Fascinating new ultrasound video proves that yawning is a behavior humans exhibit long before acquiring it socially. In-utero yawning was been documented and described by a research team of psychologists from the Universities of Durham and Lancaster, in the UK.
15 fetuses (eight girls, seven boys) were observed in four separate scans at 24 weeks, 28 weeks, 32 weeks, and 36 weeks gestational ages. The team differentiated yawning from other mouth opening based on the duration that each mouth remained open. Yawning is not yet clearly understood by science (recent explanations include brain cooling, oxygen uptake, empathy, and /or central nervous system arousal).
No word yet on if in-utero twin fetuses experience the contagious, empathy-driven yawning that affects fully grown humans and other social animals.
Video: Dr. Wolfgang Moroder
Reissland, N., Francis, B., & Mason, J. (2012). Development of Fetal Yawn Compared with Non-Yawn Mouth Openings from 24–36 Weeks Gestation. PLoS One : 10.1371/journal.pone.0050569