If you never understood what “ontogeny recapitulates phylogeny” meant in high school, don’t worry: biologists no longer think that an animal’s “ontogeny”, that is, its embryonic development, replays its entire evolutionary history. Instead, the new way to figure out how animals evolved is to compare regulatory networks that control gene expression patterns, particularly embryonic ones, across species.
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How an ancient vertebrate uses familiar tools to build a strange-looking head
