Something else happened then too. Grasping the notion of currency simply means you understand that you can exchange money for goods and services. Well, one of the researchers, during the chaotic episode mentioned earlier, observed how one of the monkeys exchanged money with another for sex. After the act was over, the monkey which was paid immediately used it to buy a grape…
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We already taught some monkeys how to use money though. (And they immediately invented prostitution.)
Citation needed
The actual research paper.
The story of the monkey prostitute
We also taught parrots how to use money and they used it to feed the poor.
https://www.smithsonianmag.com/science-nature/parrots-share-currency-help-their-pals-purchase-food-180973917/
And which one of those are we closer related to?