What this evolutionary change suggests is that becoming larger is, for some reason, a good idea when you are struggling to survive in this alternating glucose-rich/glucose-poor environment. I won't speculate on why increasing body size might be an advantage - there are many possibilities - but it looks as though it must have been so, because all twelve tribes did it. But there are lots of different ways to become larger - different sets of mutations - and it looks as though different ways have been discovered by different evolutionary lineages in this experiment. That's pretty interesting. But perhaps even more interesting is that sometimes a pair of tribes seem to have independently discovered the same way of getting bigger. Lenski and a different set of colleagues investigated this phenomenon by taking two of the tribes, called Ara+1 and Ara-1, which seemed, over 20,000 generations, to have followed the same evolutionary trajectory, and looking at their DNA. The astonishing result they found was that 59 genes had changed their levels of expression in both tribes, and all 59 had changed in the same direction. Were it not for natural selection, such independent parallelism, in 59 genes independently, would completely beggar belief. The odds against its happening by chance are stupefyingly large. This is exactly the kind of thing creationists say cannot happen, because they think it is too improbable to have happened by chance. Yet it actually happened. And the explanation, of course, is that it did not happen by chance, but because gradual, step-by-step, cumulative natural selection favoured the same - literally the same - beneficial changes in both lines independently.
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