Rendezvous 1
CHIMPANZEES
Between 5 and 7 million years ago, somewhere in Africa, we human pilgrims enjoy a momentous encounter. It is Rendezvous 1, our first meeting with pilgrims from another species. Two other species to be precise, for the common chimpanzee pilgrims and the pygmy chimpanzee or bonobo pilgrims have already joined forces with each other some 4 million years ‘before’ their rendezvous with us. The common ancestor we share with them, Concestor 1, is our 250,000-greats-grandparent – an approximate guess this, of course, like the comparable estimates that I shall be making for other concestors.
As we approach Rendezvous 1, then, the chimpanzee pilgrims are approaching the same point from another direction. Unfortunately we don’t know anything about that other direction. Although Africa has yielded up some thousands of hominid fossils or fragments of fossils, not a single fossil has ever been found which can definitely be regarded as along the chimpanzee line of descent from Concestor 1. This may be because they are forest animals, and the leaf litter of forest floors is not friendly to fossils. Whatever the reason, it means that the chimpanzee pilgrims are searching blind. Their equivalent contemporaries of the Turkana Boy, of 1470, of Mrs Ples, Lucy, Little Foot, Dear Boy, and the rest of ‘our’ fossils – have never been found.
Nevertheless, in our fantasy the chimpanzee pilgrims meet us in some Pliocene forest clearing, and their dark brown eyes, like our less predictable ones, are fixed upon Concestor 1: their ancestor as well as ours. In trying to imagine the shared ancestor, an obvious question to ask is, is it more like modern chimpanzees or modern humans, is it intermediate, or completely different from either?
Notwithstanding the pleasing speculation that ended the previous section – which I would by no means rule out – the prudent answer is that Concestor 1 was more like a chimpanzee, if only because chimpanzees are more like the rest of the apes than humans are. Humans are the odd ones out among apes, both living and fossil. Which is only to say that more evolutionary change has occurred along the human line of descent from the common ancestor, than along the lines leading to the chimpanzees. We must not assume, as many laymen do, that our ancestors were chimpanzees. Indeed, the very phrase ‘missing link’ is suggestive of this misunderstanding. You still hear people saying things like, ‘Well, if we are descended from chimpanzees, why are there still chimpanzees around?’
Chimpanzees join. White lines depict the evolutionary tree (or ‘phylogeny’) of chimps and humans, branching apart at Concestor 1 (marked by a numbered circle). The vertical right branch represents the current set of pilgrims: in this case, only humans. The left branch shows chimps splitting into two species about 2 million years ago.
If we were to zoom in on any of the lines, we would find them not solid, but crisscrossing networks of interbreeding, as depicted in the humankind diagram at Rendezvous 0. From now on we’ll continue to use this solid line representation.
Images, left to right: common chimpanzee (Pan troglodytes); bonobo (Pan paniscus).
So, when we and the chimpanzee/bonobo pilgrims meet at the rendezvous point, the likelihood is that the shared ancestor that we greet in that Pliocene clearing was hairy like a chimpanzee, and had a chimpanzee-sized brain. Reluctantly to set aside the speculations of the previous chapter, it probably walked on its hands (knuckles) like a chimp, as well as its feet. It probably spent some time up trees, but also lots of time on the ground, maybe squat feeding as Jonathan Kingdon would say. All available evidence suggests that it lived in Africa, and only in Africa. It probably used and made tools, following local traditions as modern chimpanzees still do. It probably was omnivorous, sometimes hunting, but with a preference for fruit.
Bonobos have been seen to kill duikers, but hunting is more frequently documented for common chimpanzees, including highly co-ordinated group pursuits of colobus monkeys. But meat is only a supplement to fruit, which is the main diet of both species. Jane Goodall, who first discovered hunting and intergroup warfare in chimpanzees, was also the first to report their now famous habit of termite fishing, using tools of their own construction. Bonobos have not been seen to do this, but that may be because they have been studied less. Captive bonobos readily use tools. Common chimpanzees in different parts of Africa develop local traditions of tool use. Where Jane Goodall’s animals on the east side of the range fish for termites, other groups to the west have developed local traditions of cracking nuts using stone or wood hammers and anvils. Some skill is required. You have to hit hard enough to break the kernel but not so hard as to pulp the nut itself.