A mere eight years after its creation, in 1899, the School of Biology separated into a School of Botany and a School of Animal Biology. They both moved from the basement of the Old Main Building to a wing of the third floor which they shared with Geology. Just one year later, in 1900, the School of Animal Biology shortened its name to School of Zoology.

The Old Main Building, original home of the School of Biology, and later of the Schools of Botany and of Zoology. The building was torn down in 1934.

The early focus in the new years of these Schools was on creating strong undergraduate courses that would train students for future advanced study. There wasn't much funding available for the biological sciences at the time, and not much interest in offering advanced study at UT Austin. However, over the years, the Schools began to expand and offer more course work, hire more faculty, and emphasize that these faculty members work on their own research, in addition to teaching in their areas of research more exclusively than was done before.

In 1920, the two schools were renamed into departments, the Department of Zoology and the Department of Botany and Bacteriology, and both continued to expand. They eventually called for their own dedicated building, the Biological Laboratories Building (BIO), completed in 1925. Similarly, the Department of Botany grew into the Department of Botany and Bacteriology, and would split into two separate departments by the late 1940s. More growth of the two departments resulted in outgrowing the Biological Laboratories Building where they were housed. To provide capacity for the growing biology departments, the Experimental Science Building was constructed and completed in 1951, offering the then novelty of air-conditioning.

1923 photo of UT-Austin biologists, taken at Woods Hole Biological Laboratory. From left to right: Hermann Muller, Carl Hartman, George Parker, and J. T. Patterson.

In 1970, the College of Natural Sciences was officially established as the joint home of all departments in the natural sciences, including the biology departments. In 1996, with further growth in biology, and with the advent of modern molecular and cellular biology, the distinction between Zoology and Botany seemed increasingly artificial, and hence the decision was made to reunite all of biology into a School of Biological Sciences (SBS). SBS was officially launched in 1998, with Professor David Hillis as its first director. The School did not house separate departments, but instead was subdivided into four distinct sections, the Sections of Integrative Biology (IB); Molecular Genetics and Microbiology (MGM); Molecular, Cell, and Developmental Biology (MCB); and Neurobiology (NB).

In 2013, the decision was made to return to a more traditional departmental structure, and thus the School of Biological Sciences was dissolved into three new biology departments, the Departments of Integrative Biology, of Molecular Biosciences, and of Neuroscience. The three departments closely coordinate their teaching at the undergraduate and the graduate levels, and most biology students will take classes in multiple departments. Similarly, faculty members of the three departments frequently collaborate on joint research projects.  At the same time, the three departments all maintain their own unique research focus. The Department of Integrative Biology emphasizes the study of animals, plants, and microbes, with a goal towards developing an integrative perspective of life on earth. As such, Integrative Biology is probably the most direct descendant of the original departments of Zoology and Botany.