Rudyard Kipling’s Just So Stories tell tales not so much of evolution, but of the magic and wonder of the animal world. He describes the wizard who gave the camel a hump for its laziness, and the alligator who snapped and stretched the nose of a naïve young elephant to its current lengthy proportion. Those delightful fables, published some 70 years after Jean-Baptiste Lamarck’s death, provide entertaining explanations for such evolved traits, and were clearly inspired by Lamarck’s description of adaptive change, not Charles Darwin’s. In his 1809 publication Philosophie Zoologique, Lamarck wrote of the giraffe, from whose habit of reaching for the green leaves of tall trees “it has resulted . . . that the animal’s forelegs have become longer than its hind legs, and that its neck is lengthened to such a degree that the giraffe, without rearing up on its hind legs . . . attains a height of six meters.”
Although biologists have generally considered Lamarck’s ideas to contain as much truth as Kipling’s fables, the burgeoning field of epigenetics has made some of us reconsider our ridicule. While no biologist believes that organisms can willfully change their physiology in response to their environment and pass those changes on to their offspring, some evidence suggests that the environment can make lasting changes to the genome via epigenetic mechanisms—changes that may be passed on to future generations. (first described on deskarati here)
Epigenetic changes can range from chemical modifications of histone proteins—such as acetylation and methylation—to modifications made to the DNA itself. Such changes usually cause chromatin compaction, which limits the ability of the RNA polymerase II transcription complex to access DNA, ultimately resulting in reduced messenger RNA (mRNA) and protein output. Many view epigenetics as an annotation or editing of the genome that defines which genes will be silenced in order to streamline protein production or squelch unnecessary redundancy. That annotation, they say, does not and cannot permanently change the original manuscript (i.e., DNA), but merely access to the manuscript.
Just as epigenetics was gaining acceptance within the general scientific community, scientists began reporting observations of a newly identified phenomenon called transgenerational epigenetic inheritance, or the passage of epigenetic changes from a parent to its offspring. Recent experimental work in mice, worms, and pigs has found evidence that some degree of transgenerational epigenetic inheritance may take place.
A fascinating 2008 study that looked at people born during the Dutch Hunger Winter in 1944–1945 hints at the possibility that transgenerational epigenetic inheritance also occurs in humans.1 Adults who were conceived during the famine had distinct epigenetic marks that their siblings born before or after the famine did not. These marks reduced the production of insulin-like growth factor 2 (IGF2) and affected the growth of the famine-gestated children. Notably, these marks were retained for several decades in the afflicted individuals. While these observations suggest the possibility of transgenerational epigenetic inheritance, the modifications could also have occurred in utero as a result of famine conditions rather than being inherited in the germline. Therefore, whether such a distinct phenomenon occurs in humans remains to be definitively determined.
However, in model experimental systems, there is strong evidence for transgenerational epigenetic inheritance. In one study carried out in mice, an environmental stress that resulted in aggressive behavior in males caused the same behavior in their offspring.5 Notably, the offspring had changes in the DNA methylation patterns of particular genes. Collectively, these and other transgenerational studies all point to the notion that selective pressure can be applied from the environment and passed on to daughter cells and offspring.
Edited by deskarati from Lamarck and the Missing Lnc click to read the whole interesting article.