We all read in our high school and college-level biology textbooks that organisms can’t pass on traits that they acquire during their lifetime. After the triumph of Mendelian genetics in the early 20th century, we “knew” that acquired traits aren’t heritable. Right? If the answer to the question were so simple, we wouldn’t be talking about this.
A new paper in the journal Trends in Ecology and Evolution, titled “Rethinking heredity, again,” finds that “the empirical evidence now points to the existence of a variety of inheritance mechanisms (collectively called ‘nongenetic inheritance’) that operate alongside Mendelian inheritance and allow for the inheritance of acquired traits.”
But modern ideas about “nongenetic inheritance” aren’t like Lamarck’s ideas about giraffes stretching their necks to eat leaves off the tops of trees, and then having offspring with longer necks. It doesn’t work like that, as the paper explains: “the concept of soft inheritance rejected by 20th-century genetics differs fundamentally from the current concept of ‘nongenetic inheritance.'”
Nonetheless, the paper explains “Over the past three decades, several research programs have explored various nongenetic mechanisms of inheritance that operate in parallel with Mendelian-genetic inheritance.” Examples include human culture and language being passed on from parent to offspring in a nongenetic factor, or “niche construction,” where “the activities of organisms lead to a modification of their environment which, in turn, affects selection.” But the most interesting examples come from epigenetics:
[E]xperiments on diverse animals, plants and unicellular organisms showed that parental environment, phenotype or genotype, sometimes affects offspring phenotype, a phenomenon called “parental effects” or “indirect genetic effects.” Recent discoveries in molecular and cell biology have revealed novel mechanisms, such as transgenerational epigenetic inheritance, that could account for a variety of parental effects. Empirical studies are now providing evidence that parental effects can be mediated by a range of substances in the gametes, and also parental glandular and other somatic donations, behavior and environment, and can affect a range of offspring traits
As the paper points out, many textbooks now have some catching up to do. The paper lists various such contemporary textbooks that emphatically assert the inheritance of acquired characteristics is absolutely impossible.
The overall importance of nongenetic mechanisms of inheritance remains to be seen. Nonetheless, the topic appears set to be a source of continuing debate, with major implications for whether random mutation is the only possible source of heritable genetic variation.