They differentiated in form as a result of living apart in different environments. Finches in the Galapagos Islands are adapted to exploit a variety of different niches. Beaks show a lot of variation and specialization for different functions. Similar types of changes seen th the Hawaiian honeycreepers. Similarity of embryos of all vertebrates suggests a common ancestry.
Vestigial organs suggest a common ancestry.
All mammals have similar structures whether they are used or not. Evidence of this abounds in animal and plant kingdoms. Changes in domestic animals through selective breeding. More recent lines of evidence in support of evolution All forms of life are made up of 20 amino acids. The question is not whether evolution occurs, but rather, exactly how it occurs.