According medical science is the notorious simian line [simian crease] recognized as a minor physical anomaly; what are the implications?
Why is the Simian Line (a.k.a. 'simian crease'): recognized as an unusual palmar line?
First of all, how to recognize a simian line? The presence of the classic simian line is indicated when the two horizontal creases appear to be fused into one single crease, which (usually) crosses the full palm - see the single red line displayed inside the right hand of the picture in the left column.
The presence of 3 major hand lines is considered as a typical characteristic of the human hand.
One of these three major hand lines is positioned vertical in the hand, surrounding the thumb mouse; this major line is also known as the 'life line'.
The other two major hand lines are positioned horizontal in the hand, and usually they do not cross the full palm; the distal line is known as the 'heart line', the proximal line is known as the 'head line'.
A simian line is the result of a fusion of these two major horizontal hand lines.
In medical science is the simian line classified as a minor physical anomaly (MPA). MPA's have generally no specified meaning, unless they are obsverved in combination with certain other MPA's.
Robert De Niro has a simian line in his left hand, he might be recognized as the most famous simian line holder in the world; De Niro was voted in 2002 at Filmfour.com as 'the best actor of all time', and in 2004 he was ranked as the no.1 in Empire (UK) magazine's "The Greatest Living Actor (Gods Among Us)".
Paul Broca (1877) was the first who described the unusual characteristic of the simian line (a.k.a the 'simian crease' or 'single palmar transverse crease') for the human hand. The word 'simian' refers to the fact that the hands of primates (simians) are usually featured with multiple likewise horizontal lines that transverse the full palm.
Two decades later the diagnostic significance of the simian line was established when R.L. Down discovered in 1906 that the 'single palmar crease' is a very common characteristic in Down's syndrome (after R.L. Down's father - the English physician, J. Langdon Down - had discovered Down syndrome in 1866).
In 2000 a movie was presented titled: 'The Simian Line' (a drama featuring e.g.: Cindy Crawford, William Hurt & Harry Connick Jr.) - inspired by the fact that this famous, but notorious, hand crease has touched the lives of many people around the world.
Today the (complete) simian line is known to be found in about 1 in 30 caucasian people (3%) - however, in some other populations (usually Asian populations) simian lines are more often seen - up to well above 10%.
Studies in large populations have shown that the simian lines is usually almost twice more often seen in men (caucasian men: 4%) compared to women (caucasian women: 2%).
What is in 2014 the state of knowledge about simian lines? ...more.
For a better understanding of the unusual characteristics of the simian line, one can use the section 'hand lines (palmar creases)' -
which includes the introduction of the innovative 'PIC-model' (which should serve as a helpfull 'tool' to classify the COMBINATION of the core characteristics in the three major hand lines!).
The 'PIC model' demonstrates that basically there are up to twelve types of simian lines - most of them are quite rare, but three of the simian related 'PIC types' (see the pictures below) are relatively common: each of these PIC variants can be noticed in more than 1% of the population!!
Read more about the 'complete'- and 'incomplete' simian line variants in: 'How to recognize a simian line?'
The three most common simian line variants: PIC type 211, PIC type 311d, and PIC type 321d.