Final answer:
Comparative embryology studies the similarities and differences in embryos of different species to provide evidence of common ancestry. Vertebrate embryos, including humans, exhibit gill slits and tails during early development, which are lost in terrestrial groups but maintained in aquatic groups.
Step-by-step explanation:
Comparative embryology is the study of the similarities and differences in the embryos of different species. Similarities in embryos are evidence of common ancestry. For example, all vertebrate embryos, including humans, have gill slits and tails at some point in their early development. These disappear in the adults of terrestrial groups but are maintained in adult forms of aquatic groups such as fish and some amphibians. Great ape embryos, including humans, have a tail structure during their development that is lost by the time of birth.