Why humans share so many genes with sea urchins
The surprising organism is the sea urchin. The often-cited figure of roughly 70% refers to genes humans have in common with it—not to 70% of our entire DNA being identical. The distinction matters: genomes contain vast stretches of DNA that do not code for proteins, and even corresponding genes can differ in their exact sequence.
What “in common” means
Over evolutionary time, species inherit genes from shared ancestors. When researchers compare genomes, they can identify genes in different animals that descend from the same ancestral gene. Such counterparts are called homologous genes. They may retain related roles even as their DNA changes across generations.
Sea urchins and humans look radically different, but both are animals built from many of the same cellular tools. Genes involved in basic processes—such as controlling cell growth, copying DNA, and coordinating development—are ancient and widespread. Their preservation helps explain why a marine invertebrate can have so many recognizable genetic counterparts in a human.
Shared genes do not mean shared bodies
The resemblance is in parts of the biological toolkit, not in the finished organisms. Differences in how genes are switched on, when they act, and how they interact help produce a spiny sea-floor animal rather than a human. So the striking takeaway is not that people are mostly sea urchin; it is that evolution has repeatedly adapted and recombined a deep set of inherited instructions.
