The one with the long thumb, that was big too...Evolution Together for Millions of Years
Aug 27, 2025
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A joint team of researchers from the University of Reading and Durham in the UK published a study in the Nature Portfolio that showed a clear correlation between thumb length and brain size.
The researchers analyzed 95 species of primates, including humans, chimpanzees, gorillas, and monkeys. Extinct human species and various ancient primates were also included in the study.
As a result of the study, the longer the thumb in all species, the larger the brain.
It is possible that the thumb and brain have developed together over millions of years of evolution, the researchers suggested.
As primates develop their ability to pick up and handle objects, their brains have also grown to process and utilize them.
The researchers wrote that "as our ancestors improved their ability to pick up and manipulate objects, the brain had to grow to handle the technology"These abilities have been refined through millions of years of brain evolution," he said.
In addition, the 'hominin' group, which includes modern humans and extinct human ancestors (Neanderthals, Australopithecus, etc.), had significantly longer thumbs than other primates. The human brain is also much larger than non-human primates.
Interestingly, the growing brain area with thumb length was different from previous expectations.
The researchers expected a connection with the cerebellum, which is deeply involved in exercise and coordination, but it was actually related to the neocortex, a complex layered structure that accounts for half of the human brain. The neocortex is the most recently evolved part of the cerebral cortex in the brains of mammals, including humans, and is an area responsible for processing sensory information and for cognition and consciousness. It is divided into four parts: frontal lobe, parietal lobe, temporal lobe, occipital lobe, and especially performs complex functions such as conscious thinking, sensory perception, language, spatial reasoning, and exercise command generation.
The researchers emphasized that the results are the first direct evidence that elaborate hand movements and brain evolution are linked throughout primates.
However, the researchers cannot fully explain the complexity of the various manipulative behaviors and abilities of primates only with their thumb lengths"Thumbs length can only provide general insight" he added.
He also explained that "brain size does not necessarily mean high intelligence" and that "a large brain may mean an increase in multiple brain regions responsible for various factors such as behavior, cognition, and motor control.'
This article was translated by Naver AI translator.
