Monday, July 31, 2006

On being your mother's son   posted by JP @ 7/31/2006 02:22:00 PM

John Hawks and Tara Smith both have posts on a New York Times article describing the role of events during development on health later in life. A recent article pushed for the development of a framework to describe these kind of effects.

The basic concept is simple: during development (development in utero), the fetus recieves signals that allow it to "predict", as it were, the environment where it will live. For example, there may be some way to sense whether the environment will be nutrient-poor or nutrient-rich. Based on this information, development proceeds in a way to favor adaptation to the predicted environment. However, if the prediction is wrong, for whatever reason, disease may result later in life. Importantly, the mother acts as the conduit for the environmental information, and may alter it to suit her needs.

The main example given in the article concerns metabolic disease like type II diabetes and obesity. The argument goes like this: due to basic physics, a fetus can't exceed a certain size (or couldn't, before the C-section). Thus, in a nutrient-rich environment like we have today, where a fetus would "want" to get much bigger, the mother limits the environmental signal )so as not to have a giant child), leading to a fetus that "predicts" an environment much poorer than what really exists. Once developed, the grown individual is then predisposed to gain weight. The authors put is thusly:
We argue that it is this differential rate of change between the limitations imposed by maternal constraint (which set the fetal prediction) and the reality of the enriched modern postnatal environment that has created the current high incidence of cardiovascular and metabolic disease in humans.

This is a broader framework for what some have called the "thrifty phenotype" hypothesis for the prevelance of type II diabetes, an alternative to the "thrifty genotype" hypothesis.