What do Leonardo da Vinci, Jimi Hendrix, Angelina Jolie, Barack Obama, and my two daughters have in common? Okay, yes, they're all charismatic and powerful individuals whose talents impress all who know them. But I was thinking of something else: They're all left handed! At least that's true according to published reports (though I can vouch for the last two members on the list).
Even with such famous brethren, lefties may wonder why they are the way they are—especially when they're trying to cut with made-for-righty scissors or after smudging the ink across the page as they write. After all, it's a right-handed world: Lefties only make up 10% of the population.
Lefties (and those who love them) may also wonder if there is any truth to the bandied-about idea that lefties don't live as long as righties.
What determines handedness?
It's thought that, as with most behaviors, a mix of genes and the environment determines which hand you favor. Even people considered to be ambidextrous tend to favor one side or the other.
While people who are left-handed usually have at least one left-handed relative, scientists have not yet identified a gene or genes that play a key role in determining handedness.
At some point, study into the human genome might help us understand how handedness is determined. For now, however, it's still a pretty mysterious thing.
Handedness and health
There are a lot of rumors out there about lefties being less healthy than righties. I obviously have a vested interest in the subject, since I want my lefty daughters to be as healthy (and happy!) as possible. So I did some research on the subject, and here's what I found:
It's long been suggested that left-handed people may have shorter life spans than right-handed people. The idea comes, in part, from the observation that as a population ages, the percentage of left-handed people falls. For example:
- If you gather a large group of young adults together, about 10% will be left-handed.
- But left-hand preference will be reported by about 5% of 50 year olds
- And only 1% of 80 year olds are left-handed.
In fact, a number of studies have examined whether lefties die younger, with varying results:
- Many found no relationship at all. For example, a study of pairs of Danish twins in which one twin was righty and the other lefty published in 2000 found no difference in the mortality rates.
- Others found higher mortality among left-handed women. For example, one of the most recent studies on the subject, published in the medical journal Epidemiology in 2007, found that left-handed women did not live as long as otherwise similar right-handed women. They had significantly higher rates of colorectal cancer and cardiovascular disease.
- Some actually found a longer lifespan for lefties.
The bottom line is that it's uncertain whether righties truly live longer. And if they do, it's uncertain why, though there are theories, including:
- Lefties can't survive as long in a "right-handed world". For example, lefties might have more accidents when using power tools designed for right-handed workers. This theory is backed up by studies that have found that lefties have many more accidents than righties.
- Whatever causes left-handedness – some have suggested it's a stressful event during fetal development - also causes lefties to suffer certain health problems more than righties.
- Lefties live just as long, but describe themselves as right-handed due to stigma, superstition, or because they were forced to switch handedness as a child.
Left with uncertainties
We need more research to understand handedness and whether it affects health and longevity. If it does, it will be important to figure out whether we can do anything about it.
Until more is known, don't believe everything you hear about lefties having a shorter lifespan than righties. Plenty of people who are left-handed have led rich full lives. And that's not just wishful thinking by a father of lefties.