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Not a chimp : the hunt to find the genes that make us human

by Jeremy Taylor

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Not so fast on the chimps-are-human-too hypothesis   (2013-08-05)

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by vleighton

  This book has two main divisions with an overarching theme, so it is a little confusing. Both support the overall thesis, which is: chimps may be the closest living relatives to humans, but humans are still very different from them physiologically and behaviorally. I give the book four stars because in both texts, the author dives into great detail, sometimes to the point of losing the general reader. The book is a bit polemic, but its corrective is important. Taylor believes that Jane Goodall and others have exaggerated the similarities between humans and chimps in order to promote the welfare of the chimpanzee. Chapter one preceeds the two main texts; it describes efforts to get chimps declared human to give them more legal protections.

  The two sections are of roughly equal length. The first text relates to the subtitle, which is: "The hunt for the genes that make us human." This section runs from chapters two through seven, and it details specific genes and the regulation of those genes. Chapter seven nicely summarizes the thesis of the book with regard to genes--that humans and chimps are not that genetically identical. The second section starts at chapter eight and goes through twelve. It investigates the differences in cognitive psychology and neurology between chimps and humans. Chapters eight and nine are focused on psychology and are easier reading than the others, which usually get down to brass tacks about which genes or which types of neurons are doing the work.

  In chapter two, at the beginning of the first section, Taylor chronicles the arguments about the function of FOXP2, the would-be grammar gene. Taylor shows that Gopnik, Pinker and others had rushed to proclaim FOXP2 a grammar gene; whereas, subsequent investigation shows that not to be the case: FOXP2 is important in fine motor control of the vocal apparatus in many species, including bats and song birds.

  Chapter three discusses the fight over genes that relate to a birth defect of small brains called microcephaly. The condition was related to a gene named ASPM. Researchers found that that gene seems to have been under strong selective pressure between humans and chimps and even among different groups of humans. When some researchers started to identify human groups whose ASPM seemed to have evolved most, notably in Europe, accusations of racism began to fly. Regardless of what the intra-human variation means, the gap between human and chimp definitely relates to brain development.

  Chapters 4, 5, 6 and 7 are a group that rounds out the discussion of deep genetic differences between humans and chimps. Beginning with the 1975 Wilson and King paper, it has become apparent that, while the nucleotide sequence within genes is about 98.4% the same between the two species, the regulation of those genes is quite different. In chapter 6, it is revealed that the genomes within all of the great ape and human species have rapidly evolved due to what is called "sequence duplication" (SD): whole chunks of DNA are duplicates and "littered" around the genome. Researcher Evan Eichler has called the hot-spots where this happens "duplicons." Because chunks of DNA, genes and all, are copied, there is rapid change in how genes are expressed.

  These duplications are not only implicated in rapid evolution, but they are also the source of many genetic diseases (p. 124), to which humans are prone. SDs account for another 4.8% difference between chimp and human genome (for a total difference of 6.4%). An example of a neurotransmitter gene that was created by an SD and that is an altered copy of an earlier gene is GLUD2, which is only in humans and which recycles glutamate in the brain far more efficiently that its great ape progenitor, GLUD1.

  Chapter seven discusses places where the sequence from the chimp genome is inverted (written backward) in the human and places where alternative splicings of exons cause new genetic output (such as neuropsin II). When one tallies all copy insertions, deletions, inversions, and splicings in comparing the genomes, the difference between chimp and human genomes jumps from about 1.6% to 13.3%. Taylor ends this section with the declaration that, given the research between 2004 and 2009, it astonishes him that respectable scientists are still peddling the 'chimps are us' message based on antiquated concepts of genetic proximity (146-147). The most important word describing the difference between chimp and human gene expression is 'amplification.' In humans, most brain genes have their expression settings cranked up when compared to chimps, gorillas, etc.

  The first part of the second section of the book focuses on comparative cognitive psychology. One argument offered by the 'chimps are us' camp is that chimp psychology is very similar to human psychology. Taylor argues that proponents of chimp psychology fall into the logical fallacy of 'argument from analogy.' Chapter eight uses the research of the Povinelli team at Louisiana State to show that chimps do not think like humans. The hardwired model of physics that chimps possess is much inferior to human folk physics. Povinelli also has demolished the claims of the Leipzig group that chimps have a 'theory of the mind,' that would allow them to understand the beliefs of other creatures. Even dogs outscore chimps when it comes to prosocial interpretations of behavior, as shown by Miklosi.

  Chapter nine then reviews the research on corvids (crows, ravens, etc.). That research, done by Clayton and Emery and other teams, shows that the crow family is much smarter than chimps in a number of dimensions, and that those smarts do not rely on similar brain structures shared with humans, refuting the argument from analogy. Corvids are at least equal to chimps as tool-makers, because they seem to have a better understanding of causal physics. They are also at least equal to chimps, and probably superior, at social manipulation, because they have a more robust theory of the mind (though they still do not approach human abilities). I personally liked chapters eight and nine and feel that they make important points that deserve to be well-known in the broader society.

  Chapter ten, which begins the second part of the second section, dives into the details of comparative brain structure. One problem with studying the human brain is that one may not legally study it in detail by vivisection. That having been said, Taylor argues that the human brain is not just a chimp brain inflated to a larger size. He relies on the views of neuroscientist Jim Rilling, who argues that the cerebral cortex in general dominates the brain, especially the axons that connect the reasoning frontal lobe to the planer temporale on the left side, which in most mammal brains processes sound signals and in humans parses phonemes and stores the meanings of words. So the human brain is pre-wired for language. Comparative brain scans between humans and language-capable chimps shows that the chimps inefficiently use many areas of the brain to process word meanings, while humans rely on the specialized Warnicki and Broca areas for that function. The rest of chapter 10 discusses mirror neurons and Marc Hauser's theory of moral minds. (Ironically, Hauser later had to leave Harvard over questions about his ethics.) Moral judgements seem to involve both reasoning and emotional areas of the brain.

  Chapter eleven investigates Richard Wrangham's idea that humans are a self-domesticated species. Taylor argues that a number of genes for brain chemicals have recently undergone evolution in humans. He then reviews the Belyaev domestication of silver foxes. If in the past human communities had used capital punishment for persons with an inability to control themselves in a domesticated way, then that would have provided a selection pressure for self-domestication. Taylor then discusses the properties of four neurotransmitters: dopamine, vasopressin, serotonin, and MOA. For example, humans have a wide range of variants of a dopamine gene. Some variants are associated with thrill-seeking. Could that variant have helped the part of the human species that pioneered and colonized many environments?

  The final chapter returns to the theme of the book: that humans are quite different from our nearest genetic relatives. We have much greater levels of altruism. Taylor explores reasons why this might be. For example, chimps emulate, but they do not truly imitate. Children, by contrast, use true imitation. Humans can combine information from various sources to create new insights, which seems to be out of the reach of chimps. A sophisticated theory of the mind seems tied to language acquisition. Taylor ends by worrying that through our domestication and attendant technological power, we may wreck the planet.

  As I say, this book wades too much in the details and does not help the general reader along as much as one might hope. The book has an important point, but I am afraid that that point will not reach a wide audience.


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