How a Man Produces 1,500 Sperm a Second
A man's constant supply of sperm is created in a much more complex way than previously thought, says new research that could someday lead to male birth control.
For the past 40 years scientists have thought stem cells in the testicles—also called germline stem cells—become sperm only through a simple, two-step process.
Not so. Germline stem cells, it seems, can become sperm in several different ways, according to new experiments with mice. (Explore an interactive of the human body.)
"What we're saying is there isn't a strict linear progression from a stem cell to a [sperm] cell," said study co-author Robert Braun, associate director at the Jackson Laboratory in Bar Harbor, Maine. "Sometimes the stem cells go through several cell divisions to get there, sometimes they don't."
What's more, the researchers found that a cell that's partway to becoming