The primate hands family tree shows how dominant behavior in primates can be linked with hand structure. For example, gorillas & baboons are known to belong to the most dominant/aggressive primate species and both species have a hand structure that is different from other primate species!

It is rather fascinating to see that both species (gorilla + baboon) actually have a hand structure that reminds us of the typical hand differences seen between males and females, incuding: short fingers, broad palms & a low 2D:4D digit ratio.

These biological & evolutionary patterns appear to explain why in nearly all primate species males tend to dominate females. Except for the bonobos of course, females tend to collectively dominate males by forming alliances and use sexuality to control males – interestingly, a few years ago a study reported that bonobos have a rather human-like 2D:4D digit ratio (close to 0.94)… which is illustrative for their rather high emotional intelligence. The Bonobo-society has been described as ‘extraordinarily peacefull’.

This illustrates that Sir Charles Bell was very right about the hand representing capacity, and modern science has still a long way to go in order to understand properly how the structure of the hand corresponds with behavior!

More details:
http://www.handresearch.com/news/primatology-palm-reading-primate-hands-family-tree.htm

The hand of a white faced Capuchin primate ape.

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 behavior is linked to exposure to hormone levels in the womb!

The sientists have used finger ratios as an indicator of the levels of exposure to the hormone and compared this data with social behaviour in primate groups.

The team found that Old World monkeys, such as baboons and rhesus macaques, have a longer fourth finger in comparison to the second finger, which suggests that they have been exposed to high levels of prenatal androgens. These species tend to be highly competitive and promiscuous, which suggests that exposure to a lot of androgens before birth could be linked to the expression of this behaviour.

Other species, such as gibbons and many New World apes, have digit ratios that suggest low levels of prenatal androgen exposure. These species were monogamous and less competitive than Old World monkeys.

The results 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.

HOW CAN WE UNDERSTAND THESE RESULTS?

Emma Nelson

Primate finger length 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!

SUGGESTION FOR FURTHER READING:

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