Hints: embryo spinal cord

Deep inside its head, its ear bones are forming. Now let’s look at younger and younger fetuses: eight weeks, seven weeks, six weeks. We are actually witnessing something amazing because at certain times in this early development our human embryo betrays the shapes of the embryos of some of our distant prehuman ancestors. In other words, what we are looking at now is like the embryo of a creature we evolved from millions of years ago. It’s just as if we are journeying back in time virtually rewinding evolution to show episodes in the history of life.
If we use the magnetic scanner, incredible details are revealed. We can see right through the skin of the brain and the spinal cord beginning to form, and the beginnings of an eye behind the emerging hand. Like some of the creatures that preceded us on the evolutionary tree, it has a curved spine and what might be a tail. And those amazing ear bones we saw earlier are taking shape on the outside of the head. The cells that will make them are located here, tiny grooves almost hidden behind that hand.

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