Science on Moms, Grandmothers

Just in time for Mother's Day, a new scientific study has reaffirmed the importance of mothers and grandmothers, this time in the realm of cancer genetics. "BRCA1/2 mutations, fertility and the grandmother effect" was just published in the journal Proceedings of the Royal Society B: Biological Sciences, by Jack da Silva of Australia's Adelaide University.

In the article, da Silva examines how the role of the 'breast cancer genes' BRCA1 and BRCA2 affect fertility and how mutations in them came to be as frequent in the population as they are. The text of the article is available free online, but you'll need a library with academic credentials to access the full content.

The thrust of the article is an interesting and accessible (to non-science folk) analysis of some notable features of BRCA1/2. Even though the variety of cancers associated with BRCA1/2 are brought on later in life—after reproductive age—the mutations that bring about those cancers are highly correlated to increased fertility rates, up to 48%.

The question this work posed was: if BRCA1/2 mutations have an associated increase in fertility, then why haven't they become more prevalent in the population? If offspring carrying the mutations are birthed at higher rates, then the mutations should spread through the population over generations.

The answer appeared to lie in a combination of factors: the "grandmother effect" and the nature of earlier human life as hunter-gatherers. When population records were examined, it was found that having a surviving grandmother during child rearing increased the survival odds of that child. And so while the BRCA1/2 mutations might increase fertility, they decreased the survival of grandmothers as the cancers develop later in life and this effect propagated to the grandchildren so that irrespective of their status of a carrier, having a grandmother around to help raise them made a big difference in their survival. This was observed even in fairly recent human civilizations, and as da Silva examined older civilizations' records, the effect appeared to be more pronounced.

So throughout human history grandmothers and mothers have been important not just through genetic links, but also in ways that can't be encoded in DNA.