Epilogue

• A few years later, 1359mm of rain fell on the Islands:

– The finches went crazy — the finch population increased by 400%!

– Lisle Gibbs, a graduate student of the Grants, was there and she measured every finch carefully.

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Epilogue continued…

• When Gibbs returned to Princeton and analyzed his data, he was stunned:

– Natural selection had reversed course.

– Large finches were dying:• Small seeds were everywhere, but it took too many

of them to satiate a large finch with a beak built for big seeds.

– Small finches were reproducing like crazy.

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CQ10: If small birds are selected against in one year and selected for in another, is evolution still taking place?

A: Yes.

B: No.

C: Maybe.

D: I don’t know.

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Epilogue continued…

• The cycles weren’t over yet:

– A year after the heavy rains, 53mm of rain fell.– The year after that, the grand total: 4mm.

• Galapagos weather patterns are cyclical.

• Let’s look at the finches over a longer time scale…

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The graphs on this and the following slides are details from Figure 1 in "Unpredictable Evolution in a 30-Year Study of Darwin's Finches” by Peter R. Grant and B. Rosemary Grant, Science, 26 April 2002, vol. 296, no. 5568, pp. 707–711. Used with permission from AAAS.

CQ11: How has the average body size of these finches changed 1973-2001?

A: They are much larger.

B: They are a little larger.

C: They didn’t change.

D: They are a little smaller.

E: They are a lot smaller.

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CQ12: How has the average beak size of these finches changed?

A: They are much larger.

B: They are a little larger.

C: They didn’t change.

D: They are a little smaller.

E: They are a lot smaller.

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CQ13: How has the beak shape changed?

A: They are a lot more pointed.

B: They are a little more pointed.

C: They didn’t change.D: They are a little more

blunt.E: They are a lot more

blunt.43