HANDS – Five major differences between the primate hand and the human hand!

Primate hands: the hand of a macaque!

‘Whorls’ are a common features in the hands of many primate species! What are the major differences between the hands of primate species and the human? • 1 – Primates usually have a shorter thumb than humans – the thumb of the macaque (see photo on the left) does not rearch out behond the distal border of the handpalm. • 2 – Primates usually have a lower ‘2D:4D digit ratio’ than humans – the hand of the macaque is featured with a much longer ring finger (digit 4) than the pointer finger (digit 2).

• 3 – Primates usually have more fingerprint- and palmar whorls than humans – the hand of the macaque is featured with 5 palmar whorls. • 4 – Primates always have a lower ‘ridge density’ than humans. • 5 – Primates usually have (various) palmar transversal creases, a.k.a. ’simian lines’ – the hand of the macaque has one ’simian line’. SUGGESTIONS FOR FURTHER READING: • The Monkey Palmist! • Fingerprints, toeprints, and … tailprints? • Understanding our past: the human hand vs. the primate hand! • Hands in the perspective of evolution! • Weird stories about hands & evolution! PHOTO: Impression from the back of the hand of a macaque:

PRIMATE HANDS – Finger length linked with cooperative, competitive & sexual behavior!

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? 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! 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!

Research: fingerprints are unlikely to increase ‘grip’ to our hands!

In may 2009 Dr Roland Ennos and his team at The University of Manchester presented fingerprints findings with a surprizing outcome. Fingerprints do not help primates grip, as previously thought. Instead, a fingerprint actually reduces the friction needed to hold onto flat surfaces. Dr Ennos disproved the long-held assumption that fingerprints help primates to grip with a simple machine, three strips of perspex and the right hand of Masters student Peter Warman. They tested the student’s grip on every finger + thumb at three different widths of perspex as the machine pulled the perspex strips down via a weight in a plastic cup. The researchers also tested grip at three different angles by bending both the fingers + the thumb. This wide range of testing conditions allowed them to separate pressing force from the contact area and overcome any confounding variables. The results indicate that fingertips act more like rubbers than hard solids; their friction coeficient fell at higher normal forces and friction was higher when fingers were held flatter against wider sheets and hence when contact area was greater. WHY DO WE HAVE FINGERPRINTS? Dr Ennos answers the question as follows: “The experiment was so simple, this discovery could have been made 100 years ago; but scientists make assumptions and tend to look at complicated things instead. My preferred theory is that they allow the skin to deform and thus stop blistering. That is why we get blisters on the smooth parts of our hands and feet and not the ridged areas: our fingerpads, palms and soles.” SUGGESTIONS FOR LEARNING MORE ABOUT FINGERPRINTS: • The latest news about fingerprints! • Evolutionary hand analysis: the mystery of the 5 fingers! • 20 Facts about your fingerprints, skin & dermatoglyphics!