The human opposable thumb: with reason neurologist Frank R. Wilson called it ‘the Twenty-Four-Karat thumb’. Because thumb studies in primates have revealed that only humans have ‘perfect opposable thumbs’. But there is more, because new evidence indicates that the opposable thumb has a direct correlation with self-awareness in the primate family!

Scientists say that there are two things that have given rise to man’s dominance as a species: one is the opposable thumb, the other is self-awareness. Interestingly, scientists also developed a test to assess ‘self-recognition’ (which is in psychology known as a first milestone in the development of self-awareness in young children) via the so-called ‘mirror test’.

The video below shows how this ‘mirror test’ has also been used to assess the capability for self-recognition in primates. And the table below displays a strong correlation between self-recognition and the opposable thumb in the primate family tree (+ a the bottom a picture is presented summarizing the hand characteristics seen in the listed primate species).

SOURCE: Opposable thumbs & self-awareness!

opposable-thumb-primates-table

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 video ‘Evolution of the human hand’ – presents a detailed picture of how modern science perceives the evolution of the human hand in time. The video is sort of based on Darwin’s evolution theory, but the details were delevered by experts in anthropology who studied how the hand shape, finger length & palmar creases evolved during the past 1.8 million years.

The video demonstrates how the ‘early’ humanoid hands (and primates) are typically featured with 3 or more ‘complete transverse creases’ (multiple simian lines), which are positioned horizontal in the hand + two major vertical lines. While at the end of the video displays a typical human hand featured with only 2 curved, oblique positioned ‘primary palmar creases’ (heart line and head line) + one major vertical line (life line).

And the differences between the human hand and the hands of primates served as a model for the evolution of the human hand in time – see below the hands of a man compared to the hands of a baboon, orangutang & chimpanzee.

Many other fascinating details about the evolution of the human hand are described in the work of physician John Napier, titled: Hands.

Another important figure in the history of medical science was the Scottish surgeon John Hunter, who turned the attention of science from the structure of hands to it’s function:

“Structure is the intimate expression of function”

– John Hunter, Scottish surgeon (1728-1793) –


More details about the evolution of other features of the human hand are presented in the articles:

1) The evolution & mystery of the five fingers

2) The history & evolution of the palmar lines

The hand of early hominids (30.000 years old).

The hand of Neanderthals (300.000 years old).

The hand of 'Ardi' (4.4 million years old).

A male hand + a female hand.

Hand shape varies between the two sexes: males typically have larger, relatively broader hands, while females typically have smaller, relatively narrower hands. But hand shape also varies among the various populations around the world: in Asia the avarage hand shape is relatively narrower than in European & North American countries. And there is even a link between hand shape & intelligence!

But in order to understand these patterns properly, one first has to understand the relations ship between hand shape & body length. Because in general, all longer populations in the world (males, Europeans & North Americans) typically display a relatively broad hand shape, while all small populations (females, Asians) typically display a relatively narrow hand shape.



HAND INDEX:

A good measure to describe the shape of the hand is the so-called ‘hand index’, which is defined as the ratio between the ‘hand width’ (= palm width measured at the metacapals) vs. the ‘hand length’ (= the distance between the tip of the middle finger and the distal wrist crease).

The average ‘hand index’ in human kind is close to 0.44, and is typically much higher than the ‘hand index’ seen in primates, which is typically (far) below 0.40 (though in gorillas – the largest of all primate species – the ‘hand index’ is higher than 0.40).

NOTICE: Finger length can also be measured relative to ‘hand length’ & ‘hand width’, but that topic will be discussed later.






HAND SHAPE & SEXE:

In males the ‘hand index’ is typically higher than 0.44, and measures above 0.45 are often seen. While in females the ‘hand index’ is typically lower than 0.44, and measures below 0.43 are not rare at all. These sexe differences are for a large part the result of the body height differences between males and females.


HAND SHAPE & RACE:

The average ‘hand index’ among the various races differs significantly, and is typically lower among asians. In people from China does not vary a lot from the average of human kind, but among for example people from Japan & India the ‘hand index’ is typically close to 0.43 or even lower. At least partly these differences are explained by racial differences in body height.


HAND SHAPE & IQ:

A high hand index typically correlates with a low IQ. And this link between hand shape & IQ has been confirmed in quite a few studies among various types of populations.

In a 1980 study in the former Yugoslavia reported among 540 men a negative correlation between hand index & all 10 measures for IQ.

And the two most common causes for mental retardation (Down syndrome & fragile-X syndrome) are known for having typically a relatively broad hand (= high hand index).

Regarding the sexe differences, one has to be aware of the earlier mentioned point that tall populations typically have a higher ‘hand index’. The fact that women have a lower ‘hand index’ compared to men, is largely neutralized by the fact that women are smaller than men. And therefore there one should not associate this sexe difference with IQ differences among the sexes (because so far there is no evidence for that at all).

And finally there is evidence that when the ‘hand index’ is corrected for body height, then this appears to explain a significant part of the IQ differences that are typically seen between the nations of the world. Though this issue has not been studied thoroughly.


HIGH OR LOW ‘HAND INDEX’ IN INDIVUALS:

The above describes patterns for hand shape implicate that regarding the implications of a high or low ‘hand index’ indivuals, one always has to consider sexe & race before jumping into conclusions!

Time for a hand shape palm reading… what is your ‘hand index’?


MORE ANIMAL XMAS PREPERATIONS:
Wanna know more about how other animals use their hands… and prepair for Christmas?

CHECK:
How the hands of primates explain their social behavior!
More news about the hands of animals

Researchers presented earlier today new evidence that neanderthals were more competitive & promiscuous than we are today! Maybe more surprizing is the method which the researchers used to acquire their new findings: via finger length 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.

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 hand bones of an early hominid - fosile presented by Wesley Niewhoener.

The hand bones of an early hominid

 

The rigth hand of 'Neanderthal Qafzeh 9'.

The hand bones of a neanderthal

 

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.

READ MORE ABOUT EARLIER RESULTS:
• Primate finger length linked with social behavior
• Human finger length & sexual orientation
• Evolution of the human hand & palmar creases

 In 1988 a very unusual hand therapy became available at various Spa centers in the world, named: ‘Doctor fish’. Doctor fish are a species called Garra Rufa (and Cyprinion Macrostomus) – which originate in pools near two small Turkish towns, Kangal and Sivas. In non-medical contexts, Garra rufa is called the reddish log sucker. They have long been known for their ability to treat the symptoms of skin conditions, especially: psoriasis!

“Doctor fish” – so named for their ability to produce healthy, glowing results from even the most crusty or diseased epidermis – are the key ingredient in a spa and skin treatment becoming increasingly popular across Turkey, Japan, China, Europe and the US.

The idea is that you immerse your hands, feet, or, if you are brave enough, your entire body in a warm pool that swarms with hundreds of hungry minnow-sized feeders. The fish zoom in on your most crusty, flaky or scabby skin and chomp away at it to reveal the fresh layer beneath. According to the spas and their enthusiasts, you emerge refreshed, healthy, buffed and glowing.

SUGGESTION FOR FURTHER READING:
Let’s shake hands with the hand fish!
Into the hands of ‘Paul the Octopus’!
The mystery of the five fingers!
Five things that your 5 fingers can tell you!
The difference between the human hand & the hands of primates!

Evolution: from fish to human!

The pink handfish - a.k.a. brachionichthys

TRIBUTE: THE EVOLUTION OF THE HAND

[tweetmeme source=”handresearch” only_single=false] A few weeks ago (may 2010) Australian researchers Daniel Gledhill & Peter Last from the CSIRO Wealth reported to have discovered 9 new species of the ‘handfish’, in a research that highlights an urgent need to better understand and protect the diversity of life in Australia’s oceans. But the major unanswered question is: ‘two of the handfish fins look like hands, but are they?’

Mr Gledhill described the Handfish as follows:

“Handfishes are small, often strikingly patterned or colourful, sedentary fish that tend to ‘walk’ on the seabed on hand-like fins, rather than swim. Fifty million-years ago, they ‘walked’ the world’s oceans, but now they exist only off eastern and southern Australia“.

One of the newly named species, the Pink Handfish, is known from only four specimens and was last recorded off the Tasman Peninsula in 1999.

Interestingly, if we take a look at some features of red handfish one can notice that it actually isn’t walking with the hands… but with the feet! (See the photos below)

The red handfish - a.k.a. brachionichthys politus!

And in the perspective of evolution it might actually make sense that the hands of the handfish appear to have 4 digits, and the feet have more digits – though 6 digits is really rather remarkable.

Why are 6 digits remarkable?

First of all, the 4-digit hand combined with a 6-digit foot reminds us to a typical characteristics of… amphibians, they are usually featured with 4 digits on the front limbs and 5 digits on the hind limbs!

However, while an amphibian usually spends his live some time on land and some time in the water – there is another rather funny ‘creature’ that has likewise hand- (4 digits) and foot characteristics (5 digits), named: the axolotl – a tiger salamander complex that is living in the waters of Mexico. The difference with the salamander is that the axolotl only lives in the water, just like the handfish!

The axolotl - belonging to the tiger salamander complex!

Most vertebrates have 5 digit limbs!

One should also be aware that most vertibrates (including: mammals, birds, reptiles, amphibians, and various fishes) have 5 digits on each limb. So, from the perspective of evolution it is not a coincidence that us human have 5 finger and 5 toes!

However, in this perspective it is rather remarkable that the handfish appears to have a 6 digit fin!

Would you like to shake hands with a handfish?

Evolution animation: from fish to human!

SUGGESTION FOR FURTHER READING:
The mystery of the five fingers!
Five things that your 5 fingers can tell you!
The difference between the human hand & the hands of primates!

Evolution: from fish to human!

Primate hands: the hand of a macaque!

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:
Impression from the back of the hand of a macaque.

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!