This humble, gooey Trichoplax is a "living fossil" whose progeny include everything from humans to snails. And now, say scientists, it has revealed something very strange about our brains.
Scientists have long searched for a common ancestor of all animals, suggesting perhaps that sponges might be it. But now the sponge has lost its status as mother of us all. A new study published today in PLoS Biology makes a compelling argument that the Placozoa phylum of multicellular animals (which includes our Trichoplax above) is our ur-ancestor. A research team led by Bernd Schierwater did an exhaustive analysis of everything from known animal body types to mitochondrial DNA in as many species as possible. And they now believe that this simple Trichoplax, with no muscles or brain, may be our earliest progenitor.
The Trichoplax is already an intriguing creature - it was only discovered 100 years ago. But what's even more intriguing is what it tells us about brains. Schierwater and his team believe that the brainless Trichoplax is the ur-animal that came before we divided up into lower and higher animals. What that means, according to the researchers, is that brains and nervous systems evolved twice: once in the higher animals (that's us and other complex creatures) and once in the lower animals (like snails or worms). It also means that higher and lower animals were evolving at the same time.
In their paper, the researchers write:
We conclude that the higher animals (Bilateria) and lower animals (diploblasts), probably separated very early, at the very beginning of metazoan animal evolution and independently evolved their complex body plans, including body axes, nervous system, sensory organs, and other characteristics. The striking similarities in several complex characters (such as the eyes) resulted from both lineages using the same basic genetic tool kit, which was already present in the common ancestor.
They say that such a double-evolution was possible because the Placazoans already contained a genetic "tool kit" with genes that coded for a nervous system.
The research also makes it sound as if most animal life on Earth tends to evolve towards creatures with brains.
"Concatenated Analysis Sheds Light on Early Metazoan Evolution and Fuels a Modern “Urmetazoon” Hypothesis" via PLoS Biology
"A New Look at Some Old Animals" via PLos Biology
"Scientists Zero in on Earth's Original Animal" via Live Science