In 2002, evolutionary biologist Jenny Graves shared a controversial calculation. The human Y chromosome, she wrote two years later in a commentary, "is running out of time." The male-determining sex ...

Aging men often lose the Y chromosome in a growing number of their cells—and it may be far more dangerous than once believed.

When closely related species mate, their offspring sometimes survive but cannot reproduce. This pattern often affects males first, with hybrid males frequently failing to produce functional sperm even ...