November 5, 2010
Researchers from England & Canada presented earlier this week brand new evidence that the neanderthals’ life was much more dominated by competition & promiscuity than our lifes today! Maybe more surprizing is the method that the researchers used to acquire their new findings: finger length ratio measurements!
The study, published in the Proceedings of the Royal Society B, draws upon a famous and controversial indicator of social behavior: the comparative length of the index finger and the ring finger, also known as the 2D:4D finger ratio. If the ring finger is longer than the index finger, that’s supposed to be correlated with higher prenatal exposure to androgens — resulting in a higher proclivity for aggressiveness and promiscuity.
A few numbers from the results:
• Modern humans averaged a 0.957 index-to-ring finger ratio, and were considered to be on the line between a “pair-bonded,” or monogamous, species and a middle-of-the-road species.
• Chimps, gorillas and orangutans had index-to-ring ratios in the 0.90 to 0.92 range, and were classified as “non-pair-bonded,” or promiscuous.
• An early modern human from Israel’s Qafzeh Cave, thought to be about 95,000 years old, had an index-to-ring ratio of 0.935. Based on that statistic, the researchers surmised this individual would be more promiscuous than modern humans.
• The finger bones from five Neanderthals yielded a 0.928 ratio, associated with even greater competitiveness and promiscuity. Ardipithecus’ bones took it up another notch, to 0.899. Two even older primate ancestors, Hispanopithecus and Pierolapithecus, had ratios of 0.848 and 0.908, which means they would have been tough to live with as well.
• On the other end of the spectrum, the monogamous gibbons had a 1.009 ratio … and the australopith sample came in with a ratio higher than that of modern-day humans (0.979). The implication, then, is that australopiths were monogamous.
Scientists, in collaboration with researchers at the universities of Southampton and Calgary, used finger ratios from fossilised skeletal remains of early apes and extinct hominins, as indicators of the levels of exposure species had to prenatal androgens – a group of hormones that is important in the development of masculine characteristics such as aggression and promiscuity.
It is thought that androgens, such as testosterone, affect finger length during development in the womb. High levels of the hormones increase the length of the fourth finger in comparison to the second finger, resulting in a low index to ring finger ratio (2D:4D digit ratio). Researchers analysed the fossil finger bone ratios of Neanderthals and early apes, as well as hominins, Ardipithecus ramidus and Australopithecus afarensis, to further understanding of their social behaviour.
The team found that the fossil finger ratios of Neanderthals, and early members of the human species, were lower than most living humans, which suggests that they had been exposed to high levels of prenatal androgens. This indicates that early humans were likely to be more competitive and promiscuous than people today.
The results also suggest that early hominin, Australopithecus – dating from approximately three to four million years ago – was likely to be monogamous, whereas the earlier Ardipithecus appears to have been highly promiscuous and more similar to living great apes. The research suggests that more fossils are needed to fully understand the social behaviour of these two groups.
Dr Susanne Shultz, from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford describes:
“Social behaviours are notoriously difficult to identify in the fossil record. Developing novel approaches, such as finger ratios, can help inform the current debate surrounding the social systems of the earliest human ancestors.”
And Dr Emma Nelson, an archaeologist from the University of Liverpool, argues that comparing the finger-length ratios of extinct and present-day species is a valid technique for making an indirect assessment of our long-gone ancestors’ social behavior. She said:
“It is believed that prenatal androgens (male sex hormones) affect the genes responsible for the development of the fingers, toes and the reproductive system. We have recently shown that promiscuous primate species have low index to ring finger ratios, while monogamous species have high ratios.”
“We used this information to estimate the social behaviour of extinct apes and hominins. Although the fossil record is limited for this period, and more fossils are needed to confirm our findings, this method could prove to be an exciting new way of understanding how our social behaviour has evolved.
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.
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!
SUGGESTION FOR FURTHER READING:
November 20, 2008
You may have thought it was simply a matter of being able to grip and control the ball better, but according to researchers at the University of Alberta and the University of California-Riverside, individuals with longer fingers are more inclined to voluntarily participate in intense physical exertion.
|The good news:
This means that if you absolutely detest exercising, it may not be due to laziness or lack of willpower; it might be that you’re just… short-handed.
The bad news:
Although the researchers [R.H. Yan, et al.] believe their findings are applicable to humans, the study actually involved 1,000 white mice. And you probably weren’t even aware that mice had fingers.
READ FURTHER ABOUT FINGER LENGTH & ATHLETIC ABILITY:
October 27, 2008
Look at the length of your index finger in relation to your ring finger. If your index finger is longer, you’re probably a ‘couch potato’. If your ring finger is longer, chances are you love to exercise.
Reuters Health reports that a number of previous human studies have linked finger length ratio to certain behaviors and personality traits, including aggression, athletic ability and even academic skills.
|Making a sweeping generalization, men tend to have a shorter index finger in relation to their ring finger, while the two fingers tend to be the same length in women. The so-called “male pattern”–whether it’s seen in men or women–often means there is more aggression and greater athletic ability, while the “female pattern” is associated with stronger verbal skills.
Now researchers at the University of Alberta in Edmonton in Canada have investigated the relationship in 1,000 white mice. When they selectively bred mice to enhance the trait of increased physical activity, those mice had a higher digit ratio. And although this behavior was clearly associated with digit ratio, the findings were the opposite of those observed in humans, reports Reuters. Specifically, the mice with a lower (or “male pattern”) digit ratio tended to be lazier than the mice with the “female pattern,” who took to their running wheels far more frequently.
If you’re lazy, can you blame it on the length of your fingers? Not a chance. Study co-author and associate professor of psychology Dr. Peter L. Hurd told Reuters Health, “The effect sizes for digit ratios on behavior in humans are really small, making it virtually impossible to tell anything about a single individual from their hands,” Hurd told Reuters Health. “The pattern only emerges when a great many people are examined.” He says comparing finger length to behavior is interesting because it says something about personality traits that are fixed during early development in the womb.
September 29, 2008
‘Digit ratio’ in non-human primates:
The major focuss in Emma Nelson’s ”digit ratio’ research in primates is:
|“Using digit ratios (2D:4D) to investigate social systems in anthropoids; implications for the study of the evolution of hominin sociality.”.
Variation in non-human primate 2D:4D is currently unknown. One of the aims of this project is to map differences in mean 2D:4D within and between non-human primates species.