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There was one chimp, Judy, who did stand out as an exception among the 14 tested when it came to grasping barter. "The first time we gave her a packet of cucumbers, she ate almost all of them, but then exchanged one or two and saw she got grapes back on a one-for-one basis," Brosnan recalled. "The next time she got cucumbers, she opened up the packet, gave a look, wrapped it back up and pushed it back over and got grapes. This happened for the next nine times." As the researchers tested roughly equal numbers of males and females, this standout case does not seem linked to sex, although there are often differences in behavior between the sexes in chimps. Behind the behavior: Apes lack reliable ways in the wild to enforce deals and punish individuals that cheat trading partners by running off with both commodities. In nature, the chimpanzees also lack norms of ownership regarding property — they do not store property and thus would have few chances to trade commodities. Nevertheless, as past studies have demonstrated, chimpanzees do possess highly active service economies. For instance, they trade grooming for sex or support. Chimps even trade services for meat or fruit, a commodity, "but it appears they haven't gone to a sense of full-out bartering with commodities," Brosnan said.