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by Blake Crouch

If a person’s genetic code were written into a standard-size book, that book would be a twenty-story tome consisting of three billion permutations of the letters A, C, G, and T, which represent the four nucleobases—adenine, cytosine, guanine, and thymine.

The specific arrangement of these four nucleobases creates the code for all biological life on the planet. This code is the genotype, and the way it physically expresses in a life-form (eye color, for instance), combined with its interactions with the environment, is called the phenotype. But understanding the correlation between genotype and phenotype—which DNA code programs which traits—still largely eludes us.

What allows human beings to concentrate on things amid the maelstrom of infinite stimuli is a neurological process called sensory gating. It filters out low-relevance (redundant or unnecessary) stimuli in the brain from all possible environmental stimuli. If this didn’t happen, we would experience an overload of irrelevant information in the higher cortical centers.

“It’s denial. Selfishness. Magical thinking. We are not rational beings. We seek comfort rather than a clear-eyed stare into reality. We consume and preen and convince ourselves that if we keep our heads in the sand, the monsters will just go away. Simply put, we refuse to help ourselves as a species. We refuse to do what must be done. Every danger we face links ultimately back to this failing.”

let the engines of reason guide our behavior instead of the cushions of sentiment.

We were a bunch of primates who had gotten together and, against all odds, built a wondrous civilization. But paradoxically—tragically—our creation’s complexity had now far outstripped our brains’ ability to manage it. Put simply: Our situation was fucked, and we weren’t doing enough to un-fuck it.

Humans are 99.9 percent identical in their haploid DNA/genome sequence of approximately 3.2 billion base pairs. However, while we all have roughly the same genes, there are polymorphisms—small differences in the sequence of these genes—that lead to changes in expression levels, and even alter a gene’s function. These subtle differences are what make us each unique from other members of our species.