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Why are bird wings and fly wings considered analogous structures?

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A diagram showing the tentative evolutionary relationships among hominid species over the past four million years, with skull images and labeled species names connected by solid and dotted lines to indicate proposed evolutionary pathways. — phylogeny Tentative phylogenetic scheme for the evolution of the human lineage. Solid bars indicate the time ranges during which species are thought to have existed, based on fossil evidence. Dotted lines signify evolutionary relationships between hominin species that have been proposed on the basis of the fossil evidence.

Bird wings and fly wings are considered analogous structures because they serve the same function—flight—but do not share a common evolutionary origin.123

In biology, analogy refers to functional similarity that arises independently in different species, often through a process called convergence. While both birds and flies have evolved wings to navigate the air, these structures are not modified versions of a wing present in a common ancestor. Instead, they developed separately as distinct adaptations to the same environmental challenge.23

This is distinct from homology, which describes structures that are similar because they were inherited from a common ancestor. For example, the forelimbs of humans, dogs, and whales are homologous because they share the same underlying skeletal pattern derived from a common ancestor, even though they perform different functions. Because bird and fly wings lack this shared ancestral blueprint, they are classified as analogous rather than homologous.13