Approximately 10% of the world population is left handed. As a result of this not being a common trait, “lefties” have not always been accepted by the society. In medieval Europe, they were vigorously oppressed and constantly accused of consorting with the devil. Many African cultures consider the dominant use of the left hand disrespectful and taboo. In Asia, there is still a lot of stigma associated with being left handed. But what causes left-handedness and does it only affect human beings?
One theory suggests that left-handedness is genetic and that it runs in families. The idea that handedness may be hereditary dates all the way back to Charles Darwin who, although right-handed himself, was puzzled by his left-handed son, noting that his brother, mother and grandfather were all also left-handed. Research by John Santrock and others has shown that adopted children are actually more likely to share the handedness of their birth parents than that of their adopted parents. Other studies have also indicated that, at least to some extent, handedness does indeed run in families. However, great care should be taken with blanket assertions to this effect, especially where they are based on anecdotal examples.
Another theory suggests that one’s dominant hand is determined be genetic differences in their spinal cord before they are born. This was suggested by German researchers at Ruhr-Universitat Bochum. They recruited mothers who were 8-12 weeks pregnant to examine the gene expression in their babies’ spinal cord and discovered that the motor cortex (which controls arm and hand movements via signals to the brain) and the spinal cord do not connect until the 15th week of pregnancy. However, babies show signs of right or left handedness at just eight weeks. This suggests that the brain cannot control hand preferences; it must be the spinal cord instead.
In animals, there have been some reports which suggest that they prefer one limb to the other. In cats, scientists say that such preferences are a matter of individual inclination; males generally prefer stepping out with their left paw, while females typically favor their right.
The study was conducted in owners’ homes and focused on spontaneous behavior. In total, the team analyzed data from 44 cats, 20 of which were female, collected by owners tracking which paw their cat used for taking the first step down stairs and stepping into the litter box, and which side their feline preferred to recline on. Over the course of three months, owners recorded 50 instances of each behavior. So having a dominant limb is not exclusive to human beings.
As a minority, left-handers face certain issues that most of us never think about.
For example, most everyday items, such as scissors, cameras, can openers, rulers, computer mice and watches, are mass-produced for right-handed users. Left-handers often have trouble using these objects.
However, it’s not all doom and gloom as there are some proven advantages that come with being left-handed. They are more likely to pass a test, are faster typists, have better problem solving skills, are better at some sports (especially tennis), are more likely to excel in creative and visual arts and are better at multitasking.