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The handedness of presidents of the United States is difficult to establish with any certainty before recent decades. During the 18th and 19th centuries left-handedness was considered a disability and teachers would make efforts to suppress it in their students. For this reason there are few concrete references to determine the handedness of presidents prior to the early 20th century. The first president to be described as left-handed was Herbert Hoover, though some[who?] dispute this. Before this point, there is no evidence of any left-handed president, though it was said about President James Garfield that he could simultaneously write Latin with his right hand and Greek with his left. Ronald Reagan is rumored to have been left-hand dominant, but forced by his schoolteachers and parents to switch. However, documentation of this is unreliable. If true, it would place Reagan in the category of ambidextrous presidents. It should be noted, however, that all historical photographs of Reagan signing treaties, pacts or pieces of legislation show him signing with his right hand. The same was also the case with Harry Truman, according to the biographer David McCullough.
As of 2012, five out of the last seven presidents have been left-handed. Counting as far back as Truman, the number is five (or six) out of twelve. In the 1992 election, all three major candidates – George H. W. Bush, Bill Clinton and Ross Perot – were left-handed. The 1996 election also involved three left-handed candidates: Clinton, Perot, and Bob Dole, who learned to use his left hand after his right hand was paralyzed by a World War II injury. Both major-party candidates in the 2008 presidential election – Barack Obama and John McCain – were left-handed. The percentage of the population who are left-handed is about 10%. While some write this trend off as a coincidence, others have tried to come up with scientific explanations. According to Daniel Geschwind, a professor of human genetics at UCLA, in 2008: "Six out of the past 12 presidents is statistically significant, and probably means something".
Amar Klar, a scientist who has worked on handedness, says that left-handed people "have a wider scope of thinking", and points to the disproportionately high number of Nobel Prize winners, writers and painters who are left-handed. The left hemisphere of the brain generally handles language, but in left-handed people, this division is less pronounced. One out of seven left-handers processes language using both sides of the brain, compared with just one out of twenty in the general (predominantly right-handed) population, perhaps because of a relationship between dexterity and language. An increased amount of space dedicated to language could account for enhanced communication skills as seen in Reagan, Clinton, and Obama. Klar suggests that with both halves handling language, the left-handed and ambidextrous are capable of more complex reasoning. Michael Peters, a neuropsychologist at the University of Guelph, points out that left-handed people have to get by in a world adapted to right-handers, something which can give them extra mental resilience. The American trend, however, is not replicated in other countries; only two British post-war prime ministers have been left-handed (David Cameron and James Callaghan). Winston Churchill has often been credited with being a left-hander, although he was not. No Canadian prime minister since at least 1980 has shown this trait.
|In cognitive abilities||Geschwind–Galaburda hypothesis|
|In brain||Brain asymmetry · Dual brain theory · Bicameralism|
|In eyes||Ocular dominance|
|Handedness in boxing||Southpaw stance||Orthodox stance|
|Handedness in people||Musicians · US presidents|
|Handedness related to||Sex · Maths|
|Handedness measurement||Edinburgh Handedness Inventory|
|In major viscera||Situs solitus||Situs ambiguus||Situs inversus|