The anus may have evolved from a hole originally used to release sperm

The anus is a wildly successful innovation, but how did it evolve? A genetic analysis suggests it probably began as an opening used to release sperm that later fused with the gut – an example of evolution repurposing structures.

“Once a hole is there, you can use it for other things,” says Andreas Hejnol at the University of Bergen in Norway.

It is thought that early animals evolved…