What were the main external determinants in human evolution?

The main hypothesis on this is that our ancestors lived in East Africa at the most crucial stage of human evolution, about 2-3 million years ago. There the climate became drier as a result of plate shifts (which created the Rift valley), among other things. Our ancestors had to adapt to a drier environment with fewer trees – which eventually became the savanna, hence the name “Savannah hypothesis”. It is believed that they had to travel long distances in the savannah to get food, with big game hunting becoming increasingly important.

Some adjustments for this are walking upright, possible to carry tools/weapons/children during the movements; hairless skin with sweat glands to dissipate heat; hairy skull cap (against sunstroke); adjustments in digestion and metabolism (more protein-rich foods).

The evolution of the higher mental faculties is not easily explained. This may have been necessary to forge strong social bonds, which was undoubtedly very useful for hunting, predicting seasonal changes and surviving in highly variable conditions.