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A beginner’s guide to sex
  1. John Launer
  1. Correspondence to Dr John Launer, London Department of Postgraduate Medical Education, Stewart House, 32 Russell Square, London WC1B 5DN, UK; jlauner{at}londondeanery.ac.uk

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Most doctors know remarkably little about sex. They may have learned the facts of life at school, studied family planning and sexually transmitted diseases as medical students, and had some personal experience of sexual relationships. Yet they are unlikely to have had any serious teaching about evolution, and hence to understand very much about the biological role of sex. This is a pity. Sex is a fascinating subject, not just in the most obvious sense, but because discoveries in biology in recent decades have given us a far greater understanding of males and females, and the interactions between them. In this article, I want to offer a brief review of what we now know about the evolutionary biology of sex, and the consensus that is emerging around sexual psychology.

Sexual reproduction began around a billion years ago. For around two and a half billion years before then, it was unknown: every organism reproduced by dividing rather than by coupling with another. So why didn’t every species carry on splitting rather than splicing? Darwin thought he knew the answer. He considered it the best way of producing variation in a species and therefore the widest range of different types that might survive in a changing environment. But in this case Darwin was wrong.

Since Darwin’s time it has become clear that you do not actually need sexes for this purpose: variation …

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