Ardipithecus Forces Re-examination Of Human Origins

The entire special edition of SCIENCE, mainly devoted to papers detailed the extraordinary find of a female Ardipithecus ramidus - dated 4.4 million years old - in Ethiopia has been made free to view by the AAAS. This is an astonishing find with multiple repercussions for the way we view our evolutionary relationship with the rest of the great apes and the extent to which we tend to use them - especially the chimpanzee - as some evolutionary template for the last common ancestor 6 million years ago, and aspects of our own cognition.

I have cautioned several times in NOT A CHIMP that it makes no sense to see - as Frans de Waal does - both the chimpanzee and bonobo as some kind of template for our own behaviour. My feeling has always been that it is dangerous to assume that either of these apes can tell us very much about what the last common ancestor looked like, nor how it behaved. Chimps have been evolving since that split 6 million years ago, its just that we know so very little about the details of their evolutionary trajectory since then, compared with the little we know about hominid evolution.

Ardipithecus was about 4 foot tall and had a brain about the same size as a modern chimp. But it walked upright while retaining a powerful, grasping big toe - so it is clear that it lived in woodland as opposed to open savanna, and climbed trees as well as walking on the ground. Of huge interest is its dentition and the likely fact that there is very little sexual dimorphism between male and female. The projecting canines so typical of many other primate species are already very much reduced and this, together with the fact that males are only slightly bigger than females (like us), suggests that sexual competition was very much reduced. The commentary paper by anthropologist C. Owen Lovejoy spells this all out: "One effect of chimpanzee-centric models of human evolution has been a tendency to view Australopithecus as a transitional between an ape-like ancestor and early Homo. Ardipithecus ramidus nullifies these presumptions, as it shows that the anatomy of living apes is not primitive but instead has evolved specifically within extant ape lineages. The anatomy and behaviour of early hominids are therefore unlikely to represent simple amplifications of those shared with modern apes. Instead, A. ramidus preserves some of the ancestral characteristics of the last common ancestor with much greater fidelity than do living African apes. Two obvious exceptions are its ability to walk upright and the absence of the large projecting canine tooth in males, derived features that Ardipithecus shares with all later hominids.....Loss of the projecting canine raises other vexing questions because this tooth is so fundamental to reproductive success in higher primates. What could cause males to forfeit their ability to aggressively compete with other males? What changes paved the way for the later emergence of the energy-thirsty brain of Homo? Such questions can no longer be addressed by simply comparing humans to extant apes, because no ape exhibits an even remotely similar evolutionary trajectory to that revealed by Ardipithecus."

Lovejoy posits a major shift in life-history strategy that has transformed the social structure of early hominids, reducing male-to-male conflict, and combining three previously unseen behaviours associated with their ability to exploit both trees and the land surface: regular food carrying, pair-bonding and hiding of the outward signs of female ovulation. He concludes: "Together, these behaviours would have substantially intensified male parental investment - a breakthrough adaptation with anatomical, behavioural and physiological consequences for early hominids and for all of their descendents, including ourselves".

Nothing that has happened in the field of human origins equals this find as a cautionary tale for those who would go beyond using the chimpanzee as a valuable tool for charting our origins - by virtue of it being our nearest living relative in terms of DNA - to making dangerous assumptions about how chimpanzees directly inform our own evolution and can be used as a template for it. As I have said all along - we need to keep chimps more at arms' length!

Madness, Creativity And Human Brain Evolution

The putative link between mania and creativity refuses to go away. In the final chapter of NOT A CHIMP I describe how many of the genes implicated at one time or another in schizophrenia, appear to have been positively selected both in the primate lineages and, uniquely, in the human lineage. All these positively selected genes are active in the brain where they seem responsible for synapse development, and the many energy producing processes that fuel the brain's activity. The implication is that the human brain is now running at optimum and that anything that throws a spanner into its metabolic works could produce the effects we diagnose as mental illness.

Szabolcs Keri, from Semmelweis University in Hungary has concentrated on just one of these genes that, on the one hand, develops and strengthens the communication between neurons, and, on the other, can predispose to schizophrenia - neuregulin 1. He has shown that volunteers with a certain variant of this gene perform particularly well on tests for intelligence and creativity, while, as we know, another variant of the gene is a prime schizophrenia suspect. He observes, "molecular factors that are loosely associated with severe mental disorders but are present in healthy people may have an advantage enabling us to think more creatively". The article concludes: "In addition, these findings suggest that certain genetic variations, even though associated with adverse health problems, may survive evolutionary selection and remain in a population's gene pool if they also have beneficial effects".

Spotted Hyenas Cooperate Better Than Chimps

Some fascinating research by a comparative psychologist, Christine Drea, from Duke University, who has had trouble getting this sort of stuff published in the past because it was outside the mainstream of comparative cognitive psychological research. She has shown that spotted hyenas out-perform chimps on tasks that require them to learn how to cooperate by pulling synchronously on two ropes to release a food reward from the palette they are tied to. Chimps are notoriously bad at these cooperative tasks and require extensive and long-winded teaching, but the hyenas figured out how to do it very quickly and under their own steam. When a naive animal was paired with an experienced socially dominant animal the latter would temporarily suspend dominant behaviour and submissively follow the lower-ranking animal, only to re-assert itself once the task was ended. The only pairing that performed poorly were two highly dominant animals. The tasks were performed in silence but there was a lot of mutual gaze-following going on.

So here we have a species evolutionarily remote from chimps out-performing them in very much the same way, on a very similar task, that bonobos - very closely related to chimps - do. It is yet more evidence that advanced social cognition is not strictly reflective of genetic proximity but social structure. As the article says, "Researchers have focused on primates for decades on the assumption that higher cognitive functioning in larger-brained animals should enable organized team-work. But Drea's study demonstrates that social carnivores, including dogs, may be very good at cooperative problem-solving even though their brains are comparatively smaller. "I'm not saying", says Drea, "that spotted hyenas are smarter than chimps just that they are more hard-wired for social cooperation". What I say is that cognition is taxonomically blind. It is an adaptive tool to do an adaptive job and here it arises out of social structure.