Life is the result of a special combination of atoms characterized by their constant mechanical movement. ~ Democritus
4th-century-bce Greek rationalist philosopher Democritus was a strict determinist and a matterist: believing that everything accorded with natural laws. Chance had no chance.
Democritus thought that life was maintained by the inhalation of fresh atoms, replacing those lost by exhalation. When respiration ceases, atomic recycling stops. The result: death.
Further, Democritus believed that humans, and humans alone, had a noble portion: the soul, pervading the body via psychic atoms. The soul, while distinct from the body, was material, and perished when the body died.
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Historically, there have been 3 schools of thought on what makes life special: matterism, hylomorphism, and vitalism. Another school, animism, discounts life as extraordinary.
Animism considers all objects and bodies, animate or otherwise, spiritually imbued; there is no meaningful separation between the material and metaphysical. Any perceptible entity possesses a spirit, including rocks, mountains, and rivers. Animism is not especially concerned with defining life, as all of Nature is holy.
Variants of animism form the core of various religions, including Hinduism, Buddhism, Shinto, Jainism, and other belief systems labeled pantheistic, where reality is identical with divinity. English anthropologist Edward Tylor called animism “one of anthropology’s earliest concepts, if not the first.”
Matterism, embraced by Democritus and revived by French philosopher René Descartes in the 17th century, makes life out to be a complex arrangement of materiality. To Descartes, soul was a matter of matter.
Aristotle, the ancient Greek master abstractor, concocted hylomorphism: that all things are a combination of matter and form. The form of life is in the soul.
Aristotle posited 3 kinds of souls: vegetative soul for plants, which could not move or experience sensation; animal soul, where moving and feeling are part of the package; and rational soul, found only in humans.
Aristotle believed the relationship between matter and soul is asymmetrical: matter can exist without form, but form cannot exist without matter. Therefore, the soul cannot exist without the body. Aristotle believed that purpose was the final cause of life.
Vitalism posits that living organisms possess a fundamental ingredient which distinguishes them from inanimate matter. The missing element is the spark of life, often equated with a soul.
The idea of vitalism is prehistoric. Ancient Egyptians wrote of vitalism. In the 3rd century, Greek anatomist Galen of Pergamon, the most accomplished medical researcher of antiquity, held that vital spirits were necessary for life.
In embracing the concept of souls for at least some life, vitalism underlies monotheist Western religions. Man’s dominion over the Earth is granted by The Bible. To merit this grant, Christian theologists quixotically posited the superiority of man as being sole possessor of a soul (women ever being an adjunctive afterthought). The revival of Aristotelian thought in the 12th century abetted the effort.
As science ushered in stricter empiricism during the Age of Enlightenment, vitalism lost its vitality. The spark of life was lost – replaced by faith in reductionist chemistry, wherein life was merely a peculiar molecular combination in a grand cosmic machine.
There is no special force exclusively the property of living matter which may be called a vital force. ~ Jöns Jacob Berzelius in 1836
Not all were convinced.
18th-century French physiologist Xavier Bichat is remembered as the father of modern histology and pathology. Working without a microscope, his insights are especially remarkable. Bichat introduced the notion of tissues, and maintained that diseases attacked tissues, not whole organs. Bichat also believed that life held “vital properties” beyond its material constituents.
The organizing principle, which, according to an eternal law, creates the different essential organs of the body, and animates them, is not itself seated in one particular organ. ~ Johannes Peter Müller
German physiologist Johannes Peter Müller penned his magnum opus – Elements of Physiology – between 1833 and 1840. For the first time, Müller exposited an integration of chemistry, microscopic investigation, and comparative anatomy as approaches for studying physiology.
An important facet of Müller’s study was how the senses work and are employed. Müller’s detailed explanations had an overarching theme: the presence of a soul renders each organism vibrantly whole. He claimed that the perception of sound and light waves demonstrated that living organisms held a life-energy for which physical laws could never fully account.
Following in Müller’s footsteps, 19th-century French chemist and microbiologist Louis Pasteur believed that living organisms possessed “irreducibly vital phenomena.”
One fact about vitalism is irrefutable: empirical science has no explanation for how life is even possible.