Animal experimentation, often called vivisection when performed on living subjects, is deeply rooted in the history of medicine and biological inquiry. Driven by the desire to understand the complex workings of the human body, early scientists and physicians turned to animals when cultural or religious prohibitions restricted the dissection of human corpses. This historical approach, spanning from antiquity through the early modern period, laid the foundational knowledge for anatomy and physiology. Animal subjects served as a necessary proxy, allowing for direct, empirical observation that replaced reliance on ancient texts and philosophical speculation.
Ancient Greek and Roman Pioneers
The earliest documented figures to systematically investigate living animals for medical knowledge emerged in the Hellenistic period. Erasistratus of Ceos, a Greek anatomist and physician in the third century BCE, is considered a founder of physiology due to his focus on functional biological systems. He conducted vivisections on animals to explore the structure and operation of internal organs, noting the action of heart valves and distinguishing between veins and arteries, though he incorrectly believed arteries carried air or “pneuma.”
Centuries later, Galen of Pergamon, a physician in the Roman Empire (second century CE), performed extensive dissections and vivisections on various animals. Since human dissection was forbidden in Rome, Galen’s comprehensive understanding of anatomy was primarily derived from species like pigs, goats, and Barbary macaques. His work involved live demonstrations, such as the famous experiment on a pig where he cut the recurrent laryngeal nerve to show that the brain controls the voice. Galen’s detailed descriptions, though often flawed, became the unchallenged medical authority for over a millennium.
The Renaissance and Anatomical Correction
The Renaissance era marked a significant shift toward empirical observation, challenging the long-standing authority of Galenic medicine. This movement was spearheaded by anatomists who began to gain access to human cadavers for dissection. Despite this change, animal subjects remained important, particularly for comparative study.
Andreas Vesalius, a 16th-century physician, used human dissection to correct hundreds of anatomical errors inherited from Galen. Vesalius demonstrated that many of Galen’s descriptions, such as the structure of the human jawbone, were based on the anatomy of animals (like the pig or primate), not humans. His landmark work, De humani corporis fabrica (On the Fabric of the Human Body), published in 1543, used comparative anatomy to highlight these discrepancies. Vesalius’s work redefined the role of animals, establishing the principle that direct, empirical observation must take precedence over ancient authority.
Establishing Modern Experimental Physiology
The 17th century saw the transition from anatomical description (structure) to a focus on physiological function, marking the beginning of modern biological experimentation. This shift was characterized by controlled, systematic experiments designed to test theories about how the body operated. The philosophical landscape during this time was influenced by figures like René Descartes, who argued that animals were essentially complex, soulless automatons.
Descartes’ “animal-machine” concept justified the increased use of vivisection, suggesting that an animal’s cries were merely the sound of a machine malfunctioning, not an expression of pain. This perspective made it easier for scientists to conduct repeated, invasive experiments. The most notable figure in this era was William Harvey, who used this systematic experimental approach to prove the circulation of blood.
Harvey published his findings in 1628 in Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus. He performed experiments on various animals, including dogs, fish, and snakes, observing the heart’s action and manipulating blood vessels. By calculating the quantity of blood the heart pumped every hour, Harvey demonstrated that the blood could not be consumed and regenerated, as Galen had believed, but must circulate in a closed loop. Harvey’s work, which combined direct observation, calculation, and manipulation of living systems, set the standard for the modern experimental method in biology.