Researchers have found a correlation between thumb length and brain size in primates, suggesting that as manual dexterity evolved, so did brain capacity. Long thumbs facilitate better manipulation of objects, which could enhance cognitive abilities related to action planning. A study of 94 primate species revealed that longer thumbs generally coincide with larger brain sizes, indicating an evolutionary trend. This relationship was evident across various primate species, with the exception of one early human relative, Cediva, whose thumb length was unusually long due to its arboreal lifestyle.
The study highlights that the neocortex, a brain region associated with complex cognitive functions, is linked to thumb length rather than motor control areas like the cerebellum. However, researchers caution that this finding does not imply that thumb length alone determines brain size or manual dexterity, as understanding this relationship requires more comprehensive research into anatomical and neurological factors.
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