The Beak of the Finch - Jonathan Weiner

This is book is mostly about evolution, viewed primarily through the lens of the different species of finches on the Galapagos Islands that Darwin noted when he was there briefly. Although Weiner points out Darwin didn't make much of the finches, thinking they were mostly one species.

Weiner discusses Darwin, what he wrote about natural selection and how it would work, and how Darwin didn't actually have any direct evidence of it. No one had actually seen natural selection cause one species to evolve into new species. One thing this taught me I didn't realize was that by the 1920s and 1930s, there were a fair number of scientists who dismissed natural selection because of that. A nice idea, but there was no real evidence, so ultimately irrelevant.

Most of the book, though, is spent on research done on the various finches, headed by Peter and Rosemary Grant. At the time of the book was originally published, they and their various graduate students had been traveling to the islands for two decades, banding, measuring, and observing everything they could about the finches. Weiner uses the discussions of their observations, and those of other, similar studies around the world, as a way to discuss evolution and the forces involved in more detail.

So there's a year of intense drought in the late 1970s, and this seems to push two of the species towards the extremes of their beak size. The lack of seeds meant that certain sizes had the advantage. They bred, they passed on their genes. But a few years later, there was an especially intense El Nino that brought massive rainfall, which meant a bumper crop of seed production, and this pushed things the other direction. The idea being there's this push and pull on the birds (and that the birds put on their food sources) and it won't be visible at certain scales. Pull back far enough and it looks like there's no change, but zoom in, and there's an oscillation.

(Several of my professors were fond of pointing out species don't simply hit the carrying capacity of their habitat and stop. Their population fluctuates around it from year to year, or generation to generation, depending on external factors like food, disease, climate.)

It's a very interesting book, goes into studies people were coming up with to test in the lab the hypotheses they devised about what they saw in the wild. The emerging role of DNA testing, how sexual selection can sometimes exert contrary pressure to natural selection, how our constant attempts to kill all the bugs or illnesses with drugs or pesticides are themselves causing evolution in the things we try to eradicate. That part is pretty old hat by now, but it was a good inclusion as an example of how we can exert selective pressure, whether we intend to or not.

'One finch eats green leaves, which birds are not supposed to do. Another, the vampire finch, found chiefly on rough, remote, cliff-walled islands of Wolf and Darwin, perches on the backs of boobies, pecks their wings and tail, draws their blood, and drinks it. Vampires also smash boobies' eggs against rocks and drink the yolk. They even drink the blood of their own dead.'