How did sex evolve? New discovery shows Scottish fish were first to copulate on Earth

Bicycles, telephones and bagpipes are just a few of the innovations Scotland has brought us over the years, and now we have another, much older one to add to the list – sex. 

 

It turns out that the first creatures to ever copulate on Earth were a pair of primitive bony fish called Microbrachius dicki, which inhabited the ancient lakes of what is now Scotland some 385 million years ago.

 

While looking through a box of fish fossils, a group of international researchers discovered an odd L-shaped appendage on an M. dicki specimen, which prompted them to investigate it further. 

 

They concluded that this was indeed what they suspected it might be – the male fish's genitals. "The male has large bony claspers. These are the grooves that they use to transfer sperm into the female," the project's lead researcher James Long told the BBC. 

 

The female specimen, meanwhile, had a complementary bony structure. From the anatomy of the two fish, the scientists decided that the fish almost certainly mated side-by-side. "The very first act of copulation was done sideways, square-dance style,” explained Long. 

 

When the two ancient fish came into contact in this unprecedented way, it marked the first time an animal stopped reproducing by spawning and instead mated by having sex. 

 

"We have defined the very point in evolution where the origin of internal fertilisation in all animals began,” explained Long. "That is a really big step."

 

Details of the discovery are published in the journal Nature.