Epigenetics, a very hot topic in bioethics and public health, may provide an explanation for the current obesity epidemic. Epigenetics deals with how gene activity is regulated within a cell - which genes are switched on or off, which are dimmed and how, and the transgenerational effect -- the implications for public health could be huge.
In this clip from the NOVA special, the Ghost in Your Genes, researcher Marcus Pembrey of the Institute of Child Health at University College London and his colleagues analyzed records from an isolated community in northern Sweden and found that men whose paternal grandfathers had suffered a famine between the ages of 9 and 12 lived longer than their peers; they also found that the mother's nutrition might affect a child's risk of obesity, too -- women in the Netherlands who were in the first two trimesters of pregnancy during a famine in 1944 and 1945 gave birth to boys who, at 19, were much more likely to be obese. The implication is that extended periods of feast or famine might trigger a switch to a pattern of gene expression that results in different metabolic states for future generations.
The realization that individuals can acquire characteristics through interaction with their environment and then pass these on to future generations of offspring will likely forcue us to rethink evolutionary theories such as Dawkins' selfish gene theory.