An organism's development from an embryo may contain clues about its history that scientists can use to develop relationships and build evolutionary trees. ancestral characters are often preserved in an organism's developmental stages. for example, both bird and human embryos go through a stage where they have slits and arches in their necks like the gill slits and gill arches of fish. these structures are not gills and do not develop into gills in birds and humans, but because they are so similar to gill structures in fish at this point in development scientists believe that
a) birds and humans evolved from fish.
b) all vertebrate animals have identical embryos.

c) fish, birds, and humans share a common ancestor.
d) fish evolved as a life form long before birds or humans.