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Old 05-10-2016, 01:16 PM
Colibri Colibri is online now
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Probably because our primate ancestors relied on opposable thumbs (and toes) to climb instead of climbing with claws like squirrels. They climbed mainly on smaller branches that they could get their entire hands around, rather than clinging to trunks by claws. With such a climbing strategy long sharp claws just get in the way.

Most primates, even primitive ones, have nails instead of claws on their digits, although lemurs retain a claw on one toe for grooming.

Marmosets, which climb up trunks like squirrels, have claws on most toes but have a nail on the thumb.

Some other animals that climb using opposable digits like opossums have a nail on the thumb but claws on the other digits.