A Modest Comeback for Lamarck, and a Reminder of the Edge of Evolution
In a modest comeback for long-discarded Lamarckian ideas of offspring inheriting traits their parents acquired, Columbia University Medical Center researchers have succeeded in showing how such a mechanism could actually work. Anyway, in roundworms. It is reported this week in Cell.
What's interesting is that the mechanism involves passing on an adaptive advantage by breaking or silencing gene functionality. Sound familiar? It's not unlike what we've seen in Richard Lenski's famous long-term experimenting with E. coli, which has so far show mainly how the Darwinian mechanism -- which supplanted Lamarck in evolutionary thinking -- seems to do its work not by creating gene function but by degrading it. Michael Behe has written about this extensively, in The Edge of Evolution and elsehwere, pointing out the radical limit it imposes on what mutation and selection can accomplish. No Darwinian advocate has successfully answered Behe's challenge.
But back to those worms. The forbearers picked up immunity to the Flock House virus, the only virus known to afflict this particular hearty species (C. elegans), and communicated the benefit to their descendants in a germ line extending up to 100 generations. That's about a year's worth of worms. Researchers conferred the initial immunity by inducing RNA interference (RNAi), an essentially destructive process that can happen in nature or in the lab. It involves introducing a double-stranded variety of RNA (dsRNA), which in turn wipes out messenger RNA (mRNA) associated with a gene. This renders the gene, bereft of its vital mRNA, inoperable.
It was the now inactive gene that accounted for the helpful resistance to the virus. Surprisingly, this gift got passed down in the somatic cells (as opposed to gametic ones) -- inheritance by a kind of chain of "memories," which actually work by the receipt of viral RNA molecules (viRNA) from parents to children. Oliver Hobert, who lead the research, told Science Daily
Sometimes, it is beneficial for an organism to not have a gene expressed. The classic, Darwinian way this occurs is through a mutation, so that the gene is silenced either in every cell or in specific cell types in subsequent generations. While this is obviously happening a lot, one can envision scenarios in which it may be more advantageous for an organism to hold onto that gene and pass on the ability to silence the gene only when challenged with a specific threat. Our study demonstrates that this can be done in a completely new way: through the transmission of extrachromosomal information.This is turning into a trend. Darwinian evolution has been observed to confer benefit by breaking genes, a process that by itself cannot invest a creature with new functionality of the kind that, according to conventional evolutionary theory, it must do in order to build up new species.
In a weird echo, Lamarck is now shown not to have been completely wrong about inheritance but only in the sense that, like the Darwinian mechanism, the Lamarckian one works by knocking things out, not building them up.