For billions of years, single-celled creatures had the planet to themselves, floating through the oceans in solitary bliss. Some microorganisms attempted multicellular arrangements, forming small ...

Theories about how animals became multicellular are shifting as researchers find greater complexity in our single-celled ancestors. From one came many. Some 700 million years ago, a single cell gave ...

Animals, from worms and sponges to jellyfish and whales, contain anywhere from a few thousand to tens of trillions of nearly genetically identical cells. Depending on the organism, these cells arrange ...