Long Thumbs and Large Brains Co-Evolved in Primates, Giving Humans Our Most Unique Traits

What are thumbs and brains in common? According to recent research, their growth has been linked throughout primates, which suggests that long inches and large brains of modern humans have emerged simultaneously over time.

The recent study in Communications biology,, Supports the theory that the primates’ hands and heads have camera. The growth of one occurred with the growth of the other in lemurs, monkeys, even homes, leaving our own species with two of our most unique features.

“We have always known that our big agile brains and fingers have distinguished us, but now we can see that they have not evolved separately,” said Joanna Baker, biologist at Reading University, according to a press release. “While our ancestors have improved to collect and manipulate objects, their brain had to develop to manage these new skills. These capacities have been refined through millions of years of brain evolution. ”

Find out more: An introduction to the history of human evolution

The coevolution of hands and heads

Our dextere thumbs and our big brains have benefited our species in many ways. They allowed us to create the tools, technologies and cultures that have helped us prosper for thousands of years. But the history of the evolution of these features is always surprisingly troubled.

Some scientists have suggested that these traits have evolved together, for example, emerging together during the evolutionary time, because more complex movements required more sensorimotive control. But the evidence of this theory remained relatively limited.

To fill this gap in research, Baker and his colleagues analyzed the bones and tissues of 95 primates – including existing and extinguished species and a handful of hominines, as Homo sapiens,, Homo neanderthalensis, And Homo Naledi – To retrace their evolution over millions of years.

By looking at the length of the thumb and the mass of the brain (measured or estimated from the volume of the brain or the brain cavity), the researchers revealed that the species which had longer thumbs – which are associated with increased dexterity – were also the species which had a greater brain.

A motif through the primates

According to Baker and his colleagues, hominins have had the longest thumbs and the biggest brains by far. But the relationship between the length of the thumb and the mass of the brain was solid in other primates, and it remained strong even when Homo sapiens have been completely deleted from the analysis.

“Our results involve a robust association between brain size and manual dexterity,” wrote researchers in their study. “We interpret our results to indicate a sustained historical coevolution between the size of the brain and dexterity through the order of primates, reflecting significant neural costs of manipulation behaviors.”

Learn more: Chimpanzees can learn continuously as they age, a factor of human evolution

Thumbs and brain

Of course, the size of our hands and our heads has long been considered a factor in the success of our species, but never before the coevolution of these two features have been so deeply traced throughout the primates line.

However, Baker and his colleagues were surprised to see that thumb growth was associated with brain growth in only one of the expected two areas.

In fact, the researchers had thought that the longer thumbs would be linked to a larger cerebellum as well as to a wider neocortex, because the first controls movement and coordination while the second focuses on sensory treatment, cognition and consciousness. But their results indicated that the longer thumbs were only linked to a larger neocortex.

“We therefore reveal the intriguing possibility that the neural processes involved in the evolution of manual dexterity between primates involve mainly neocortical regions,” they wrote in their study. “An exciting avenue of future research would be to test this idea more.”

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