Though Epstein’s project in The Sports Gene is ostensibly to seek out the gene, or genes, that predetermine athletic excellence, the result of his project is a more moderate thesis on the interplay between genetics and environment. He embraces the answer to sports’ biggest biology questions by saying that it’s not just genes, and it’s not just environment; rather, it’s both. Epstein uses a machinery metaphor throughout the book to articulate this message, saying: “It’s always a hardware and a software story. The hardware is useless without the software, just as the reverse is true. Sport skill acquisition does not happen without both specific genes and a specific environment” (51).

In “Beat by an Underhand Girl,” Epstein explains how an expert baseball hitter doesn’t react more quickly but rather processes information more quickly than an average person because of his multitudes of experience (i.e., “software”). In “Major League Vision and the Greatest Child Athlete Sample Ever,” Epstein reveals that biological visual acuity informs how fast and well a hitter can see the cues in the first place (i.e., “hardware”) before his brain processes them.

Throughout the book, Epstein discovers genes that predispose certain individuals and groups of people to have a higher aerobic capacity, to be higher responders to training, and to have higher levels of hemoglobin in their blood—but for every genetic discovery Epstein makes, there’s an environmental discovery.