Well if all life evolved all life should be related to each other if it isnot and we see that for example that some or none of the animals do not fit into this relationship tree then we can assume that evolution cannot be the cause of diversity of life on earth.
That is an argument about universal common descent not evolution. Evolution could still be true even if there were multiple distinct lineages of life with discrete origins. Our current understanding of the history of life on Earth would be radically re-written, but not evolutionary theory.
TTFN,
WK
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