Interesting observations. I’ve thought about twins and brain structure too, but I am a computer scientist not a neuro-scientist so I might be completely wrong.

Interesting observations. I’ve thought about twins and brain structure too, but I am a computer scientist not a neuro-scientist so I might be completely wrong. Serious mental illness seems to be of higher incidence in the population than I would expect given evolutionary pressures due to its affect on survival. This suggests perhaps some unexplained benefit to mental illness for survival of an individual’s genes despite its seeming like a disadvantage. (As is the case for sickle cell anemia or nearsightedness) Alternatively, I surmise that brain structures are not fully coded by genes, but develop through a system that is chaotic, in the sense of being very sensitive to initial conditions, and so despite the brain development system being controlled by genes the outcome in terms of exact neural connections is to some degree unpredictable due to the slightest differences in the environment between individuals (even identical twins). Evolution implies that the development of a brain can not be straightforward given how rarely genius appears in the population.