If you want kemono that is more animal, go to wildcritters.net (not wildcritters.ws). Humanity has always been sex obsessed. The original gods were fertility gods. The ancient Greeks marked roads and paths with hermai: gigantic ithyphallic eidolons. They were literally using cocks are road markers. As for muscles, the evolutionary perspective is that muscles mean fitness, which means you aren't likely to drop dead either by being hit by another caveman with a rock or due to withering illness. Animals prefer healthy mates, so the human animal seeks muscular counterparts (I don't believe this, but it's one perspective: my belief is that fetishes is fetishes and they ain't gonna be rationally accounted for [too many variables]).
Also, to back up the fact that this is not just 'nowadays,' I would like to bring up the fact that Greek, Nordic, and Celtic mythology are all rich in bestiality.