Sex differences:
males vs. females & the hand!

On the basis of body hair and fat percentage one can say that the male body constitution resembles more to the body constitution of apes - the female body constitution is more different compared to the body constitution of apes.


The sequel of this page indicates that various aspects of the hand confirm the idea that in the perspective of evolution the female body constitution varies more from the primate body constitution - compared to the male body constitution. Provide these insights a solid basis for the frequently heard assumption that men have a more 'primitive' nature compared to women?




Apes usually have a very short thumb,
men have a shorter thumb compared to women


In the section the function of the hand is described that the human thumb is relatively long compared to the ape's thumb.

In general one can say that the male thumb is a bit shorter compared to the female thumb. You can determine the length of your thumb by putting your hand on a flat surface, and by pushing your thumb towards your palm. With the proximal phalange of the index finger as a point of reference you can now observe the length of your thumb. Usually the tip of the thumb ends near the middle of the proximal phalange of your index finger - see: the line in the figure. In case the tip of the thumb ends near this line you can conclude that the length of your thumb is: 'normal'.
When you measure the thumbs of a few males and females among your acquaintances you will very likely notice that in the hands of the males the thumb is usually not long in both hands.

In my dissertation study I have studied this aspect of the hand in 30 males and 75 females. The results are depicted below. The figures indicate that in the hands of over 60% of the studied males the thumb is (a bit) short in at least one hand (compared to less than 40% in the studied females). Whereas a (bit too) long thumb is observed in about 20% of the studied females (compared to less than 10% in the studied males).


[REMARK: I have discovered the relation between 'male-female differences' and thumb length in the first half of 2003. This implicates that my observations in the hands of the test subjects in my 1997 dissertation study were not influenced by presumtions on this matter]





The 'human digital formula' (2D>4D)


The concept 'human digital formula' is introduced by Wood Jones (The principals of anatomy as seen in the hand, London: Churchill, 1930). Jones discovered that in the hands of apes the absolute length of the ring finger is always longer than the index finger: the phenomenon is being described by Wood Jones by means of the concept: the 'simian digital formula'.

In the human hand the absolute length of the ring finger is usually longer than the index finger as well. However in some people the absolute length of the index finger is longer than the ring finger. Wood Jones refers to this condition as the 'human digital formula'.

The picture on the right concerns a hand including the 'human digital formula' (the arrows have the same length!) .

The figure below presents data from the dissertation study follow-up. These data indicate that the 'human digital formula' is more observed in both the right- and left hands of the studied females compared to the studied males.


The British biologist John Manning observed a likewise result in quite some populations from different countries (a longer index finger is much more frequently observed in the hands of females compared to males), and Manning concludes on the back of his book:

"... The 2D:4D ratio is the only prenatal sexually dimorphic trait that measurably explains conditions linking testosterone, estrogen, and human development; the study of the ratio broadens our view of human ability, talent, behavior, disposition, health, and fertility."

By the way, Manning didn't study the possibility that other features of the hand show likewise male-female differences. Nevertheless my research results indicate that the morphological male-female differences in the length of the little are actually much more significant compared to the ratio of the index finger and ring finger (= 2D:4D ratio)!!!:




The length of the little finger


The figure below show data from the dissertation study follow-up. These data show that in about 75% of the studied females the little finger is shorter than 3/4 of the length of the middle finger. In the hands of the studied males this condition is observed in about 35%. Conclusion: the studied females show relatively frequently a short little finger!


The hands of apes are known to have a long ring finger ... and a long little finger. In other words: the research data indicate related to the little finger indicate that the body constitution of males resembles more to the body constitution of apes - regarding the length of the little finger the female body constitution appears to be positioned at a further distance from the body constitution of apes.



Other features of the hand


The simian line has earned its name from the fact that this line is frequently observed in the hands of apes (simians). The simian is also known to be observed twice more frequently in the hands of males compared to the hands of females. More info about the simian line is described in the section neuroticism.

The classical work of Cummins & Midlo 'Finger Prints, Palms and Soles' (p.170) describes that the hands of apes show about 2 to 3 times more frequently 'complex' dermatoglyphic patterns (loops and whorls) compared to the human hand. A research study presented by Schaumann & Alter (Dermatoglyphics in medical disorders, 1976, p.78-80) on 200 males and 200 females from Northern-America shows that in all fingers and all palmar zones the studied males appear to have more 'complex' patterns compared to the studied females.

More info about 'complex' patterns in the dermatoglyphics is presented in the section autism.



MORE ABOUT THE SIMIAN CREASE:
The Simian Line: a notorious hand crease!




CONCLUSION:

Next to the male-female differences concerning body hair and
fat percentage (breasts!!?), thumb length & finger length distributions, as well as simian line & dermatoglyphics distributions provide evidence to assume that during the evolution the female body constitution has evolved further away from the body constitution of apes - the male body resembles more to the 'primate' body constitution.


Martijn van Mensvoort - Hand Research

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