AS EVERYBODY knows, global warming will introduce tropical diseases such as malaria into northern countries, including Britain. But the efforts of the malaria expert Paul Reiter show that everybody is wrong. Mosquito-borne tropical diseases do not threaten the industrialised world.

Reiter, of the Louis Pasteur Institute in Paris, has made some fascinating observations. First, he notes that during the Little Ice Age of the 17th century, when fairs were held on the frozen Thames, malaria was endemic in Britain. Oliver Cromwell died of it in 1658. As recently as the 1920s, moreover, more than 600,000 Russians died of malaria, and cases were reported as far north as the Arctic Circle.

For malaria to flourish, winter temperatures can be as cold as they like, while summer temperatures need reach only 15C (59F). Malaria, in fact, left Europe because industrialisation allowed us both to drain the swamps and develop insecticides and antimicrobials. Also, modern farming engages few people but many animals on the fields, so the mosquitoes feed on animal, not human blood — and farm animals do not incubate human malaria.

Britain, therefore, has long been warm enough to sustain malaria and other mosquito-borne diseases, which were eradicated by measures that will continue to work even if the temperature does continue to rise.

• WHY DO humans and chimpanzees have such large testes? And why are gorilla testes so small? The answer may lie in sperm warfare. For promiscuous animals such as ourselves and chimps, each male’s sperm has to race to the egg against the sperm of other males, so males do best to produce many sperm. Gorillas, however, are harem animals, so the females are faithful and their master need produce few sperm.

  This hypothesis has now been tested in the laboratory. Javier delBarco-Trillo, of the University of Memphis in Tennessee (a town, incidentally, that lost its city charter in 1879 after the mosquito-borne disease of yellow fever had killed half its population) has counted the number of ejaculations, and the number of sperm produced with each ejaculation, of the shamefully promiscuous meadow vole.

  When meadow moles fornicate in peace, the males ejaculate some six times and produce 100 million sperm. But when the animals fornicate in a cage that is impregnated with the smell of other male meadow voles, the number of ejaculations does not rise but each is more effective, producing on average 170 million sperm. Males produce more sperm the more they fear that their females might be impregnated by others. Over evolutionary time, the testes of promiscuous animals will thus enlarge.

  Penises, too, are larger in promiscuous species such as ourselves and chimps, but that is apparently an aesthetic choice: when females are allowed to choose their partners, they choose the well-endowed. But, gorilla females having no choice, gorilla penises are small.

• WHICH BRINGS me to another piece of aesthetic science. Why have we humans, uniquely among the apes, lost our body hair? Body hair protects animals against cold and heat, and we are vulnerable without it. Charles Darwin suggested that we lost our hair for sexual reasons, namely that humans — and females in particular — have used their naked skin as a canvas on which to paint, tattoo, pierce and otherwise clothe themselves to attract mates. He suggested, indeed, that art originated in such mating rituals. Can we prove this?

We know that art was invented by Cro-Magnon humans (us) who left Africa between 50,000 and 100,000 years ago and who displaced the Neanderthals, who had no art. And we also know that there are three sorts of lice that infect humans, including head lice and body or clothes lice.

Presumably clothes lice evolved from hair lice when we lost our body hair and invented clothes. Mark Stoneking, of the Max Planck Institute in Leipzig, has now used molecular biology to determine when the DNAs of the two species diverged. It was some 70,000 years ago, coinciding with the replacement of Neanderthal humans by ourselves, the artists.

Darwin was right. Art evolved as nakedness evolved, so the one could sustain the other.

The author is a clinical biochemist and Vice-Chancellor of the University of Buckingham