(Article was presented in 2003 - updated in 2017)
Apes are generally known to have very short thumbs,
human males have a shorter thumb compared to human female
The 'human digital formula': 2D>4D
The concept 'human digital formula' was introduced by Wood Jones (The principals of anatomy as seen in the hand, London: Churchill, 1930). Jones discovered that in the hands of apes [Hominidae] the absolute length of the ring finger is typically much longer than the index finger: the phenomenon is being described by Wood Jones by means of the concept: the 'simian digital formula'.
Nevertheless, in the human hand the absolute length of the ring finger is usually also slightly longer than the index finger. However, in some people the absolute length of the index finger actually 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 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."|
The length of the little finger
Other features of the hand?
For example, 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, a disorder which is known to have a higher prevalence in males than in females!
• HAND SHAPE:
One could even argue that the full hand shape is a signficant factor here! Because most ape- and monkey species show a tendency to have a relatively 'long' hand shape relative to the typical human hand proportions. Technically, this aspect can best be studied via the hand width to hand length ratio - the so-called 'hand index'.
In humans the 'hand index' is generally close 0,45, but is also known to be much higher (1% to 5%) in males than in females. However, in most ape- and monkey species the 'hand index' is generally found to be well below 0,40 - with only two exceptions: gorillas and baboons... two of the most violatent primates species!
Historically, population-level right- or left handedness has been considered a hallmark of human evolution - the debate about whether nonhuman primates may or may not exhibit population-level handedness is actually not even within sight. However, it is interesting to notice that both the tendency towards left-handedness and ambidexterity is typically more prevalent among males.
So, in a way one could argue here that some of the biological reasons why aggression gets associated to represent typical 'male-like' behavior... is reflected by the fact that males tend to have a relatively wide hand shape that is often featured with e.g. a low digit ratio, and/or fingerprint whorls, and/or a simian line, and finally even the tendency towards left-handedness and ambidexterity: males are about 3x more likely to be left-handed than females!
Next to the rather typical biological male-female differences that manifest via body hair and fat percentage (breasts!!?), finger length ratios, the prevalence of the simian line, dermatoglyphics distributions and the full hand shape provide evidence to assume that during the evolution the female body constitution has evolved further away from the body constitution of apes - therefore it appears fair to claim that the male body clearly resembles reminds us to the 'primate' body constitution!
The combination of the following 8 hand factors can be recognized
to represent an extraordinary male-like mix of (primitive) hand factors:
• excessive hair on the dorsal side of the fingers
• skinny appearance [lack of fat]
• 2D:4D digit ratio close to 0,90
• thumb length [1D] equals pinky length [5D]
• single palmar crease [simian line]
• 10 fingerprint whorls / 5 palmar patterns
• extraordinary broad hand shape [hyperbrachycheir]
• ambidexterity / left-handedness