Posts
Another Nail in Lamarck's Coffin
Last month I did a post on the role of E. coli in defeating the notion of Lamarckian evolution. I mentioned that there have been attempts to revive Lamarckism, specifically for bacteria. Essentially, there was experimental evidence that suggested that when bacteria are under stressful conditions, they can increase their mutation rate in order to increase their chance of hitting on a helpful mutation.
This week's Proceedings of the National Academies of Sciences has a paper dealing with this topic. Here is the abstract (but the full article is free to read):
Several bacterial systems show behavior interpreted as evidence for stress-induced mutagenesis (adaptive mutation), a postulated process by which nongrowing cells temporarily increase their general mutation rate. Theoretical considerations suggest that periodic stress-induced general mutagenesis would not be advantageous in the long term, due to the high cost of deleterious mutations. Alternative explanations have been tested for very few of the systems used as evidence for stress-induced mutation. In one prominent system, mutants resistant to rifampicin (RifR; rpoB; RNA polymerase) accumulate in cell populations that “age” on solid medium with little net growth. Mutant accumulation was initially attributed to stress-induced general mutagenesis in nongrowing cells. Evidence is presented that these RifR mutants accumulate because they grow faster than parent cells during the aging period. Direct tests revealed no increase in the frequency of other mutant types during the aging period.
Marie Wrande, John R. Roth, and Diarmaid Hughes. Accumulation of mutants in “aging” bacterial colonies is due to growth under selection, not stress-induced mutagenesis. PNAS 2008 105:11863-11868
3 comments:
I thought what was more interesting was, after basically a century of being discounted in the west Lamarkian evolution was making a comeback by noting traits passed down to children that aren't part of DNA.
Clark,
I presume that you are referring to to epigenetics. First, it seems like a rather weak Larmarckism at best. Second, not that I follow it closely, but I find myself persuaded by the argument that epigenetics is overrated as a concept. For example, see here and here.
Jared, I agree with what those posts are saying.
I think the reason some see it as useful to distinguish is that these traits can be passed down several generations and appear to be more reasonable to separate from general environmental factors. So for instance a particular chemical might affect three or four generations.
But I'll be the first to admit it's a blurry concept. But if one is talking inheritable traits independent of our modern concept of DNA then it seems it fits the criteria. The problem is when one considers modern chemistry how it should be discussed. And there I can see both sides.
Post a Comment