FLICKR, MIKE NELSON

Hot weather has long been linked to violence, but whether or not it is the cause of our species’ bad temperedness remains unclear. In fact, a study conducted at the turn of the 21st century suggested that at around 80 degrees Fahrenheit, assault rates no longer increased with temperature, but actually started to drop. This led some researchers to suggest that perhaps moderate levels of heat, and thus discomfort, provoke aggression, while extreme heat and discomfort made people want to flee, Wired Science reports. Another theory holds that because many displays of violence depend on social opportunity—as the weather increases, and people spend more time outdoors, violent crime rises, but as the temperatures become too hot to handle, and people retreat indoors, the trend stops.

But reanalyzing the data in 2005, Iowa State University psychologist Craig Anderson found that the trend of increased violence with...