Having a member of my own family with a Simian Line, I can say that some of the indications mentioned below are most definitely observed in my own experience.
The Single Palmar Crease or Simian Line is the name given to the joining of the heart line and head line. The quadrangle area between the Head Line and Heart Line is lost in such a hand. This line signifies that the bearer’s emotions and mental powers are blended together. Normally, such a person will take things to extreme, they are intensive. Alternative names for this line are the simian crease, transverse palmar crease and simian fold.
On occasion this line can be related to a serious genetic abnormality, such as down-syndrome. The scientific work in regard to the relationship between the Simian line and congenital research is quite extensive. Purvis-Smith in the Australian Pediatric Journal (1972) wrote an article on his research between the relationship of down syndrome dermatogram. He concluded that there was a close relationship between presence of the Simian Line and the disease.
Research in 1963 by Davies and Smallpiece concluded that there was a high proportion of Simian Lines in newborn babies that suffered neo-natal death or still birth. As far back as 1866 Langdon-down concluded that this line is normally seen in children of the mentally retarded.
There is much evidence that scientifically there is relationship between diseases and palmar creases. In 1971, Chaube arrived at the conclusion that patients with schizophrenic disorders generally have a simian line. They took Palmar prints of 127 patients and 536 normal people to try to understand the differences between those suffering from schizophrenic problems. The summary of the work was that a relationship existed between the Simian Line and their schizophrenic patients. Another test was later carried out by Bali (1983) which came to the same conclusions. In recent times, this line has been documented as a 'minor physical anomaly' (MPA) at birth. This means that it is a minor birth mark at birth.
Many palmists always focus the Simian line with the negative influences. Although rare, this line normally appears on people that have a tendency to have problems communicating with other people. The ancient palmists predicted that these people will always have emotional problems. They move from one emotion to another. There is also a strong feeling of enjoying conflict. They are believed to be jealous of other people but they seem to be able to detach themselves when in an argument.
On a positive note, people with this line are normally brilliant in many areas of their life. They focus on work and can be quite loving, caring and happy. The only downfall is that sometimes they focus on one activity too much and find little time for anything else. If the bearer is religious they may become a fanatic. If the bearer is an accountant he may be a workaholic. If the person is a housewife they may clean all the time... in other words this person gives everything to his or her desires! They have the greatest will of all.
There is a challenge trying to relax, they generally tend to work hard at their careers, having a strong desire for accomplishment. Subjects having this line stand out from the crowd. They are normally found on people from religious backgrounds or specific political groups.
A person with a Simian line tends to easily lose control and often commit crimes when his/her emotions, feelings and desires are aroused and, thus, such a person is not necessarily a criminal. But if the hand is brutal, the Mount of Venus large, full and red, nails and fingers short, and the mount of Mars is large, he/she will be a criminal who may commit murder to satisfy his/her desires. Such persons are not strong enough to control the passions that rage within them. In a nutshell, the Simian line denotes extremism and single-mindedness.
Persons with such a line have tremendous tenacity or intensity of character, for good or evil. The characteristics of those individuals with a simian line are the equal intensity with which they love or hate. In addition, they are extremely egocentric, generally very "wrapped up" in what they want to the exclusion of everything and everybody. The world exists for them alone, and anything that interferes with their enjoyment of it, or their designs upon it, is pushed ruthlessly out of the way. They have plenty of feelings and their emotions are often violent and unstable. Their feelings are always concerned with themselves.
The Simian line also signifies a great power of concentration. If there are other unfavorable signs in the hand, the person uses mental strength to achieve selfish purposes so cleverly that few will suspect their diabolical aims, and they usually will succeed in avoiding trouble with the law. However, despite their shrewdness, such persons sometimes act like an emotionally immature child.