Mammal’s yawn based on how large their brain is. The bigger the brain, the longer they will yawn.
Researchers have found evidence that the length of a yawn can indicate how big your brain is, and how many neurons you have, which could explain why humans yawn longer than other mammals.
With the latest findings pointing to brain size being a leading factor into how long a yawn lasts, the evidence suggests that Gallup might have been right all along because a larger brain would need a longer yawn to cool down, as compared to a smaller brain.
It’s important to make a distinction here that the team isn’t saying that if you yawn longer than another person, you are somehow smarter than they are. They are simply showing that - as humans - we have the largest brains and, therefore, need to yawn longer. They never make the jump to actual intelligence.