Left-handed people are known to be highly prone to some mental issues such as schizophrenia, a mental disorder affecting 1% of the world's population, characterized by impaired perception and severe behavioral shifts, or dyslexia (a neurological learning disability) in children, due to the asymmetry of the brain. They have been also found to have a lower biological fitness.

But a new research has shown that this situations has changed in recent decades, following a decrease of such cases at the beginning of the 20th century. Now, lefties make up about 11% of the population, but in the 1900, they only made up a 3 %. "Left-handedness is important because more than 10 percent of people have their brains organized in a qualitatively different way to other people. That has to be interesting. When the rate of a [variable trait] changes, then there have to be causes, and they are interesting as well.", said lead researcher Ian Christopher McManus of the University College London.

The team watched at a series of films done between 1897 and 1913 by early filmmakers Sagar Mitchell and James Kenyon. The researchers detected 391 arm-wavers in the old films and compared the percentages of lefties and righties from those movies to a "control group" of "wavers" from Google Images.

Only 15 % of those in the old films waved with their left hand, while the left-handed made up 24 % in the Google search. Comparing this data with that gathered from researches of handedness in writing, revealed that left-handed waving is more common than left-handed waving. "The earlier Victorian rates of left-handedness are broadly equivalent to modern rates, whereas rates then decline, with the lowest values for those born between about 1890 and 1910," said McManus.

The lefties in the Victorian films were typically older, discarding the hypothesis of higher rates of mortality among left-handed people. It is more likely that at the turn of the 20th century, with the emergence of the universal education and the industrial revolution, left-handedness proved a disadvantage people for learning to write, as left-handed people clumsily employed machines made for right-handers.

"That would have exacerbated the stigma that any visible minority can experience, and the result could have been that left-handers found it more difficult to find marriage partners, marrying later, and hence having fewer children so that fewer of the relevant genes went into the gene pool," McManus told LiveScience. "And we do have evidence that around the turn of the 20th century left-handers had fewer children than right-handers."