Sexual reproduction that involves two partners is far less efficient than self-fertilization — at least, from the perspective of evolution. So why did creatures like humans ever start having sex with each other? According to a new study, we did it to fight parasites. We spoke with the researchers to discover what this …

When a pair of freshwater fish species reproduce together, they create hybrids who are able to reproduce asexually. This ability should offer the hybrids an unstoppable evolutionary advantage...so why aren't we bowing down before our asexual fish hybrid masters?

The embryos of a male and female twin can sometimes fuse into a single fetus with both male and female sexual organs. Now an imaginative biologist has figured out how this could lead to conceiving a son without a father.