Regardless of their source, cells share so many features that the untrained eye examining individual specimens would be hard-pressed to distinguish mouse from mastiff, turtle from tarantula, housefly from human. That’s remarkable. Surely our cells must show an obvious and significant distinguishing imprint. Yet they don’t. The reason, established during the past few decades, is that all complex multicellular life descended from the same single-celled ancestral species. Cells are similar because their lineages radiate from the same starting point.22
