Friday, October 2, 2009

Reverse Evolution?

The New York Times has an article questioning if evolution can run backwards.

The Belgian biologist Louis Dollo was the first scientist to ponder reverse evolution. “An organism never returns to its former state,” he declared in 1905, a statement later dubbed Dollo’s law.

To see if he was right, biologists have reconstructed evolutionary history. In 2003, for example, a team of scientists studied wings on stick insects. They found that the insects’ common ancestor had wings, but some of its descendants lost them. Later, some of those flightless insects evolved wings again.

Yet this study did not necessarily refute Dollo’s law. The stick insects may indeed have evolved a new set of wings, but it is not clear whether this change appeared as reverse evolution at the molecular level. Did the insects go back to the exact original biochemistry for building wings, or find a new route, essentially evolving new proteins?
What follows next is a fairly high-level summary of Dr Thornton's U of Oregon research on changing protein receptors. Basically, what he found was he could change forward "ancestral" proteins by altering a limited number of receptors. However, to change backward modern proteins, additional modifications needed to be made. He deduced that during evolution, in addition to specific changes to ancestral proteins that actually account their ability to do new things, there are also "silent" changes (that evolved by chance along with the significant changes) that don't actually affect the behavior of the modern ones. However, they do prevent the modern proteins from going back to the original function (unless they too are removed). Since the ancestral proteins can go forward with or without the silent changes, but the modern proteins only work in the ancestral form without the silent changes, reverse evolution is far less likely to occur.

In other words, if our kids start having tails, it's not because we are not going back to monkey-style tails, but rather whatever new configuration happens to be most beneficial to our survival. Sorry, Jonathan Coulton, but we're not De-Evolving.

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