Short answers, pulled from the story.
Aristotle divided the animal kingdom into two distinct groups: those with blood, which we now call vertebrates, and those without, the invertebrates. He spent two years on the island of Lesbos dissecting and observing creatures to prove that animals were living organisms with their own internal logic.
The year 1551 marked a turning point when Conrad Gessner published the first volume of his four-part work spanning 4,500 pages. This publication is widely considered the beginning of modern zoology because he integrated information from ancient sources with the results of his own investigations.
Charles Darwin published his theory of evolution by natural selection in 1859. This publication fundamentally altered the trajectory of zoology by placing the theory of organic evolution on a new footing and forcing a reconstruction of animal classification upon a genealogical basis.
The year 1953 saw Francis Crick and James Watson determine the double helical structure of the DNA molecule with the aid of Rosalind Franklin's data. This discovery opened up the realm of molecular biology and allowed scientists to answer questions regarding the structure of the gene and the mechanisms of genetic inheritance.
The origin of biogeography is widely accredited to Alfred Russel Wallace, a British biologist who had some of his work jointly published with Charles Darwin. Biogeography studies the spatial distribution of organisms on the Earth and unites concepts from evolutionary biology, taxonomy, ecology, and physical geography.