Humans and sea urchins share an embryonic development that prioritizes the anus

Humans are members of the deuterostome lineage, a group of animals defined by a specific embryonic sequence where the first opening, the blastopore, becomes the anus rather than the mouth. This shared trait, which emerged roughly 610 million years ago, links vertebrates with echinoderms like sea urchins and sea cucumbers. During development, our mesoderm forms from pouches in the gut, a process called enterocoely that is distinct from the way insects and worms are built.