Book Review: Innate: How the Wiring of Our Brains Shapes Who We Are

Around the world, all populations of humans are essentially the same. The differences that make us who we are lie in differences among individuals, which result from only 0.1% of the entire human genome. This 0.1%, in combination with variance in our environment, could potentially write the code for our unique intellectual capabilities, personalities, and tendencies. Kevin Mitchell’s book Innate: How the Wiring of our Brains Shapes Who We Are is an exploration of the role of genetics— the study of inherited variance— in the brain’s underlying circuitry, and thus some of the characteristics that define us as human.

Innate roams through the genetic underpinnings of disease, genius, and personality, tackling obvious and not-so-obvious themes in genetics. For instance, it is clear how genetics play a role in inherited disorders like sickle cell anemia, but “there is no obvious function at a cellular level that relates in this same way to traits like extraversion, or intelligence, or handedness” (Mitchell). Yet, we often refer to these traits as being passed down from our parents, or as behaviors that “run in the family.” Innate aims to quell our speculations about how these complex traits are actually encoded in the brain (or not encoded at all). The central theme of Mitchell’s book is that it is not the innate characteristics of our brain circuits that shape our psychological traits, but rather, how these circuits develop.

“This leaves open a mystery, ‘some other factor’ as Mitchell calls it, that hasn’t been answered by science—yet.”

Genetics isn’t easy, which could make portions of Innate difficult for novice science readers. A quick primer: Within each cell, threadlike structures called chromosomes contain genetic information that gets written into functional proteins. Genetic variance, individual differences in genetic sequences, contribute a great amount to the individual differences in traits and behavior that result from the genes, chromosomes, or proteins. Such differences can emerge from different types of genetic variance, but the most interesting type may well be mutations, when changes in the genetic code are caused by random processes or environmental factors. (For instance, some brain malformations occur due to mutations in genes necessary for brain development!)

But variance can also come from nurture, or different factors in one’s environment. Nurture seems to play a role in intelligence, personality traits, and brain plasticity in early development. Yet genes and environment together don’t seem to solve all answers. As Mitchell notes, only 40-50% of variation in personality is due to genetic differences, and the shared family environment is not accountable for the rest of variation. This leaves open a mystery, “some other factor” as Mitchell calls it, that hasn’t been answered by science—yet. Additionally, the genetics of specific traits, especially those as complex that Mitchell aims to address, requires an understanding of how traits are distributed in the human population. As such, much of Innate provides readers with a soft understanding of Mitchell’s field of scientific research.

“Understanding the nature of genetics in shaping who we are.”

These complicated processes are well-explained in Innate, thanks to Mitchell’s background as a geneticist studying how genes shape the brain’s wiring. His research is no stranger to high-profile academic journals like Nature, Cell, and Nature Genetics and has largely focused on using animal models to explore genetically-based processes in neurodevelopment. Mitchell is also clearly passionate about communicating science, as many of the topics explored in Innate are also present in early draft forms on his blog. This accumulated expertise is evident in Innate, and so is his practiced writing ability, but it’s less clear in the book’s organization, which lacks a clear roadmap. (For instance, the “gene” is not defined until three chapters into the book.) There is a chapter seemingly dedicated to intelligence, one for the human eye, and one on sex differences, but it isn’t clear why one chapter precedes another. However, this will be appealing to casual readers, who will find that they can open to any chapter of Innate without worrying about whether or not they’ve read previous chapters. Additionally, all types of readers will find portions of text that serve as robust summaries of topics or methods central to neuroscience. For instance, as difficult as genetics can be, Mitchell describes the techniques of genetic research quite well, as he also does for magnetic resonance imaging (MRI) methods.

It is difficult to read Innate without thinking of other books about genetics. For instance, Sidhartha Mukherjee’s The Gene: An Intimate History (2016) tackled a similar theme with a stronger sense of history. Other purveyors of the human brain have also done so with less reliance on metaphor than Mitchell, though it is understandably tricky to explain the toughest aspects of genetics without relying on some analogies. But providing an encyclopedic history of genetics doesn’t seem to be the goal of Innate; where Innate excels is its integration of modern research and methods into an ages-old debate on whether genes determine fate.

Innate ends on the implications of understanding the nature of genetics in shaping who we are, and Mitchell doesn’t shy away from these murky waters. The recent news of the genetically edited babies in China reminds us, genetics can be controversial, bringing to mind ethical issues like eugenics or determinism. Mitchell waits until the final few pages to tell readers that for complex phenotypes, like most aspects of intelligence and personality, genes do not determine, they predispose. And even with advanced gene editing techniques like CRISPR, the realm of gene prediction is culpable to variance in genetics and environment, which render any predictions probabilistic.

However, Innate also implores readers to consider the positive power wielded by genetic research. There are many such potentials to consider, like genetic testing, intervention, and prevention in cases such as cancer or Alzheimer’s disease. Mitchell believes that, for genetics, “the pace of discovery will only accelerate.” If so, what will his next book be about?

Image of book with DNA spiraling outwards towards the front cover of Innate

Feature image by Michal Roessler & Jooyeun Lee .

Innate: How the Wiring of Our Brains Shapes Who We Are
By Kevin J. Mitchell
264 pages. Princeton University Press. $29.95

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Gabrielle Torre

Gabrielle-Ann is a PhD student at Georgetown University and studies the neural correlates of reading, IQ, and socioeconomic status. She is broadly interested in using neuroimaging methods to ask questions about human cognitive behaviors and abilities. Previously, she studied brain-behavior relationships in healthy aging at the University of Arizona, where she developed a love for literature and creative writing. She still enjoys reading and writing, as well as live music, gender studies, and eating.