BY: PHILLIPE DE JOCAS
It’s hard to believe that evolution – the great endless cycle of livin’, breedin’, mutatin’, and dyin’ – has gone on unabated for more than four billion years. In that time, fish have crawled out onto land, amphibians have developed into reptiles, dinosaurs have fallen out of trees enough times to evolve into birds, and, yes, eventually, one day a hominid came up with the bright idea to hop out of the trees and start walking upright. This is, of course, a slightly abridged history of it all, but given enough time and genetic accidents, evolution can transform just about anything into anything. So where did it all begin?
Charles Darwin, naturalist, explorer, and father of the entire modern biological movement, once waxed philosophical about the origins of life – speculating that the first organisms must have evolved in some “warm little pond” with just the right conditions to allow for the development of complicated life forms. We know today that the real story about how life got started is far more tangled and complicated than he could ever have imagined.
It goes without saying that the hunt for our very oldest ancestors, who swam in warm shallow oceans more than 500 million years ago, isn’t particularly easy. Fossils of these creatures are vanishingly rare and only fossilize under the exact specifications. Even the biggest specimens we’ve uncovered are frustratingly tiny, most hover around the size of a grain of sand. It goes without saying that any kind of new discovery in this field is a great breakthrough.
In January 2017, a group of Chinese scientists working from Xi’An’s Northwest University discovered the oldest known ancestor of humans – and, by extension, all other vertebrates. Dubbed Saccorhytus, the creature measures a little under a millimetre long and probably eked out a living on the seabed between grains of sand. Saccorhytus is the oldest known “deuterostome,” a primitive and now extinct group that scientists believe is the common ancestor to all known vertebrate species. Not only is it the ancestor of you and me, but it’s also a member of the lineage that would lead to frogs, cows, chickens, sharks, hippos, and Tyrannosaurus rex. As one of the oldest known multicellular animals, Saccorhytus predates several of the big splits that would divide the vertebrates from other creatures such as the ancestors of starfish or squid. What sets vertebrates and deuterostomes apart from other life-forms is “bilateral symmetry:” each half of our body is a horizontal mirror image of the other. Conversely, creatures like starfish and jellies operate on “radial symmetry,” with their appendages radiating out from a central core. Our simpler body plan would eventually allow us to develop hard skeletons to better support our weight – chew on that, octopuses!
As you might expect, Saccorhytus kicked it old school. In an era when internal organs had yet to achieve their modern complexity, what few internal systems this bag-like creature possessed all performed multiple duties, a crude and rather generalist system. Saccorhytus’ large “mouth,” for instance, served as an all-purpose orifice. Scientists believe it consumed food through this gaping hole, and (wait for it)…it also used the same hole to cough up the excrement it processed from its simple digestive system. Or, in layman’s terms, it pooped out of its mouth. Frogs, dinosaurs, birds, apes, even humans – we all got our start by pooping out from our mouths.
The next time you’re pinned down at a party and forced to endure an endless litany of boring stories, remember the spirit of Saccorhytus. Perhaps this humble proto-vertebrate lives on in the pithy tales of windbags and blabbermouths – turning primitive digestive endeavors into true verbal diarrhea.
