Longer Thumbs, Bigger Brains
Study Finds Evolutionary Link Between Thumb Length and Brain Size in Primates
A study has found that the longer the thumb, the larger the brain.
According to reports from The Guardian and BBC in the United Kingdom on August 27 (local time), a joint research team from the University of Reading and Durham University in the UK recently investigated the relationship between the thumb and the brain in primates, including humans.
The research team examined a total of 94 primate species, including humans and five ancient human species, as well as chimpanzees, gorillas, orangutans, lemurs, marmosets, and baboons. Both living animals and fossils were included in the study. The researchers compared the length of the thumb bones to the other finger bones in each species to determine the relative length of the thumb, and collected data on brain weight and cranial cavity volume to classify brain size.
The results showed that most ancient human species, including modern humans, have longer thumbs compared to other primates. In addition, species with relatively longer thumbs tended to have larger overall brain sizes. The research team suggested that primates with longer thumbs would have had an advantage in survival, as they could handle tools more effectively and grasp objects more precisely. Based on this, the researchers concluded that the thumb and the brain influenced each other and evolved together. As primates became able to manipulate objects more skillfully using their thumbs, their cognitive abilities and neural processing capacities also developed, leading to increased brain size.
Dr. Joanna Baker, who led the study, explained, "We already knew that humans have large brains and dexterous fingers compared to other animals, but now we can see that the brain and fingers did not evolve separately." According to the research, longer thumbs are associated with the parts of the brain responsible for processing sensory information, cognition, and consciousness. Dr. Baker added, "As our ancestors became more skilled at picking up and manipulating objects, their brains had to grow to handle these new skills."
However, there are limitations to this study. The research team noted that further research is needed to determine exactly how the neocortex-the part of the brain connected to longer thumbs-supports manipulation abilities. Additionally, thumb length and brain size alone cannot fully explain the dexterity or brain evolution of primates. For example, Australopithecus sediba, an early human species, had an unusually long thumb compared to its brain size, but this was likely related to its lifestyle rather than precise tool-making abilities.
This study was published on August 26 in the international journal Communications Biology.
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