Part 1, Chapter 6 Summary

Trevor Price observed the finches the year after the drought. He banded all the hatchlings and knew every bird upon sight. He also made the discovery that the young needed to be big, but the adults needed to be smaller. Big could be a liability if the dry season arrived before the fledgling had fully matured.

Natural selection is one facet of evolution; the other is sexual selection. Price watched the finches for three years and found changes in sexual selection during this time. The years directly after a harsh dry season were different then if the dry season was mild. It proved what Darwin tried to explain in "The Descent of Man." But it also went past his theory to show how sexual selection can change due to natural selection.

John Endler has been working with guppies in Venezuela and...