Selection during pregnancy

Carl Zimmer writes about a new paper in Trends in Genetics where the authors argue that natural selection during pregnancy is an important driver of recent evolutionary changes:

Women nourish their fetuses by raising the level of sugar in their blood. That’s a dangerous game, because it threatens to throw off their own delicate balance between sugar and insulin. If that balance gets out of whack, women may suffer gestational diabetes. The Harvard researchers suggest that the shift to high-carb agriculture in Europe led to more women dying of gestational diabetes. Women with mutations that lowered their blood sugar level during pregnancy were favored by natural selection. And today, European women enjoy the benefits of that suffering: a low risk of gestational diabetes.

A woman in Bangladesh has a very different history behind her. Her ancestors ate fish, unprocessed rice, and other foods with modest levels of carbohydrates. In that environment, women with mutations that increased their blood sugar during pregnancy might have had healthier children than women without them.  Throw those genes into a modern Western city, and trouble looms. Women with low-sugar genes are now drinking soda and eating bread, ice cream, and lots of other food loaded in carbs. They don’t have the evolved defenses to keep them from developing gestational diabetes.

From New York birth data, Women of European descent have less than a 4 per cent chance of developing gestational diabetes during pregnancy, compared to around 20 per cent for Bangladeshi women.

The paper also points to recent evolution relating to production of vitamin D, altitude and malaria.