People acted as zoologists long before the study of zoology existed as we know it today. Zoology, in a crude form, has existed since people became interested in animals. Animals, such as the dog for example, have evolved along with us. Primitive farmers, shepherds, and hunters all noted characteristics in animals and then used them too their advantage whether it be a dog protecting their flock or their flock itself. They studied the animals, their habits and behavior and without even realizing it, acted as zoologists.
The written history of zoology arguably began with Aristotle in the 4th century BC. Aristotle took a lot of notes on animals he observed which later formed the foundation for the studies of Saint Albert Magnus during the 13th century. Magnus was a Dominican friar and Bishop of the Catholic church who dedicated his life to expanding upon the work of Aristotle, thus he dabbled in early zoology. Until the 1800s, his writings were the most advanced in both zoology and all of the natural science.
During the 1500s, a number of important European universities were founded and people, of course, had interest in studying animals. In 1651, the German Academy of Sciences opened and completely focused on plant and animal research. The Royal Society of London opened its own similar school a decade later, followed by another institution in Paris, France. This interest continued well into the 1700s. Even President Thomas Jefferson was extremely interested in animals during that time. Anton von Leeuewenhook's improvements upon the microscope caused zoology and numerous other fields to take off, far expanding up on the work of Aristotle and Magnus.
The 19th century is considered by some the golden age of zoology. During the time, thanks to the microscope, cells were identified as the building blocks of life. Life processes could then be observed at the microscopic level, which meant animals could be studied at the microscopic level. The 19th century was also the era of Charles Darwin. To many, Darwin's work is what lead to modern zoology as we know it today. Darwin's theory of evolution, published in 1859, revolutionized all of the natural sciences, not just zoology. His work lead to changes in how members of the animal kingdom are classified as well as modern taxonomy, which are integral parts of the study of zoology.
Breakthroughs in DNA research during the 1900s have again revolutionized zoology, much in the same way that the microscope did. Zoology today is a diverse field where specialties range from animal behavior, to physiology and genetics, to simply specializing in only one group of animals like mammals or reptiles. Paleontology is the study of the history of animals and their evolution. Zoogeography is the branch of zoology concerned with the distribution of animals. Zoology has a long history and has come a long way from its primitive origins in which humans observed animals as a method of survival.