11 March 2008

How Marmorkrebs can make the world a better place

One of the longest-running (and least productive) arguments in biology is “nature versus nurture.” The pendulum has swung back and forth many times, but with the research success of genome sequencing for many species (not the least of which has been humans), there is definitely a tendency to give a lot of weight – often unwarranted – to genetics.

This New York Times article talks in some detail about how much emphasis DNA gets in explaining “what we are.”

“I’ve spent the last 10 years of my life researching how much genetic variability there is between populations,” said Dr. David Altshuler, director of the Program in Medical and Population Genetics at the Broad Institute in Cambridge, Mass. “But living in America, it is so clear that the economic and social and educational differences have so much more influence than genes. People just somehow fixate on genetics, even if the influence is very small.”

Marmorkrebs show very beautifully that DNA is not destiny.

Despite that Marmorkrebs are all genetically identical (as Martin and colleagues showed), there is substantial variation across individuals (as Vogt and colleagues showed).

The picture in this entry shows two juvenile Marmorkrebs. Believe it or not, they are about the same age. They have been kept for a couple of months in the same environment, same food, same lighting conditions, and so on. Yet one is about 60% longer than the other, which probably means it’s about 400% greater in mass. (When length doubles, volume goes up by a factor of eight.)

It’s been really fascinating to watch them grow, knowing they are all the same genetically. In a tank of ten animals, the big individual in the picture noticeably pulled away from all the others in growth, one was noticeably smaller than its peers, and the other eight were much more similar in size.

It’s one thing to know intellectually that your genes are only part of what determines how you end up. It’s something entirely different, and more powerful, to see it unfolding right in front of your eyes. Strong, obvious cases like this could do much to give people a more balanced view of the “genes as destiny” argument, which has been used to justify some really horrible treatment of people over the years.

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