From one came many. Some 700 million years ago, a single cell gave rise to the first animal, a multicellular organism that would eventually spawn the incredible complexity and diversity seen in animals today. New research is now offering scientists a fresh perspective on what that cell looked like, and how multicellularity could have emerged from it—a transition that marks one of the most pivotal events in the history of life on Earth.
For well over a century, it has been widely assumed that the ancestors from which the first animal evolved were simple blobs of identical cells. Only later, after the animals formed their own branch on the tree of life, did those cells start to differentiate into various cell types with specialized functions. But now, painstaking genomic analyses and comparisons between the most ancient animals alive today and their closest non-animal relatives are starting to overturn that theory.
The recent work paints a picture of ancestral single-celled organisms that were already amazingly complex. They possessed the plasticity and versatility to slip back and forth between several states—to differentiate as today’s stem cells do and then dedifferentiate back to a less specialized form. The research implies that mechanisms of cellular differentiation predated the gradual rise of multicellular animals.