Unique

July 15, 2020
A professor of neuroscience at Johns Hopkins School of Medicine probes the individual traits that make us who we are. Linden looks at how heredity interacts with experience and "the inherent randomness in the development of the body." Although he notes that we have only a general understanding of how molecular mechanisms come together to make us individuals, he fearlessly delves into genetic factors, the experience-driven expression of genes, and the subtle changes in the number, position, biochemical activity, and movement of cells within the developing nervous system. The author picks apart those aspects that are biologically regulated and those that are the product of social experience--attachment, social warmth, neglect, and bullying--and describes how they affect brain development. There are a variety of sex manifestations that don't always sort easily into male and female, and gender is even more variable. Linden provides lucid examinations of the range and dynamism of sexual expression. Regarding food preferences, the author writes, "we have succeeded by being food generalists. As a species, we can't be overly predetermined when it comes to food. We must adapt to local availability through learning." However, there is clear evidence of genetic variation in taste sensors as well as life-stage influences on taste sensation. After a foray into gene expression and how it addresses some particular challenge--e.g., high-altitude living "in the Semien Mountains of Ethiopia or the high Tibetan plateau"--Linden moves on to the contentious role of population genetics, systematically refuting pseudo-scientific racist arguments. The author untangles the cultural, biological, and socio-economic factors at play, the fallacy of selective pressures, the fluidity of racial populations, heritable and nonheritable components, and the crystallized and malleable elements of intelligence. Ultimately, the author concludes, "interacting forces of heredity, experience, plasticity, and development resonate to make us unique." A sturdy, scientifically grounded, and anecdotally engaging study of the factors that shape us.

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