Sex traced to fish found in Scottish lake
Scientists believe they have discovered the origin of copulation.
An international team of researchers says a fish called Microbrachius dicki is the first-known animal to stop reproducing by spawning and instead mate by having sex.
The primitive bony fish, which was about 8cm long, lived in ancient lakes about 385 million years ago in what is now Scotland.
The research is published in the journal Nature.
Lead author Prof John Long, from Flinders University in Australia, said: "We have defined the very point in evolution where the origin of internal fertilisation in all animals began.
The BBC's science correspondent Rebecca Morelle reports.
20 Oct 2014