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Human embryos have lizard hand muscles that disappear before birth / Boing Boing



New high-resolution 3D images of human embryos show a variety of muscles "present in our ancestors but not normally present in adult humans." For example, there are hand muscles that appear temporarily in human embryos but usually disappear before birth. According to the researchers, our human ancestors lost these "muscles from the back of their hands about 250 million years ago, when mammals and reptiles split on the evolutionary tree." From Science News:

These appearing and disappearing or atavistic muscles are remnants of evolution, says biologist Rui Diogo of Howard University in Washington, DC, with birth, he says. "Losing and specializing, that happens in human evolution."

Other animals have retained some of these muscles. Adult chimpanzees and human embryos have epitrochleo-cuneiform muscles in their forearms, but most adult humans do not. About 250 million years ago, ancestors of human mammals lost dorsometacarpal muscles on the back of their hands as mammals and reptiles split on the evolutionary tree. Lizards still have these muscles, and they are found in human embryos but are lost during development or fuse with other muscles and are absent in most adults.

Relationship between Ontogenesis and Evolution " (Development)

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David Pescovitz

David Pescovitz is co-editor of Boing Boing. On Instagram he is @pesco.

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