November 20, 2012
Polydactly (extra fingers) is one of the 10 most common pediatric orthopedic conditions, and this condition has been studied as early as the days of Charles Darwin, who suggested that the condition of having more than the usual number of fingers or toes (polydactyly) was an ancient trait, now mostly formant, that occasionally reappears due to some hereditary misstep.
Basically, there are three polydactyly variants:
A – most common is the variant featured with an extra pinky (see picture above)
B – less common is the variant featured with an extra thumb
C – rare is the variant featured with an extra index finger, middle finger or ring finger
A few (recent) reports about polydactyly:
Last summer professor John T. Manning re-designed his popular 2D:4D digit ratio theory about finger length ratio development in the hand. While he had already mentioned the role of prenatal sex steroids, now the updated theory now focusses on the balance between sexe hormones (androgens) testosterone & oestrogen during the development in the whomb!
Professor Manning presented his revised theory in the PNAS magazine under the title: ‘Resolving the role of prenatal sex steroids in the development of digit ratio‘.
Manning’s new working hypothesis now includes e.g. the following 7 key-elements:
1 – The 2D:4D digit ratio results from the balance between prental androgens testosterone & estrogen;
2 – A high 2D:4D digit ratio results from relatively low testosterone concentrations – OR relatively high estrogen concentrations;
3 – A low 2D:4D digit ratio results from relatively high testosterone concentrations – OR relatively low estrogen concentrations;
4 – The ring finger (= digit 4D) is featured with many more hormone receptors compared to the index finger (- digit 2D), therefore the 2D:4D digit ratio is mostly driven by changes in the length of the ring finger (due to prenatal hormone concentrations);
5 – Studies in human & animals indicate that the link between prenatal androgens and 2D:4D digit ratio is generally stronger for the right hand;
6 – 2D:4D Digit ratio varies with sexe: males generally have longer fourth digits relative to second digits than females;
7 – 2D:4D Digit ratio varies with ethnicity.
A quote from Manning’s article:
“Armed with this list of skeletogenic genes linked to 2D:4D, we can now be more focused in our examination of the links between 2D:4D and the etiology of sexdependent behaviors and diseases of the immune system, cardiovascular disorders, and a number of cancers.”
“Prenatal sex steroids [i.e., prenatal testosterone (PT), prenatal estrogen (PE)] are often implicated in the etiology of behaviors and diseases. They show sex differences (higher concentrations of PT to PE in males), with PT peaking at the end of the ﬁrst trimester, and cause permanent “organizational” changes in the brain and other organ systems. It has een suggested that relative levels of PT and PE may have differential effects on fertility, speed, strength, aggression, autism, many cancers, and heart disease.”
September 6, 2011
Wearing your heart on your sleeve is merely an adage, but most people do display their emotions – even if unintentionally – on their faces. Women tend to be better than men at reading other people’s subtle facial cues, especially cues from the eyes. Because of the gender difference in cognitive empathy – the ability to notice and correctly interpret body language – psychobiologistsscientists that study psychology from a biological perspective, or vice versa have hypothesized that testosterone – a sex hormone present in much higher levels in males versus females levels – could play a role in “mind reading” ability, or lack thereof.
A new study in PNASProceedings of the National Academy of Sciences validates this hypothesis by demonstrating that a dose of testosterone can make women lose some of their cognitive empathy. Researchers recruited 16 young women (age 20-25) to participate in their study. The women were given either a testosterone pill or a placebo, and then tested on their ability to assess emotions based on photographs of eyes. The test the women took is called the Adult Eyes Test, and is available for free from the Autism Research Center at the University of Cambridge. Here’s a sample question (formatting is slightly modified):
For the correct answer, click here.
Each woman was tested twice – once with placebo and once with real testosterone (in random order; they didn’t have any idea which was which). 75% of the women performed worse on the “mind reading” test after taking testosterone than after taking a placebo. So to a first approximation, an artificial increase in testosterone levels impaired women’s abilities to interpret facial expressions.
But the results aren’t quite that simple. Some women were less affected by the extra testosterone than others, and the researchers had a hunch that this could relate to their exposure to testosterone in the womb. All fetuses are exposed to testosterone while developing, but to different extents. There is a simple way to qualitatively measure fetal testosterone exposure – this parameter is believed to be correlated to the adult ratio of ring finger length to index finger length (see picture at the top of this post).
Larger ratios of ring finger to index finger lengths correspond to higher fetal testosterone levels. This study showed no difference between the inherent expression-reading ability of women exposed to higher vs. lower doses of testosterone in the womb. However, the women with longer ring fingers (higher fetal testosterone) seemed to be more easily impaired when given a dose of testosterone in pill form.
Thus, this study demonstrated that (1) testosterone administered to women can impair their ability to read facial expressions, and (2) women who experienced more testosterone in the womb are more sensitive to the effects of testosterone administered as adults. Nothing further can be definitively gathered from these results, but they seem to suggest that men’s testosterone levels could be to blame for their increased confusion about what others (especially women!) are thinking/feeling.
PS. A brand new study reported by researchers from Florida has recently (sep 2011) presented proof that fingers have hormonal receptors!
The following finger length study presents a likewise effect:
How lingerie can sharpen the financial mind!
January 18, 2011
Most people are aware that they have fingerprints. But few people are aware of the likewise dermatoglyphic features in their palms. One of the most interesting characteristics of the palmar dermatoglyphics concerns the so-called AtD-angle: which concerns the angle between the a- triradius (under the index finger), the axial triradius (near the wrist), and the d-triradius (under the pinky finger).
A 2010 STUDY:
A 1980 STUDY:
December 29, 2010
Earlier this month, British researchers published new research presenting a link between the relative length of the index finger and the risk of developing prostate cancer. In men with an index finger longer than the ring finger the chances are 33% higher for not developing the disease.
Often such studies are qualified by non-experts as “nonsense” – initially because of the association with classical palmistry. Usually a main argument of concern is the seize of the studied sample: many ’2D:4D digit ratio’ studies have been focused relatively small samples, and usually with the statistics were simly not strong enough to be applied to individuals. But those arguments can not be used to the describe the new British study!
The new British research involves a study where the hands of 1,524 prostate cancer patients were examined, which were compared with a control group of 3,044 men.
It can also be noted that Professor John Manning described in his second book ‘The Finger Book‘ with great details the suspected link between the ’2D:4D digit ratio’ and prostate cancer – a complex theory about of role glutamine chains in the sensitivity of hormone receptors, which in their turn play a role in the activation of testosterone in the body:
“…The various forms of the androgen receptor have important consequences for our health and behaviour. For example, African-American men have shorter glutamine chains (high sensitivity to testosterone) than white men. Short glutamine chains are associated with an increased susceptibility to prostate cancer, and this may in part explain why the incidence of prostate cancer is higher in African-Americans than in white Americans. …”
In short, there seems to exist a triangular relationship between: 1) the high percentage of prostate cancer in Americans with African ancestry, 2) the length of the glutamine chains, and 3) the length ratio between index finger and ring finger.
The importance of the new British study can be recognized in the fact the use of preventive screening for prostate cancer – which is anno 2010 usually done through the use of a blood test – is still an object of confusion. Simply because the benefits of the screening devices are still very unclear. Meanwhile it is a fact that prostate cancer is known as the No. 1 cause of death from cancer in men (see picture below).
The British researchers therefore are speculating about how to add a practical application of their finger length study to the traditional methods of prostate cancer prevention screening!
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 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.
What does finger length say about athletic ability? An experiment with six athletes: all 5000 meters specialists… the outcome is simply astonishing.
Professor John T. Manning explains:
“… What I should be able to do is look at the differences between the ring finger and index finger, and on that basis rank these runners: first, second, third, fourth and so on. In theory that should work.”
Comment voice explains:
“In practice we’re providing professor Manning with photocopies of the athletes hands. And in return he’s risking his reputation by providing us with the results of a race that has yet to be run.”
You can take a look at the outcome of this remarkable experiment from the BBC’s “Secret of the Sexes” – surely you will enjoy it, probably you will remember the outcome easily!!!
SUGGESTION FOR FURTHER READING:
February 10, 2010
Portrait of Giacomo Casanova by Pietro Longhi.
In the history of the world literature there are many references to variations in the length of fingers. But of all revelations none are more lively than the informative comment in the memoirs of Giacomo Casanova (Jacques Casanova de Seingalt, 1725-1798). Finger professor John T. Manning points points out in ‘The Finger Book’ to an anecdote of Casanova – who has been described as the ‘world’s greatest lover’.
Manning writes on page 2 of his second book ‘The Finger book‘:
“Casanova was an eighteenth-century musician, gambler, soldier, philosopher, writer, librarian, aspiring priest and, of course, womaniser. It is anecdotal but entirely unsurprising that we find from his diaries that he had a ring finger noticably longer than his index finger.”
“Casanova’s adventures took him across Europe, and it is during his stay in Spain that we learn of the relative length of his fingers. At the time Casanova was enjoying the hospitality of the German neoclassical painter Anton Raphael Mengs. Today Mengs’s work is often regarded as cold and contrived, but at the time he was seen by many as Europe’s greatest living painter, and Goya was one of his many students.”
“In the course of his stay Casanova’s relations with his host were less than cordial. Mengs was openly scathing at what he saw as Casanova’s neglect of his religious duties, and he even attempted to evict Casanova from his household after he had failed to take the sacrament at Easter. Casanova meanwhile complained that Mengs was a lascivous, bad-tempered, jealous, avaricous drunkard who beat his children to excess.”
“It is against this background of growing mutual dislike that Casanova recounts a dispute in which he drew Mengs’s attention to the hand of the pricipal figure in one of his paintings, claiming that it was faulty because the ring finger was shorter than the index finger. Mengs assured him this was the correct human condition, showing Casanova his own long index finger and short ring finger. Laughing, Casanova displayed his badge of prenatal masculinity, and asserted that he was sure that his ring finger, unlike Mengs’s, was ‘like that of all children descended from Adam’. A wager of a hundred pistoles was made, and a hurried comparison with the ring fingers of the painter’s servants showed the ‘Casanova pattern’ to be the more common.”
Peters et al. (2002) reported that Casanova made two clear statements: first, that the ring finger is relatively longer than the index finger and, second, that this is the case for both men and women. What follows is a quote from the work of Casanova (The Memoirs of Casanova: Spanish Passions) about one of his conversations with the German neoclassic painter Anton Raphael Mengs.
QUOTE FROM CASANOVA (1794):
… Once I dared to tell him that he had made a mistake in the hand of one of his figures, as the ring finger was shorter than the index. He replied sharply that it was quite right, and shewed me his hand by way of proof. I laughed, and shewed him my hand in return, saying that I was certain that my hand was made like that of all the descendants of Adam.
“Then whom do you think that I am descended from?”
He got up, threw down brushes and palette, and rang up his servants, sayin,-
“We shall see which is right.”
The servant came, and on examination he found that I was right. For once in his life, he laughed and passed it off as a joke, saying-
“I am delighted that I can boast of being unique in one particular, at all events.”
SUGGESTION FOR FURTHER READING:
Thom Yorke thumbs & the simian line…
The simian line (a.k.a. ‘simian crease’) is the most studied line of the human hand. Despite it’s associations with Down syndrome (+ a rainbow of other medical problems), quite a few famous people have the simian line. Radiohead’s leadsinger Thom York has a variant of the classic simian line in his right hand – an ‘incomplete simian crease‘. What do we know about the most ‘notorious’ of all hand lines?
Having a simian line is not very uncommon at all: about 2% to 4% of the population has this rather remarkable hand line – though in Asia the percentages are higher up to above 10% in Chinese people.
Rather remarkable – despite the strong links with various medical problems – some believe that the simian line can also be recognized as a ‘gift marker‘ which could relate to strong personality characteristics that bring stamina, intensity and strong concentration.
More Thom Yorke thumbs of his simian line:
Another fascinating characteristic of the hands of Thom Yorke concerns his fingerlength: his ring finger is much longer than his pointer finger.
Interestingly the long ring finger has historically been associated with musical abilities. Professor John Manning (Liverpool University) presented in 2000 a study which pointed out that the hands of male symphony musicians are characterised with a likewise combination: the low ‘digit ratio’ – of 2D:4D finger ratio (2D = index finger; 4D = ring finger).
Quote from Professor John T. Manning’s book ‘digit ratio’ (page 121):
“Sorell (1968) pointed out that musical ability has been linked with very long ring fingers for many years. He illustrated this with handprints from composers such as Alexander Tcherpenin and Edgar Varese, but the most powerful image he showed in this context was that of a cast of Franz Liszt’s right hand (Sorell 1968, 187). In this cast Liszt’s ring fingers is strikingly dominant in length, with the middle phalanx making up an apparently disproportionate part of the finger. These are anecdotal observations, but measurements of casts and photographs of the hands of eminent musicians may wel reveal very low 2D:4D ratios.”
By the way, extreme digit ratios (finger lengths) are – just like the ‘simian crease’ (Thom Yorke) and the ‘clubbed thumb’ (Megan Fox) – recognized as a ‘minor physical anomaly’ (MPA).
SUGGESTION FOR FURTHER READING: