Frans de Waal taught the world that animals had emotions

The young male chimps at Burgers’ Zoo in Arnhem were fighting again. They were running round their island, teeth bared, screaming. Two in particular were battling until one definitively won, and the other lost. They ended up, apparently sulking, high in widely separate branches of the same tree. Then young Frans de Waal, who was observing their wars for his dissertation, saw something astonishing. One held out his hand to the other, as if to say “Let’s make it up.” In a minute they had swung down to a main fork of the tree, where they embraced and kissed.