This study found that rat fetuses receiving poor nutrition in the womb become genetically primed to be born into an environment lacking proper nutrition. As a result of this genetic adaptation, the rats were likely to grow to smaller sizes than their normal counterparts. At the same time, they were also at higher risk for a host of health problems throughout their lives, such as diabetes, growth retardation, cardiovascular disease, obesity, and neurodevelopmental delays, among others. Although the study involved rats, the genes and cellular mechanisms involved are the same as those in humans.
In other words: malnourished mothers have smaller children with less caloric needs but who have sacrificed neural and physical health for that small, but maybe decissive, advantage for their extreme enviroment.
What I wonder is wether some of such epigenetic alterations can actually stuck in the upcoming generations, as another research showed recently. If so, poverty, particularly extreme poverty, could have harmful long-lasting effects in whole populations and social classes (not just in the original sufferers but also their descendants). Of course, I also wonder if such epigenetic modifications (assuming they can be transfered through generations) can be reversed by improving the conditions of living and especially nutrition.
And I do wonder about the apparent changes in size in prehistorical human remains may have been caused by nutrition. I recall in fact a paper (sorry no reference right now) in which it was shown that prehistorical Indians were much larger than contemporary Europeans, while today the situation is exactly the opposite. And I also wonder about the apparent reduction in size (including brain size) among humans in general since Paleolithic times. These phenomenons don't seem to have been caused by population replacements at all but could well have been caused by nutritional difficulties (maybe caused by Neolithic or maybe the ones that triggered Neolithic - hard to tell). .