Other traits like height, health, beauty vary and are influenced by genetics. Intelligence varies between species, and is therefore, at least in part determined by genetics.
Presuming that there are only mentally disabled and normal people is the weird hypothesis. The baseline idea should be that it varies just like health and height. Affected by both genetics and outside factors such as malnutrition and injuries.
Presuming that there are only mentally disabled and normal people is the weird hypothesis. The baseline idea should be that it varies just like health and height. Affected by both genetics and outside factors such as malnutrition and injuries.