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PRI's Environmental News Magazine

Finches Change

Air Date: Week of July 22, 1994

Jonathan Weiner, author of The Beak of the Finch, is interviewed about observations in natural selection in these small birds. Weiner also reflects on human choices in consumption and sustainability.

Transcript

NUNLEY: Perhaps the most famous creatures of the Galapagos are its 13 species of finches. Charles Darwin was fascinated by the diversity of their beaks, which permit each type of finch to specialize in eating certain kinds of foods. Darwin decided the finches had all evolved from one common ancestor, a crucial step in his development of the theory of evolution. For more than a century, Darwin's theory remained unproven, and while it was accepted as fact by the scientific world, no one had ever actually witnessed natural selection in action. Researchers assumed the process of evolution was just too slow for humans to observe. But over the past 20 years, Princeton biologists Rosemary and Peter Grant have actually seen evolution in progress. Over many generations they've watched the finches of one tiny island in the Galapagos evolve in response to changes in the weather, food supply, and other conditions. Their work, and that of the Galapagos as a crucible of ongoing evolution, is chronicled in The Beak of the Finch: A Story of Evolution in Our Time, by Jonathan Wiener. Mr. Weiner joins us now from the studios of WHYY in Philadelphia. Thanks for coming in.

WIENER: It's good to be here.

NUNLEY: All right. What sorts of changes have the Grants seen in the finches over the years?

WEINER: They've seen changes of many kinds. They've seen changes through the pressure of droughts and floods on the island, which transform the island sometimes from desert to jungle in a heavy rain or, again, from jungle to desert in the space of a dry season. Those are selection pressures that create enormous, enormous upheaval among the birds, and lead to evolutionary change mostly in their beaks. They've also seen selection created by the birds themselves. Every rainy season, at the start of the year, they select among each other, and that sexual selection pressure, as Darwin called it, also produces measurable change in the birds and their beaks.

NUNLEY: Now what about human-generated changes? I'm talking about the kind of pressures that are described in Martha Honey's report that we just heard. How have they affected evolution among Darwin's finches in the Galapagos?

WEINER: In some cases dramatically. I saw this myself. When I visited the Grants I stopped in Puerto Ayora, the fishing village on the island of Santa Cruz, and there the birds are really the sparrows of the village. They're underfoot all the time; they're in the roads, they're in people's gardens, they're pecking at seeds on the window sills. I fed them out of my own hands. That feeding of the finches is a change in the selection pressures that these birds are under. And the result seems to be that the birds are fusing. They are losing their distinctive beaks, and they seem to be melding, morphing, into one Darwin's finch. The reason is that they're no longer under the same selection pressure in the village that they are in the uninhabited outlying islands. And so they don't need all that specialized equipment. And very rapidly, in the space of a century or so, they seem to be losing it.

NUNLEY: How are we affecting evolution on a grander scale; that is, worldwide?

WEINER: This time that we are living in now is a time of enormous evolutionary upheaval. For better or for worse, this may be the most dramatic time for us to have watched evolution since evolution began, because here we have an ecological dominant, ourselves, that is transforming every continent, transforming the conditions of life for every living thing on the planet. Think of the ozone hole, for instance. That's dosing all of life around the South Pole with a greatly increased ultraviolet radiation. And that produces selection pressures as intense as anything in the Galapagos on the plankton and on all that feeds on the plankton. Where also through hunting, for instance, or poaching, producing new selection pressures. Elephants in some of the most heavily poached preserves and rainforests in Africa have moved toward tusklessness. The reason is that those without tusks are much less likely to be shot by a poacher. And so inadvertently, the poachers are driving the evolution of the elephants in precisely the opposite direction the poachers themselves would like.

NUNLEY: Near the end of your book you talk about a group of cactus finches who effectively cheat on the rest of the flock in a way that could some day endanger the entire species. Now, is this a parable for the impact people may be having on the planet?

WEINER: That's the way it struck me when I first heard about it. Cactus finches, which depend entirely on these cactus for their survival, were landing on the flowers, pulling them open with their beaks, snipping the stigma, that tall tube which otherwise would poke them in the eye as they reached in, reaching into the flower, and getting some pollen and some nectar that the other birds couldn't get because they were still waiting for the flowers to open. By doing that, those stigma snippers were destroying the flowers, and they were in effect eating the seed corn. They were reducing their own food supply for the next months and years. But they got an immediate benefit by doing it, and so they prospered and they continue to do it year after year. It's quite possible that one of these years they will do what they've almost done several times in the Grants' experience already. They'll drive their own kind extinct on Daphne Major. The way we're behaving right now as a species is very much like those cactus finches. We're consuming the resources of the planet at a great rate. So we are also eating the seed corn. And again, Darwin's process can't arrest that. Only our own conscious planning and forethought and legal systems can prevent that.

NUNLEY: I want to thank you, Jonathan Weiner, who is the author of The Beak of the Finch: A Story of Evolution in Our Time. Thanks so much for joining us.

WEINER: Thank you very much.

 

 

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