Evolution__3rd_Edition

..
3 The
Evidence for Evolution
H ow can it be shown that species change through time,
and that modern species share a common ancestor? We
begin with direct observations of change on a small scale and
move out to more inferential evidence of larger scale change.
We then look at what is probably the most powerful general
argument for evolution: the existence of certain kinds of
similarity (called homologies) between species b similarities
that would not be expected to exist if each species had
originated independently. Homologies fall into hierarchically
arranged clusters, as if they had evolved through a tree of life
and not independently in each species. The order in which
the main groups of animals appear in the fossil record makes
sense if they arose by evolution, but would be highly
improbable otherwise. Finally, the existence of adaptation in
living things has no non-evolutionary explanation, though
the exact way that adaptation can be used to suggest
evolution depends on what alternative is being argued
against.