Biology: Concepts of Heredity and Change Prior to the Rise of Evolutionary Theory
Biology: Concepts of Heredity and Change Prior to the Rise of Evolutionary Theory
Various concepts of heredity and change among living things predate Charles Darwin's Origin of Species (1859). Indeed, Charles Darwin (1809–1882) was not the first to propose the idea of evolution, and concepts of inherited characteristics predated the work of Gregor Mendel (1822–1884). In the fifth and sixth centuries BC, ancient Greek philosophers, called the pre-Socratics, first postulated the idea of the transmutation of species. Aristotle (384–322 BC) subsequently rejected his predecessors' ideas in favor of a “chain of being” in which species were fixed and immutable, a view later adopted by the early Christian Church. In the eighteenth century, thinkers of the Enlightenment revisited the idea of transmutation. The first paleontologists, such as Baron Georges Cuvier (1769–1832), as well as geologists like Charles Lyell (1797–1875) and biologists like Jean-Baptiste Lamarck (1744–1829) gathered anatomical and fossil evidence that suggested species had become extinct in the past and did evolve. Charles Darwin's own grandfather, Erasmus Darwin (1731–1802), also helped develop the first comprehensive theories of transmutation.
Historical Background and Scientific Foundations
In the sixth century BC, a group of philosophers arose in the town of Miletus in Greece. The pre-Socratics—extant before the philosopher Socrates (c.470–399 BC)—were the first thinkers to postulate that events in the natural world, such as weather and the creation of species, were due to processes in nature, not to divine intervention.
One of the first questions they tackled was the nature of change—what was the process of the transmutation of matter and living creatures? Thales (c.624–546 BC), proposed that Earth was created from water, much as dirt silts on river deltas, and that the solid, liquid, and gaseous states of water accounted for the diversity of matter that he saw around him. His disciple Anaximander (c.610–546 BC) also thought that Earth existed first in a fluid state, and he proposed that gradually out of the water's depths dried, fishlike humans formed, developing to the point at which they could live on land. He also suggested the view that humans originated from animals of another sort, positing that if they had come into existence as human beings needing fostering care for a long time, they would not have been able to maintain their existence. His colleague Xenophanes (c. sixth to fifth centuries BC) was the first to realize that fossils were the remains of ancient organisms.
Other pre-Socratics, such as Empedocles (c.495–c.435 BC) believed that change was the result of the interaction of four elements: fire, water, earth, and air. The forces of love and hate acted upon these elements. The contact between forces and elements, after a long series of trial and error interactions, led to the first plants; thus, they were spontaneously generated from inert matter. Plants eventually gave rise to animal life, and Empedocles believed some combinations of animal parts produced more viable creatures. The unworkable combinations produced animals that soon went extinct.
Aristotle, on the other hand, rejected the views of the pre-Socratics completely. He was influenced by his teacher Plato (c.427–c.347 BC), who held that living species were merely imperfect copies of an ideal type. He thought that ideal types existed outside of the material world as blueprints for life. Since the ideal types did not change, Plato asserted that living species could not vary too significantly. Aristotle thus examined the natural world for evidence of a divine order, devising a hierarchical arrangement of natural forms, termed the Chain of Being. In the Chain of Being, species were arranged in a linear fashion along a scale: God, man, mammals, egg-laying animals, insects, plants, and nonliving matter. His ideas formed the basis for the Western concept of a fixity of species, each of which has a typical form, and his ideas were widely spread by students in his school in Athens, the Lyceum, the world's first known university.
Aristotle's taxonomy within the Chain of Being also survived because of the empirical accuracy of his meticulous observations. He studied more than 500 animal species, dissecting many of them and publishing his results in his Generation of Animals and Investigation of Animals. He achieved his systematic and detailed results by making use of the science of logic, a discipline of study that he founded.
The Middle Ages and Renaissance
Aristotle's thoughts about the fixity of species survived into the Middle Ages, and his scientific investigations were incorporated into Christian theology by St. Thomas Aquinas (c.1225–1274) in his Summa Theologica. Aquinas, a theologian who taught at the University of Paris, was particularly struck with the intellectual power of Aristotle's logical argument, thinking it was possible to use it to understand God. Aristotle had written about the Prime Mover, who was behind all motion and change in the universe, and Aquinas thought the Prime Mover was a veiled reference to the Christian God. Aristotle's belief in the fixity of species also was favorable to the Christian belief that the universe was stable, ordered, and created by divinity. The sheer bulk of lectures in logic, biology, physics, meteorology, and other subjects that survived from Aristotle's Lyceum also meant that Aristotelian thought became the basis of the curriculum at medieval universities in Europe.
Therefore, the Chain of Being was still the dominant theory used to describe the natural world in the Middle Ages. Biological studies largely were studies of the characteristics of flora and fauna thought to be parts of fixed species. Bestiaries included detailed descriptions of real and legendary animals intermixed with their literary and heraldic symbolism, and medieval herbals described the medicinal purposes of plants.
With the advent of the Protestant Reformation in the sixteenth century, there came a new emphasis on the wording of the Bible and a new form of natural history based on scripture. In his Annals of the World, published from 1650 to 1654, Anglo-Irish biblical scholar James Ussher (1581–1656) carefully examined the Bible for clues to indicate when Earth was created. In his scriptural chronology, he claimed every species of organism had been created at 9:00 a.m. on Sunday, October 23, 4004 BC, whereupon they had remained permanently unaltered.
The sixteenth and seventeenth centuries not only saw the influence of Protestantism, but the origins of modern science. The first scientific society in the world, The Royal Society, was founded in the 1660s, and Galileo, Newton, and Kepler made great discoveries in astronomy and physics. The twin influences of this scientific revolution and Protestantism gave rise to natural theology. Natural theologians like seventeenth-century Englishman John Ray (1627–1705) thought that the power of God could be shown by studying the material universe; the existence of laws of physics and the precise adaptation of species to their environments seemed to indicate a divine intelligence. Natural theologians postulated that natural processes could not produce such a complex and dynamic system. Because John Ray thought that species were created according to orderly patterns,
he designed a new taxonomy that classified species solely on the basis of their comparative anatomy, moving away from the medieval bestiary tradition. Ray's work influenced the modern system of taxonomy and binomial nomenclature created by Carl Linnaeus (1707–1778; also known as Carolus Linnaeus or Carl Linné) in the eighteenth century. Natural Theology also continued to have adherents such as English theologian William Paley (1743–1805) until the mid-nineteenth century.
The eighteenth century was regarded by some as an Age of Enlightenment in which rational discourse would replace human superstition. Many seventeenth-century Enlightenment thinkers, called philosophes, questioned religion, asserting that it was irrational and harmful to human development. Their move away from biblical creation stories led to other alternative theories, such as those proposed by thinkers like Georges LeClerc, Comte de Buffon (1707–1788).
Buffon was an aristocrat, naturalist, and keeper of the King's Garden in France. This appointment allowed Buffon free time to write his 44-volume encyclopedia Historie Naturalle (Natural History), as well as Les Epoques de la Nature (The Ages of Nature), published in 1788, in which he posited that Earth was much older than 6,000 years. Buffon claimed the environment acted directly on organisms through what he called organic particles, which were the result of heat on aqueous, oily substances. In the 1740s, the work of John Needham (1713–1781) seemed to demonstrate that microorganisms could spontaneously appear in flasks of broth. (This experiment was later disproved by Lazzaro Spallanzani [1729–1799], who repeated the experiment with sealed flasks in which no microorganisms spontaneously appeared). Buffon strongly supported the idea of spontaneous generation, postulating natural forces created the first living things without God being necessary.
Buffon also stated that it would be impossible for humans to understand a plan of creation, even if one existed, as the mind of God was inscrutable and relatively unconcerned with human affairs. Nonetheless, Buffon theorized that new species on Earth spontaneously generated in two major episodes. He asserted that the first episode occurred when Earth's climate was much hotter. These early species eventually died out, Earth's climate cooled, and then a second episode of spontaneous generation occurred. Buffon thought that all species living during his time emerged during this second episode.
Buffon's theories of species adaptation were echoed in the Zoonomia, Or, The Laws of Organic Life, published from 1794 to 1796, of English physician and poet Erasmus Darwin. Erasmus Darwin proposed the self-improvement of a species, through a constant effort to adapt to the environment (transformism or transmutation). He argued that life consisted of “one living filament”, connecting all current forms to one common ancestor, writing about his theory in a poem, “The Temple of Nature” (1802):
Organic life beneath the shoreless waves
Was born and nurs'd in ocean's pearly caves;
First forms minute, unseen by spheric glass,
Move on the mud, or pierce the watery mass;
These, as successive generations bloom,
New powers acquire and larger limbs assume;
Whence countless groups of vegetation spring,
And breathing realms of fin and feet and wing.
Similar ideas were developed more extensively, if less poetically, by the French zoologist and botanist Jean-Baptiste Lamarck. Lamarck proposed the theory of the inheritance of acquired characteristics, in which organisms passed down bodily characteristics they had acquired while adapting to their environments. For instance, in this model, the giraffe's long neck is a product of thousands of generations of animals stretching up to meet the leaves of trees. Before the work of Mendel and the discovery of genes, Lamarck's ideas influenced many nineteenth-century biologists, including Charles Darwin.
Geological Theories: Cuvier and Lyell
Geological discoveries in the eighteenth century also seemed to challenge ideas about the fixity of species. By studying fossil evidence, Baron Georges Cuvier (1769–1832), a state councilor under three successive kings of France and the first vertebrate paleontologist, realized that species must go extinct. His claim was a challenge to the received idea that fossilized organisms must still survive in parts of the world that were unexplored, and that they were the remains of living species. For instance, mammoth bones were thought to be remains of elephants. Via detailed studies of elephant anatomy, Cuvier demonstrated that fossil mammoths of Europe and Siberia were different than living species.
Cuvier also proposed the theory of catastrophism after studying geological strata, which seemed to reveal vast upheavals in the past. Cuvier theorized that only catastrophic events changed the geologic structure of Earth and caused species extinction, a theory he called catastrophism. As he stated, “Why has not anyone seen that fossils alone gave birth to a theory about the formation of the earth, that without them, no one would have ever dreamed that there were successive epochs in the formation of the globe?” (Discourse on the Revolutions of the Surface of the Globe).
In the early nineteenth century, Charles Lyell published his Principles of Geology (1830–1833). It was an assault on the catastrophism of Cuvier, proposing that changes within the Earth are direct causes of uniform events. Lyell stated that most changes in the physical world were the result of gradual and ordinary geological processes, like erosion, that can be observed today. In order to allow for this gradual change, Lyell theorized that Earth must be very old, and the increased age of the earth further opened the way for the evolutionary point of view, later providing a gift of time for Charles Darwin's principles of natural selection.
Modern Cultural Connections
When Charles Darwin commenced his trip on the H.M.S. Beagle (1831–1836), a trip that provided much of the data for his Origin of Species, he carried two books with him—John Milton's fictional Paradise Lost and Charles Lyell's Principles of Geology. Milton's work was a poetic hymn to the biblical story of Genesis and the expulsion from paradise, and Lyell's work questioned biblical stories of creation. At the beginning of his scientific career, Darwin was thus literally between two world-views, one of natural theology and one of transmutation. It was left to him to use his empirical observations of species in the Galápagos Islands and Central and South America to make his transition to the revolution of the evolutionary world.
See Also Biology: Cell Biology; Biology: Comparative Morphology: Studies of Structure and Function; Biology: Developmental Biology; Biology: Evolutionary Theory; Biology: Genetics; Biology: Genetics, DNA, and the Genetic Code; Biology: Ontogeny and Phylogeny; Biology: Paleontology; Biology: Sociobiology.
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Anna Marie Eleanor Roos