“Cells that end up as neurons make one set of choices, while muscle cells make a different set of choices,” says Megason. But exactly how these embryonic stem cells make their choices is still shrouded in mystery.
UNITED AND DIVIDED
Multicellular life forms are the new kids on the block, evolutionarily speaking. They first appeared on Earth roughly 600 million years ago, at least two billion years after their single-celled ancestors evolved. For reasons we still don’t fully understand, single cells began to replicate, eventually forming more complex organisms.
“On the first day, they mostly just divide, so at the end of the day they are a round ball of cells,” Megason says. “But when you come back the next morning, that ball of cells has turned into a little fish. It has eyes, a beating heart; it has muscles and can wag its tail.””
Read more: https://news.nationalgeographic.com/2018/05/embryo-stem-cells-genetic-roadmap-development-science-spd/