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Simian lines

SIMIAN LINE RESEARCH - The notorious Single Palmar Crease!


The Simian Line, a.k.a. simian crease
or single palmar transverse crease!

13 Simian line research sections, including e.g.:
history, ethnicity, genetics, disease, personality, famous people & much more!

Single transverse palmar crease: research.

Robert De Niro has a simian line.

According medical science the 'single palmar transverse crease' (a.k.a. simian line) is recognized to represent a minor physical anomaly. What are the implications? And can the simian line bare any significance in personality psychology? How come that simian lines became recognized to represent an unusual palmar line variation? This article describes the fundamental significance of the simian line + how it became recognized as a 'minor physical anomaly'!

First of all: how to recognize a simian line? The concept of the classic simian line can be recognized to represent a 'complete' fusion between the two horizontal palmar creases (heart line & head line), leaving the presence of a single line that is featured with the impression that something appears to be missing (see the right picture below leaving the impression of a single line). The prevalence of a 'complete' simian line in both hands is generally estimated to be around 1% in Europeans and up to 3% in Asians.

Normal major hand lines. Simian line, a.k.a. simian crease of single transverse crease.


Normal major hand lines.

A complete fusion between the heart- and head line is only seen in the concept of the simian line; this unique characteristic is missing in the concept of in respective the Sydney line, extended heart line, and Suwon crease (in the latter is a 2nd head line required to create a fusion between only the upper head line & the heart line).

The simian line is known to have the highest prevalence in the so-called 'trisomy syndromes', which represent a group of genetic disorders featured with an extra chromosome that creates 'trisomy' in one of the 23 chromosome pairs. The two most common trisomy syndromes represent in respective:

- Down syndrome (trisomy 21), where the prevalence of the simian line is usually reported to be around 40%;
- Edwards syndrome (trisomy 18), where the prevalence has been confirmed to be around 70% - which is higher than in any known human (sub-)population around the world.

Interestingly, in both Down syndrome and Edwards syndrome the simian line is often featured with another (more rare) form of 'fusion' between lines - which manifests through the formation of a 'single interphalangeal crease' in the 5th digit (pinky finger): see picture below.

Fused creases in palm- & fingers: simian crease + single interdigital crease.

NOTICE: The combination of simian line + single crease on 5th finger is occasionally also present in trisomy 13, partial trisomy 9p & Cornelia de Lange syndrome.

Simian line percentages close to 50% have also been reported in e.g. the more rare trisomy 8 (Warkany syndrome) and trisomy 13 (Patau syndrome).

Beyond the extraordinary high prevalence inside the trisomy syndromes, relatively high simian line prevalence has also occasionally also been reported in a wide spectrum of diseases and disorders. This explains why the simian line became recognized as a minor physical anomaly (MPA) in medical science, which represent relatively minor (typically painless and, in themselves, harmless) congenital physical abnormalities.

Individual MPA's are known to have no specified diagnostic value; however, in combination with certain other signs (e.g. other MPAs) they can become significant for a specific disorder. For example: the combination of a simian line & single interphalangeal transverse crease (see picture above) represent a strong diagnostic sign for the presence of a trisomy syndrome. Additionally, the dermatoglyphics in the hand have been recognized to serve the purpose to finish the process of diagnosis in this perspective in order to find the one and only trisomy syndrome involved for the person - phantom pictures for the hand in trisomy syndromes are presented inside the Down syndrome section + inside the mini-course section 'diseases'.

However, the simian line in isolation from other likewise significant signs represents in itself a relatively harmless (neutral) sign. And though rarely, it has also been spotted in the hands of a few world famous celebrities - including American actor Robert De Niro (see below), who has often been described to have a personality with strong tendency towards introversion and he described to have relieved his shyness through performing.

NOTICE: In general, shyness as a construct is conceptually distinct from the well-known dimensions of introversion and neuroticism - which both appear for many people not to represent quite the most favorable expressions of personality...!

Actor Robert De Niro has a simian line in his left hand.

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 atFilmfour.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).

During the 20th century the simian line became linked with a 'rainbow' of syndromes, diseases & other medial problems. And in modern 'Hand Analysis' the simian line has also been linked with various psychological personality characteristics (usually featured with a slight negative connotation, sometimes as a 'gift marker'). In 2017 the very first 'psychodynamic profile for the simian line' has become available, which suggests that simian line holders typically show an inclination to exhibit a low score for the 'General Factor of Personality'!

A quick summary of the effects seen in major diagnostic themes:

• Simian line is 20x more common in Edwards syndrome
• Simian line is 15x more common in Patau syndrome
• Simian line is 10x more common in Down syndrome
• Simian line is 5x more common in Fragile-x syndrome
• Simian line is 3x more common in Diabetes Mellitus
• Simian line is 3x more common in Schizophrenia
• Simian line is 2x more common in Cognitive efficiency low scorers
• Simian line is 2x more common in Neuroticism high scorers
• Simian line is 2x more common in Marfan syndrome
• Simian line is 2x more common in Psoriasis
• Simian line is 2x more common in Rheumatoid Arthritis

(All relative to control population prevalence statistics, which are supposed to represent the general population)

Movie (film): The Simian Line (2000)

In the year 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 2018 the state of knowledge about simian lines? ...more.

- TIP -

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 helpful '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?'

Example of PIC-variant 211: the complete simian crease, attached to life line. Example of PIC-variant 311d: incomplete simian crease - head line attached to heart line, head line disconnected from life line. Example of PIC-variant 321d: incomplete simian crease - heart line attached to head line, head line connected with life line.

The three most common simian line variants:
PIC type 211 (complete), PIC type 311d (incomplete), and PIC type 321d (incomplete).

[More details available in the section: 'What can hand lines reveal?']

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