Vestigal organs provide evidence of organic evolution in the category

The most direct evidence of organic evolution is :

Homologous structures among organisms provide evidence for evolution in that these structures are.

Vestigeal organs occur as

What provides the evidences for the evolution?

In what way homologous organs provide evidence for evolution ?

The study of homologous structures in mature organism provides evidence for the evolutionary relationships among certain groups of organisms. Which field of study includes this evidence of evolution?