I think humans have come from a carrion-eating background. Eating a dead animal before rigor-mortis has finished is too much for people. Our meat (excepting fish) must be 'aged' to make it tender. I discovered this when I once killed a chicken to eat, but didn't age it. After cooking it was too tough to be palatable.

In the real world of hunter-gatherers, whan an animal is killed, they eat the organ meats first, and let the muscle tissue age for days before cooking it. The only other alternative is to boil a freshly-killed animal for hours and hours to tenderize it.