Speedy Evolution in Galapagos Finches


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Podcast available: Speedy Evolution

One of the tenets of evolutionary biology is that it requires time, but some microevolutionary changes can occur with surprising rapidity. The Grants have studied Darwin's finches in the Galapagos for over 30 years and have observed many changes. Recently they reported a change in the beak size of the medium ground finch on Daphne Major. In 1977 a drought reduced the number of small seeds available for the birds, forcing them to rely on larger seeds requiring considerable force to open. Within a couple generations, beak size, and hence ability to open large seeds, had increased. In 2003 a second drought, combined with the presence of large ground finches with substantially larger beaks, drastically decreased the number of large seeds available. Now ability to eat small seeds became an asset. The attrition rate for large beaked birds was horrendous, leaving very few individuals with large beaks to reproduce. The beak of the medium ground finch was quickly reduced to pre-1977 size. This paper is important because it shows how fast change can occur, and it demonstrates an interplay between environmental effects (the droughts) and population numbers (presence or absence of the large ground finch) can drive evolution in different directions.


Darwin’s Finches Evolve Before Scientists’ Eyes
Goudarzi, S., LiveScience, July 13, 2006

Competition Drives Big Beaks Out of Business
Pennisi, E., Science 311, 156 (2006)

Evolution of Character Displacement in Darwin's Finches
Grant, P. R. and Grant, B. R., Science 313 , 224(2006)

Darwin’s Finches by Dr. Robert Rothman

Darwin’s Finches – Wikipedia

AIBS video presentation by Peter and Rosemary Grant
“What Darwin’s Finches Can Tell Us About Evolution”

Jonathan Weiner. 1994. The Beak of the Finch: A story of Evolution in Our Time. Alfred A. Knopf.


1. What trait was tracked in this study? How does this trait influence survival?

2. How long did it take for measurable changes to occur in the trait?

3. What environmental factors influenced changes in the trait?

4. Predict what would happen to the beak size of the population if there was another drought.



Natural Selection and Variation in Birds
Level: Advanced middle school, high school, introductory college
Time: Two 50 minute class periods
Overview: A single lesson to introduce students to the concept of variation within a population. Students measure a particular trait (bill size) in a collection of specimens and analyze the distribution within a population. Excellent materials and teacher guide.