Rewinding History

Some of the most interesting history thought-experiments consider the question of the inevitability of important world events. Was the South destined to lose the US Civil war due to its inherent disadvantages, or could some strategic blunder have turned the tide? The question of contingent history has a parallel in biological evolution. The difference is that science is now beginning to give us the tools to draw actual conclusions about what would happen if we could “rewind” the clock of evolution and play it again. We can start to identify the contingent calf-paths in our ancestry, and distinguish them from the traits, like flying and vision, which have evolved separately multiple times different lineages. The similarity between  marsupials and placentals is commonly cited as strong evidence that not everything is by accident. However, the amplifying effects of the “rich-get-richer” is a hallmark of network behavior. Just as the choice, possibly based on minor considerations existing centuries ago, of whether a tiny settlement might be built on bank of the river or the other can dictate the location of a modern metropolis, small, accidental changes may get locked-in by evolution.

We now have the opportunity to watch history play out again, either by doing it ourselves and growing 20 years of bacterial generations, as in the Lenski lab, or by resurrecting ancient genes from 500 million years ago and inserting them into modern specimens. The picture that is forming from these experiments is, as in history, a mix or randomness and inevitability that shows the importance of individual mutation events that can “potentialize” or “actualize” a given adaptation. There is likely to be a crucial, revolutionary advance hit upon by evolution that, by itself, does not totally provide for the trait, but is close enough so that some among the population of its descendants are, under the right external conditions, strongly favored to have a large advantage when they perfect the trait. So the response to our question should be “how far back do you want to rewind?” 

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Author: lnemzer

Assistant Professor Nova Southeastern University

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