“This circuit makes us desire certain foods and causes addiction to tobacco and other drugs,” said University of Montreal researcher and study co-author Johannes Frasnelli, in a news release. “Not all odours trigger this reaction. Only those associated with reward, such as food or satisfying a desire, cause this activation.”
What's more, the mothers' reward circuits showed far more activation than those of the non-mothers; for moms the sensation one gets when sniffing an infant presumably feels even more like the feeling of having obtained food. Thankfully for the continuation of our species, this Medean – or is it Swiftian? – impulse is fleeting: the researchers hypothesize that the reward circuit's response evolved to encourage mothers to feed and protect their kids, not to really eat them.
It's unknown whether the increased response among mothers is the result of biological changes to the brain caused by childbirth or a consequence of the new mothers having sniffed their own babies.
Men were not part of the experiment, so it's still unknown whether baby smells can activate their reward circuits in the same way. Anecdotally, women seem more likely than men to vocalize their baby-eating impulses, but that may just be a difference in how the two genders communicate.
In any case, smell seems to play an important role in the bond between mothers and their children. After spending no more than an hour with their newborns, 90 percent of mothers can identify their babies by smell alone. Mothers even rank their own babies' No. 2 as No. 1: A 2006 study found that mothers tend to regard the smell of their own baby's poop as less disgusting than that of someone else's baby.