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.