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Here’s a simple example. The wooly mammoth inhabited the northern parts of Eurasia and North America, and was adapted to the cold by bearing a thick coat of hair (entire frozen specimens have been found buried in the tundra). It probably descended from mammoth ancestors that had little hair - like modern elephants. Mutations in the ancestral species led to some individual mammoths - like some modern humans - to be hairier than others. When the climate became cold, or the species spread into more northerly regions, the hirsute individuals were better able to tolerate their frigid surroundings and left more offspring than their balder counterparts. This enriched the population in genes for hairiness. In the next generation, the average mammoth would be a bit hairier than before. Let this process continue over some thousands of generations, and your smooth mammoth gets replaced by a shaggy one. And let many different features affect your resistance to cold (for example, body size, amount of fat, and so on), and those features will change concurrently. The process is remarkably simple. It requires only that individuals of a species vary genetically in their ability to survive and reproduce in their environment. Given this, natural selection - and evolution – are inevitable.11
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