The manner in which a person folds
arm
In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between t ...
s is one of the clearest dynamic morphological characteristics by which each person can be assigned to one of two alternative
phenotype
In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological prop ...
s. Once adopted, manner of arms folding across the
chest
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
does not change throughout the lifetime and persons easily give up the unusual folding position, most commonly at the first attempt. It has been shown that the phenotypes of these properties are distributed independently with left-handed and right-handed people.
If, after arms folding, the right arm is above the left
forearm
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in ...
, the phenotype is characterised as R (right; the right type), and in the opposite case, i.e. if the left arm is positioned above the right, it is the phenotype L (left; left-type).
Factors and history
Falk and Ayala (1971) found that variations in arm folding are largely inherited, but these variations are not governed by existing Mendelian models. In this regard, Ferronato et al. (1974) found no significant correlation between parents and children. Individual type of arms folding is slightly less studied than the manner of
clasping hands. In search of the main factors that determine this dimorphism, the same difficulties emerge as with clasping hands. However, utilising the findings and the views of many authors,
it can be concluded that the manner of arms folding is hereditary and that it inherits the model that does not fit into the genetics concept of simple Mendelian characters, although in this respect there are contradictory findings.
The main conclusion is that the manifestation of alternative phenotypes with these characteristics is irrespective of sex and age, and that it is not related to handedness.
Supporters of the assumptions that genetic factors play an important role in forming these properties, are reinforced by the data of a very heterogeneous frequencies of alternative phenotypes (R and L) in the explored portion of the world's population. But the point of view that basic genetics could explain the phenomena has also been put in discussion. It is not accepted by all researchers. Luria (1947/1970) proposed left-top positions in arm folding (AF) and hand clasping (HC) to be signs of "latent left-handedness". The human being is more right-handed as animals. It is supposed that left-handedness could be latent. Experiments support Luria's proposition that a left-top preference in Arm Folding points to "latent" left-handedness, but only if associated with a right-top preference in Hand Clasping.
Phenotype ''R'' distribution
The data in the following table summarize ''R'' distributions in various areas as concluded by the cited studies.
See also
*
Hand clasping
Hand clasping is the superposition of each finger of one hand over the corresponding finger of the opposite hand. When clasping the hands, a person tends to interlace the fingers in one of two ways. People who hold the fingers of the right hand abo ...
*
Arm
In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between t ...
*
Forearm
The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is most often used to describe the entire appendage of the upper limb, but which in ...
References
External links
*{{Cite web, url=https://learngendev.azurewebsites.net/content/basics/observable/, title=Observable Human Characteristics, publisher=Genetic Science Learning Center, work=Learn.Genetics
Basic Genetics
Arm
Gestures
Human population genetics
Classical genetics