In the 1970s the biologist Ronald Ericsson came up with a way to separate sperm carrying the male-producing Y chromosome from those carrying the X. He sent the two kinds of sperm swimming down a glass tube through ever-thicker albumin barriers. The sperm with the X chromosome had a larger head and a longer tail, and so, he figured, they would get bogged down in the viscous liquid. The sperm with the Y chromosome were leaner and faster and could swim down to the bottom of the tube more efficiently. Ericsson had grown up on a ranch in South Dakota, where he’d developed an Old West, cowboy swagger. The process, he said, was like ‘cutting out cattle at the gate. The cattle left flailing behind the gate were of course the X’s, which seemed to please him. He would sometimes demonstrate the process using cartilage from a bull’s penis as a pointer. In the late 1970s, Ericsson leased the method to clinics around the U.S., calling it the first scientifically proven method for choosing the sex of a child. Instead of a lab coat, he wore cowboy boots and a cowboy hat, and doled out his version of cowboy […]