Brain architecture suggests the following evolutionary pathway for monkeys and apes
This evolutionary pathway describes a sequential development of the brain associated
with the addition of layers of brain tissue - predominantly on the dorsal part of
the cerebral cortex. It can be seen that at least four layers of white matter have
been added between the weasel type brain and the human brain.
The African monkeys, although genetically very similar to the apes, appear to have
undergone reversion of their brain morphology to a slightly more primitive type.
Highly evolved brains are expensive on energy requirements and the baboon way of
life may not require such intelligence.
From a cranial morphology point of view, this evolutionary tree is consistent with
a gradual and progressive development of a basal mammal’s skull such as a mustelid.
The chromosome number for each stage presents a less clear pattern.
The diploid number of chromosomes for each mammal type are listed below.