Friday, January 2, 2009

Time as an Independent Variable

As part of a commemoration of Charles Darwin's 200th birthday in February, this is one of twelve elegant examples of evolution selected by the editors of Nature:

An Evolutionary Arms Race, Frozen in Time. Predator and prey evolve together; the adaptations of one driving adaptations in the other. But how can one study this over time, in detail? Biologists from Belgium's Catholic University of Leuven used water fleas and parasitic mites that had been preserved in the mud of a lake's bottom. The sediments were precisely dated and their inhabitants revived, allowing researchers to mix species from different eras and directly measure their developing capacity for infection and escape.
This is not even the most famous instance of ongoing research with experiments that use time as an independent variable: a brilliant experiment by Blount, Borland, and Lenski takes this approach, as explained by PZ Myers:
We can't rewind the whole planet, but with careful design, we can set up populations that can be rewound. Lenski has done this by setting aside 12 separate populations of E. coli 20 years ago, each one evolving independently and in its own direction. So far, over 44,000 generations have passed in the flasks in Lenski's lab. This is a long time, and at the typical mutation rates present in these creatures, it means that every nucleotide has been mutated singly multiple times in the population — in other words, there has been ample time to thoroughly explore the single substitution search space. In addition, a sample of each population was taken and frozen every 500 generations, so they can go back in time at will and examine their genome or even restart the line.
The denialists who say evolution can't be experimentally validated because it describes events lost to the past are simply not looking.

(H/T 3QD)

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