When talking to researchers for the genetics portion of our Inheritance show, one thing that consistently came up is that it's difficult for science to study the effects maternal lineage has on offspring.
Some listeners noticed this too, notedly in our segment "You are what your grandpa eats," in which we explored a Swedish study that looked at the effects of food availability on boys between the ages of about 9 and 12 years old, and how those effects showed up in the future sons and grandsons of those boys. Quick recap: for those boys that experienced famine in their tweens, when they grew up to be fathers, they actually passed a health benefit onto their offspring; their kids, and grandkids, were less at risk for heart disease, and diabetes. For those who had lives of plenty, it turns out their kiddos (and grandkiddos) would have a higher frequency of heart attacks and diabetes.
A pretty provocative study. But what about the effect grandmothers, or mothers, have on the offspring? Lars Olov Bygren, the lead researcher on the Swedish study, said that his group did study both the male and female lines but, and it's a big but -- "the maternal influence of this special kind, from availability of food during childhood, is difficult to discern -- probably because there are so many signals between mother and the fetus or child, and this might hide a similar influence as in the male line."
What does Bygren mean by "so many signals"? Well, pregnancy is a very intimate, boundary-smudging process, in which mother and baby share not only genes, but hormones, blood, cells, chemicals, bacteria, and more. If you're trying to isolate the effect that genes -- and only genes -- have on the baby, and isolate that effect over multiple generations... it's a tall order. Like trying to hear a whisper in a room full of crying babies. But if you look for the effect in the paternal line, there's one thing and one thing only to study: sperm. It's more of a clear cut process (as "clear cut" as genetics can be, that is).
That's not to say science isn't extremely interested in what mothers are contributing -- on the contrary, they're doing their best to understand it. In fact, Bygren says that his group sees some kind of "involvement" between a maternal grandmother, her son, and the son's daughter, but they aren't sure exactly what that involvement is. And as for a connection between grandfathers and granddaughters, his team didn't see an influence on cardiovascular or all-cause mortality like they did with grandfathers and grandsons. So the big research results, like the kind of data-driven paternal studies Bygren talked about in our Inheritance show, are still in the making. Hopefully those findings are on their way with future studies -- with larger sample sizes and new techniques, scientists should be better able isolate the whisper in all the noise.
In the meantime, we'll keep our ears perked for any upcoming maternal studies -- and you should too, we'd love to know if you see anything.