Lauren, Publicity Assistant
Not a Chimp: The Hunt to Find the Genes that Make Us Human is an exploration of why chimps and humans are far less similar than we have been led to believe. Genome mapping has revealed that the human and chimpanzee genetic codes differ by a mere 1.6%, but author Jeremy Taylor explains that the effects of seemingly small genetic difference are still vast. In the post below, he discusses how the discovery of “Ardi” deals a fatal blow to the chimpanzee ancestor myth.
Jeremy Taylor has been a popular science television producer since 1973, and has made a number of programs informed by evolutionary theory, including two with Richard Dawkins.
When discussing differences between chimpanzees and humans, I enjoy telling the hoary old joke about the traveler, lost in the midst of the Irish landscape, who approaches a farmer in a nearby field for directions. “Well,” says the farmer, on hearing his request, “If I were going to Kilkenny I wouldn’t start from here!”
I share this to highlight the point that we have chosen the chimpanzee as the bench-mark comparison with humans to help us answer the big questions as to how we evolved into humans, and when, for the simple reason that it is our nearest relative in terms of living DNA and behavior. But that does not mean that chimpanzees are cheek by jowl with us or that chimpanzees represent the perfect starting point. Those myriad genome scientists need no reminding from me that necessity has forced comparison with a species that is actually separated from us by twelve million years of evolutionary time since the split from the common ancestor–six million years for the branch that led to us, plus six million for the branch that led to them. Although we know even less about chimpanzee evolution than the precious little we have learned about the genetic changes that led to modern humans, it is clearly reasonable to assume that chimpanzees have not remained evolutionarily inert these past six million years and may well have evolved as far and as fast as we have–though not in the same direction.
Nevertheless, a number of primatologists who should know better, many great ape conservationists, large swathes of the science media, and therefore much of the lay audience, have become bewitched by incessant talk over the last few years about the extraordinary genetic proximity between apes and humans–what I call the 1.6% mantra–and the many cognitive and behavioral similarities that appear to have eroded the old idea of human uniqueness: tool manufacture and use, empathy, altruism, linguistic and mathematical skills, and an intuitive grasp of the way others’ minds work. All this has led to claims that chimps should be re-located, taxonomically, within the genus Homo, that they are more our brothers than our distant relatives, and that they should be therefore be accorded human rights. It has also led to the assumption that the common ancestor of chimps and humans must have looked and behaved very much like chimpanzees today and that our deep human ancestors must have clawed their way to us via a knuckle-walking chimpanzee-like stage before coming down from the trees, developing bipedality and bounding off into the savannas that were rapidly replacing dense forests due to climate change.
This “chimps are us” cozy day-dream has been dealt a welcome (to me) wake-up call by the publication of the discovery and analysis of the fossilized remains of Ardipithecus ramidus–”Ardi.” At 4.4 million years of age, she is perilously close to the time of the split from the common ancestor–and, as one of the main researchers, Tim White, is repeatedly quoted, “Ardi is not a chimp. It’s not a human. It’s what we used to be.” Ardi was clearly bipedal–she had a pelvis with a low center of gravity and had a foot structure which acted like a plate, allowing her to launch herself forward as she walked. Her hands were more flexible than a chimp’s, would have allowed careful palmigrade movement when in the forest canopy which would have supported her weight, and, crucially, would have presented more recent human ancestors with less evolutionary distance to travel to achieve the highly dexterous human hand essential for sophisticated tool use. Plant and animal remains found with her point to an environment of mixed forest and grassland in which she foraged omnivorously for nuts, insects and small mammals.
Was our common ancestor much more like Ardi than a chimp? Is the chimp we see today the result of six million years of specialized evolution away from this extraordinary biped with its mixture of primitive and derived features? Ardi seems fated to join two other odd-ball ancestors we have dug up in recent years: Sahelanthropus tchadensis (Toumai), who dates to approximately seven million years ago, around or before the split from the common ancestor–and Orrorin tugenensis, which dates between 5.8 and 6.1 million years. It is claimed that both were bipedal, though so little of the total skeleton in each case has been retrieved that these claims are open to dispute. Orrorin seems somewhat more similar to modern humans than the famous Lucy, Australopithecus afarensis, is three million years older, and appears to have inhabited a similar mixed forest/grassland environment as Ardi. These misfits may have been very similar, or identical to, the common ancestor, and represent a much better approximation of the deep roots of the human tree than do chimpanzees.
Chimp-hugging conservationists have been over-playing their cards on chimpanzee-human proximity for years. Recent genomic research has unearthed a number of important structural and regulatory mechanisms at work in genomes that widen the gap between humans and chimps, and recent fascinating cognitive research with dogs and members of the corvid family of birds has shown that species that diverged hundreds of millions of years ago from both chimps and humans can out-perform chimpanzees on cognitive tests involving following human cues and in the making and use of tools, respectively.
We are not “the third chimpanzee”–chimps with a tweak. The difference between human and chimp cognition, in the words of American psychologist Marc Hauser, is of the order of the difference in cognition between chimps and earthworms. Chimpanzees–and the other great apes–are the only species for which we erect the idea of near-identity as the motivating force for conservation. We don’t beseech the general public to save the white rhino because we share over 80% of our genes with it, or the tropical rain-forest because we share over 50% of our genes with the banana. Although I would be first into the firing line in the battle to save chimpanzees and their natural environments from extinction I believe this resort to chimp-human proximity is a distraction and the wrong way to go about it. As Ardi is showing us, it is high time we stopped ourselves falling prey to this narcissistic anthropomorphism that brands chimpanzees as the “nearly man.” Chimps are not us!