You get this ending if you evolve by upgrading anything that isn't your wisdom right at the end of chapter 5. I. If you are all the way to the left in this row of the chart, you can get another alternate ending which comes next in this playlist.
I bet humans call them barbarians only because they envy their hair.
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46 Okunen Monogatari~The Shinka Ron~ (also known as E.V.O. - The Theory of Evolution via its...