Inherited learning? It happens, but how is uncertain
As a biological concept, the inheritance of acquired characteristics has had a wild roller coaster ride over the past two centuries. Championed by Jean-Baptiste Lamarck at the beginning of the 19th century, it soared to widespread popularity as a theory of inheritance and an explanation for evolution, enduring even after Charles Darwin published On the Origin of Species. Then experimental tests, the rise of Mendelian genetics, and the wealth of discoveries substantiating chromosomal DNA as the principal medium of genetic information in complex organisms all but buried the idea until the mid-20th century. Since then, the theory has found at least a limited new respectability with the rise of “epigenetics” (literally, around or on top of genetics) as an explanation for some inherited traits.
Most recently, some researchers have found evidence that even some learned behaviors and physiological responses can be epigenetically inherited. None of the new studies fully address exactly how information learned or acquired in the somatic tissues is communicated and incorporated into the germline. But mechanisms centering around small RNA molecules and forms of hormonal communication are actively being investigated.
“The major outstanding question is not whether these [epigenetic inheritance] effects are happening, but what are the mechanisms by which these changes are happening,” wrote Nicholas Burton, an epigenetics researcher at the University of Cambridge, in an email. “There is certainly still spirited debate on this topic and I suspect this debate will continue for awhile yet. It will be very exciting to see what comes of it.”
The evolutionary “why” for epigenetic inheritance is also an area of active investigation because it’s paradoxical. If learned adaptive behaviors can be passed on to the next generation, that would seem to eliminate the necessity for certain standard evolved changes to the genome. On the other hand, if epigenetically transmitted traits are adaptive, why not hardwire them into the genome so that they can be inherited more stably? [Continue reading…]