The majority of our cells subjugate their individuality, devoting themselves to assisting the reproduction of the minority that are capable of it: ‘germ-line’ cells in the testes or ovaries, whose genes are destined to travel, via sperms or eggs, into the distant future. But genetic relatedness is not the only basis for subjugation of individuality in fruitful division of labour. Any sort of mutual assistance, where each side corrects a deficiency in the other, can be favoured by natural selection on both. To see an extreme example, we dive inside the gut of an individual termite, that
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