evolution theory history darwin lamarck mendel genetics

A Brief History of Evolutionary Thought - Part I

Evolutionary biology has come a long way since the Origin of Species was published in 1859. Today let’s discuss the history of evolutionary thinking, focusing on the earliest, and often surprising, roots of the science.

Today, I’ll be taking us back to the beginning of life science, and discussing the evolution of, well, the way we think about evolution. All science has philosophy at its roots, and evolutionary biology is certainly no exception. The field of biology can trace a path back to Plato and Aristotle, who both subscribed to the essentialist view. Essentialism says that for any specific entity there is a set of attributes which are necessary to its identity. For example, a chair has a set of attributes (legs, seat, back) that make it a chair rather than, say, a stool. Any given species also has a set of identifying attributes, and an individual can be classified as a member of that species if it satisfies that list.

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Figure 1. A chair has a set of attributes (legs, seat, back) that make it a chair rather than, say, a stool. But how does a chair compare to a throne? (Source: public domain)

Carl Linnaeus, the famous Swedish botanist, physician, and zoologist who formalized the modern system of naming organisms we know today as binomial nomenclature, epitomized the essentialist view of biology. He named and grouped organisms based on their similarities and differences – as any good essentialist would do. Linnaeus was, by all accounts, a religious man who believed that he could find a deeper understanding of God by studying his creation. Many naturalists of his day, and before, were similarly minded – religion was omnipresent, and most scientists of the time were religious.

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Figure 2. Carl Linnaeus formalized the modern system of naming organisms we know today as binomial nomenclature. Shown here is the cover page of Linnaeus’ magnum opus, published in 1735. (Source: public domain)

Over the next fifty years, naturalists began moving away from a strictly religious interpretation of their science. James Hutton and Charles Lyell dared to suggest that the Earth was older than the Bible might indicate. Georges Cuvier noticed that fossils of animals were found in locations that did not include extant populations of those animals, suggesting local extinctions were possible, contrary to the predominant religious beliefs of the time. By the late eighteenth century, the idea that life might not have been completely static since the beginning of creation had begun to percolate through the scientific community, though these ideas were mainly restricted to the fringes of academia and society.

Contrary to what you might think, Darwin was not the first to suggest a mechanism by which species could change over time. Jean Baptiste Lamarck argued in favor of evolution via the use and disuse of certain body parts. For example, a giraffe originally had a short neck, but over its lifetime of stretching in order to reach leaves on taller branches, its neck grew. The longer-necked giraffe would pass that change down to its offspring, who would then stretch that neck even further, and so on until we reach the long-necked giraffe seen today. However, his mechanism for evolution lacked plausibility; after all, people could certainly gain muscles through repeated use, but a very heavily muscled parent did not necessarily lead to a heavily muscled baby.

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Figure 3.Lamarckian evolution, as exemplified by a giraffe. (Source: public domain)

Another naturalist would shortly propose a more believable mechanism to explain changes in species over time. Charles Darwin, influenced by Thomas Malthus and by his own travels in South America and the Galapagos Islands, saw all life as a struggle for existence. He suggested that such a struggle led to a natural selection of organisms that were more “fit”, better able to survive and reproduce and thereby pass on those traits which made them well-suited for their environment. He believed that all living things are related. Over 150 years later, countless lines of evidence have verified Darwin’s crucial ideas – that all living creatures are related, that evolution is responsible for the differences between them, and that natural selection has a large role in shaping evolution. Of course, how those traits were passed on was still very much a mystery to Darwin, but that mechanism too would soon be elucidated.

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Figure 4.The first known drawing of a phylogenetic tree, a diagram describing the relatedness of organisms. (Source: public domain)

Gregor Mendel, a German monk, would posthumously become known as the father of modern genetics. His simple research growing pea plants would go on to establish foundational principles in the field of inheritance. For example, he found that by crossing a pure-bred green pea plant to a pure-bred yellow plant, all of the offspring would be yellow; however, if he allowed those offspring to self-fertilize, approximately 3/4s of the next generation would be yellow, but some would be green. He proposed that each offspring plant inherited a copy of the color gene from each of its parents and believed that the green copy was masked by the yellow. He was operating at the same time as Darwin, yet there is no substantial proof that Darwin would have heard of Mendel or his work before Darwin died in 1882. And yet, Mendel’s research provided the very mechanism by which traits were passed on that was missing in Darwin’s theory of evolution, and it would go largely unnoticed until the early twentieth century.

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Figure 5. An example of Mendel’s experiments with genetics. (Source: The Tech Museum of Innovation).

The marriage of Mendelian genetics with Darwinian evolution early in the twentieth century has proven to be incredibly fruitful. This Modern Synthesis of biology, and the steps we’ve made since then, will form the basis of my next post. Until then, I hope you’ve enjoyed this brief walk through evolutionary history!

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