A left handed individual is a 1 who utilizes his left manus for major motor activities such as as throwing a ball. However these people can also utilize their right manus for mulct motor activities such as as writing, eating etc. Type A pure left-hander would be one that usages their left manus for all activities. Therefore writing is not always the right manner to find if one is left handed or right handed.
There are many baleful theories for the causes for left-handedness. For example, it is thought the rise of the usage of ultrasound in the womb to find the growing of the fetus; may have got increased the rise in people with left handedness. It is speculated that ultrasound can effectuate encephalon development during early foetal life and childhood malignances leading to the enhanced usage of the left manus in immature children although it makes not look to consequence neurological development. However the indicant that ultrasound exposure impacts the encephalon and motor development virtues additional scientific research beyond epidemiological surveys to set up such as a role. A proper scientific function for this theory is yet to be established.
It is also suggested that there is a nexus between prenatal testosterone and encephalon asymmetry. Hormones control most portion of our development and most importantly during early foetal development. Exposure to fluctuations in testosterone causes encephalon cells or nerve cells to transmigrate to the right hemisphere or side of the encephalon that controls the left side of the organic structure and hence left-handedness. Surprisingly, testosterone exposure in the womb also increases susceptibleness of left animal trainers to autoimmune diseases such as as arthritis in later life.
Recently the LRRTM1 factor also expressed in the encephalon of human embryos was discovered to be associated with cognitive behaviour and left-handedness.