It is interesting to ask why all this should happen. Why does what a mother eats, or how she feels, change the development of her baby in the womb?
These changes may be an evolutionary mechanism to prepare the baby to be ready for the environment into which they are going to be born. This has been called the Predictive Adaptive Response (see Gluckman and Hanson 2004).
If, in prehistoric times, a mother was living in a dangerous environment, she would have felt stressed.
Many of the changes caused to her fetus by prenatal stress may have helped her child to survive. (See Glover 2011).
For example being more anxious, can make one more vigilant, and thus quicker to spot something dangerous in the distance, like a snake. Having readily distracted attention, as happens with ADHD, may make one notice a rustle in the undergrowth more easily, whilst being more aggressive may make it easier to quickly get rid of the danger.
Importantly, the degree to which offspring are affected is directly related to the severity of the mother’s stress during pregnancy. This supports the above theory, in which a more dangerous environment will cause the mother more stress, thereby increasing the severity of the effects on the offspring. In these circumstances a child whose attention is even more readily distracted may be better equipped to deal with the prevailing danger, e.g. a large number of predators.
What is also interesting is that maternal stress during pregnancy appears to have sex-specific effects on the resulting offspring. Animal models have demonstrated that male offspring are more likely to display learning deficits and increased aggression, whilst females are more prone to anxious behaviour and hyper-responsiveness of the HPA axis (See Weinstock 2007).
These sex-specific differences can potentially be explained by extending the theory above. Since females are traditionally the primary care givers, then an increased level of anxiety may help them to remain vigilant in a dangerous environment, whilst exploratory males would experience greater exposure to threats and increased aggression may increase their chances of quickly and successfully resolving conflict.
However, what was helpful in dangerous prehistoric times is not so helpful in our modern society, in which education and concentration are highly prized.