I thought Eve came from Adam's rib; it turns out it is thought testosterone developed from estrogen:- "Sex hormones, including testosterone, evolved 500 million years ago — before the first vertebrate animals — from the “mother” of all steroid hormones, estrogen. -"Age isn't the only cause of low testosterone; obesity is, too. With more body fat, more testosterone gets converted to an estrogen called estradiol, which further inhibits testosterone production."