History of evolutionary thought

From Wikipedia, the free encyclopedia

The Tree of Life as depicted by Ernst Haeckel in The Evolution of Man (1879) illustrates the 19th-century view that evolution was a progressive process leading towards man.

Evolutionary thought, the idea that species change over time, has roots in antiquity, in the ideas of the Greeks, Romans, Chinese and Muslims. However, until the 18th century, Western biological thinking was dominated by essentialism, the idea that living forms are unchanging. This started to change when, during the Enlightenment, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of paleontology with the concept of extinction further undermined the static view of nature. In the early 19th century, Jean-Baptiste Lamarck proposed his theory of the transmutation of species, which was the first fully formed scientific theory of evolution.

In 1858, Charles Darwin and Alfred Russel Wallace published a new evolutionary theory, which was explained in detail in Darwin's On the Origin of Species (1859). Unlike Lamarck, Darwin proposed common descent and a branching tree of life. The theory was based on the idea of natural selection, and it synthesized a broad range of evidence from animal husbandry, biogeography, geology, morphology, and embryology.

Darwin's work led to the rapid acceptance of evolution, but the mechanism he proposed, natural selection, was not widely accepted until the 1940s. Most biologists argued that other factors drove evolution, such as inheritance of acquired characteristics (neo-Lamarckism), an innate drive for change (orthogenesis), or sudden large mutations (saltationism). The synthesis of natural selection with Mendelian genetics during the 1920s and 1930s founded the new discipline of population genetics. Throughout the 1930s and 1940s, population genetics became integrated with other biological fields, resulting in a widely applicable theory of evolution that encompassed much of biology—the modern evolutionary synthesis.

Following the establishment of evolutionary biology, studies of mutation and variation in natural populations, combined with biogeography and systematics, led to sophisticated mathematical and causal models of evolution. Paleontology and comparative anatomy allowed more detailed reconstructions of the history of life. After the rise of molecular genetics in the 1950s, the field of molecular evolution developed, based on protein sequences and immunological tests, and later incorporating RNA and DNA studies. The gene-centered view of evolution rose to prominence in the 1960s, followed by the neutral theory of molecular evolution, sparking debates over adaptationism, the units of selection, and the relative importance of genetic drift versus natural selection. In the late 20th century, DNA sequencing led to molecular phylogenetics and the reorganization of the tree of life into the three-domain system. In addition, the newly recognized factors of symbiogenesis and horizontal gene transfer introduced yet more complexity into evolutionary history.

Adaptation
Genetic drift
Gene flow
Mutation
Natural selection
Speciation

Evidence
Evolutionary history of life
History
Modern synthesis
Social effect
Theory and fact
Objections / Controversy

Cladistics
Ecological genetics
Evolutionary development
Human evolution
Molecular evolution
Phylogenetics
Population genetics

Antiquity

Greeks

Greek philosophers discussed ideas that involved forms of organic evolution. Anaximander (c. 610–546 BC) claimed that life had originally developed in the sea and only later moved onto land, and Empedocles (c. 490–430 BC) wrote of a non-supernatural origin for living things.[1] Empedocles even suggested a form of natural selection, which Aristotle summarized as, "Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish..."[2]

Plato (c. 428–348 BC) was, in the words of biologist and historian Ernst Mayr, "the great antihero of evolutionism",[3] as he established the philosophy of essentialism, which he called the Theory of Forms. This theory holds that objects observed in the real world are only reflections of a limited number of essences (eide). Variation is merely the result of an imperfect reflection of these constant essences. In his Timaeus, Plato set forth the idea that the Demiurge had created the cosmos and everything in it because He is good, and hence, "... free from jealousy, He desired that all things should be as like Himself as they could be." the creator created all conceivable forms of life, since "... without them the universe will be incomplete, for it will not contain every kind of animal which it ought to contain, if it is to be perfect." This idea, that all potential forms of life are essential to a perfect creation, is called the plenitude principle, and it greatly influenced Christian thought.[4]

Aristotle (384–322 BC), one of the most influential of the Greek philosophers, is the earliest natural historian whose work has been preserved in any real detail. His writings on biology were the result of his research into natural history on and around the isle of Lesbos, and have survived in the form of four books, usually known by their Latin names, De anima (on the essence of life), Historia animalium (inquiries about animals), De generatione animalium (reproduction), and De partibus animalium (anatomy). Aristotle's works contain some remarkably astute observations and interpretations, along with sundry myths and mistakes—reflecting the uneven state of knowledge during his time.[5] However, for Charles Singer, "Nothing is more remarkable than [Aristotle's] efforts to [exhibit] the relationships of living things as a scala naturæ".[5] This scala naturæ, described in Historia animalium, classified organisms in relation to a hierarchical "Ladder of Life" or "Chain of Being", placing them according to complexity of structure and function, with organisms that showed greater vitality and ability to move described as "higher organisms".[4]

Chinese

Ideas on evolution were expressed by ancient Chinese thinkers such as Zhuangzi (Chuang Tzu), a Taoist philosopher who lived around the 4th century BC. According to Joseph Needham, Taoism explicitly denied the fixity of biological species and Taoist philosophers speculated that species had developed differing attributes in response to differing environments.[6] Humans, nature and the heavens were seen as existing in a state of "constant transformation" known as the Tao in contrast with the more static view of nature typical of Western thought.[7]

Romans

Titus Lucretius Carus (d. 50 BC), the Roman philosopher and atomist, wrote the poem On the Nature of Things (De rerum natura), which provides the best surviving explanation of the ideas of the Greek Epicurean philosophers. It describes the development of the cosmos, the Earth, living things, and human society through purely naturalistic mechanisms without any reference to supernatural involvement. On the Nature of things would influence the cosmological and evolutionary speculations of philosophers and scientists during and after the Renaissance.[8][9]

Middle Ages

Islamic philosophy and the struggle for existence

Whereas Greek and Roman evolutionary ideas died out in Europe after the fall of the Roman Empire, they were not lost to Islamic scientists and philosophers. In the Islamic Golden Age, early theories on evolution were taught in Islamic schools.[10] John William Draper, the 19th-century scientist, philosopher and historian, discussed the 12th-century writings of al-Khazini as part of what he called the "Mohammedan theory of evolution". He compared these early ideas to later biological theories, arguing that the former were developed "... much farther than we are disposed to do, extending them even to inorganic or mineral things."[10]