The hand of a white faced Capuchin primate monkey.The human hand & the hand of some primates.

Finger length in primates linked with cooperative, competitive, and sexual behavior!

Research at the universities of Liverpool and Oxford into the finger length of various primate species has revealed that cooperative, competive & sexual behavior is linked to exposure to hormone levels in the womb!

The British scientists used finger length ratio measurements as an indicator of the levels of exposure to the hormone and compared this data with social behaviour in primate groups.

Primates such as baboons and rhesus macaques, have a low ‘2D:4D digit ratio’ (= a longer fourth finger [ring finger] compared to the second finger [pointer finger]), and these species tend to be highly competitive and promiscuous.

While gibbons and many New World monkey species have higher ‘2D:4D digit ratio’ (but still lower than the average human digit ratio), and these primate species were monogamous and less competitive than Old World monkeys.

The results also show that Great Apes, such as orangutans and chimpanzees, expressed a different finger ratio. The analysis suggests that early androgen exposure is lower in this groups compared to Old World monkeys. Lower androgen levels could help explain why Great Apes show high levels of male cooperation and tolerance.

Emma Nelson

Primate researcher Emma Nelson explains:

“It is thought that prenatal androgens affect the genes responsible for the development of fingers, toes and the reproductive system. High androgen levels from a foetus or mother during pregnancy, may alter gene function and lead to subtle changes in relative digit length and the functioning of the reproductive system. Finger ratios do not change very much after birth and appear to tell us something about how very early androgens affect adult behaviour, particularly behaviour linked to mating and reproduction.”

ILLUSTRATION: A comparison of the human hand with primate hands reveals that only the human hand is featured with a long opposable thumb!
Comparison of primate hands: only the human hand is featured with a long opposable thumb!


Finger length linked with social behavior!
Understanding our past: “the primate hand vs. the human hand”!
Evolution of the human hand & the mystery of the 5 fingers!