Apes with larger thumbs in proportion to their hands also have larger brains, new research has shown
Apes with larger thumbs have larger brains, particularly in the neocortex, a new study has shown.

A study led by lead author Dr Joanna Baker of the University of Reading looked at 94 primate species, including lemurs, early hominins and humans.

The study found that monkeys with larger thumbs in proportion to their hands also had larger brains. This relationship was not just found in humans, but across all primates. Even when human data were excluded, the relationship remained.

The study showed that the neocortex (which is associated with consciousness, sensation, and action planning) in particular grew larger, while it was expected that this would be related to the cerebellum (which is responsible for movement and balance), but this was not the case.

The study suggests that manual dexterity and brain development are linked. As apes became more skilled at grasping and using objects with their hands, their brains, especially the part that does thinking and planning, grew.