Only a man could have invented the term ‘fun bags’. But why does the sight of a mammary make men weak at the knees?

A new book called The Chemistry Between Us points to an ancient neural circuit that turns boys’ brains into boob detectors at puberty.

Emory University neuroscientist Larry Young, who studies perplexing social behaviours, said the imagined role of breasts changed from a source of nourishment to a source of sexual interest and pleasure around puberty, as a way of making women feel more bonded to their man.

Now for their second (less creepy) theory…

Then again, it might be sheer opportunism. The fact that humans’ go-to sex possie is face-to-face may have inspired evolution to favour frontal anatomy. Unlike, say, monogamous voles, whose nipples hang towards the ground, Young said in the book he co-authored with Brian Alexander.