From single cells to complex creatures: New study points to origins of animal multicellularity

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 themselves into a variety of tissues and organs, such as the gut, muscles, and sensory systems. While not all animals have each of these tissues, they do all have one tissue, the germline, that produces sperm or eggs to propagate the species.