Although there have been many different scientific traditions throughout world history, a new global discourse around science emerged in Western Europe in the 19th century. Europeans pointed to the continuing expansion of their colonial power, as well as their military and technological success, as evidence of the efficacy of Western science, which came to dominate on a global scale (Elshakry 2010). The movement toward a global science centered in Western Europe began with formulation of the Scientific Method.
The Scientific Method was first codified by Francis Bacon (1561–1626), an English politician who was likely influenced by the methods of inquiry established by Ibn al-Haytham centuries prior (Tbakhi and Amr 2007). Bacon has been called the founder of empiricism for proposing a system for weighing the truthfulness of knowledge based solely on inductive reasoning and careful observations of natural phenomena. Ironically, he died as a result of trying to scientifically observe the effects of cold on the putrefaction of meat. On a journey out of London, he purchased a chicken and stuffed it with snow for observation, catching a chill in the process. One week later, he died of bronchitis (Urbach, Quinton, and Lea 2023).
The second important development with regard to evolution was the concept of a species. John Ray (1627–1705), an English parson and naturalist, was the first person to publish a biological definition of species in his Historia Plantarum (History of Plants), a three volume work published in 1686, 1688, and 1704. Ray defined a species as a group of morphologically similar organisms arising from a common ancestor. However, we now define a species as a group of similar organisms capable of producing fertile offspring. In keeping with the scientific method, Ray classified plants according to similarities and differences that emerged from observation. He claimed that any seed from the same plant was the same species, even if it had slightly different traits.
The modern period of biological classification began with the work of Carl von Linne (“Carolus Linnaeus”) (1707–1778), a Swedish scientist who laid the foundations for the modern scheme of taxonomy used today. He established the system of binomial nomenclature, in which a species of animal or plant receives a name consisting of two terms: the first term identifies the genus to which it belongs and the second term identifies the species. His original SystemaNaturae, published in 1736, went through several editions. By the tenth edition in 1758, mammals incorporated primates, including apes and humans, and the term Homo sapiens was introduced to signify the latter (Paterlini 2007).
Georges-Louis Leclerc, Comte de Buffon (1707–1788), was a prominent French naturalist whose work influenced prominent scientists in the second half of the 18th century. Buffon’s idea that species change over time became a cornerstone of modern evolutionary theory. His technique of comparing similar structures across different species, called comparative anatomy, is still in use today in the study of evolution. He published 36 volumes of HistoireNaturelle during his lifetime and heavily influenced two prominent French thinkers who were to have significant impacts on our understanding of evolution, Georges Cuvier and Jean-Baptiste Lamarck.
Georges Cuvier (1769–1832) was a paleontologist and comparative anatomist (Figure 2.6). One of his first major contributions to the field of evolution was proof that some species had become extinct through detailed and comprehensive analyses of large fossil quadrupeds (Moore 1993, 111). The idea of extinction was not new, but it was challenging to demonstrate if a fossil species was truly extinct or still had living relatives elsewhere. It was also challenging in that it ran counter to religious beliefs of the time. The Bible’s Book of Genesis was interpreted as saying that all species had been created by God in the seven days it took to create the world and that all created species have survived to this day. Extinction was interpreted as implying imperfection, suggesting God’s work was flawed. Also, given that the Earth was calculated to have been created in 4004 B.C.E., based on biblical genealogies, there would not have been enough time for species to disappear (Moore 1993, 112).
Cuvier was so knowledgeable in this field that he became famous for his ability to reconstruct what an extinct animal looked like from fragmentary remains. He demonstrated that fossil mammoths differed from similar living creatures, such as elephants. His many examples of fossils telling the stories of animals that lived and then disappeared were taken as incontrovertible proof of extinctions (PBS 2001). Where Cuvier went awry was his hypothesis of how extinction worked and its causes. As part of his study of comparative anatomy, Cuvier made observations of stratified layers of rock, or sediment, each containing different species. From this, he drew conclusions that species were “fixed” and did not evolve, but then went extinct, and that different assemblages of fossils occurred at different times in the past, as evidenced by the sedimentary layers (Moore 1993, 118). Cuvier explained this through a theory of catastrophism, which stated that successive catastrophic deluges (akin to Biblical floods) swept over parts of the Earth periodically, exterminating all life. When the waters receded from a particular region, lifeforms from unaffected regions would repopulate the areas that were destroyed, giving rise to a new layer of species that looked different from the layer below it. This theory implied that species were fixed in place and did not evolve and that the Earth was young. In fact, Cuvier postulated that the last catastrophe was a deluge he believed occurred five to six thousand years ago, paving the way for the advent of humans (Moore 1993, 118). Cuvier’s catastrophism became part of an ongoing and vociferous debate between two schools of geology. The catastrophists believed the present state of the earth was the consequence of a series of violent catastrophes of short duration, while the uniformitarians thought it was the result of slow acting geological forces that continue to shape the earth.
James Hutton (1726–1797) was one prominent proponent of uniformitarianism. Based on evidence he found at sites in his native Scotland, Hutton argued that the Earth was much older than previously thought. Examining the geology of Siccar Point, a cliff site on the eastern coast of Scotland (Figure 2.7), Hutton concluded that the intersection of the vertical and horizontal rocks represented a gap in time of many millions of years, during which the lower rocks had been deformed and eroded before the upper layers were deposited on top. From this, Hutton argued sediments are deposited primarily in the oceans, where they become strata, or layers of sedimentary rock. Volcanic action uplifts these strata to form mountains, which are then subject to erosion from rain, rivers, and wind, returning sediment to the oceans (Moore 1993, 121). Hutton’s Theory of the Earth (1788) demanded vast periods of time (known as “deep time”) for such slow-working forces to shape the earth. At the time, he was heavily criticized for this view, as it contradicted the biblical version of the history of creation.
Another Scotsman, who was to become a highly influential geologist and a close friend of Darwin, was Charles Lyell (1797–1875). Lyell was originally a lawyer who began his studies of Geology at Oxford under the tutelage of catastrophist William Buckland, from whom he diverged when Buckland tried to find physical evidence of Noah’s flood from the Christian Bible. Lyell was instead intent on establishing geology as a science based on observation. Building upon Hutton’s ideas (published 50 years earlier), Lyell traveled throughout Europe, documenting evidence of uniformitarianism. During his travels, he cataloged evidence of sea level rise and fall and of volcanoes positioned atop much older rocks. He also found evidence of valleys formed through erosion, mountains resulting from earthquakes, and volcanic eruptions that had been witnessed or documented in the past (University of California Berkeley Museum of Paleontology n.d.). Lyell also espoused the principle that “rocks and strata (layers of rock) increase in age the further down they are in a geological sequence. Barring obvious upheavals or other evidence of disturbance, the same principle must apply to any fossils contained within the rock. The lower down in a sequence of rocks a fossil is, the older it is likely to be (Wood 2005, 12).”
Lyell published the first edition of his three-volume Principles of Geology in 1830–1833 (Figure 2.8). It established geology as a science, underwent constant revisions as new scientific evidence was discovered, and was published in 12 editions during Lyell’s lifetime. In it, he espoused the key concept of uniformitarianism—that “the present is the key to the past.” What this meant was that geological remains from the distant past can be explained by reference to geological processes now in operation and directly observable.
Jean-Baptiste Lamarck (1744–1829) was the first Western scientist to propose a mechanism explaining why and how traits changed in species over time, as well as to recognize the importance of the physical environment in acting on and shaping physical characteristics. Lamarck’s view of how and why species changed through time, known as the “Theory of Inheritance of Acquired Characteristics,” was first presented in the introductory lecture to students in his invertebrate zoology class at the Museum of Natural History in Paris in 1802 (Burkhardt 2013). It was based on the idea that as animals adapted to their environments through the use and disuse of characteristics, their adaptations were passed on to their offspring through reproduction (Figure 2.9). Lamarck was right about the environment having an influence on characteristics of species, as well as about variations being passed on through reproduction. He simply had the mechanism wrong.
Lamarck’s theory involved a three-step process. Step one involves an animal experiencing a radical change in its environment. Step two is the animal (either individual or species) responding with a new kind of behavior. Step three is how the behavioral change results in morphological (meaning physical) changes to the animal that are successfully passed on to subsequent generations (Ward 2018, 8). Lamarck’s most famous example was the proposition that giraffes actively stretched their necks to reach leaves on tall trees to eat. Over their lifetimes, the continuation of this habit resulted in gradual lengthening of the neck. These longer necks were then passed on to their offspring. Lamarck’s theory was disproved when evolutionary biologist August Weismann published the results of an experiment involving mice (Figure 2.10). Weismann amputated the tails of 68 mice and then successively bred five generations of them, removing the tails of all offspring in each generation, eventually producing 901 mice, all of whom had perfectly healthy long tails in spite of having parents whose tails were missing (Weismann 1889).
How giraffes actually ended up with long necks is a different story. In an environment where the food supply is higher off the ground, and perhaps less available to competing species, giraffes who happened to have slightly longer necks (due to random individual variation and genetic mutation) would be more likely to survive. These giraffes would then be able to reproduce, passing along the slight variation in neck length that would allow their offspring to do the same. Over time, individuals with longer necks would be overrepresented in the population, and neck lengths overall would increase among giraffes. Unfortunately, Lamarck’s ideas challenged the scientific establishment of the time and were rejected. He was discredited and harassed “to the point of loss of money, reputation, and then health” (Ward 2018, 9).
The final piece in the evolutionary puzzle leading up to the theory of natural selection was put forth by Thomas Malthus (1766–1834), who published An Essay on Population in 1798. Malthus lived in England during the time of the Industrial Revolution. It was a time of great poverty and misery when many people migrated from the countryside to squalid, disease-ridden cities to work extremely long hours in dangerous conditions in factories, coal mines, and other industrial workplaces. Birth rates were high and starvation and disease were rampant. Malthus struggled to explain why. His answer was basically the idea of carrying capacity, an ecological concept still in use today. Malthus suggested the rate of population growth exceeded the rate of increase of the human food supply. In other words, people were outgrowing the available food crops. He also suggested that populations of animals and plants were naturally constrained by the food supply, resulting in reductions in population in times of scarcity, “restraining them within the prescribed bounds” (Moore 1993, 147). But, despite significant challenges, some individuals always survived. This was the key to later understandings of evolutionary change in species over time.