Scott Turner Describes the Largely Forgotten History of Evolutionary Theory
In my previous articles, I outlined the first three videos in Scott Turner’s online course on evolution. They provide an overview of the course and lay the philosophical foundations (here, here). Today I will outline the lessons on the historical development of evolutionary theory, a history that has been largely forgotten.
Turner begins by describing the evolutionary theories that preceded Darwin. Those who followed in the traditions of Plato and Aristotle (see my previous article) held that life was fundamentally distinct from nonlife. In contrast, those in the atomist tradition (modern scientific materialism) believed that life was not distinct from nonlife. It was simply another configuration of atoms, so it could be reduced to physical mechanisms. Those who held to the former view are termed vitalists. The form of vitalism popular in the 18th century was known as metaphysical vitalism. Its proponents postulated that intangible forces imparted life to matter and directed organisms’ actions.
The most famous metaphysical vitalist was Jean-Baptiste Lamarck (1744-1829). He coined the term “biology,” and he distinguished the study of life as a distinct discipline. He also proposed the first coherent theory of evolution. He connected the then postulated vitalist force that drove the increasing complexity of an embryo developing into an adult with the force driving the evolution of organisms toward increasing complexity, such as a worm evolving into an insect.
He also connected the postulated force directing an organism to adapt to its surroundings, such as a rabbit’s fur turning white during the winter, with the force driving the evolution of an organism toward a new form that was best adapted to its environment. This “adaptive force” would cause characters such as a giraffe’s neck to grow longer, stronger, and stouter. Altered characters would be inherited in the next generation. After several generations, the continuous accumulation of changes could potentially lead to significant evolutionary modifications.
The fatal flaw with metaphysical vitalism was that it invariably led to circular reasoning. Any process in life could be explained by a vital force that drove that process. But the only evidence for such forces were the processes the forces were invoked to explain. This tautology led to metaphysical vitalism’s eventual demise.
Another form of vitalism, not afflicted by circular reasoning, was known as process vitalism. Process vitalism was pioneered by medical professor Theophile de Bordeu (1722-1776). He studied how honey bees coordinated their behavior to form a swarm. He reasoned that the persistence of the individual bee lives depended on the persistence of the swarm, and the persistence of the swarm resulted from each bee engaging in ongoing negotiations and mutual accommodations with the other bees. These actions were directed toward the end goal of preserving the swarm, and by extension the individual lives. The swarm was a kind of organism where its qualities arise through the activities of negotiation and mutual accommodation of all for the whole. This same process was believed to occur in actual organisms in order to drive environmental adaptation.
Since the process directs organisms toward an end goal, it was inherently teleological. Turner argues that process vitalism and its underlying teleology is the foundation for most of 19th-century biology. This claim is supported by geneticist J. B. S. Haldane (1892-1964) who famously stated, “Teleology is like a mistress to the biologist; he dare not be seen with her in public but cannot live without her.”
One of the most prominent process vitalists was the zoologist Georges Cuvier (1769-1832) who founded vertebrate paleontology and comparative anatomy. He mapped the sedimentary layers of the Paris Basin to pioneer the field of stratigraphy, and he first identified the different geological eras according to the species that inhabited them. He developed a model of evolution based on process vitalism.
He organized animals into four large categories that corresponded to four major body types:
- Vertebrata: mammals, birds, reptiles, amphibians, and fishes
- Articulata: insects and crustaceans
- Mollusca: snails, clams, and shelled creatures
- Radiata: echinoderms, coelenterates, and sea anemones
He regarded his categories as distinct logical types. He rejected Lamarck’s view that life gradually increased in complexity over time. Instead, he argued that it changed in discrete “catastrophes” where organisms changed dramatically in geological instances. Paleontologists came to some of the same conclusions in the 20th century in what is termed the theory of punctuated equilibrium.
Cuvier integrated process vitalism into his evolutionary theory by arguing that an organism had to function well through its parts existing in particular relationships with the other parts. Each organism met its own “conditions of existence” through its parts interrelating in different ways. For instance, an herbivore possessed a set of teeth that functioned together properly to eat plants. No organism would ever acquire half herbivore and half carnivore teeth since such an organism would not be viable.
He supported his theory through his pioneering work in quantitative anatomy. He integrated the qualitative description of an animal with quantitative measurements of the relative sizes of its bones. He called the quantitative relationships the correlation of parts. He noticed that the correlation of parts for a given type of animal was different from those of other animal types. The bone ratios were always optimized to meet an organism’s needs.
Cuvier integrated his observations from the fossil record with the correlation of parts in his theory of evolution. He maintained that animals did not significantly change until some catastrophic event dramatically altered the environment and thus disrupted the conditions of existence. Geologists eventually discovered clear evidence of such catastrophes, such as the asteroid impact that possibly led to the extinction of the dinosaurs. In response, an animal’s parts would reorganize around the new conditions of existence resulting in a sudden, often dramatic transformation. The animal would then remain largely the same until some new catastrophe.
Scott Turner sees his evolutionary theory as continuing in the tradition of process vitalism. And he, like Lamarck, connects the process of an organism adapting to its environment during its lifetime with evolutionary adaptation in a lineage. Both types of adaptation are directed by an organism’s cognition.
The Roots of Darwin’s Theory
Turner also describes the various influences and circumstances that both shaped Charles Darwin’s thinking about evolution and enabled his theory’s rise to dominance. Those influences include his grandfathers’ evolutionary views, the Scottish enlightenment, the industrial revolution, and the political upheavals brought by the French Revolution. Turner also narrates the observations and interactions that forged Darwin’s theory of natural selection. Included are Darwin’s interactions with Alfred Russel Wallace who is credited as co-discovering the theory and the influence of economist and demographer Thomas Malthus. Throughout the discussion, Turner foreshadows the looming crisis that Darwin’s theory would soon face.
Scott Turner welcomes any feedback to his course. His contact information and publications can be found at his website.