Click on the cover to link to OUP's e-catalogue then turn to the biology section.

Interview Podcast with George Miller

Interview Podcast with George Miller
Click on the pic to link to the NOT A CHIMP podcast on Blackwell's Website

Preface to "Not A Chimp: The Hunt For The Genes That Make Us Human"

In many ways, this book is born out of frustration for a professional career in popular science television where ideas about comparative primate cognition, and the similarities and differences between us and our primate relatives, have continually circled me but constantly evaded my grasp in terms of the opportunity to transform them into science documentary. On the plus side, keeping a watching brief for over a quarter of a century on subjects like comparative animal cognition and evolution allows you to watch a great deal of water flow under the bridge. Fashions come and fashions go - specifically, perspectives on the similarity - or otherwise - of human and ape minds.

I remember the first Horizon science documentary about the chimpanzee Washoe, the great ape communicator, using American Sign Language to bridge the species barrier. And, later, Kanzi the bonobo jabbing his lexicon. These were the apes, as Sue Savage-Rumbaugh has put it, that were "on the brink of the human mind".

I remember when the pre-print of Machiavellian Intelligence, by Andrew Whiten and Dick Byrne, plopped onto the doormat of the BBC Antenna science series office in 1988. Suddenly primatology had become a great deal more exciting. Could primates, and especially higher primates like chimpanzees, really be as full of guile, as dastardly, as cunning, and as manipulative as the eponymous Florentine politician? Could they really reach deep into the minds of other individuals to see what they believed and what they wanted, and turn that information into deception?

I remember discussing primate cognition with a young Danny Povinelli, as we sat finger-feeding ourselves shrimp gumbo and new potatoes out of plastic Tupperware containers in a Lafayette restaurant surrounded by an alligator-infested moat, before returning to his kingdom - the New Iberia Research Centre - where the University of Louisiana had lured him back to his native deep South by turning a chimpanzee breeding centre for medical laboratory fodder into a primate cognition laboratory with one of the largest groups of captive chimpanzees in the country. He looked like a kid who had just been thrown the keys to the tuck shop.

In those days Povinelli shared the zeitgeist - spread by Whiten's and Byrne's work, and started by Nick Humphrey and Alison Jolly before them - that, since the most exacting and potentially treacherous environment faced by chimpanzees and other primates was not physical, but the social environment of their peers, they had evolved a form of social cognition very much like our own, in order to deal with it. This was further elaborated into a full-blown "social brain" hypothesis by Robin Dunbar, who related brain neocortex size to social group size throughout the primates and up to man. Povinelli's early work reflects this optimism for the mental life of apes, but both ape-language and ape-cognition research was subjected to a cold douche of searching criticism during the 1990s, and misgivings set in regarding the effectiveness of the experiments that had been constructed to guage ape cognition. Now the worm has turned again, with a number of research groups emerging with bolder and bolder claims for the Machiavellian machinations of primate minds, only to be powerfully countered by the curmudgeonly skepticism, chiefly by Povinelli, that these researchers are merely projecting their mental life onto that of their subjects; that, rather in the frustrating manner of Zeno's arrow that could never quite reach its target because it continually halved its distance to it, no experiment constructed thus far can actually get inside the mind of a chimp and show us exactly what it does and doesn't know, or how much, about the minds of others or the way the physical world works. One influential part of the world of comparative animal cognition talks of a continuum between ape and human minds and shrinks the cognitive distance between us and chimps to almost negligible proportions, while another returns us to the unfashionable idea that human cognition is unique, among the primates, after all.

When I began writing this book the working title was "The 1.6% that makes us human". My aim had always been to scrutinize the impression put about in the popular science media that humans and chimps differ by a mere 1.6% in our genetic code - or even less - and that it therefore makes complete sense that this minuscule genetic difference translates into equally small differences in cognition and behaviour between apes and man. However, contemporary genome science and technology, over the last few years, have dramatically advanced the power and resolution with which scientists can investigate genomes, eclipsing the earlier days of genomic investigation that gave rise to the "1.6% mantra".

As with comparative cognitive studies, conclusions on chimp-human similarity and difference in genome research depend crucially on perspective. To look at the complete set of human chromosomes, side by side with chimpanzee chromosomes, at the level of resolution of a powerful light microscope, for instance, is to be overwhelmed by the similarity between them. Overwhelmed with a sense of how close our kinship is with the other great apes. True, our chromosome 2 is a combination of two chimp chromosomes - giving humans a complement of 23 chromosome pairs to 24 in chimps, gorillas and orang-utans - but even here you can see exactly where the two chimp chromosomes have fused to produce one. The banding patterns you visualize by staining the chromosomes match up with astonishing similarity - and that banding similarity extends to many of the other chromosomes in the two genomes. However, look at a recent map of the chromosomes of chimps and humans, aligned side by side, produced by researchers who have mapped all inversions - end-on-end flips of large chunks of DNA - and the chromosomes are all but blotted out by a blizzard of red lines denoting inverted sequence. Now you become overwhelmed by how much structural change has occurred between the two genomes in just 6 million years. True, not all inversions result in changes in the working of genes - but many do - and inversions might even have been responsible for the initial divergence of chimp ancestor from human ancestor.

The extent to which you estimate the difference between chimp and human genomes depends entirely on where you look and how deeply. Modern genomics technology has led us deep into the mine that is the genome and has uncovered an extraordinary range of genetic mechanisms, many of which have one thing in common. They operate to promote variability - they amplify differences between individuals in one species. We now know, for instance, that each human is less genetically identical to anyone else than we thought only three years ago. When we compare human genomes to chimpanzee genomes these mechanisms magnify genetic distance still further. I have tried, in this book, to follow in the footsteps of these genome scientists as they dig deeper and deeper into the "Aladdin's Cave" of the genome. At times the going gets difficult. Scientists, like any explorers, are prone to taking wrong turnings, getting trapped in thickets, and covering hard ground, before breaking through into new insights. I hope that those of you who recoil from genetics with all the visceral horror with which many regard the sport of pot-holing will steel yourselves and follow me as far as I have dared to go into Aladdin's Cave. For only then will you see the riches within and begin to appreciate, as I have, just how limited popular accounts of human-chimpanzee genetic difference really are. Let me try and persuade you that this is a journey, if a little arduous at times, that is well worth taking.

There are a number of scientists around the world who have the breadth and the vision to have begun the task of rolling genetics, comparative animal cognition, and neuroscience into a comprehensive new approach to the study of human nature and this is part, at least, of their story. They strive to describe the nature of humans in terms of the extent to which we are genuinely different to chimpanzees and the other great apes. Somehow, over 6 million years, we humans evolved from something that probably resembled a chimpanzee (though we cannot yet be entirely sure) and the answer to our evolution has to lie in a growing number of structural changes in our genome, versus that of the chimpanzee, that have led to the evolution of a large number of genes that have, effectively, re-designed our brains and led to our advanced and peculiar human cognition.

If you don't believe me, hand this book to your nearest friendly chimpanzee and see what he makes of it!

Wednesday, 12 August 2009

Precursors To Human Language Neuro-circuitry Found In Macaque

The two main language areas of the human brain - Broca's Area and Wernicke's Area - are connected by a major bundle of fibres called the arcuate fasciculus, which also ramifies extensively in the temporal lobe and in areas adjacent to Broca's Area in the frontal lobe. From what areas of the primate brain did the brain structures necessary for language evolve? Michael Petrides and Deepak Pandya, in this PLoS Biology article, report detailed tracing of pathways in the macaque brain they think are those evolutionary precursors. The detailed forensic work is made possible by the injection of radiographic dyes into the white matter nerve fibres. The dye runs along the network allowing tracing to occur. This is their summary:

"Two distinct cortical areas in the frontal lobe of the human brain, known as Broca’s region, are involved with language production. This region has also been shown to exist in nonhuman primates. In this study, we explored the precise neural connectivity of Broca’s region in macaque monkeys using the autoradiographic method to achieve a level of detail impossible in the human brain. We identified two major streams of connections feeding into Broca’s area: a ventral stream from the temporal region, which includes areas processing auditory, multisensory, and visual information and a dorsal stream originating from the inferior parietal lobule and the adjacent superior temporal sulcus. Our detailed connectivity analysis illuminates the pathways via which posterior cortical areas can interact functionally with Broca’s region, in addition to contributing to an understanding of the evolution of language. We suggest that a fundamental function of Broca’s region is to retrieve information in a controlled strategic way from posterior cortical regions and to translate this information into action. This fundamental function was adapted during evolution of the left hemisphere of the human brain to serve language."

Specifically, what they have found is that one of the component parts of Broca's Area, area 45, and a related ventro-lateral area, is involved with the controlled retrieval and selection from non-verbal memory in the monkey and in the right - or non-dominant hemisphere of the human brain. In the human, this area on the left side of the brain has been co-opted for language. Specifically they say:

"During the evolution of the human brain, these high-level forms of programming (the basic elements of which are already present in the macaque monkey brain) came to include complex syntactical structure (e.g., hierarchical level of control) that is
necessary for language, and which has been argued to be a major contribution of Broca’s region. If we were to extrapolate these arguments on the basis of the present monkey anatomical study, our recording study in the monkey, and our functional neuroimaging studies of the human right hemisphere homologue of Broca’s region, we
could say that a common primate circuitry was adapted, during millions of years of evolution, in the human brain for the strategic retrieval and selection of information from verbal memory (including the mental lexicon) in posterior temporo-parietal
cortical regions by one component of Broca’s region, area 45, and the transformation of this selected conceptual information into gestural/speech acts by the other component of Broca’s region, area 44, via its connections with motor structures, such as the premotor cortex, the basal ganglia, and the rostral inferior parietal lobule. Our suggestion here is simply that an area that served higher control of action in the macaque monkey may have been adapted for the control of complex hierarchical sequences of gestural and vocal action with the evolution of communication leading to human speech."

This neatly links the complex hierarchical welding of phonemes into language with the complex and bewilderingly fast oro-facial movements necessary to articulate language in the larynx. When might this evolutionary process have occurred? The authors note that some degree of leftward asymmetry has been found in the planum temporale (associated with Wernicke's Area) in chimps as has left hemisphere dominance or the oro-facial movements involved in learned communicative vocalizations. Also, handedness has been noted for chimps connected to tool use, suggesting a left hemisphere specialization for control of complex actions involving the right hand. Remarkable asymmetry of Broca's cap has been discovered in endocasts of Homo erectus skulls, suggesting the various precursors were coming into place before manifesting themselves, much more recently, in a language faculty. The authors conclude:

"These findings are consistent with suggestions that specialization for the control of action and gesture may have preceded specialization for language. Note also that our close primate relatives, chimpanzees and bonobos, use arm/hand gestures more flexibly in their natural communication across contexts than facial expressions and vocalizations. The above facts suggest that the use of gestures for early forms of communication may have been an adaptation distinguishing the Hominoidea from other primates, and that the use of vocalization in the form of modern speech emerged much later with the evolution of language in the narrow sense, i.e., a uniquely human adaptation. It is interesting in this respect that the supralaryngeal vocal tract of humans differs significantly from those of other primates, making the human vocal apparatus unique in transmitting information at fast rates."

Thus language appears to be a combination of ancient, modern and unique evolutionary developments in the primate and hominin lineage.

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