Aristotle is called the father of zoology. He pioneered the observational and theoretical study of animals. Zoology has grown to include the study of animals' anatomy, physiology, genetics, embryology and ecology.
Zoology, originally primarily concerned with discovering and documenting new species, was subdivided between vertebrate and invertebrate zoology. Further subdivision occurred because invertebrates comprise 97 percent of animals.
Zoology in the 21st century is more concerned with studying the environmental factors impacting the survival of animals. This branch of zoology is called comparative animal physiology, since it studies how animals obtain energy, cope with changing temperatures and any other problems associated with species survival.