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Universal common descent

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Universal common descent is the hypothesis that all life on Earth is descended of a single proto-organism, and that the complexity and variety of life is the result solely of mutation, recombination, natural selection, and genetic drift.

It contrasts with baraminology and discontinuity systematics, the hypotheses that life originated in a discrete number of distinct, fully developed forms.

Arguments for universal common descent

  • Homology: It is argued that the similarities shared by lifeforms supports the conclusion that they are related. While such similarities are consistent with common descent, critics argue that similarity does not necessarily imply common descent. Two marble statues, for instance, may share many similarities in design -- but their similarity does not support a conclusion that they are descended of another statue. Designers typically reuse and tweak designs -- therefore, since homology is reasonably consistent with both universal common descent and creationary explanations, the evidence does not support the conclusion.
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