If you look closely at the Tree of Life on our website, you will see a question mark on the ctenophore branch.
Science is about inquiry. Sometimes what is originally proven to be true turns out to be false upon further inquiry. And science is a continuous inquiry process.
In the case of sponges, Shape of Life has lots of material referring to sponges as the first animal. But, scientists have been questioning the sponges’ position on the tree of animal life for decades, with proponents for sponges and others for ctenophores (comb jellies) doing research to prove their point. Now, some scientists have shown, using genetics, that in fact comb jellies are the first animal.
It’s In the Genes!
Both animals are soft-bodied and therefore don’t leave fossils. Researchers from the Monterey Bay Aquarium Research Institute (MBARI), UC Berkeley and the University of Vienna mapped linkages between genes on specific chromosomes, which are deeply conserved throughout time. They analyzed the sets of genes that are always found together on a single chromosome, in organisms from humans and dogs to crabs and corals. The scientists provided “clear evidence that comb jellies were the first animals” followed by sponges. The comb jelly lineage is a unique one whose ancestors diverged before the common ancestor of all other animals.
“We developed a new way to take one of the deepest glimpses possible into the origins of animal life,” said Darrin Schultz, the lead author, a former researcher at MBARI who is now a postdoctoral researcher at the University of Vienna. “This finding will lay the foundation for the scientific community to begin to develop a better understanding of how animals have evolved.”
