Evolution in One Lesson

Graham Bell may well have written the best book on evolution since The Selfish Gene. Most works on evolution are either overly speculative or incomprehensible to anyone without a degree in chemistry. Bell’s Selection: The Mechanism of Evolution hits a perfect middle ground, inter-weaving 175 central lessons of evolution with fascinating experimental details. Did you know that biologists have deliberately tried to breed the biggest mice on earth? It only took 35 generations to increase average weight by 7 standard deviations, from 25g to 43 g.

Selection reads like a well-organized treatise on intermediate microeconomics. It begins with the “Crusoe economics” of biology: asexual organisms. We can illustrate the basics of evolution using simple RNA viruses, and there are plenty of experiments that do so. If you want to increase the speed of reproduction, for example, all you have to do is put your RNA viruses in a resource-rich environment, and evolution does the work. After laying these building blocks, Bell branches out to more complex cases: selection on several characters, social selection, sexual selection.

Like a lot of good economics, Bell’s lessons are obvious upon reflection, even though few of us could have figured them out on our own. Here is a simplified version of one of his thought experiments on the advantages of sex:

Suppose there are three equally important genes. Designate the more fit allele + and the less fit allele -. You start with the following two strains: +– and -++. In an asexual reproduction, the -++ strain takes over, because it has two + genes and its rival only has one +. But with sexual reproduction, one-eighth of the offspring of the two strains are +++. The future is theirs.


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