Hints: embryo ear bones millimeter gills

Millions of years ago, the embryo of a distant ancestor of ours would have shared with us many of these features. As well as giving rise to us, it gave rise to all sorts of other creatures. And in those creatures, these features we're looking at here have evolved quite differently. We can actually see it happening with the ear bones, because those very same grooves that in us would have become our ear bones, in this creature become something else entirely. This is the embryo of a fish. Here is its heart. And it too has a curved spine and the tiny grooves here, just a fraction of a millimeter long, have evolved to become not ear bones, but supports for its gills.
So, sometime long, long ago, this sort and I shared a common ancestor. And like them it too had little bones around its gills which helped it to breathe. But as we evolved, these little bones were adapted for an entirely different job purpose to become the intricate mechanism of our ears.

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