The science of zoology began since the first human being was curious about all other animals. In ancient Greece, the curiosity became known as natural history. Scholars like Galen and Aristotle, only two of the many natural historians, wrote extensively about what differentiated animals from human beings.
There were both insights and errors from these ancient scientists. For example, Aristotle believed that males had more teeth than females. This was not questioned until centuries later. Pliny, another scholar, recorded observations of many plants, animals and their interactions, thus setting the foundation and groundwork for zoology.
By the middle ages, zoology was updated by many Muslim scholars. One crucial contribution proposed by Al Jahiz in his work, "Book of Animals," was that environment selected traits, a fore-running theory of evolution. He also noted several aspects of predator and prey relationship. Al Jahiz even discussed roles of climate and environment that selected for darker-skinned people (melanin and pigment), a theory verified by modern science about adaptation.
In the 1500s Swiss scientist Conrad Gesner wrote a "History of Animals." He is credited as being the father of zoology. In Europe until the Renaissance, the field was then addressed by many great thinkers such as Linnaeus and Buffon. In the mid 1700s Carl Linnaeus classified hundreds of plant and animal species, inventing the modern methods of taxonomy, which discovers, describes and names different species. Buffon added volumes of information in the study and classification of species, emphasizing observation of organisms and their behavior, in their environments.
The invention of the microscope by Leeuwenhoek and use of it by Robert Hooke, opened up many new windows to all organisms and their shared traits. It was learned that all species are made up of smaller organisms.
A hundred years later, naturalists such as Lamarck, Alfred Russell Wallace and Charles Darwin would draw upon their many predecessors to greatly advance the field of zoology. Charles Darwin, by carefully describing the workings of natural selection, is credited with discovering what many had suspected. Life could be generated from smaller organisms and cells into more complex and diverse forms.
In modern times, the field of zoology has many sub-fields. Instead of the five categories of classification, modern biologists have three: archaea, eubacteria and eukaryota. The eukaryotes include all plants, animals and fungi that have cellular structures with enclosed nuclei. Modern disciplines have much shared knowledge, cross-over fields and even "umbrella" fields, such as ecology and environmental science, which study the interactive aspects of all living organisms on Earth.
That human beings are animals dependent upon all other animals and organisms is perhaps the greatest discovery of all. It teaches humanity that belonging begins at the molecular level. It is critically important to the health and well being of all species that biodiversity and interactive systems are kept sustainable by following Nature's laws of abundance.