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Speaking of ways evolution can happen, there’s also co-evolution


We were just speaking about successful hybrids that could wipe out parent species, as a form of evolution that is not magic.

There is also co-evolution, where life forms change over time because of their relationship to each other. In “Bug Me: Our Bodies Need Microbes and Worms” (Wall Street Journal, June 30, 2012), Matt Ridley tells us,

A recent study by Howard Ochman at Yale University and colleagues found that each of five great apes has a distinct set of microbes in its gut, wherever it lives. So chimpanzees can be distinguished from human beings by their gut bacteria, which have been co-evolving with their hosts for millions of years.

A new experiment by Hachung Chung in Prof. Dennis Kasper’s laboratory at Harvard Medical School shows that this microbial specificity has consequences for health. Researchers bred mice with no gut “flora” at all, then filled their guts with either normal mouse bacteria or normal human bacteria. In both cases the microbes flourished, producing an equal quantity of both individual cells and species.

But the immune system of the mice with human gut flora was markedly less active. In some way, the mouse immune system did not recognize the human gut flora and did not properly develop. When the researchers filled a mouse gut with rat bacteria, the same thing happened: that is, not even the rat bacteria are similar enough to stimulate the mouse immune system. More.

Clearly, the bacterial population in each case evolved, and could not just devolve back via some reset button.

That said, the bacteria did not become rats, mice, or humans. But we did not promise you magic, did we?


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