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KOMPAS.com – Recent research reveals shocking facts: Primates with longer thumbs tend to have a larger brain size. This finding shows that the evolution of the brain and hands go hand in hand, not on a separate path.
This study analyzes 94 primate species, both alive and extinct. From lemur to humans, the same pattern continues to appear: the longer the thumb, the greater the size of the brain. Even when human data is removed from the analysis, this trend remains strong.
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Why is the long thumb important?
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Long thumb allows precision clutches – the ability to hold beans, hold sticks, to form stones into tools. According to research, the more skilled our ancestors in manipulating objects, the greater their brains develop.
Dr. Joanna Baker of the University of Reading explains: “We always know that the big brain and agile fingers distinguish us, but now it is clear that the two are not evolved separately. When our ancestors are increasingly adept at holding and manipulating objects, their brains must develop to support this skill.”
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Shocking relationship with neocortex
Initially, the researchers suspected that the length of the thumb is associated with cerebellum, the part of the brain that regulates movement and coordination. However, the results actually show a close relationship with neocortex, the area of the brain that is responsible for awareness, thought, and sensory processing.
This indicates that the evolution of the thumb is not only about movement, but also increases cognitive demands. Controlling fine hand movements requires planning, adjustment, and focus, all of which are controlled by neocortex.
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Although the length of the thumb is an important indicator, the agility of the hand is also influenced by other factors such as the proportion of the finger, joint structure, and the role of the fifth finger. Researchers measure “Manipulation Workspace”, which is the range of thumb movements and other fingers in moving objects. As a result, species with long thumb have a wider space – and this is in line with the size of their brain.
Hominin and exception
Most hominins follow this pattern, but there are exceptions. For example, Australopithecus sediba Having a long thumb, but the brain is not as big as expected. In fact, the biomechanical model shows that this species is not too proficient in the movement of the thumb. That is, long thumbs do not guarantee high skills without the support of the cerebrum.
As well as Man naleediwhich has a long thumb but the size of the brain is relatively small. This case proves that the hand cannot be learned separately from the brain.
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Researchers also found that the expansion of neocortex to support hand control is likely to have a broader impact, including language evolution. The use of tools and speaking skills both require complex planning, sorting, and control. This shows that brain tissue that develops for the hands also supports language skills.
Humans are at the end of the spectrum of this evolution. We have the longest thumb and the largest brain among the primates, a combination that allows us to create tools, shape culture, and build civilization.
However, the relationship between intelligence and agility of this hand does not appear suddenly. This relationship existed long before humans were born, forming the path of evolution for millions of years.
In essence, scientists conclude that the ability to think of humans is never separated from our ability to hold and form objects. Intelligence is born from action. Our brain grows because our hands demand it.
This study was published in the Journal of Communications Biology.
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