The origin of the human brain has been traced back to primitive central nervous systems in worms and bugs, researchers now say.Humans and other vertebrates evolved from an ancient common ancestor that also gave rise to insects and worms, scientists have long known. But they're of course quite different today. Vertebrates have a spinal cord running along their backs, but insects and annelid worms such as earthworms, which have simple organs that barely resemble a brain, have clusters of nerves organized in a chain along their bellies. So biologists have long assumed these systems—key to ultimately putting a brain to use—arose independently, only after the split.
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