The Origin of Vertebrates - Part 3: How Chordates Got Their Chord (19:09)

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In Part 3: How chordates got their chord, Marc Kirschner (Harvard Medical School) discusses how the overall body plan of vertebrates, arose from the invertebrates based on knowledge of the commonalities in their developmental mechanisms. Here again, the acorn worm, offers the key comparison, being close enough to us to share some recognizable features, but far enough away to indicate the direction from whence we came.

The Origin of Vertebrates - Part 2: Telling the Back from the Front or What the Chordates Invented (27:47)

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In Part 2: Telling the back from the front or what the chordates invented, Marc Kirschner (Harvard Medical School) discusses why we look like invertebrate animals turned upside down, i.e. vertebrates have their central nervous system on their backs and invertebrates have it on their bellies.