New Scientist:

What's more, in another west African study, this time in Ivory Coast, a "market" has been described where chimps exchange commodities in the shape of both social behaviours including grooming and sex, and resources such as meat.

...In the rainforest of Tai national park in Ivory Coast, Boesch and colleague Cristina Gomes have analysed enough data from their observations of 44 chimps over 22 months to conclude that the apes really are trading commodities. They conclude that male chimps do indeed swap meat in return for sex - something that has been disputed in the past - and for support in aggressive encounters. Grooming was perhaps the lowest value commodity, only exchanged for reciprocal grooming (Behavioural Ecology and Sociobiology, DOI: 10.1007/s00265-011-1227-x).

So Africa is not only the continent that gave the world the big brain, but also the market. Markets were in Africa for possibly millions of years before they appeared anywhere else. The Dark Continent is the birthplace of everything that is essentially human.