The Gene: An Intimate History

by Siddhartha Mukherjee

The SRY gene indubitably controls sex determination in an on/off manner. Turn SRY on, and an animal becomes anatomically and physiologically male. Turn it off, and the animal becomes anatomically and physiologically female. But to enable more profound aspects of gender determination and gender identity, SRY must act on dozens of targets—turning them on and off, activating some genes and repressing others, like a relay race that moves a baton from hand to hand. These genes, in turn, integrate inputs from the self and the environment—from hormones, behaviors, exposures, social performance, cultural role-playing, and memory—to engender gender. What we call gender, then, is an elaborate genetic and developmental cascade, with SRY at the tip of the hierarchy, and modifiers, integrators, instigators, and interpreters below. This geno-developmental cascade specifies gender identity.