I think you're making the common mistake of mixing up voluntary exchange and capitalism. Voluntary exchange, the exchange of goods, money, or services for other goods or services, is a feature of capitalism but it's not exclusive to it by any stretch of the imagination.

The issue many have with capitalism is capital accumulation, which involves the investment of money or other financial instruments with the goal of receiving a financial return, leading to the increasing concentration and centralization of the means of production into the hands of a small number of rich capitalists.

Using your analogy, it wouldn't be orangutans paying another for a bed of leaves. It would be orangutan 1 paying orangutan 2 for a bed, who then kept 60% of the food and paid a third orangutan the remaining 40% to make a bed of leaves. Orangutan 2 then gradually uses its food to buy up all the leaves so other orangutans then have to do 100% of the bed making while orangutan 2 gets a cut of the food simply for owning the leaves. Since the other orangutans can no longer make their own beds, the orangutan capitalist increasingly reduces the amount of food it pays them. Eventually orangutan 2 has more food than it needs, but it uses this food to keep accumulating even more food at the expense of other orangutans having less food than they need.