From Newsgroup: sci.anthropology.paleo


https://www.reading.ac.uk/news/2025/Research-News/Primate-thumbs-and-brains-evolved-hand-in-hand

Longer thumbs mean bigger brains, scientists have
found - revealing how human hands and minds evolved
together.

Researchers studied 94 different primate species,
including fossils and living animals, to understand
how our ancestors developed their abilities. They
found that species with relatively longer thumbs,
which help with gripping small objects precisely,
consistently had larger brains.

The research, published today (Tuesday, 26 August)
in Communications Biology, provides the first
direct evidence that manual dexterity and brain
evolution are connected across the entire primate
lineage, from lemurs to humans.
...


https://www.nature.com/articles/s42003-025-08686-5
Human dexterity and brains evolved hand in hand
Abstract
Large brains and dexterous hands are considered
pivotal in human evolution, together making
possible technology, culture and colonisation of
diverse environments. Despite suggestions that
hands and brains coevolved, evidence remains
circumstantial. Here, we reveal a significant
relationship between relatively longer thumbs rCo
a key feature of precision grasping - and larger
brains across 95 fossil and extant primates using
Bayesian phylogenetic methods. Most hominins,
including Homo sapiens, have uniquely long thumbs,
yet they and other tool-using primates conform to
the broader primate relationship with brain size.
Within the brain, we surprisingly find no link
with cerebellum size, but a strong relationship
with neocortex size, perhaps reflecting the role
of motor and parietal cortices in sensorimotor
skills associated with fine manipulation. Our
results emphasise the role of manipulative
abilities in brain evolution and reveal how
neural and bodily adaptations are interconnected
in primate evolution.
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