Isn't this argument kindof pointless since all categories above the species level are arbitary?
Common descent is a great (only) explanation for the heirarchial nature by which we classify all life, but it doesn't give us any insights into how we should make our classification. How much genetic divergence do two species need to be considered to be in different genuses? Families?
To expect all of our groups across the tree of life to be consistent with regard to mutational distance seems a little absurd. The classifications are meant to help us, not to be some objective reality.
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