What makes a southpaw?

When I went to school, our teachers were instructed to punish lefties, what a barbaric rule that was. There are many theories about lefties, mostly guesswork. It could be that lefties are in the category of the 'perfect pitch', a talent some people have.
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Why are so many U.S. presidents southpaws?
March 7, 2008
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Is it just coincidence or is there something more sinister in the fact that four of the last six American presidents have been left-handed?
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Bill Clinton, Gerald Ford, Ronald Reagan and George Bush Sr. all used their left hands for everything from brushing their teeth to signing their names and, on occasion, shaking hands.
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As it turns out, the two front-runners for their respective parties' presidential nominations today, Barack Obama and John McCain, are lefties as well. (So is Democrat Al Gore who many believe won the presidency in 2000.)
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"Lefthanders specialize in areas like architecture, art, engineering, acting, some fields of medicine and law," says Elias. "It's not that we tend to elect left-handed politicians, but we tend to elect lawyers. Clinton, Ford, Truman were all lawyers and Hoover was an engineer. These are all fields where you find left-handers. Reagan was an actor, also a field that attracts left-handers."
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http://www.cbc.ca/news/background/science/...presidents.html
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http://www.todaysparent.com/preschool/educ...=251&page=1