The Evolution of Evolution: Darwin's Gemmule Theory Revisited
We’re beginning to find evidence that epigenetics can, in fact, influence the next generation in a way that’s at least partially Lamarckian.
Professor Rob Martienssen leads the plant biology group at CSHL, where he focuses on epigenetic mechanisms that shape and regulate the genome, and their impact on development and inheritance. His work on transposons or "jumping genes" in plants and in fission yeast revealed a link between heterochromatin and RNA interference. His work, along with that of his colleagues, was awarded the “Breakthrough of the Year” by Science magazine in 2002. He has also developed reverse genetics strategies using transposons in maize and Arabidopsis that have become powerful and widely used tools in plant genetics research. He was one of 13 scientists nationwide who was named an HHMI-GBMF Investigator last year.
The advances in genetics have been absolutely amazing over the last few decades since the discovery that DNA was the hereditary material. For example, we’ve sequenced the genomes of many, many different organisms, including at this point, hundreds of plant genomes. And so we now can read the genetic code very easily.
In the last decade or couple of decades we’ve realized that there is an epigenetic code, a second code, if you like, that’s layered on top of this DNA sequence and can drastically influence both the normal development of a plant or an animal as well as the inheritance of these traits.
So for example, in the 19th century the famous botanist Jean-Baptiste Lamarck proposed the idea that is now called the Inheritance of Acquired Traits in which he suggested that maybe the experience of an organism in one generation could somehow lead to changes in the progeny that would benefit them in the next generation. He famously thought that the giraffe’s neck had been extended by reaching higher and higher into trees for nutrition.
While we don’t think that Lamarck’s ideas should be interpreted too literally, we’re beginning to find evidence that epigenetics can, in fact, influence the next generation in a way that’s at least partially Lamarckian. So one of the most important discoveries in the last decade has been a phenomenon called RNA Interference where small RNAs can very drastically influence the activity and the importance of genes.
One of the discoveries that my lab was part of was seeing how those small RNAs could actually make more permanent changes in the chromosome that could be inherited from cell to cell. So that actually provides a potential mechanism for Lamarckian Inheritance because the small RNAs can arise from anywhere in the body. They can move around and implant. We know that they move around a lot and potentially could influence the inheritance of chromosomes in the germ line.
It was actually Darwin who first realized this potential. He was a big fan of Lamarck. A lot of people don’t realize that, but in The Variation of Animals and Plants under Domestication he wrote that if Lamarckian Inheritance—the inheritance of acquired traits—was true, then there must be some property arising in the body that could enter the germ line and change the germ line for the next generation. And Darwin called these gemmules—which is a wonderful name and we think small RNAs are very good candidates for those gemmules.