Symmetry is so fundamental to multicellular life that it can be easy to overlook. In fact, symmetry only seems to stand out in the notable instances where it’s quite obviously broken, such as in the case of the male fiddler crab, which possesses one smaller claw and an opposite claw that’s many times larger. In this short video, Laila Moubayidin, a Royal Society University Research Fellow at the John Innes Centre in Norwich, England, discusses why symmetry came to dominate life on Earth, and how many complex life forms, such as humans, transitioned from radial to lateral symmetry. Moubayidin also breaks down how life forms can evolve to break symmetry once they’ve established it, how some animals possess different degrees of symmetry across a lifetime, and the many ways in which humans lack perfect symmetry.