Studies conducted in England during the industrial revolution have shown that children born to poor families were on average shorter than those born to wealthy parents. The most likely explanation for the difference in height is difference in

The answer is nutrition. Much like the difference between the height of people today and our grandparent's generation. Improved nutrition among wealthy families means that the bodies of the members of those families could reach their full potential height as limited by their genetics, and environmental factors did not come into play. In other words, the heights of poorer people are limited by both nurture and nature, whereas those of wealthyl people are limited only by nature.