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AAAS / Science file
Researchers measured the length of fossilized fingers from Ardipithecus and other ancestors on humanity's family tree, then compared them with modern-day species in hopes of figuring out how aggressive and promiscuous long-gone species might have been.
The oldest-known species on humanity's family tree was built to be pushy and promiscuous, while another long-ago ancestor known as Lucy was lovey-dovey. Early humans and Neanderthals were more competitive than we are. At least those are the conclusions that researchers reached after sizing up the fingers of extinct and present-day primates.
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 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. The finger-length ratio also has been linked to sexual orientation as well as sporting prowess and musical ability.
(Did you just look at your fingers?)
Emma Nelson, an archaeologist from the University of Liverpool, extended the finger-length ratio study to a wide range of species. She and her colleagues measured bones from modern-day species such as gorillas, chimps, orangutans and the white-handed gibbon. They also looked at fossil bones or previously recorded measurements from extinct hominids ranging from Neanderthals (which co-existed with humans until about 30,000 years ago) to Australopithecus afarensis (Lucy's species, going back 3.1 million years) and Ardipithecus ramidus (the oldest human-linked fossil species, going back 4.4 million years).
Nelson 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.
"It is believed that prenatal androgens affect the genes responsible for the development of fingers, toes and the reproductive system," she explained in a news release. "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 behavior of extinct apes and hominins."
Nelson previewed her findings a year ago at the Society of Vertebrate Paleontology's annual meeting, where she talked about naughty Neanderthals and monogamous australopiths. The newly published paper draws upon additional samples, including the finger lengths for Ardipithecus, or "Ardi." So here are the numbers:
- 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.
The big question is whether there's anything substantial to this analysis. Nelson acknowledged that the fossil record was sparse, and that more fossils were needed for study, but she insisted that "this method could prove to be an exciting new way of understanding how our social behavior has evolved."
Other researchers have tried to make guesses about the social behavior of extinct hominid species by looking at sexual dimorphism -- that is, the differences between the male and the female of a species. If the males were significantly larger, the assumption is that they were built to have their way with many females in a promiscuous social setting. This has generated a fair amount of debate, particularly when it comes to assumptions about australopiths.
Nelson and her colleagues suggest that the finger-length ratio could serve as an additional tool for making more educated guesses about ancient social behavior.
"Social behaviors are notoriously difficult to identify in the fossil record," one of Nelson's fellow authors, the University of Oxford's Susanne Shultz, said in the news release. "Developing novel approaches, such as finger ratios, can help inform the current debate surrounding the social systems of the earliest human ancestors."
When this research first came to light last year, University of Wisconsin anthropologist John Hawks cautioned against reading too much into fossilized fingers. He said the index-to-ring ratio "may be correlated with mating system in primates, but that doesn't mean it's a good predictor of mating system. ... As fossil hominins go, I wouldn't expect the story to go any further -- there just aren't many hands, so there's never going to be a significantly predictive result."
Be sure to read Hawks' posting from last year, and feel free to weigh in with your comments below ... that is, after you've finished checking out your fingers.
Update for 2 a.m. ET Nov. 3: John Hawks provided some additional thoughts in response to my e-mail inquiry:
"The 2D:4D ratio really is a subject of a lot of research in psychology and developmental biology, and it really does reflect prenatal hormone exposure. However, it is not a good predictor of any social behaviors.
"In addition to the problem of using a poor predictor, this study has another problem that we often face with fossils -- there are very few of them, and it's not obvious which sample of living primates we should be comparing with them.
"The living apes do vary in mating structure, but they also have huge differences in hand anatomy because of locomotion. Those anatomical differences between species do not necessarily have any relationship to the neurological correlates of prenatal hormones -- even though the variation in hormone exposure is an important cause of variation within species.
"For example, Ardipithecus has fingers and hand proportions that are right within the range of other apes. So when we see that they have a 2D:4D ratio right in the range of other apes, the natural hypothesis is that this reflects their overall hand proportions. Australopithecus, Neandertals and modern humans obviously had humanlike hand proportions, and their 2D:4D ratio may simply reflect this.
"If you were going to do this study right, you would look far beyond the apes to take in many kinds of primates with different social systems. Then you could see whether closely related species have 2D:4D ratios that track their mating systems. Without this, we are really looking at a single evolutionary event -- the rise of the hominins -- which may be unique for many reasons besides mating system."
In addition to Nelson and Shultz, the authors of "Digit Ratios Predict Polygyny in Early Apes, Ardipithecus, Neanderthals and Early Modern Humans but Not in Australopithecus" include Campbell Rolian and Lisa Cashmore.
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Leave a Comment:
pseudo science? give it the finger;-)
Do you think that the human finger lengths will continue to change and evolve, now that the main tool allot of us use is the computer keyboard?
If I put my left pinky finger on the "esc" button on my laptop keyboard, I can only reach to f12 with my thumb! Four keys I can't reach with one hand! DAMN! C-mon mother nature, lets make these fingers longer, quicker, to accommodate the computerizationizing of man!!
Did they examine toes, too, in this study? Now I'm lookin at and analyzing my toes!
Why does evolution take so long? I read somewhere that it could take 10,000 years or more for evolution to change ONE hair! Evolution takes so long to occur that we never notice it happening!
WHY?????
This study makes me think about deeper things. I approve this message and study.
Joany,
Evolution is still taking place, unfortunately we won't be around to see it. Horses once had three toes, they developed into one (hoof), The ostrich has two toes which will one day become one, much like the horses hoof. Wonder what we will look like in a couple thousand years? That's why I'm using my anti-wrinkle cream, want to look good then :-)
This article is "Finger lickin good"!
phrenology for the modern age.
I know an expert on trepanation I could refer you to.
"Makes perfect sense to me."
It's time to measure the fingers in red states.
my index finger isn't longer than my ring finger :(
I bet she believes in phrenology (the study of bumps on the head to predict personality) as well.
If I hold my hand extended and then relax it, my ring finger gets longer by a huge difference (actually matches up with the middle finger then) so how am I supposed to know if my fingers are actually longer than the other...measure it? I don't know if this proves anything. They are always studying weird crap like this.
Wasn't there a study recently that said homosexuality can be predicted by how big the pinky toe of your closest sibling was or something? Researchers these days really need to learn the difference between correlation and causation. And what makes a good sample size.
Seems to be going way out to establish correlations. Since the data was not given from which the conclusions were drawn I cannot in, good conscience, consider this anything more than non science. Science should not be defined by what little data there is to form a conclusion.
Actually... these new results are not 'surprizing' at all:
Apes have longer ring fingers than neanderthals - and neanderthals have longer ring fingers than us human today!
Interestingly, one can add to this sequence... that males have longer ring fingers than females!
Maybe this could help us understand why males are more promiscue than females? Anyway, there are quite a few other related '2D:4D finger length ratio' reports available. Here you can find a sample of some interesting publications which presented other fascinating facts:
http://www.handresearch.com/news/digit-ratio.htm
By the way... despite that there has never been any single study which has indicated that 'finger length ratios' can be used as a reliable tool, Professor John Manning (a.k.a. the 'Finger Professor') has conducted at least 2 experiments with athletic sprinters and long distance runners. And his results are fascinating (twice predicting the right winner of a race!), see:
http://handfacts.wordpress.com/2010/03/05/finger-length-predicts-the-results-of-a-5000-meters-athletics-race/
When will people finally understand that this is not 'pseudo-science'!?
"The fnger (sic) bones from five Neanderthals yielded a 0.928 ratio, associated with even greater competitiveness and promiscuousness."
Whatever happened to the word "promiscuity"?
Ha, good "point" ... will make the fixes. Sorry about the typo and the wordirificosity.
Who funded this?
Funding is disclosed at the end of the paper, with initials referring to the individual researchers: "S.S. is supported by a Royal Society Dorothy Hodgkin Fellowship. C.R. was supported by a National Science Foundation Doctoral Dissertation Improvement grant (BCS 0647624), Canadian Natural Sciences and Engineering Research Council (NSERC) Graduate Scholarship and Alberta Children's Hospital CIHR Postdoctoral Training Grant. L.C. received a Small Research Project Grant from a British Association for Biological Anthropology and Osteoarchaeology. L.C, E.N. and this publication were funded by the British Academy Centenary Project; from Lucy to Language: The Archaeology of the Social Brain."
I think if this were true we'd see a lot more pornographic caveman paintings on cave walls.
Considering what remote tribes do and what ancient civilizations did (Kama Sutra, some ancient Japanese drawings, and clay figures of pre-history nudes), you would think there would be more cave drawings of such things. They painted hunting, but not procreating? I bet there's some out there somewhere.
LOL
There are. Many of the earlier depictions of humans on the walls include indications of their biological sex. Also, the many venus figures found from human prehistory are quite detailed when depicting the female sexual organs, but much less detailed in other areas.
@JOKERSWILD1 you're typical. Nothing to be bummed about.
I would add to Dr. Hawk's comments that this topic maintains a lively debate. In psychology, the predictive ability of the 2D:4D ratio is limited and the literature does contain some apparently contradictory results. However, there do appear to be small but still significant relationships between basic personality traits and the finger ratio. Stature, handedness, and function of the hand do indeed need to be considered to get a more precise understanding of the relationship between finger ratio and behavior, especially when comparing across species. I would not, however, discount this line of scientific study and its potential implications for interspecies variation in social/sexual behavior.
I know there's always exceptions to the rule and whatever, but looking at the 2008 USAToday article linked in the third paragraph, the results are completely opposed to what I see with myself. It says having a longer ring finger is linked to a higher aptitude in music and spatial ability, along with heterosexuality and athletic endurance. My ring fingers are several millimeters shorter than my index fingers, but I'm very musically inclined, I have a strong spacial awareness, I like the ladies and I can run real good-like (though I didn't really do sports in high school). Also, I don't tend to see a correlation between many athletic people and musical people, yet they're both somehow branded by the length of their ring fingers? I could maybe believe the testosterone link, but I'd need to see a much bigger cross-section of the population to take any of it as realistic.
My ring finger is longer, I'm promiscuous!
However, I have big feet and that wivestale doesn't seem to be holding true :(
I understand that knowing more about our ancestors helps us learn about us but wouldn't the money spent on studies of this kind better be used looking for cures to disease? I bet the pharmacy companies fund these studies so real scientists don't "waste" their time looking for those pesky cures.
Non-medical science is not a waste of money.
This study just gave you a tool to assess the next guy you meet in less than 30 seconds. Not too bad!
Should we wonder why the linked articles on sexual orientation and sports/musical prowess described exactly opposite results for heterosexual men and women?
These findings are proving what palmistry has been saying all along, that relative finger lengths show personality characteristics. I am glad that now scientific research is being conducted and this could give more credibility to palmistry, of which finger reading is a significant part. A lot of my analysis is based entirely on finger lengths:
http://palmistryforyou.com/
It is a painstaking job, measuring finger lengths and then reading the personality especially because (as a commentator above has pointed out) fingers can look different from different angles. Unfortunately, the scientific findings do not give an in-depth explanation and I feel they jump to certain conclusions. Reading finger lengths is far more complex than it seems. It is not A= B although scientists love that sort of thing. The truth is that the index finger represents a person's desire to dominate, it represents ambition and the Self. If this finger dominates the hand it is not a good sign as it shows a person who is out of balance with the characteristics shown by the other fingers. Napoleon had this sign and that is why in his arrogance and over confidence met his waterloo.
They could do a nice, comprehensive survey among the existing human population to test it, but they don't. They prefer studying extinct primates with very few skeletons--because they don't really want to test their conclusion, do they?
The coelacanth was said to be the first fish that walked on land--it was said to be extinct so it was unavailable for actual observation--observation is what science was originally based on, as opposed to speculation.
Sadly for evolutionists, fishermen caught one of these "living fossils" and everyone found out why they were so hard to find they were considered extinct. The coelacanth lives at depth and does not approach the surface of the water, or dry land, at all.
"The coelacanth is a lobe-finned fish, similar in form to the ancestor of all terrestrial vertebrates. It was a coelacanth-like fish that originally evolved legs and began to walkon land 360 million years ago."
Hmmm...didn't they get the point that their idea of what the lobe-fins were used for in the coelacanth had nothing to do with walking??? Guess not.
http://www.wisegeek.com/what-is-a-coelacanth.htm
But there's no indication from finger length as to how many lazy, dimwitted boyfriends with bad haircuts a gal can acquire over a lifetime, is there? Naw, I vote thumbs down on this. Too amorphous and not backed up by personal experiences on the part of the scientists. Monkeys and apes in the field don't count -- they have no taste in clothing, haircuts or partners, they just go for whoever picks the most fleas out of their coats.
I don't believe a word of this. As accurate as a mood ring.
Disclaimer: I've only read this article, not the paper.
Given that, I'm in biological ant., 2D:4D is pretty contentious.
I think it's pretty undisputed that the last common ancestor of humans/chimps would have pretty freakin' long fingers - apes have much longer fingers than we do, check out a picture of a chimps hand...given this, I would want there to be some sort of attempt to control/account for the changes experienced as our fingers became relatively shorter, as well as an attempt to control for finger length and ecological variables like if the species lives in trees, holds onto branches, etc. Even if 2D:4D means what we think it might in humans (which is super contested), how do we know it means that in animals that have radically different uses for and general morphology of the hand?
Does the 2D:4D of my dog mean something?
My ring-finger is almost 1/4" longer than my index finger, but all my fingers are short, so I guess that means that I'd be an out-of-control, hyper-sexed freak if I wasn't so repressed. HaHaHa
On a more serious note: Welcome to Club Crock-A-Poo!
Most women have a longer ring than index finger, most men have the opposite condition. The index is longer than the ring. I don't know how this item fits with that, but it's well established as a gender difference (in addition to configurational differences of the genitilia) in humans that has been known for a long time...