Yawning might seem like a pointless facial malfunction, but scientists now believe that this weird buccal gymnastic actually helps to cool the brain and improve circulation, leading to an increase in arousal. As such, it stands to reason that animals with larger brains need to do bigger yawns, which inspired a team of researchers to conduct one of the cutest studies in the history of science.
Watching YouTube clips of yawning animals – which have been compiled into a montage below – the researchers studied how long different species tend to yawn for, and then compared this with their number of cortical neurons, which gives an indication of brain complexity.
They discovered that as the number of cortical neurons increases, so too does yawn length, and have published their findings in The Royal Society Biology Letters. On the whole, primates – which are famous for their intelligence – yawn for longer than other mammals, while rodents like mice, rats, and rabbits only need to yawn for about a second and a half in order to cool their puny brains.
Humans, which have around 12 billion cortical neurons, perform the longest yawns, lasting for between six and seven seconds. Elephants, meanwhile, have approximately 11 billion cortical neurons, and yawn for about half a second less than people.
Importantly, the team notes that the size of the anatomical structures responsible for yawning – such as the jaw and cranium – are not relevant to the length of an animal’s yawn, as large-headed creatures like horses and gorillas have much shorter yawns than humans.
Based on this information, they are reasonably confident that brain size – and, more specifically, brain complexity – is the most reliable indicator of yawn length, which would seem to confirm that the purpose of yawning is related to brain function.