Question

Embryology is the study of development. How can embryological evidence tell you if two species share a common ancestor?

Answer 1

Homologous structures

Answer 2

If you look at two species in their embryogenic stage. their bones and their forms look similar and you can differentiate too.
if you look at a fish and a human... 
humans wont have the the fins protruding in the fishes embryo, showing how different they are. <span />