Toward a Biology Worthy of Life > Evolution and the Illusion of Randomness > Brief excerpt
A project by Stephen L. Talbott

The giraffe’s long neck (1)

To see the failty of the fitness concept most clearly, you need only look at actual attempts to explain why a given trait renders an animal more (or less) fit in its environment. For example, many biologists have commented on the giraffe’s long neck. A prominent theory, from Darwin on, has been that, in times of drought, a longer neck enabled the giraffe to browse nearer the tops of trees, beyond the reach of other animals. So any heritable changes leading to a longer neck were favored by natural selection, rendering the animal more fit and better able to survive during drought.

It sounds eminently reasonable, as such stories usually do. Problems arise only when we try to find evidence favoring this hypothesis over others. My colleague, whole-organism biologist Craig Holdrege, has summarized what he and others have found, including this: First, taller, longer-necked giraffes, being also heavier than their shorter ancestors, require more food, which counters the advantage of height. Second, the many browsing and grazing antelope species did not go extinct during droughts, “so even without growing taller the giraffe ancestor could have competed on even terms for those lower leaves.” Third, male giraffes are up to a meter taller than females. If the males would be disadvantaged by an inability to reach higher branches of the trees, why are not the females and young disadvantaged? Fourth, it turns out that females often feed “at belly height or below.” And in well-studied populations of east Africa, giraffes often feed at or below shoulder level during the dry season, while the rainy season sees them feeding from the higher branches — a seasonal pattern the exact opposite of the one suggested by the above hypothesis.

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