Thumbs for Thoughts 

From carving stones to swiping screens, humans have always been considered special thanks to the dexterity of their hands. 

Now, new research analyzing both fossils and living animals has linked bigger brains with longer thumbs across 94 different primate species, from lemurs to humans. 

“For the first time we have been able to link two of the most distinctive features of humans, hand anatomy and brain size,” study author Robert Barton said in a statement. “These are key features that enable humans and other primates to literally grasp and manipulate their world.”  

Humans and their extinct relatives stand out for having both unusually long thumbs, useful for gripping small objects precisely, and remarkably large brains. 

“Large brains and dexterous hands are considered pivotal in human evolution, together making possible technology, culture, and colonization of diverse environments,” the researchers wrote. 

Yet, this relationship is not unique to the human lineage, as research found that even when human data were excluded from the analysis, the correlation between thumb length and brain size persisted. 

Researchers expected longer thumbs to be linked to the cerebellum, a brain region highly involved in movement and coordination.  

Instead, the neocortex is the part of the brain connected with longer thumbs. This is a complex, layered brain region that makes up roughly half of the human brain’s volume and which communicates with the cerebellum to jointly coordinate behavior using sensory information, the statement explained. Scientists were surprised to find that only one of the two major brain regions they expected to be involved in the growth process actually was. 

“We’ve always known that our big brains and nimble fingers set us apart, but now we can see they didn’t evolve separately,” study author Joanna Baker said in another statement. “As our ancestors got better at picking up and manipulating objects, their brains had to grow to handle these new skills. These abilities have been fine-tuned through millions of years of brain evolution.”