Jai Ranchhor Makhanchor

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The evolution of the peacock’s tail is an example of a process that

Darwin called sexual selection.

8 Sexual selection occurs when a trait is

selected not because it promotes an organism’s survival, but because it

promotes its reproductive success. Darwin saw sexual selection as

something separate from natural selection; these days, however, most

biologists view it as a subtype of natural selection. Either way, sexual

selection is a powerful force in evolution. With their sexual preferences,

females force males to dance or sing or hang upside down flapping their

wings. Most of the beauty and color in nature comes from sexual selection:

the scent and appearance of flowering plants; the rainbow plumage and

melodious songs of many songbirds – and, according to some, the art,

music, and humor of Homo sapiens.

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From an organism-centered perspective,

adaptations are designed to enhance the organism’s inclusive fitness. From

a gene-centered perspective, on the other hand, adaptations are designed to

propagate the organism’s genes. To be more precise, adaptations are

designed to propagate the genes giving rise to them. Spikes and shells are

designed to propagate the genes giving rise to spikes and shells; peacocks’

tails are designed to propagate the genes giving rise to peacocks’ tails; and

nipples are designed to propagate the genes giving rise to nipples. Of

course, for any particular individual, a useful adaptation benefits all the

genes in its genome, not just those that helped build the adaptation. But

across vast numbers of individuals and over vast periods of time, the genes

responsible for the adaptation come to share genomes with essentially every

other gene in the gene pool.

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