Before Charles Darwin, the leading evolutionary theorist was Jean-Baptise Lamarck, who believed organisms acquired traits over their lifetimes that they then passed onto their children. This theory has been roundly disproved...but in the case of roundworms, Lamarck was actually right.
The classic example of Lamarckian evolution is giraffes. According to Lamarck, giraffes developed their long necks by stretching them upwards to feed on tall leaves. In his view, some giraffes managed to stretch their necks out over the course of their lifetime, giving them an advantage over the other giraffes which they then passed onto their children. While some of his basic mechanics weren't far off from what Darwin ultimately developed, Lamarck was led astray by his emphasis on acquired traits instead of the random mutations that underpin Darwinian evolution.
But now, two centuries later, Lamarck is getting a small measure of vindication. In at least one species, evolution by acquired traits really does exist, according to researchers at Columbia University. Lead author Oded Rechavi explains:
In our study, roundworms that developed resistance to a virus were able to pass along that immunity to their progeny for many consecutive generations. The immunity was transferred in the form of small viral-silencing agents called viRNAs, working independently of the organism's genome."
This isn't the first time scientists have found latter-day evidence for Lamarckism, but all previous findings have been deeply controversial in part because nobody could figure out a clear biological mechanism to explain them. Indeed, one of the most famous examples involves humans, as Dr. Rechavi explains:
"The classic example is the Dutch famine of World War II. Starving mothers who gave birth during the famine had children who were more susceptible to obesity and other metabolic disorders — and so were their grandchildren."
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Now, thanks to these roundworms, the researchers have found a biological mechanism for Lamarckian evolution: RNA interference, or RNAi. This process is used by cells to mute certain genes and is often used to beat back viruses and other threats to the genome. RNAi destroys messenger RNA, or mRNA, which is needed to communicate with various genes. Without their mRNA, genes basically shut down and become inactive.
Crucially, when RNAi silences a gene, this silencing is passed on to any subsequent offspring. That sounds very much like an adaptation through acquired traits, but this process has remained enigmatic until now. The researchers looked at roundworms, which use RNAi to fight off viruses and confer immunity, which is very unusual. They found that even a hundred generations after the initial infection, the roundworms still carried the immunity acquired by their distant ancestor.
The experiment was set up so that the roundworms couldn't gain the immunity in the Darwinian way, through random mutations. It really does appear that RNAi allows certain traits acquired during a roundworm's lifetime to be passed on to its descendants. Study leader Dr. Oliver Hobert comments:
"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. The beauty of this approach is that it's reversible."
The researchers hope to someday unlock the full potential of Lamarckian inheritance, which is something that they believe all organisms have the capacity for, including humans. Dr. Rechavi explains:
"The basic components of the RNAi machinery exist throughout the animal kingdom, including humans. Worms have an extra component, giving them a much stronger RNAi response. Theoretically, if that component could be incorporated in humans, then maybe we could improve our immunity and even our children's immunity."
Via Cell. Top image by Conservation Concepts on Flickr. Image of roundworms via the USDA.