I guess the first capitalist was the ace hunter gatherer caveman who was rewarded with the best and biggest portion of the day's kill. He did not want it, so he traded it for an extra spear.
Eventually he had a cave full of spears. By then, he was old and couldn't hunt. If the others used his amassed spears then it would mean hunters could hunt instead of making spears instead. The band of humans would be more productive. If they decided not to simply steal the spears from the old alpha hunter, how much would this extra productivity be worth and should they still give hum the choicest cut of mammoth or sabre-tooth?
On the other hand, the retired alpha hunter is a wily old codger. His old wife came from a different band of humans. Their lands are now impoverished and they are facing hunger. Their young men would be willing to hunt the land of the Alpha hunter's band and give him meat plus half the antlers and ivory.
So capital, saving and specialisation make labour more productive. How much they are relatively worth is the question