Beware analogies because they can expose you when you get them wrong, making you look like a tit. A more detailed explanation using evolution can be found here. The scientist explains how a biological evolutionist has to think about such why questions as men having nipples:
… evolution is a process constrained by many factors including history, chance, and the mechanisms of heredity, which also explains why particular attributes of organisms are not as they would be had they been “designed” from scratch. Nipples in male mammals illustrate a constrained evolutionary result.
Plus Daniel Dennett explains some useful possible benefits of religion in the development of Homo sapiens in Breaking the Spell.
On both counts “having no useful purpose” is wrong. The original tweet no longer appears now.
Article written by John Sargeant on Homo economicus’ Weblog