We have named 1.5 million animal species, and millions more may be waiting
Zoologists have formally described roughly 1.5 million kinds of animal, yet estimates suggest the true total could reach 8 million. The science of animals began with cave artists and Aristotle's notebooks, and it is still finding new species today, sometimes hiding inside a single frog that turned out to be several.
Zoology is the branch of biology devoted to animals: how their bodies are built, how they develop, how they behave, where they live, and how they fit into ecosystems, whether they are alive today or long extinct. The name comes from two Ancient Greek words meaning animal and study. People were watching animals closely long before anyone called it science. Cave art in France around 15,000 years old renders bison, horses and deer with real care, and early farming societies across the Near East, Mesopotamia and Egypt recorded hunting, fishing and herding, even placing animals among Egyptian hieroglyphs.
The formal discipline is usually traced to Aristotle in the fourth century BC. He sorted creatures into those with blood and those without, a split that roughly matches our vertebrates and invertebrates, and spent two years on Lesbos describing local wildlife and asking what each body part was for. Four centuries later the Roman physician Galen learned anatomy by dissecting animals, since cutting up human bodies was forbidden. Some of his conclusions were wrong, but questioning him was treated as heresy for centuries, and anatomy stalled until the European Renaissance revived hands-on observation through figures such as Vesalius, Harvey and Linnaeus.
Microscopes then opened a hidden world. Leeuwenhoek saw microorganisms, and with Hooke's support the idea took hold that living things are made of cells rather than arising spontaneously. Darwin's 1859 theory of evolution by natural selection gave the field a unifying story, and animals were reclassified by ancestry. Mendel's 1865 pea experiments went unappreciated until the early twentieth century, when genetics grew quickly, and the 1953 work on the double helix launched molecular biology.
Classification still anchors the field. Linnaeus grouped species by shared features; today those groupings are revised to reflect common descent, often using DNA sequences. That is how a single Chinese and Vietnamese tree frog, Zhangixalus puerensis, was recently shown to hide four distinct lineages, two of them described as new species. Zoology also informs conservation, guiding protection of endangered animals and the design of wildlife corridors.
Source: Zoology
