Commenter pumpkinhead recently mentioned that five out of the last eight presidents were left-handed, stating :

This does not make them superior to right handers, it just means that they can more readily tap into to those brain regions that give them that edge over others in a presidential race.

An article by Lance Welton describes a terrifying theory about why humans are supposedly becoming more left-handed:

Between 1968 and 1973, a fascinating experiment took place at the University of Maryland. Led by the startlingly creative scientist John B. Calhoun(1917-1995). Its aim was to understand what would happen if Darwinian selection massively weakened. [Death Squared: The explosive growth and demise of a mouse population, by John B. Calhoun, Proceedings of the Royal Society of Medicine, 1973] In creating this “Mouse Utopia” (pictured right) the experiment replicated post-industrial conditions in the West, where child mortality has fallen from 40% to about 1% since 1800, due to dramatically improved medicine and living conditions. The results were horrifying: increasingly bizarre behaviour patterns, a collapse in reproduction, eventual extinction. Are we in our own “Mouse Utopia” in which Darwinian selection has collapsed? The latest piece of evidence for this: we are becoming more left-handed….

…being left-handed is associated with numerous markers of “developmental instability”—that something has gone wrong; a situation generally reflective of “mutational load.” Left-handed people display elevated levels of depression, autism, slightly lower IQ (an average difference of about one point), outlier high IQ (which often happens due to mutation as it is associated with poor mental and physical heath) or outlier low IQ, psychopathic personality, homosexuality, pedophilia, transsexuality, and of numerous physical conditions, such as allergies. Unsurprisingly, southpaws thus end up with low a lower average socioeconomic status…

So, if Darwinian selection has collapsed, then we should be becoming more mutated and, therefore, more left-handed and higher in all of the correlates of left-handedness, including low intelligence. And this is exactly the finding of a recently-published study by British psychologist Michael Woodley of Menie and his team. [Sinistrality is associated with (slightly) lower general intelligenceA data synthesis and consideration of secular trend data in handedness, By Michael Woodley of Menie et al., HOMO, May 2018].