Kavli Meeting: Moving Beyond Darwin
In his talk last week, biologist Mike Lynch started by telling the audience he didn't like the term "Darwinism". I don't either, and I've written several posts on the misleading way that creationists label people as "Darwinists" to make science look like ideology. We don't call physicists Einsteinians or astronomers Hubbleites, though they, like biologists, use and appreciate the contributions of those who laid the foundations of the fields.
Lynch is visiting from Indiana University for a program on the evolution of cooperation and multicellularity. He doesn't like the term Darwinism because he says it trivializes all the new ideas and advances that have come about in the subsequent 150 years.
Lynch's work focuses on mutations - a piece of the puzzle that Darwin didn't know about. Darwin figured out that for natural selection to work, traits that endowed "fitness" had to be heritable. Evolution couldn't work unless traits could be passed from parents to offspring. But how?
We now understand that mutations in DNA lead to variations in traits that can be passed down generation to generation. But there's still much we don't understand. While natural selection is important, some traits we see in ourselves and other living things can come about randomly, through a process called genetic drift. Mutations that don't endow an organism with any advantage can still spread through a population randomly, especially if there's some kind of a bottleneck.
If just a small number of people survive some cataclysm, for example, they might all just happen to have blue eyes, and that random occurrence would lead to a lot more blue eyed people once the bottleneck opened up again.
Lynch said he's interested in better understanding the relative roles of natural selection and random drift, and investigating how fast organisms accumulate mutations – the good, the bad and the indifferent.
Measuring mutation rates is tricky because natural selection tends to kill off individuals carrying harmful mutations, thus preventing most genetic errors from ever spreading. But how fast would living things accumulate mutations if you took the influence of natural selection away?
Lynch came up with a way to measure mutation rates while removing the influence of natural selection. With a number of different communities of organisms, including the worm c. elegans, he randomly selected individuals from each generation and used them to start a new community. That way he removed the competition that would normally determine who had the most surviving offspring. The mutations in the worms he chose at random would be passed on whether they were advantageous, deleterious or neutral.
What he saw after a few generations of this process were some weird mutant worms – worms with oddly formed genitalia and crooked tails. His experiments also showed evidence for a minimum rate of mutations. There seemed to be a limit to how faithfully these organisms could copy their DNA.
Lynch's experiments also included a number of single-celled organisms, such as Deinococcus radiodurans, which is intriguing because it can live in strong acids and even the high radiation environment of a nuclear reactor. It has some unusual mechanisms for keeping its DNA from becoming scrambled.
What about mutation rates in humans? We can't very well put people through the same kinds of experiments. But geneticists have tried to compare children with their parents, said Lynch, and estimate that we all carry on the order of 100 mutations that can't be found in either parent. How these influence the future trajectory of human evolution is another topic of ongoing science - reserach that's streching far beyond Darwinism.
More talks are coming this week - on biology and physics. On Friday I get to give a talk about the way science gets covered in the media.
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