Evolution by Steve Jones

Author:Steve Jones [Jones, Steve]
Language: eng
Format: epub
ISBN: 9781405929455
Publisher: Penguin Books Ltd
Published: 2016-11-25T00:00:00+00:00

Evolution by accident

Random events play a large part in evolution (as they do in physics). In 1929 a speedy French destroyer was sent from the African port of Dakar to deliver mail to Brazil. It had some unwelcome passengers: malaria-infected mosquitoes. Previous ships had taken so long to make the trip that the stowaways died en route, but the new vessel got there in record time, and some survived. Soon, a great malaria epidemic began.

There is now much less diversity in that parasite in Brazil than in Africa, for only a tiny sample had made it across the ocean. That single accident did more to change its identity than had thousands of years of natural selection in its native land.

Other diseases have been through even smaller bottlenecks. The agents of leprosy, smallpox and plague all descend from animal parasites. They are diverse in their original hosts but vary scarcely at all in their millions of human victims, as proof that they began with a single invasion. The agent of plague, for example, is almost identical across the globe; and the remains of bones from London’s ancient epidemics bear almost the same genetic signature as do the plague bacilli of today. Perhaps a single bite of an unlucky human by an infected flea long ago led to a disease that has killed millions.

The inhabitants of remote islands have much the same history. Hawaii has its own unique plants, snails, insects and birds, but most have almost no DNA variation, evidence that each descends from a few ancestors who arrived long ago. One Act of God (if not God himself) can have dramatic effects on evolution.

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