Zoonomia; Or, The Laws of Organic Life, Vol. I Informative Summary


Erasmus Darwin’s “Zoonomia; Or, the Laws of Organic Life,” published in 1796, presents a comprehensive exploration of the principles governing animal life. Darwin, a prominent physician and poet, sought to classify and analyze the various motions and sensations that comprise the human experience. He argues that all animal motions originate from the “sensorium,” a living principle or spirit of animation that resides throughout the body.

Darwin proposes that this sensorium acts in four distinct ways: irritation, sensation, volition, and association. He meticulously defines these faculties, demonstrating how they interact with the body’s fibrous tissues, leading to both conscious and unconscious actions. The book delves into the mechanics of muscular contraction, the workings of the nervous system, and the role of various organs, such as the stomach, intestines, liver, and glands, in maintaining bodily function.

Key Findings:

  • Darwin’s “Zoonomia” offers a groundbreaking exploration of the connection between mind and body, predating modern neuroscience.
  • The book highlights the importance of understanding the various forms of animal motions and the complex interactions between the senses, muscles, and the sensorium.
  • Darwin emphasizes the role of stimuli in triggering both physical and mental actions, and he proposes a theory of how these stimuli interact with the sensorium to produce sensation, volition, and association.
  • The book examines the influence of habit and repetition on animal behavior, demonstrating how actions become linked together through association, contributing to learned behavior and instinct.
  • Darwin explores the intricacies of dreams and reveries, offering insights into the workings of the unconscious mind and the nature of perception.


  • The Sensorium: Darwin introduces the concept of the sensorium, a vital principle that resides throughout the body and controls all its motions. This principle acts through various faculties, such as irritation, sensation, volition, and association, which are responsible for our conscious and unconscious actions.
  • The Nature of Motion: The book provides a detailed analysis of animal motion, differentiating it from the motions of inanimate matter and explaining the mechanics of muscular contraction. Darwin argues that all motions originate from the sensorium and are influenced by stimuli, sensations, volitions, and associations.
  • The Power of Association: “Zoonomia” emphasizes the role of association in shaping animal behavior, both conscious and unconscious. This concept, which underpins learning and instinct, explains how actions and ideas become linked together through repetition, creating complex chains of behavior.
  • The World of Dreams: Darwin explores the nature of dreams, revealing them as a complex interplay of sensation and association. He explains why dreams are often illogical and inconsistent, why we can be surprised when we wake up, and why we sometimes forget our dreams.
  • The Intricacies of Digestion and Secretion: “Zoonomia” provides a detailed account of the digestive process, from the role of the stomach and intestines to the action of glands and absorbents. It explores how stimuli affect these functions and how they can become disordered, leading to various diseases.
  • The Importance of Temperament: Darwin describes four distinct temperaments, each with a predisposition towards different types of diseases: decreased irritability, increased sensibility, increased voluntarity, and increased association. He explores the characteristics of these temperaments and how they relate to a person’s susceptibility to various ailments.
  • The Nature of Contagion: Darwin offers a fascinating theory of contagion, proposing that it acts not by entering the blood but through a process of sympathetic or associated motions between different parts of the body. He explains how this mechanism can account for the unique properties of specific contagious diseases, such as their ability to be transmitted only once.
  • The Evolution of Animals: “Zoonomia” presents a groundbreaking argument for the gradual evolution of animals from a single living filament. Darwin points to the similarities in structure between various animal species and the changes they undergo over time, both before and after birth, to support his theory. He also explores the role of imagination in shaping the offspring of animals.

Historical Context:

Darwin’s “Zoonomia” was published at a time of great scientific and intellectual ferment. The Enlightenment had sparked a renewed interest in observation and experimentation, and groundbreaking discoveries in fields like astronomy, chemistry, and medicine were revolutionizing scientific thought. Darwin’s work, with its emphasis on observation, classification, and the interrelationship of mind and body, reflected this spirit of scientific inquiry. It also served as a precursor to the work of Charles Darwin, who would later develop the theory of evolution by natural selection.


  • Animal motions originate from the sensorium, a living principle or spirit of animation residing throughout the body. This theory is based on the observation that animal motions cannot be explained by mechanical or chemical principles alone.
  • The sensorium acts in four distinct ways: irritation, sensation, volition, and association. These faculties, Darwin argues, govern all our actions, both conscious and unconscious.
  • The muscles and organs of sense are made of moving fibres, which contract in response to stimuli, sensations, volitions, and associations. Darwin uses this principle to explain various animal actions, from the beating of the heart to the formation of ideas.
  • The actions of the heart and arteries are stimulated by the distention caused by the blood. This explains why these vessels continue to pulsate even after being removed from the body.
  • All glands have a peculiar taste or appetency, which allows them to select specific particles from the blood for secretion. This explains why different glands produce different fluids, even though they all draw their materials from the blood.
  • The sense of touch is the most important sense for acquiring knowledge, particularly in humans. Darwin credits the human hand’s dexterity and sensitivity to the species’ superior intelligence.
  • The sense of smell plays a crucial role in animal behavior, guiding them towards food and mates. Darwin cites various examples of animals using their sense of smell to find sustenance and attract partners.
  • The lacrymal sack is a gland that secretes tears, which serve to moisten and clean the eye and are also associated with various emotions. Darwin describes the various stimuli that can trigger the production of tears, including the dryness or coldness of the air, and explores how they become associated with feelings like grief and joy.
  • The process of digestion is highly complex and involves a combination of chemical and animal processes. Darwin emphasizes that digestion cannot be fully replicated outside the body of a living animal or plant.
  • The placenta is a pulmonary organ that oxygenates the blood of the fetus. Darwin argues that the placenta performs a similar function to the gills of fish, absorbing oxygen from the mother’s blood.
  • The liquor amnii surrounding the fetus is nutritious, and the fetus swallows it into its stomach and bowels. This explains why new-born infants have meconium, or first feces, even before taking any nourishment from their mothers.
  • The embryon is produced by the male, while the mother provides the nidus and sustenance. Darwin uses the example of vegetable buds and bulbs to support his theory, arguing that these forms of reproduction do not require a female parent.
  • The imagination of the male parent can influence the form, color, and sex of the offspring. Darwin believes that the extremities of the seminal glands imitate the motions of the organs of sense, producing offspring that reflect the father’s imagination.
  • All warm-blooded animals likely descended from a single living filament, which evolved over time into the diverse species we see today. This theory, which predates the work of Charles Darwin, emphasizes the importance of the process of evolution in shaping the natural world.
  • The periods of many diseases, especially those that are triggered by external stimuli, are influenced by the moon and sun. Darwin explains how the gravitational pull of these celestial bodies can affect the chemical composition and stimulation of the blood, contributing to the cyclical recurrence of certain ailments.
  • Fever-fits are not an effort of nature to relieve herself, but rather a consequence of the perpetual and incessant action of the arterial and glandular systems. Darwin refutes the prevailing theory of spasm, proposing that fever-fits result from the body’s natural processes becoming disrupted.
  • The primary and secondary parts of associated motions can reciprocally affect each other, leading to a phenomenon called sympathy or consent of parts. Darwin explains how this principle can account for the transmission of pain and inflammation from one part of the body to another.


  • One-third of our lives is spent in sleep.
  • An apple can give up six hundred times its bulk of air during fermentation.
  • The white of an egg can absorb as much as six hundred times its bulk of water.
  • A viper’s heart can continue to pulsate for many minutes after being removed from the body.
  • The female bear sheds tears in grief.
  • The remora can hold fast to a ship while it is sailing, even when offered a piece of pork.
  • The white ants of Africa build pyramids eight to ten feet high.
  • A horse can distinguish between a person with a gun and one without.
  • The “Old Soldier” fish uses the shell of a dead fish to protect itself.
  • The uett-uett bird of Senegal warns other birds of the approach of a man.
  • The mother turkey uses a specific call to warn her young of danger.
  • A dog can be taught to guard sheep, hunt, set, and even find truffles.
  • Pelicans form large circles in the water to drive fish towards their beaks.
  • The caterpillar of the ichneumon fly preys on the silk-producing material within the cabbage caterpillar.
  • A young lady with epilepsy experienced a calm talkative delirium for an hour after a violent convulsion.
  • The heart of a person experiencing a panic attack can beat as fast as 150 times per minute.
  • A person with anasarca can discharge as much as 18 pints of urine per day.
  • One of Dr. Percival’s hands imbibed nearly an ounce and a half of water in a quarter of an hour.
  • The blood of a person with the small-pox will not infect others.
  • A man who had been drinking heavily voided a quart of black viscid material by stool.
  • The salivary glands of a person taking mercury can produce a great deal of saliva.


  • Sensorium: The living principle or spirit of animation that resides throughout the body, controlling all its motions.
  • Irritative motion: A contraction of muscles or organs of sense caused by the stimulus of external bodies.
  • Sensitive motion: A contraction of muscles or organs of sense caused by pleasure or pain.
  • Voluntary motion: A contraction of muscles or organs of sense caused by desire or aversion.
  • Associate motion: A contraction of muscles or organs of sense caused by their previous association with other motions.
  • Association: The linking together of ideas and actions through repetition and habit.
  • Catenation: The reciprocal introduction of fibrous and sensorial motions in progressive trains or tribes.
  • Instinct: Actions of animals that seem to be neither directed by their appetites, taught by experience, nor deduced from observation or tradition.
  • Reverie: A state of mind in which a person becomes absorbed in their thoughts and loses awareness of their surroundings.
  • Vertigo: Dizziness or a sensation of spinning, often caused by unusual motions or stimuli.
  • Drunkenness (Intoxication): A state of mind and body caused by the ingestion of excessive alcohol or other intoxicating substances.
  • Temperament: A permanent predisposition to certain classes of diseases.
  • Synocha: An irritative fever with strong pulse (inflammatory fever).
  • Typhus: An irritative fever with weak pulse (nervous fever).
  • Syncope: A temporary suspension of the vital functions, characterized by a weak pulse and loss of consciousness (fainting).
  • Catalepsy: A state of rigidity and immobility, often accompanied by an absence of consciousness.
  • Inflammation: A painful response to injury or irritation, characterized by redness, swelling, heat, and pain.
  • Contagion: The transmission of a disease through the transfer of infectious material.
  • Hæmorrhage: The excessive loss of blood, often from ruptured vessels.
  • Anasarca: A swelling of the tissues due to the accumulation of fluid in the cellular membrane.
  • Ascites: An accumulation of fluid in the abdominal cavity (dropsy).
  • Diabetes: The excessive excretion of urine, often containing an abnormally high amount of sugar.
  • Gout: A painful inflammatory condition of the joints, often affecting the big toe.
  • Madness (Insanity): A severe mental disorder characterized by disordered thoughts and behavior, and often accompanied by delusions and hallucinations.
  • Hemicrania: A painful condition affecting one side of the head, often around the eye and temple.
  • Pleurisy: An inflammation of the membrane lining the chest cavity.
  • Hepatitis: An inflammation of the liver.
  • Schirrosity: A hard, tumor-like growth, often in the liver or lymphatic glands.
  • Oxygenation: The process by which blood absorbs oxygen from the air or water.
  • Placenta: The organ that connects a fetus to the uterus, providing nourishment and oxygenation.
  • Liquor Amnii: The fluid that surrounds a fetus in the womb.
  • Meconium: The first feces of a newborn infant.
  • Appetency: A natural inclination or desire, particularly in reference to the selection of nutritious particles by the cells, glands, and absorbents.


  • The Sensitive Plant (Mimosa): This plant’s leaves contract when touched, demonstrating a form of vegetable irritability.
  • The Venus Flytrap (Dionæa muscipula): This plant traps insects with its spiny leaves, showcasing a more complex form of vegetable irritability.
  • The Electric Eel (Gymnotus electricus): This fish can generate a powerful electric shock, which acts as a stimulant to induce muscular contractions in prey.
  • The Electric Torpedo: This fish also possesses electric organs and uses them to stun its prey.
  • The Swallow: This bird migrates long distances, demonstrating a complex form of learned behavior and a well-developed sense of direction.
  • The Cuckoo: This bird deposits its eggs in the nests of other birds, a strategy for reproduction that requires a level of cunning and manipulation.
  • The Tailor Bird: This bird constructs its nest by sewing leaves together with fine fibers, illustrating an advanced level of problem-solving and tool use.
  • The Ant: This insect demonstrates complex social behavior, including the ability to care for its young and to transport its eggs to optimal environments.
  • The Wasp: This insect displays an impressive ability to construct its nest and to use its mandibles to manipulate its prey.
  • The Elephant: This intelligent animal exhibits a remarkable capacity for learning, using its trunk for various tasks and demonstrating a sense of empathy and protective instincts.
  • The Cat: This creature demonstrates a sense of self-care, washing its face and ears to keep its fur clean, and it uses its whiskers to sense the environment.
  • The Horse: This animal, despite often appearing docile, can be trained for a wide range of tasks and possesses a keen sense of hearing. It also displays a level of social interaction, as seen in the behavior of horses in a group.
  • The Crow: This intelligent bird demonstrates problem-solving abilities, such as using tools to access food, and it has a strong social structure that allows it to communicate and cooperate.
  • The Pelican: This bird collaborates with others to catch fish, demonstrating a complex form of social interaction and communication.
  • The Dormouse: This animal enters a state of hibernation during the winter, a survival strategy that requires a level of awareness and adaptation to the environment.
  • The Snake: This creature hibernates during the winter, highlighting the influence of external stimuli on animal behavior.
  • The Salmon: This fish migrates upstream to lay its eggs, illustrating a complex instinctual behavior.
  • The Spider: This creature constructs intricate webs to trap its prey, demonstrating a level of ingenuity and adaptation to its environment. It also displays a fascinating ability to feign death when threatened.
  • The Bee: This insect demonstrates a complex social structure, exhibiting remarkable communication and cooperative behaviors in the construction of its nest and the collection of honey.
  • The Gnat: This insect undergoes a significant transformation from a larval state in water to an aerial adult, illustrating the remarkable adaptability of some animal species.
  • The Tadpole: This creature changes from an aquatic creature with gills to a terrestrial creature with lungs, highlighting the evolutionary process of adaptation.
  • The Polypus: This animal reproduces by budding, highlighting the diversity of reproductive strategies in nature.


Erasmus Darwin’s “Zoonomia” is a fascinating and groundbreaking exploration of the principles governing animal life. The book, written decades before the rise of modern neuroscience, offers a detailed and insightful account of the various forms of animal motion, the workings of the senses, and the intricate interactions between the body and the mind. It explores the roles of stimuli, sensation, volition, and association in shaping behavior, and it offers intriguing theories on the origins of instinct, dreams, and even the evolution of animal species. While “Zoonomia” may not be a complete scientific treatise, it reflects Darwin’s keen observational abilities and his commitment to scientific inquiry. It serves as a testament to his pioneering spirit and his remarkable ability to anticipate some of the key principles that would later be advanced by his grandson, Charles Darwin.

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