Waves of interest in researching lefties

Research suggests that the increase in left-handers began in the early 1900s.

Chris McManus, psychologist at University College London, wondered what had happened earlier. Was 3 percent a dip, or the previous norm?

It so happened that a treasure trove of documentary-film footage known as the Mitchell and Kenyon collection — short films of ordinary people shot between 1897 and 1913 — had been discovered and were being restored, causing a sensation in the U.K.

Working with a student, McManus looked for waves by left vs. right arms in more than 100,000 individual frames, finding 391. They estimated the arm-wavers' ages, grouping them into five sets of birth years (the oldest were born in 1841). Then they used a formula to convert left and right waves into left-handedness and right-handedness.

The number of wavers seen at different ages varied widely, so accuracy was very rough. Still, it was enough to reveal a trend — a decline in left-handedness through the Victorian era — that was nearly the reverse of the following century. The findings were published in September in the journal Current Biology.

McManus, who authored the 2002 book "Right Hand, Left Hand," speculated that the decline in the 19th century might have been related to increasing literacy and industrialization, which made left-handers more visible — and more subject to societal pressures to write with the right hand.

But he believes there's still more to the story.