There are many differences between men and women that create delicate asymmetries in a relationship.   But few are as polarizing and mysterious as a man’s appreciation of his own farts.

Beneath the Dutch ovens, pulled fingers, and silent but deadlies, there must be a scientific explanation and I believe that, as usual, it all boils down to evolution and sex.

Monogamy is relatively rare among animals and for good reason.  Monogamous males forego the opportunity to have offspring by other mates.  This sacrifice in quanitity is evolutionarily beneficial for the male only if monogamy has some offsetting benefits.  The obvious benefit would be the male’s investment the survival probability of the offspring in the monogamous relationship.  But the return on this investment is always threatened by the female’s incentive for cuckoldry:  secretly being impregnated by a superior male and passing on the burden of rearing to the cuckold.

The only way this incentive can be mitigated is the presence of a signature that identifies the child as the true descendant of the monogamous father.  There are in principle many ways this signature could have evolved, but natural selection favors solutions that piggyback on existing physiology and minimize incidental costs.  The passing of gas makes an ideal signature because of two facts.  First, the rapid development of intestinal flora means that infants are already especially gassy.  Second, as documented by Professor Hugh Kuddachize of the University of Wafting, the susceptibility to various lactose-feeding bacteria is determined by genes on the Y-chromosome.

That is, a male infant’s farts will smell similar to those of his biological father.  This enables the father to determine parenthood at an early stage.  And because the mother can’t know in advance whether the child will be male or female, this 50% detection probability is enough to dissuade her from sneaking around.  And the father’s pleasure at the smell of his son’s farts is Nature’s incentive mechanism to keep him at home while still shielding him from cuckoldry.

The humorous byproduct of this development of course is that men love the smell of their own farts.  And we can now understand the asymmetry.  There is no uncertainty about maternal parentage, so no need for any signature.  On the other hand, bacterial infection of the intestine is a signal of the child’s health and Nature accordingly programs the mother to respond to the olfactory expression with alarm.  The father’s farts carry the same signature and induce the same response.

Understanding our evolutionary origins helps us understand ourselves and in this case it teaches us to appreciate and indeed cherish the gas that keeps the family together.