It's one of the reasons you find a family that becomes all doctors or all farmers, even if they were separated from their biological family at birth.
It's why tigers in India that are afraid of men, are still afraid of men even when (moved and) raised with other tigers that are not. How can that be explained?
It's been a well known fact that anything the mother does during pregnancy greatly affects the child. Like mercury poisoning will cause birth defects. Or when a mother is stressed during the pregnancy, it caused colic because the babies nervous system is irritated.
In Bragg's book "The Miracle of Fasting" he explains that toxic parents create toxic children, and that without fasting, there is often no way to release the toxins. So each generation we create a more toxic generation.