I've always assumed reproduction was pretty straightforward, but scientists might one day be able to create babies with just sperm.
To understand reproduction better, scientists have created healthy baby mice by chemically tricking sperm into fertilising artificial eggs.
They're still a very long way from being able to do this in humans, though. Only 1 in 4 mouse pregnancies were successful, and it's unlikely the idea will be allowed in humans in the near future. But eventually it could help couples struggling to conceive, and even allow same-sex partners to become biological parents together.