Physically, sneezing resembles a fast yawn, Provine writes, which points to an evolutionary connection between the two acts. Yawning, which is present in more animals and shows up earlier in human development, may have evolved first; sneezing may have arisen out of the yawn to clear irritants, dried secretions (aka boogers) and potential pathogens from the nose.
A fourth of adults have an inherited tendency to sneeze or an increased ability to sneeze around bright light, a phenomenon called the photic sneeze reflex. Some say that light-induced sneezing is a meaningless neurological quirk, but Provine suggests that it evolved as a “daybreak ritual” that provides daily nasal cleansing. The fact that the photic sneeze often can’t be repeated too soon seems to support a theory of a health-promoting cleanse triggered daily by the sun (or artificial light in modern times). The benefit, however, may be offset by the dangers inherent in the closed-eyed nature of the sneeze, car crashes among them.