In a common metaphor used to describe human fertilization, sperm cells are competitors racing to penetrate a passive egg. But as critics have noted, the description is also a “fairy tale” rooted in ...

Human bodies have to be built from a single egg cell that's fertilized by a sperm cell. Many rounds of cell division occur as the body is developing, and it seems that there are plenty of chances for ...

The international body representing stem-cell scientists has torn up a decades-old limit on the length of time that scientists should grow human embryos in the lab, giving more leeway to researchers ...