Copulation was in among vertebrates. Then it was out. In, then out again. In-out. This may seem like a bad joke but it’s true to the historical record, according to recent discoveries in the fossils of the earliest vertebrates. Scientists at Flinders University in Adelaide, Australia discovered that 380 million years ago vertebrates reproduced by copulation (internal fertilization), but then switched to external fertilization for “tens of millions of years.”
But copulation wouldn’t be denied! According to NewScientist, “vertebrates lost and regained the ability to efficiently deliver sperm internally, many times over.” But “copulation was such fun, evolution discovered it again and again.” No early vertebrates were interviewed about the fun part. But the lack of genitalia found in the newly discovered fossils indicates that if it was fun, the fun disappeared for 10 or 20 million years.
