A longer yawn may correlate to a bigger brain size, according to a new study which also found that the animals with bigger brain are more variable in the length of their yawns.

Researchers from the State University of New York in the US looked at the videos of 29 mammals yawning to calculate the average length of their yawns.

Although yawning has long been considered a stereotyped action pattern, these findings reveal substantial variation in this response and highlight the importance of measuring yawn duration in future research.

Yawning may have the dubious distinction of being the least understood, common, human behavior’. Unfortunately, 30 years later, we still know relatively little about the biological significance of this evolutionarily conserved response. The difficulty in uncovering the ultimate function(s) of yawning may, in part, be owing to the fact that it can be elicited by numerous stimuli and researchers have by and large overlooked subtle distinctions in the expression of this behaviour. Based on the current findings, we believe yawn duration deserves further attention. We close by offering suggestions for future research in this area 

Source: DOI: 10.1098/rsbl.2016.0545