How Did Ancient Greek Philosophers Imagine the Origin of Life on Earth?

The question of how life originated on Earth has fascinated humanity long before the advent of modern science. Ancient Greek thinkers were at the forefront of this search, being the first to attempt to explain the emergence of life without the intervention of supernatural forces. This transition from myth to logos laid the foundation for natural philosophy.

Ancient abiogenesis was not a single theory. In this practical guide, we will trace the evolution of the views of ancient scholars. We will begin with the Milesian school, where Thales of Miletus and Anaximander sought the material origin (arche)—water or the indefinite apeiron, capable of generating life. Then, we will examine the mechanistic approach of Democritus and, finally, analyze Aristotle's doctrine of the continuous self-generation of life from non-living matter. Understanding these concepts will allow you to see how the history of biology began and how humanity's first scientific hypotheses were formed.

Preparation: Mastering the Context of Natural Philosophy and the Concept of the Arche

To understand how the ancient Greeks conceived of the origin of life, it is necessary to undertake an intellectual journey into the era when European science itself was being born. Before dissecting specific hypotheses about the origin of living organisms, we must master the foundation upon which they were built. This foundation was natural philosophy—the speculative study of nature, freed from the dictates of religious dogma.

Within this intellectual revolution, two interconnected processes played a key role: the gradual replacement of mythological narratives with rational explanations of the world and the search for a single fundamental basis of all existence. Without understanding these basic concepts, it is impossible to assess the boldness and originality of the first biological conjectures of antiquity.

From Myth to Logos: How Ancient Thinkers Rejected Supernatural Creation

The transition from a mythological worldview to a rational one (from myth to logos) was a turning point in the history of human thought. Before the appearance of the first philosophers, the Greeks explained the origin of the world and living beings through theogony and the will of the Olympian gods. Life was considered the result of divine creation or the caprice of supernatural forces.

In the 7th–6th centuries BCE, early thinkers—natural philosophers—undertook an intellectual revolution. They rejected anthropomorphic gods in favor of seeking natural causes. Instead of mythical chaos and divine intervention, they proposed the concept of an ordered cosmos subject to objective laws of nature.

This shift manifested in the following key aspects:

• Demystification of Nature: Elemental phenomena and the genesis of organisms were no longer attributed to the will of the gods.
• Search for Natural Causes: The emergence of life began to be viewed as a physical, rather than a sacred, process.
• Rational Justification: Blind faith gave way to logical proof and observation of natural cycles.

Thus, early natural philosophy laid the foundation for the scientific understanding of biogenesis, replacing supernatural creation with the concept of matter's self-development.

The Concept of the Arche and Its Role in the Cosmogony of Early Philosophers

The concept of the arche is a key element without which the ancient view of biogenesis cannot be understood. For early natural philosophers, the arche (Greek: ἀρχή) did not merely mean the initial building material, but the eternal, living fundamental basis of all existence, capable of self-development. This idea is closely linked to hylozoism—the belief that all matter is inherently animated and contains the source of motion.

In the cosmogony of the Presocratics, the emergence of life from the arche occurred according to natural laws:

• Dynamics of Elements: Through condensation, rarefaction, or eternal motion, the single arche generated physical opposites (heat, cold, dryness, moisture).
• Natural Transition: Life arose at the intersection of these opposites as a systematic stage in the development of the cosmos.
• Self-Organization: The appearance of organisms was viewed as a physical process of the initial substance becoming more complex under the influence of external factors, such as sunlight or heat.

Thus, the concept of the arche laid the foundation for the first theories of spontaneous generation, linking the origin of life to global physical processes.

Step 1. Examining the Milesian School's Hypotheses on Watery and Moist Origins of Life

The transition from the abstract concept of the arche to specific natural elements began on the coast of Ionia. It was here, in Miletus, that philosophers of the 6th century BCE made the first attempts in European thought to explain the emergence of living beings without the intervention of the Olympian gods, relying solely on observation of nature.

The thinkers of the Milesian school paid attention to the fundamental role of moisture and heat in the processes of growth and decay. They hypothesized that life was not created from nothing, but naturally developed from a primary material substrate under the influence of physical processes. Let's examine how the first natural philosophers connected the genesis of organisms with the element of water and moist soil.

The Concept of Thales of Miletus: Water as the Source and Basis of All Life

Thales of Miletus (c. 624–547 BCE) entered history as the first European philosopher to make a revolutionary transition from mythological explanation of the world to a rational one. He defined water as the arche of all existence.

For Thales, water was not merely a chemical substance, but a living, dynamic element possessing internal activity. Observing nature, the philosopher concluded that:

• All food is moist;
• The seeds of all living things have a moist nature;
• The Earth itself rests on water, like a tree or a ship.

In the context of the origin of life, Thales's concept asserts that life arises directly from the moist environment naturally, without the intervention of the Olympian gods. Water, for Thales, is animated (hylozoism), making it capable of generating living organisms. This elemental materialism laid the foundation for subsequent ancient theories of abiogenesis, linking the origin of organisms to the physical properties of primary matter.

Anaximander and the Apeiron: Spontaneous Generation of Life in Swamps and Early Ideas of Human Evolution from Fish

Anaximander, a student of Thales, took the next step in abstracting the arche, proposing the concept of the apeiron (the boundless)—an indefinite and infinite substance from which opposites emerge: hot and cold, moist and dry. Their interaction initiates the process of cosmogenesis and biogenesis.

According to Anaximander, the first living organisms arose through spontaneous generation in moist mud or swampy soil under the influence of solar heat. He claimed that the first animals were covered with prickly scales or a moist covering. As the water bodies dried up, these creatures came onto land, adapting to the new conditions.

A special place in his natural philosophy is occupied by the hypothesis regarding the origin of man. Understanding that a human infant requires long-term care and could not survive independently in primitive conditions, Anaximander proposed that the first humans evolved inside giant fish-like creatures. Upon reaching maturity, they emerged onto land, shedding their scales. This speculative notion is considered the first idea in history of human evolutionary origin from aquatic ancestors.

Step 2. Examining the Materialistic Abiogenesis of the Atomists

By abandoning the principles of the Milesian school, ancient thought took a radical step toward systematic materialism. The animate water and the boundless apeiron were replaced by a strict mechanistic view of the world proposed by the atomists. Within this paradigm, the emergence of life ceased to be the result of divine will or the qualitative transformation of elements.

The atomist philosophers proposed a revolutionary view for their time: living organisms form exclusively through natural physical processes. The random collision of the smallest indivisible particles and their adhesion in the Earth's primary substrate gave rise to the first organic forms. Let us examine exactly how this concept unfolded in the works of key representatives of atomism.

Democritus's Theory: The Emergence of Living Beings from River Silt and the Combination of Atoms

Democritus of Abdera took a radical step forward by completely excluding divine intervention and animism from cosmogony. The basis of his concept of abiogenesis is strict atomistic materialism. According to Democritus, the entire world consists of indivisible particles—atoms—moving in a void.

The philosopher explained the process of life's genesis purely mechanically:

• Atom Adhesion: Under the influence of external conditions, atoms of different shapes (rough, hooked, smooth) collide and firmly connect with each other, forming complex structures.
• The Role of River Silt: Democritus asserted that the first living beings arose directly from sun-heated river silt and moist earth. Water and soil, under the influence of solar heat, began to "ferment," forming peculiar putrefactive bubbles within which organisms formed from the chaotic movement of atoms.
• Materiality of the Soul: Even the soul, Democritus considered material, consisting of the smallest, most mobile, round, and fiery atoms that penetrated bodies from the surrounding environment and set them in motion.

Thus, for Democritus, life is not a divine gift but a predictable result of the physical interaction of material particles under favorable environmental conditions.

Random Genesis Without Divine Design in Epicurus's Works

Epicurus developed Democritus's atomistic concept, adding a crucial element: the idea of the random deviation of atoms (clinamen). This allowed for the explanation of the emergence of the world and life without invoking divine providence or rigid mechanistic determinism.

According to Epicurus, atoms continuously fall in the infinite void. Thanks to spontaneous deviation, they collide, adhere, and form complex bodies. During the youth of the Earth, it possessed an excess of heat and moisture, functioning as a maternal womb. It literally "gave birth" to living beings from the soil, much like grasses and trees grow on it today.

The philosopher completely rejected teleology. Nature acts blindly and experimentally:

• First, various combinations of flesh arose, including non-viable monsters.
• Only those organisms that could protect themselves, find food, and reproduce survived.

This spontaneous evolutionary selection excluded the participation of gods in biogenesis, making the appearance of man a result of happy chance in physical interactions.

Step 3. Examining Aristotle's Theory of Continuous Spontaneous Generation

The transition from the chaotic collision of atoms in Democritus and Epicurus to the strictly ordered cosmos of Aristotle marked a new stage in ancient biology. The Stagirite rejected the idea of pure chance, proposing a systematic and teleological view of nature. In his philosophy, the emergence of the living is not a single historical act nor a game of blind chance, but a continuous, systematic process occurring right before our eyes.

Aristotle combined the empirical observations of his time with a deep metaphysical concept. He argued that life can spontaneously arise from non-living matter where suitable conditions are created. To understand exactly how the great philosopher explained this transition, we must examine his hierarchical view of the world and the unique mechanism of connecting the passive substrate with the formative principle.

Aristotle's Ladder of Nature: The Transition from Non-living Matter to Complex Organisms

Aristotle systematized the understanding of the living by proposing a concept known as the "Scala Naturae" (Ladder of Nature). According to his doctrine, all nature represents a continuous hierarchical scale ascending from simple to complex. The boundary between non-living matter and living organisms is not absolute for Aristotle—it is blurred and gradual.

The hierarchy of the "Ladder of Nature" is as follows:

1. Inorganic World (minerals and elements): Possess only potential being, lacking vital force.
2. Plants: Possess a "vegetative" soul, responsible for growth, nutrition, and reproduction.
3. Zoophytes (intermediate forms): For example, sponges and anemones, which link the plant world with the animal world.
4. Animals: Possess a "sensitive" soul, capable of sensation and movement.
5. Human: The apex of the terrestrial hierarchy, endowed with a "rational" soul.

In this system, spontaneous generation acts as a natural bridge between the steps. Non-living matter (silt, clay), gradually becoming more complex under the influence of heat, smoothly transitions into the simplest organisms, erasing the rigid boundary between the living and the non-living.

Interaction of Passive Matter and Active Form (Soul) as the Mechanism of Spontaneous Generation

When explaining the transition from non-living to living, Aristotle relies on his fundamental concept of hylomorphism—the doctrine of matter and form. Any natural object arises from the combination of a passive substrate and an active organizing principle.

In the process of spontaneous generation, these roles are distributed as follows:

• Passive Matter: Moist earth, silt, decaying flesh, moss, or sea sand. By themselves, they lack life and represent only the potential possibility for it to arise.
• Active Form (Soul): The formative force that orders the matter. Aristotle linked this to the vital psychic heat (pneuma) contained in the air, water, and sunlight.

When solar heat or air acts upon the moist environment, the hidden vital forces are activated. The active principle literally "imprints" form onto the passive substrate, endowing it with a vegetative or sensitive soul. This is how, in the philosopher's view, eels are born from silt, and insects from decaying matter.

Step 4. Systematizing the Knowledge Gained and Comparing Ancient Ideas with Science

Having studied the path from Thales' moist primordial substance to Aristotle's complex metaphysics, we have reached a key stage—the systematization of these doctrines. Ancient thought did not merely propose speculative scenarios for the origin of life; it laid the foundation for two fundamentally different approaches to knowing nature: elemental materialism and teleology.

Now, we must compare these concepts with each other and trace their surprising evolution on a global historical scale. We will see how the seemingly naive conjectures of ancient Greek natural philosophers anticipated modern scientific debates on abiogenesis and profoundly influenced the establishment of biological science.

Comparison of Pre-Socratic Elemental Materialism and Aristotle's Teleological Concept

By systematizing ancient views on biogenesis, we discover a fundamental rift between two key approaches: the elemental materialism of the Pre-Socratics (and the atomists allied with them) and Aristotle's teleological system.

For clarity, let's compare their key parameters:

Comparison Criterion	Elemental Materialism (Pre-Socratics, Atomists)	Aristotle's Teleology
Primary Driver of the Process	Chance, mechanical collision of atoms, or physicochemical properties of the elements (water, apeiron, mud).	Purpose (telos), the matter's striving to realize its internal form.
Role of Matter	Matter is active in itself; the primal substances (water, air) possess an inherent capacity to generate life.	Matter is passive. It is merely a substrate (potential) that is animated by an active form (soul).
Presence of Design	Complete absence of a divine or rational plan. Life is a byproduct of cosmogenesis.	Presence of immanent purposiveness. Every organism is rationally structured to perform its function.

The Pre-Socratics sought the answer to the question, “From what does life arise?”, reducing everything to physical primaries. Aristotle, however, shifted the focus to the question, “For what and how is it formed?”. His concept united the material substrate with the ideal formative principle, creating the basis for the systematic classification of living nature.

How Ancient Abiogenesis Influenced the Development of Medieval Science and Modern Biology

The legacy of ancient thinkers determined the vector of natural science development for two millennia, passing from blind faith in authorities to the rigorous scientific method.

• Medieval Scholasticism and the Reception of Aristotle. In the Middle Ages, Christian science fully assimilated Aristotle's teleology. The idea of spontaneous generation was not disputed but was reinterpreted: the “active form” (soul) animating passive matter came to be interpreted as a divine decree. Beliefs that insects arose from decay and mice from dampness remained generally accepted until the modern era.
• Experimental Refutation. The naive concept of abiogenesis was only overturned by the experiments of Francesco Redi (17th century) and Louis Pasteur (19th century), which proved the impossibility of the spontaneous generation of complex organisms under modern conditions.
• Return to Origins in Modern Biology. Paradoxically, the modern theory of biochemical evolution (the concept of the “primordial soup” by Oparin and Haldane) ideologically inherits from the early natural philosophers. The idea of the emergence of the first organic compounds in the ancient ocean resonates conceptually with Thales' moist primordial substance, Democritus' mud, and Anaximander's evolutionary conjectures.

Ancient philosophy laid the conceptual foundation upon which modern science continues to seek answers about the origin of life.

Conclusion

Summing up our historical and philosophical tour, it can be confidently asserted that Greek thought achieved a colossal intellectual breakthrough, moving the question of life's origin from the realm of religious myth into the domain of rational knowledge. It was in the works of ancient thinkers that the concepts that defined the trajectory of natural science for centuries originated.

To summarize the key ideas we examined, we highlight the main milestones of ancient protobiology:

• Miletian School (Thales, Anaximander): Laid the foundations of elemental materialism, linking the emergence of organisms to the moist environment and primal substances (arche), and also put forth the first conjectures about the evolutionary transition of living beings from water to land.
• Atomists (Democritus, Epicurus): Proposed a mechanistic model of abiogenesis, explaining the appearance of life as the random conjunction of atoms in primordial mud without divine intervention.
• Aristotle: Systematized accumulated knowledge within the concept of the “ladder of nature” and developed the theory of continuous spontaneous generation, based on the dualism of passive matter and active form (soul).

Studying these concepts is not merely paying homage to the past, but a key to understanding how the scientific method was formed. The ancient hypotheses of spontaneous generation of life, despite their empirical naivety, became the first theoretical models anticipating modern debates on chemical evolution and the origin of the organic world. By looking into the ideas of the ancient Greeks, we discover that the fundamental questions of biology and philosophy remain unchanged throughout the millennia.