Common descent is inheritance from shared ancestors. It explains why related organisms share many corresponding structures and sequences even when their present environments and functions differ. Biological homology concerns that historical correspondence, whereas convergent evolution can produce similar features independently.
A phylogenetic tree represents a hypothesis of branching descent. Its internal nodes denote shared ancestry, and an extant outgroup provides a comparison rather than a living copy of the ancestor. Evidence from multiple characters helps distinguish a relationship from the misleading history of one isolated trait.
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