Final answer:
The presence of small, nonfunctioning leg bones in snakes is evidence of vestigial structures, indicating that these organisms have ancestors that had functioning legs. Vestigial structures support evolution by showing the changes species have undergone, revealing their descent from a common ancestor. This is a strong indication of evolutionary history rather than a result of other factors such as genetic mutation or parallel evolution.
Step-by-step explanation:
The presence of small, nonfunctioning leg bones in some snakes is evidence of vestigial structures. Vestigial structures are anatomical remnants that were fully functional in the organism's ancestors but are no longer used in the same capacity or are completely nonfunctional. An example of this is the pelvic bones in snakes, which are vestigial because they are remnants of limbs from reptilian ancestors. This concept supports the evidence of evolution because they show that organisms have adapted through time and that parts which were once necessary may become reduced or unused as species evolve.
Vestigial structures provide evidence for evolution by indicating that a species has undergone changes where a once useful structure has lost its original function over time. This is indicative of the organisms' evolution from a common ancestor that originally used those structures. It is not a result of genetic mutation, parallel evolution, nor is it an adaptive trait that came about through evolutionary adaptation, but rather a trace of an organism's evolutionary history and descent from a common ancestor.
Legless lizards also provide a similar case to snakes, where the leg structures are so reduced they do not serve their original purpose, further strengthening the idea that these vestigial structures are a result of past evolutionary changes and shared ancestry.