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Science The more that scientists discover genes that influence behavior, the more they find that they work through nurture; and the more we find that animals learn, the more we discover that learning works through genes. Mark Ridley, Nature Via Nurture One of the longest-running puzzles in human nature, which became one of the most contentious scientific arguments of the 20th century, was whether behavior is dictated more by nature (heredity) or by nurture (the environment). The 21st century has seen the mapping of the human genome and with it has appeared fairly conclusive evidence that the nature/nurture argument is a false dichotomy: it's not a case of either/or, it's both. However, it's not necessarily both in the way that's traditionally been imagined-that a person is born with some (arguable) percentage of their slate already genetically written upon, and the unwritten portion is filled in by the environment. Instead, behavior seems to be dictated by a complex interplay between genes and the environment. This is the position that science-writer Mark Ridley takes and elaborates upon in Nature Via Nurture: Genes, Experience, And What Makes Us Human (Harper Collins, 2003). His argument is moderate, elegant, and persuasive. When, in 2001, the human genome was fully mapped, some scientists thought its paltry 30,000 genes couldn't possibly account for the complexity of human behavior. Ridley recounts experiments, begun in 2000, in which work on a single gene molecule (Dscam) from a fruit fly yielded over 38,000 different proteins. While staking no claim that every gene will exhibit so many variations, Ridley concludes: "A genome that can produce hundreds of thousands of different proteins had easily enough combinatorial capacity to specify human nature in excruciating detail, without even bothering to use nurture." Yet Ridley is far from being a biological determinist. When writing about schizophrenia, for example, he presents evidence from case studies that, along with genetic causes, viruses and diet may contribute to its development. A key factor in the interplay between nature and nurture, which Ridley devotes a chapter to, is how genes express themselves in the 4th dimension, over time. In the creation of an organ, of which the human brain is a spectacularly complex example, there are genes that switch on other genes, which then switch on others, and so on, until there are scores of genes involved in the formation of the simplest neural pathway. Through this interplay of switches-their transcription factors and promoters-genes are expressed or suppressed. But often, whether a switch is thrown or not is determined by environmental factors as diverse as nutrition and love. This process is ongoing after conception and continues after birth. The acquisition of language, the unfolding of sexuality, and basic personality traits are determined by the expression of genes that are guided by the environment. The market has been flooded with books on heredity and the genome, including James Watson's new horse's-mouth history of his discovery of DNA winning the Nobel prize. So why do I plug Nature Via Nurture? Because Ridley both knows his science and is a gifted writer. The book ingeniously braids together a history of 20th century behavioral science, titillating biographical insights about the players, the latest discoveries in genetic research, and the moral, philosophic, and political implications of it all. His inclusion of insights by writers like Shakespeare, William James, and J. D. Salinger both illuminates and elucidates the scientists themselves. Like the scientist/writer, Stephen Pinker, he is canny enough to know when and how deeply to explain science's workings under the hood. Toward the end of the book, when dealing with culture and evolutionary psychology, Ridley spikes the text with recent speculative theories, like the idea that language may have developed in early humans as a kind of extended "grooming," performed by apes and our hominid ancestors. Since both language and manual dexterity are centered in Broca's area of the brain, and vocal "calls" use a different part of the brain, to a number of scientists it seems possible that language originated in gestures and not in vocal sounds. A later possibility might be that as human groups grew too large to allow hand grooming, vocal expressions about grooming developed-i.e., nit-picking may have evolved into gossip. Nature Via Nurture also makes it clear that the scientific ego is prone to exaggeration and erroneous conclusions, and that the soft sciences are badly in need of a structural overhaul, one that should include more genetic research. According to Ridley we are merely "scratching at the door of a chamber of secrets," and the mapping of the genome is just a crude key to its entry. But as he also says, "The more we understand both our genes and our instinct, the less inevitable they seem." Or, as he quotes Stephen Pinker, "If my genes don't like it, they can go jump in the lake."
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