Beak of the Finch

by Jonathan Weiner

Occasionally I stay up late at night to finish a new Carl Hiassen or Linda Barnes novel; last week, I was up late finishing Beak of the Finch, by Jonathan Weiner. I can't remember the last time I lost sleep for a work of non-fiction, but this book is well-written, easy to read, and continually interesting.

Beak of the Finch details a fascinating study of evolution in action among the emblematic and eponymous Galapagos finches. The book is not an evolutionary bible - it doesn't mention, for example, the classic problem of how wings evolved (see some of Stephen Jay Gould's writings for that); nor is it a point-by-point refutation of creationism. Instead, it is an account of how evolution actually works, day by day and year by year.

Weiner begins by pointing out what was, until recently, a major drawback of evolutionary science: namely, the lack of actual experimental data. Darwin's Origin of Species is, in many ways, a thought experiment, positing the Theory of Natural Selection to explain the facts of evolution, and citing supporting data ranging from fossils to pigeon breeding; yet the power of natural selection to actually modify and create species is left undemonstrated, explained by supposition, partly because Darwin thought it was too gradual to be demonstrable.

Peter and Rosemary Grant's study of the Darwin finches is not the first experimental study of evolution, but it is among the longest running and most thorough, and is, according to Weiner, canonical in its field. The Grants have studied Darwin's finches now for 20 years or more, since 1973, in the ideal natural laboratory of a Galapagos island. They have watched the finches live and die through drought and flood, studying the changing food supply, and measuring, always measuring, those famous beaks as they varied in size from generation to generation. They measured the beaks of the finches that survived, and procreated, and the beaks of the finches that died.

I don't want to give too much away, so I won't explain their findings, but let me offer this quote:

"Once, just as I was beginning a lecture," says Peter Grant, "a biologist in the audience interrupted me: 'How much difference do you claim to see,' he asked me, 'between the beak of a finch that survives and the beak of a finch that dies?'

"'One half of a millimeter, on average,' I told him.

"'I don't believe it!' the man said. 'I don't believe a half of a millimeter really matters so much.'

"'Well, that's the fact,' I said. 'Watch my data and then ask questions.' And he asked no questions."

"None," Rosemary agrees. "And he sat there scowling."

The Grants are demonstrating what Darwin thought was too slow and gradual to be demonstrated: evolution in action.

Interspersed throughout is an account of Darwin, his original trip in the Beagle, and some of the 20 years of work that prefaced Origin of Species. A lot of this was new to me, and I found it interesting in its own right, but it also lent a background and texture to the accounts of the Grants on the same islands 100 years later, studying the finches that Darwin, despite popular conception, mostly ignored.

In addition, as you might expect, are accounts of other experimental studies of evolution, with subjects ranging from Drosophila to guppies. One elegant experiment that tickled my fancy was conducted on crossbills, whose peculiar bill shape allows them to feed efficiently on pine cones. Craig Benkman and Anna Lindholm trimmed the beaks of some crossbills (painlessly, like trimming your toenails), and as their beaks grew back, measured the increased effectiveness of each crossbill in opening pine cones. They thus demonstrated the advantage even a slightly crossed bill gave to the primogenitor, and the incremental advantage its descendants received as their bills changed bit by bit in each generation. One half of a millimeter matters so much for survival.

Evolution, Beak of the Finch compellingly argues, is happening all the time. The sparrows and jays at your feeder, the coneflowers and bluestem in the prairie, the insects and bacteria who grow increasingly resistant to our attacks, all are populations whose characteristics from generation to generation are in a sort of Brownian motion; each generation might look the same to our so casual eye (who can distinguish half a millimeter at a distance of even 3 feet?), but the requirements of finding food, finding mates, and producing offspring are a filter that every generation finds both omni-present and effective.

© 1995, Greg Tillman.

latest update: May 30, 2001
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