Animal testing, the use of nonhuman animals in scientific and medical experiments, evolved over millennia as physicians and scientists sought to understand the body. Historically referred to as vivisection, the practice progressed from simple anatomical observation to the complex, controlled physiological research seen today. This progression shifted the purpose of animal use from mapping physical structure to proving systemic function and standardizing experimental methodology.
The Foundational Practices of Antiquity
The earliest recorded instances of using animals to study human anatomy and physiology date back to ancient Greece, where thinkers like Aristotle dissected animals. The most prolific early practitioner was Galen of Pergamon, a Roman physician who lived in the second century CE. Roman law prohibited the dissection of human cadavers, forcing Galen to rely on animals to map the body’s interior structure.
Galen frequently conducted dissections and vivisections on animals such as pigs, goats, and Barbary macaques, believing their anatomy closely mirrored that of humans. His method was observational and deductive, aiming to create a comprehensive map of the body’s organs, nerves, and vessels. In one famous public demonstration, Galen vivisected a pig and cut its laryngeal nerves, showing that the animal’s squealing immediately ceased, demonstrating the nervous system’s role in voice production. This reliance on animal models formed the foundation of Western medical knowledge for over a thousand years, though it led to anatomical errors when findings were directly applied to humans.
The Renaissance and Anatomical Discovery
The resurgence of anatomical inquiry during the Renaissance shifted the focus of animal research from mapping anatomy to proving systemic biological functions. This movement toward quantifiable proof was advanced by the English physician William Harvey in the 17th century. Harvey challenged the long-standing Galenic theory that blood was continually consumed and produced by the liver, proposing instead that blood circulated throughout the body.
In his 1628 work, Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, Harvey used experiments on living animals, including dogs, eels, and cold-blooded creatures, to demonstrate the heart’s function as a pump. By observing the slow-beating hearts of animals near death, he perceived that the heart’s contraction (systole) was the active phase driving blood outward. He also used quantitative evidence, calculating that the volume of blood pumped per hour far exceeded the total amount contained in the body, proving circulation. Harvey’s work introduced measurement and experimental manipulation to physiology, overturning fifteen centuries of established anatomical belief.
Formalization of Experimental Physiology
The establishment of a systematic, controlled laboratory methodology using animals, the precursor to modern animal testing, is attributed to the 19th-century French physician Claude Bernard. Bernard is recognized as the “founder of modern physiology” for formalizing the experimental method in medicine. He argued that physiological understanding must be grounded in reproducible, hypothesis-driven investigation conducted in a controlled environment.
Bernard’s most enduring theoretical contribution was the concept of the milieu intérieur, or the internal environment. He posited that the body’s cells live in a stable internal medium, and that the constancy of this environment is necessary for “free and independent life.” His systematic approach used vivisection to study complex physiological and pathological processes, such as the glycogenic function of the liver and the action of poisons like curare. This transition moved the practice from anatomical demonstration to the controlled, systematic experimental medicine that underpins modern drug testing and toxicological research.