Researchers with Columbia University are claiming direct evidence of inheritance of acquired characteristics:
“In our study, roundworms that developed resistance to a virus were able to pass along that immunity to their progeny for many consecutive generations,” reported lead author Oded Rechavi, PhD, associate research scientist in biochemistry and molecular biophysics at CUMC. “The immunity was transferred in the form of small viral-silencing agents called viRNAs, working independently of the organism’s genome.”
This type of inheritance, while considered controversial not too long ago, is becoming more and more accepted by biologists.
According to the strict Darwinian view of inheritance, traits that are acquired during life are not passed on to offspring — for instance, a body builder will not pass on his “buffness” to his children. All that he can pass on is his basic genetics, which may or may not include a predisposition to a muscular build. The benefits of his training, however, can’t be inherited.
Prior to Darwin, scientist Jean-Baptiste Lamarck proposed a theory of evolution in which acquired characteristics were passed on. The common example was giraffes — Lamarck’s theory proposed that giraffes have long necks because, as each generation stretched their necks out to reach higher leaves, their necks lengthened. They then passed on acquired lengthened necks to their offspring.
Darwin’s theory repudiated this view. Instead, according to Darwinian evolution, the giraffes that already have the longest necks (due to their genes) are the most successful at reproduction and passing on their long-necked genes, meaning that the next generation of giraffes has a higher proportion of long-necked giraffes. Later discoveries of Mendelian genetics and the structure of DNA only confirmed this Darwinian view, and it is still clear that this Mendelian/Darwinian view of inheritance is still the basis of how genes and traits are passed down from generation to generation.
Still, it was mainly the tremendous success of the Mendelian/Darwinian view rather than a complete refutation of the Lamarckian view that accounts for the former’s dominance. As biologists learn more and more about the complexities of cells and genes, however, it is becoming apparent that the simple genetic view is not the whole picture, and that Lamarck may have been on to something after all. While the inheritance of genes according to Mendelian rules still clearly provides the foundation of heritability, evidence continues to mount that other factors come into play around this central Mendelian process. Biologists are finding clues that some traits are passed down not through genes, but through epigenetic factors, and that many of these traits arise as a directed response to environmental conditions — just as Lamarck suggested.
In the study linked above, researchers found that roundworms could pass on resistance to viruses via small RNA strands that function as attackers of the viral RNA. Cells are able to use a system called RNA interference (RNAi) to neutralize the RNA genomes of certain viruses. The researchers were able to demonstrate that the RNAi based resistance to the viruses persisted in later generations of roundworms — even when the RNAi machinery which produces the initial RNAi response was deactivated. In other words, the later generations of roundworms inherited their resistance via their parents’ acquired resistance, not through either genetics or by developing their own resistance.
I suspect that we will find more instances of epigenetic inheritance in the future, and while it will not challenge the basic core of inheritance and evolution through the genome, I wouldn’t be surprised if it turns out to nevertheless have some important implications.