Between Chimps and Bonobos

If humans evolved from a species in between the patriarchal chimpanzee and the matriarchal bonobo 1, maybe their balance between the mutualism of the bonobos and competition of the chimpanzees is what caused them to evolve farther than either. However, in small groups, there is more mutualism, whereas in large groups, there is more competition, so as humans first became to live in larger groups, the balance between the two was lost. Small groups were turned into large groups through aggression, but this would have happened as much under matriarchy as well as patriarchy, as even if the attackers would have been fewer, so would’ve been the defenders. 

1 PLoS: A Molecular Phylogeny of Living Primates