Humans are traditionally understood to possess only five senses, but now new research into our evolutionary past suggests that there may have been a time when our distant ancestors had an enhanced 'sixth sense' which we have since lost, according to a Cornell University press release.
No, this doesn't mean that our ancestors could see dead people. But it does mean that they could likely detect weak electrical fields much in the same way that sharks, paddlefishes and certain other aquatic vertebrates still do today.
The study, which was published in the journal Nature Communications, suggests that our electroreceptive ancestor would have lived some 500 million years ago and likely gave rise to the vast majority of modern-day vertebrates, a group that includes some 30,000 species of land animals, as well as an equal number of ray-finned fishes.
Researchers were even able to paint a picture of what this common ancestor would have looked like. Like other electroreceptive creatures living today, it would have been an aquatic organism-- likely a predatory marine fish with good eyesight, jaws and sharp teeth. It would have used its sixth sense to pinpoint the location of moving prey, and possibly also to communicate.
The ancient extrasensory fish would have represented a common ancestor of both the ray-finned fishes, or actinopterygians, and the lobe-finned fishes, or sarcopterygians-- the latter of which eventually gave rise to land vertebrates, such as us. It therefore establishes an evolutionary link between the many known electroreceptive ray-finned fishes, like paddlefish and sturgeon, and the few land animals that still retain the sense.
"This study caps questions in developmental and evolutionary biology, popularly called 'evo-devo,' that I’ve been interested in for 35 years," said Willy Bemis, Cornell professor and a senior author of the paper.
Evo-devo, which is an informal title for evolutionary developmental biology, compares the developmental processes of different organisms to determine their ancestral relationships. Until this research was completed, little was understood about the common evolutionary relationships that existed between animals with electroreceptive organs and those without them. For instance, scientists were largely left to wonder whether such organs evolved independently along different ancestral lines or whether there really was a deep evolutionary relationship.
The reason for the mystery rests with the fact that water conducts electricity better than air, so most land vertebrates lost their electroreceptive organs once they permanently lunged out of the sea. Only a few semi-aquatic land animals, such as the Mexican axolotl, retained the sense-- an important clue for researchers.
The deep evolutionary link was thus confirmed after the researchers witnessed how electrosensors in the Mexican axolotl develop in precisely the same pattern, from the same embryonic tissue, as they do in ray-finned fishes like paddlefish.