Ordinarily Tim Adkinson, a trucker, sleeps in the back of his vehicle. But on a warm night at the end of March, he checked into a hotel in Austin, Texas. He had dressed up smartly: white linen shirt and chinos, hair brushed forward in an attempt to mask his receding hairline. On his wrist he wore a yellow paper wristband. This accessory was meant to signal to the people he’d meet that evening that he was single, open to dating and, most importantly, looking to procreate—a lot. “I’m 32 years old and I haven’t had any kids,” Adkinson told me....