The name of Charles Darwin and the theory of evolution are so closely linked that most people are unaware of the history of the theory “before” Darwin, and other evolutionary theories.
Fortunately, the history of science is far from dull. It is full of engaging characters, extraordinary insights (as well as accidents), stories of persistence, and academic infighting. The “story” behind a theory can be as exciting as a detective novel, especially when it involves a paradigm shift of great magnitude.
The possibility that a process of evolution could explain the diversity but similarity among species was not unique to Charles Darwin. The idea has a rich history beginning with Aristotle. However, for the purpose of this post, only the ideas within a century before the publication of the “Origin of Species” will be presented. Even this list is not exhaustive, but hopefully illuminating.
It is essential to recognize that an understanding of embryology and even earth history was in its infancy in the 18th and 19th century. Both fields of study had an impact on the prevailing ideas about the inheritance of traits. Even vague germs of genetic inheritance can be found at this time. The proposed mechanisms were incorrect, but the primary insights open a window onto the scientific thinking of that time.
Erasmus Darwin (1731-1802)
Erasmus Darwin was considered a leading intellectual in 18th century England, and no wonder. Not only was he a physician, naturalist, and botanist, he was a well-known poet and philosopher. In one of his master works, “Zoonomia” or “The Origins of Life,” he presented the idea that life evolved from “one living filament”—what one might now call a common ancestor. How did this occur? Erasmus does indeed invoke the “Greatest Cause” as the source for the impetus by which living matter diversifies, but he clearly wrestled with mechanisms to explain how. In his view, competition played a role, as did interactions with the environment, as proposed by Lamarck (see below), but his approach is now termed “integrative”:
“Erasmus Darwin… used his observations of domesticated animals, the behaviour of wildlife, and he integrated his vast knowledge of many different fields, such as paleontology, biogeography, systematics, embryology, and comparative anatomy.”
And yes, he was Charles Darwin’s grandfather.
John Hunter (1728-1793)
Seventy years before Charles Darwin published his “Origin of Species,” another naturalist, biologist, and “the father of scientific surgery,” John Hunter, proposed that species gradually evolved via mutations. Hunter collected and dissected hundreds of specimens. (Apparently, he is a somewhat controversial character because he often stole freshly buried cadavers to dissect them!) According to Dr. Kuhn in his article “Dissecting Darwinism”:
“[Hunter’s] considerable samples represented the entire initial display of the Royal College of Surgeons Museum. In two lengthy volumes, entitled Essays and Observations on Natural History, Anatomy, Physiology, Psychology, and Geology, he identified the remarkable similarity of muscles and organs between various species.”
Similarities of structures among species are referred to as “homologous” structures, an observation which played a key role in a debate in 1830.
The Paris Debate of 1830: Form and Function
In 1830 at the Academie des Sciences in Paris, a famous debate took place between two anatomists, Georges Cuvier and Geoffroy Saint-Hillaire, concerning the permanence of organic forms versus a progressive evolution based on the requirements of function. The difference of their opinions regarding the priority of form and function is explained in this essay.
Cuvier argued that there was an essential relationship among the functioning parts of an organism. This internal organization was key to an organism’s relationship with the environment. Because he believed there was a certain permanence to the forms found in nature, there was no rational mechanism by which one species could change into another.
Geoffroy on the other hand argued that Cuvier’s principles could not explain “homologous structures.”
For Geoffroy, these structural similarities revealed an “ideal pattern” which he believed was one of the universal laws of nature. In modern terms, this idea of repeating patterns and their independent appearance in various species and locations is referred to as convergence.
Jean-Baptiste Lamarck (1744-1829)
Jean-Baptiste Lamarck was a French naturalist who was perhaps the first to articulate a “coherent” theory of the evolution of species over time or “transformisme.” He stated that this change resulted from two forces: the force of increasing complexity and the force that “drives organisms to adapt to their environment.” This latter force operated through two natural laws:
- Through use and disuse, individuals gain or lose characteristics during their lifetime.
- Characteristics acquired during an individual’s lifetime are inherited from one generation to the next.
These two tenets are now known collectively as the “theory of the inheritance of acquired traits.” Somewhat fancifully, Lamarck believed that an organism’s interaction with the environment created a swelling in the organism that was passed on to subsequent generations. This inherited swelling contained the new trait which then could be “improved” by the next generation’s interactions with the environment.
Darwin’s Theory of Pangenesis
Darwin originally was not opposed to Lamarck’s tenet of use/disuse as a mechanism for evolution. According to this article by Dao Ho, Darwin had a hypothesis of his own:
“In support of Lamarck’s theory, Darwin proposed a supplementary hypothesis which he termed ‘Pangenesis’ in his book “Variation in Plants and Animals Under Domestication.” Darwin suggested that environmental cues can induce somatic cells to shed microscopic “gemmules” or “pangenes,” which circulate in the blood and eventually reach the gonads to accumulate in germ cells. The gemmules, in essence, are a mode of information transfer from somatic cells to germ cells, thus affecting the phenotype of the next generation.”
Without empirical evidence, the theory of pangenesis was rejected by most of the scientific community at the time. Eventually, Darwin ended up rejecting this theory himself. What is interesting is that in modern terms Darwin’s pangenes“are very reminiscent… of non–DNA-based modes of inheritance (i.e., prions, noncoding RNAs, and exosomes).”
Theories of Natural History
Two other scientists emerged in the 18th century who had an enormous impact on the study of natural history, in particular on the definition of species: Comte George Leclerc Buffon (1707-1788) and Carolus Linnaeus (1707-1778). Most of us are familiar with Linnaeus who is considered the father of taxonomy. He based his classification system on similarities of physical structures and methods of reproduction. These logical divisions resulted in the use of binomial nomenclature: naming organisms by genus and species. There could be many species in one genus.
Buffon’s reflections and method of inquiry lead to a dramatic redefinition of an organic species. He no longer saw “species” as an abstract concept or a “universal” as defined in Aristotelian and scholastic terms but as “the historical succession of ancestor and descendant linked by material connection through generation” (Stanford Encyclopedia).
The idea of species is still a contentious issue!
Additionally, George Cuvier (1769-1832) (mentioned above) and his expertise on the study of fossils and the findings of geologist Charles Lyell (1797-1875 ) form part of the scientific backstory of Darwin’s theory of evolution.
Evolutionary Theory Continues to Evolve
Evolutionary theory has a rich history which did not end with the publication of the “Origin of Species.” Whether it is the modern synthesis, punctuated equilibrium, or theories of convergence, new scientific and historical evidence needs to be integrated into a widening understanding of the processes of evolution. Some old ideas are being resurrected with new mechanisms to explain them. According to the philosopher, Thomas S. Kuhn, paradigm shifts such as created by the idea of evolution have always generated heated debates, strong resistance, and even accusations that new theories are ignoring “science”!
So it has been and always will be in the great human endeavor to understand the workings of the universe. Theories are proposed, discarded or confirmed, altered over time. What is needed is patience and an openness to new data. Let us remain confident in the ability of the rich western intellectual tradition to be a firm foundation for an expanded understanding of the universe.
Cover Image: Plate from Georges Cuvier’s “Le Règne Animal,” 1828 edition / Rvalette / CC BY-SA