How can these forelimbs explain how life changes over time?

Homologous structure of four different animals

The illustrations show the vestigial structures of four different species that once had a function in an ancestral organism but no longer have a function today.

These illustrations show the variety of bone structures that exist among different species and how life has changed over time as new species develop.

These illustrations show the progressive development of the forelimb in a species over time, one example of how life has changed over time.

These illustrations show the homologous forelimbs of four different species with enough similarities to suggest all had a common ancestor.