Therefore, even if the behaviour isn't advantageous to the individual (while it is undoubtedly advantageous to the group) would not the trait still be passed down because it is not so disadvantageous as to warrant deselection - especially if it confers a general advantage to the whole?

Cannot this logic be applied to those species that produce sterile offspring? If giving birth to some sterile offspring does not destroy utterly the parent's prospects of reproductive success, since they may produce other offspring that are fertile, why should a variation with the tendency to produce some sterile offspring be wiped out of existence if producing sterile offspring does not hinder their fitness as an individual and enhances the fitness of the family or group?

I throw this question out into the void.

Further thoughts on Chapters VII-VIII

I don't have much else to say on chapters VII-VIII that I didn't say in class, though some of these points were raised after some folks left so I'll repeat them here for everyone's benefit.

1. I love chapter VII, full of really interesting stuff. So full, in fact, that on p. 237-238 Darwin can just toss off the idea of kin selection/group selection as an explanation for the evolution of altruistic (self-sacrificing) sterile workers, and then move on to focus on what he considers the really difficult problem of explaining the evolution of distinct worker castes. We'll return to the ideas of kin and group selection, the distinction between them (or lack thereof), and their implications for humans, nearer to the end of the term (Darwin himself did come back to kin/group selection in Descent of Man). Darwin also notes in passing that the existence of distinct castes of sterile workers refutes Lamarckism ("oh by the way, I've refuted one of the most important biological ideas of all time"). And the long discussion of how bees could build complex, geometrically-perfect, wax-economizing honeycombs by following simple behavioral rules is extremely modern-sounding, perhaps the most modern-sounding passage in the entire book so far. The idea that simple biological rules, followed by 'dumb' individual agents, can yield complex, apparently-intelligent outcomes, and that we can demonstrate this by mathematical modeling, is not just a modern point of view but a cutting-edge point of view. That is, both the hypothesis, and Darwin's way of evaluating it, are bang up-to-date. They should hire Darwin at the Santa Fe Institute. The discussion of the evolution of brood parasitism is mostly off-base, but even Darwin's incorrect hypotheses are at least imaginative.

2. In contrast, I found chapter VIII a slog. It's Darwin's upteenth argument against the idea that species were specially created and are qualitatively different than varieties. It's ok, we believe you, please stop! What struck me most about this chapter is that it's perhaps the first time I've seen Darwin miss a clear opportunity to foreshadow a very important modern idea. Darwin thinks that hybrid sterility is just 'incidental'. But if hybrid matings don't lead to fertile offspring (either because they lead to no offspring at all, or only to sterile offspring), then selection will favor any trait that prevents hybrid matings in favor of productive matings (i.e. "assortative mating"--mating with those who are similar to you). Selection will also disfavor hybrid mating if hybrid offspring are fertile, but are less fit than their parents, for instance because the hybrids are intermediate between the parents and so aren't well-adapted to the 'niche' of either parent (or to any other niche--they're 'jacks of all trades and masters of none'). In short, it's very common that selection will favor what are now called isolating mechanisms. We need to understand how those mechanisms work, because they're the flip side of the origin of species. If you want to understand how species split, you need to also understand what keeps them from merging. Writing in the the 6 Feb. issue of Science, UBC's Dolph Schluter reviews evidence for what's now called "ecological speciation", which is essentially the modern version of Darwin's own idea about how species originate. Schluter highlights the importance of isolating mechanisms.