| Development of Evolutionary
Thought | Evolution
and Religion |
Teaching evolution can be fraught with difficulty: it is probably the only scientific theory to be rejected on grounds of personal belief. Because of this, it may be that we should move from simply teaching a series of facts and concepts to looking at the development of the theory of evolution, and placing it in its social and historical contexts.
William Cobern, who has written a number of papers on the teaching
of evolution, has commented (1994) "Teaching evolution at
the secondary level - is very much like Darwin presenting
the Origin of Species to a public who historically
held a very different view of origins." To meet this challenge,
"teachers [should] preface the conceptual study of evolution
with a classroom dialogue ... informed with material on the
cultural history of Darwinism." He goes on (1995, p. 295),
"I do not believe ... that evolution can be taught effectively
by ignoring significant metaphysical (i.e. essentially religious)
questions. One addresses these issues not by teaching a doctrine,
but by looking back historically to the cultural and intellectual
milieu of Darwin's day and the great questions over which
What follows is an attempt to provide that historical setting, with information on the key players who developed biological and geological thinking and provided the scientific context in which Darwin could have his momentous insight.
The historical and social context of Darwinism
Ask, "Who developed the concept of evolution?" and most people
will probably answer "Charles Darwin". But, while Darwin amassed
a huge body of evidence for the fact of evolution and, more
importantly, provided a mechanism - his
of natural selection - by which it could proceed, the idea
of evolution has been around much longer.
17th Century: John Ray: the "species" concept
The first scientist (in the modern sense of the word) to
carry out a thorough study of the natural world was the Englishman
John Ray (1627 - 1705). Ray was a brilliant student who, unusually
for his time, did not take holy orders on completing his degree
at Cambridge (largely due to the social and religious upheavals
associated with the Civil War, but also because of his own
personal beliefs). Forced to resign his Fellowship at the
university, he was sponsored by his friend Francis Willughby
(1635 - 1672), who shared Ray's scientific interests, to develop
his catalogues of the living world. Ray's particular interests
lay with plants, for which he developed an early classification
system based on physiology and anatomy. During this work Ray
established the modern concept of a
noting that organisms of one species do not interbreed with
members of another, and used it as the basic unit of taxonomy.
Ray also studied fossils, recognising them as having formed from once-living organisms, and grappled with the contradictions between the Biblical account of creation and the evidence of change and extinction that he saw in his fossils. Deeply religious, he rejected any possibility of an old and changing Earth, as did all scholars of his time.
Online biography of John Ray available at
Online biography of Francis Willughby available at
18th Century: Carl Linnaeus & the modern taxonomic system
Ray's ideas on taxonomy were picked up and extended by the better-known
Carl Linnaeus (1707 - 1778). He was fascinated by plants, paying
botany much more attention than was required for his medical studies
at university, and took up the new idea that plants reproduced sexually,
using differences in reproductive structures to develop a system
for classifying plants. He moved on to study animals, and to help
make sense of the huge volume of data accumulated during his teaching
and research gave all his specimens a descriptive Latin binomial,
or two-word, name. Linnaeus used these names systematically in his
classification system, which he published as "Systema naturae".
The "Systema" built on Ray's earlier work and catalogued
the diversity of living things in a cohesive and logical manner
- the now-familiar hierarchical way of arranging organisms, from
the all-inclusive Kingdoms through Classes and Orders to the Genus
and Species of each living thing. Linnaeus went so far as to include
humans in his system, and believed that humans and the great apes
were so closely related that they should be placed in the same genus.
However, he didn't actually do so, to avoid contradicting church
Although a religious man who believed that all species were created together, Linnaeus still gave some thought to the apparent age of the Earth. Fossils were now well-accepted as the remains of past creatures, sometimes found far from the sea, and he was uncertain that this distribution could have been achieved in the time provided by the Biblical flood. He was not alone in this, as contemporary scholars of both science and history were beginning to question the calculations of Archbishop Ussher that gave the age of the Earth as 6000 years.
Online biography of Carl Linneaus available at
Buffon on evolution and the age of the Earth
The Frenchman Georges Louis Leclerc, Comte de Buffon (1707 - 1788), was both intellectually brilliant and extremely hard working (though he viewed himself as naturally lazy) and produced an enormous body of work over his lifetime. He set out the current knowledge of the whole of natural history in the 44-volume "Natural History" ("Histoire Naturelle"), a series that greatly increased popular interest in science. He also contributed to the debate over the age of the Earth (begun by Isaac Newton), suggesting that our planet had formed in a molten state and that its gradual cooling must have taken far longer than the 6000 years Ussher and other theologians allowed (or the 50,000 permitted by Newton). In fact, unlike previous scientists, Buffon attempted to answer this question by experimental means, something that has been described as "a landmark event in science" (John Gribbin, 2002).
Buffon also gave consideration to the concept of evolution
- a concept that was in circulation long before Charles Darwin
provided a mechanism by which evolution could occur
- wondering about the role of
organs, which appeared to give the lie to
the idea that creation achieved perfection of form, and about
the possibility of species descending from earlier ancestors.
Online biography of
Georges Louis Leclerc available at
Erasmus Darwin's thoughts on evolution
Charles was not the first in his family to consider the concept of evolution. His grandfather Erasmus Darwin (1731 - 1802) was a successful country doctor who published widely in many scientific fields. He was also a poet, and his book "The Loves of the Plants" introduced the public to the intricacies of plant taxonomy and reproduction. Another book, "Zoonomia", set out Erasmus' ideas on evolution. He was aware that modern species were different to fossil types, and also saw how plant and animal breeders used artificial selection to enhance their products. He knew that offspring inherited features from their parents, and went so far as to say that life on Earth could be descended from a common ancestor. While Erasmus believed in the original creation of life, his God was "hands-off" from that point on. His ideas were not widely accepted in England, but in France Lamarck was developing similar views of evolutionary change.
Online biography of
Erasmus Darwin available at
Online biography of
Jean-Babtiste Lamarck available at
However, Lamarck's ideas were also to be rejected, and to understand why, we need to look at the role played by Georges Cuvier.
Cuvier's contribution to palaeontology
Georges Cuvier (1769 - 1832) was interested in biology from childhood, an interest that he developed further while living in the French countryside during the Revolution. He read both Linnaeus and Buffon and worked on his own ideas on classification and taxonomy, before joining the Museum of Natural History in Paris, studying and writing on comparative anatomy. His work was extremely useful in interpreting the remains of fossil animals and relating them to living species. Cuvier also classified animals according to their body plan (as vertebrates, molluscs, those with jointed exoskeletons and those with radial symmetry), a major advance in thinking about relationships. His extensive studies of fossils gave rise to the science of palaeontology, and he recognised that particular groups of fossil organisms were associated with certain rock strata. This last finding meant that it became possible to place the strata into order by relative age of the fossils.
Online biography of
Georges Cuvier available at
The catastrophism model of Earth's history
Cuvier's palaeontological studies told him that large numbers had become extinct. To explain this, he used the concept of catastrophism: a series of catastrophes, one of which was recorded in the Biblical story of the flood, had caused repeated waves of extinction. Areas were then repopulated by migration from unaffected areas: there was no room in this model for the evolution of new species. In his view, life had existed unchanged on Earth for hundreds of thousands of years, ever since the Creation. Cuvier's adherence to the concept that species were "fixed" and unchanging meant that he rejected the model of evolution developed by his fellow Frenchman, Lamarck.
Lamarck's concepts of evolution and inheritance
Jean-Baptiste Lamarck (1744 - 1829) also worked at the Natural History Museum in Paris, but his views on species were the opposite of Cuvier's. His model of evolution proposed that individuals were able to pass to their offspring characteristics acquired during their own lifetimes. (At the time this was a perfectly acceptable model of change, given that nothing at all was known about the processes of inheritance.) But what annoyed Cuvier was Lamarck's proposal that species did not go extinct, but instead evolved into another form. In fact, Lamarck went further, stating that evolution produced more complex organisms from simple ancestors, and that this process of change took time.
Etienne Geoffroy Saint-Hillaire (1772 - 1844) elaborated on Lamarck's views. Like Lamarck, he felt that the environment could produce changes in living things, but went on to suggest that if these changes were harmful, then the organism would die; only those well-adapted to the environment would survive. This is a foretaste of Darwin's theory of natural selection, but Geoffroy never went on to develop his idea further. This is because both his suggestions, and Lamarck's ideas about inheritance of acquired characteristics, were thoroughly ridiculed by Cuvier. And since Cuvier was such a prominent scientist, his attacks carried a lot of weight. Most scientists accepted the principle of catastrophism that he championed so strongly, until the work of Englishmen James Hutton and Charles Lyell.
Online biography of
Etienne Geoffroy Saint-Hillaire available at
James Hutton and the principle of uniformitarianism
James Hutton (1726 - 1797) made a significant contribution to the understanding of the geological processes that shaped the Earth. He was a keen chemist but also developed a strong interest in geology. Hutton recognised that the Earth was extremely old. He saw that there was no need for global catastrophes to shape the surface of the Earth. Instead, given sufficient time, the gradual ongoing processes of erosion, sedimentation, and uplift could produce the geological features he saw. This concept became known as the principle of uniformitarianism.
Without the concept of an extremely old, and slowly changing, Earth, Darwin would not have had the time available for his model of evolution to work. In fact, Darwin specifically applied Hutton's concept of gradual change, or gradualism, to his model of how species evolved.
Online biography of
James Hutton available at
18th century: Charles Lyell
Charles Lyell (1797 - 1875) went to Oxford to study mathematics and law but turned to geology after being introduced to Hutton's work. He met Gideon Mantell, who had discovered several different dinosaurs in English rocks, and this led him to the serious study of geological history. Lyell travelled widely in Europe, where he observed ancient raised seabeds separated by lava flows, and became convinced that Hutton's model of gradual geological change was correct. He collected a large amount of supporting evidence for uniformitarianism and set this out in the "Principles of Geology", a book that had a tremendous influence on Darwin. As well as building on the idea of gradual long-term natural changes as the shaping force of the Earth's surface, Lyell considered the origins of plants and animals. While he believed in the special creation of all species now in existence, he also recognised that many species had become extinct and been replaced by others.
Online biography of
Charles Lyell available at
Thus, by the time Charles Darwin became interested in natural history, many of the concepts crucial for his thinking had been developed.
Charles Darwin and the theory of evolution by natural selection
Charles Robert Darwin (1809 - 1882) was one of six children born to Robert & Susannah Darwin. Robert was a well-respected local doctor and also something of a private investment banker; the family was always very well off. Charles was fascinated by science, particularly natural history, from a young age. His father wished him to become a doctor, but the traumatic experience of observing an operation on a non-anaesthetised child caused Charles to reject that career and he became took classes in geology and natural history, particularly marine biology.
Robert Darwin still wished his son to have a career and so arranged for him to study for the clergy at Cambridge. Many country clergymen managed to combine their priestly duties with an interest in natural history, so this seemed the obvious thing for Charles to do.
However, Charles once more ignored his official studies and took classes reflecting his interest in the natural world, including botany and geology. His teachers in these courses viewed Darwin as an outstanding and hardworking pupil, but his father was still set on him becoming a country parson.
The summer after he graduated from Cambridge, Charles received a letter that was to change his life. His botany professor, John Henslow, had put his name forward to join the crew of HMS Beagle, on a surveying expedition to South America. Contrary to popular myth, this was not the naturalist's position (which was filled by the ship's doctor). Instead, the Beagle's captain, Robert FitzRoy, required a "gentleman companion" to provide company and conversation on the voyage. FitzRoy found Darwin acceptable and the Beagle left on what was to be a five-year voyage on December 27, 1831. Darwin was yet to turn 23.
Robert Darwin (who was paying Charles' expenses) expected that his son would settle down on the voyage and come home ready to take up a country parish. His university tutors and scientific friends had different expectations: Charles was to collect scientific specimens and send them back to England. This sort of amateur collecting was a significant hobby for the upper classes in Darwin's time - and provided a livelihood for less well-off men such as Alfred Russel Wallace, who was later to provide the impetus for the publication of "On the Origin of Species".
Darwin's thinking was enormously influenced by the work done by previous scientists. Not least of these was Charles Lyell. Darwin took Lyell's "Principles of Geology" for reading matter on the voyage. What he read, and later confirmed at first hand in South America, led him to accept the uniformitarian approach to Earth's history. This is significant because it allowed for the vast age of the Earth, necessary for his model of gradual evolutionary change.
Darwin travelled extensively in South America while the Beagle continued its surveying duties. He made extensive fossil collections and noticed that these fossils were found in regions now occupied by their slightly different descendants. This led him to think about factors affecting a species' distribution. He also found evidence supporting Lyell's theory of gradual geological change, such as fossils and ancient sea beds now far from the sea, and witnessed first-hand how a large earthquake could raise the land.
He also visited the Galapagos Islands and noted how the finches and iguanas there resembled those of the South American mainland. Contrary to the usual story, "Darwin's finches" did not provide him with a "eureka!" moment. He noticed how the islands' giant tortoises varied from island to island, but the significance of the varied finch species did not strike him until after his return to England.
Darwin was greeted with considerable scientific acclaim on returning home. This was due to the quality and quantity of the scientific specimens he brought with him, and in fact he first made his name as a geologist, not a biologist. Robert Darwin became resigned to the fact that his son was going to follow his own path, and Charles settled down to writing about his travels, and studying his specimens. And he began to develop his theory of evolution by natural selection as a coherent explanation for his observations on the form and distribution of species, tying it into the concepts developed by other thinkers such as Lyell, Lamarck and Malthus. While he quickly produced an outline of this theory, Darwin was to spend the next 25 years refining it and amassing still more supporting evidence. It took a letter from Alfred Russel Wallace to push him into publication.
Online biography of
Charles Robert Darwin available at
Alfred Russel Wallace arrives independently at a theory
Alfred Russel Wallace (1823 - 1913) did not have the same advantages in life as Charles Darwin. Largely self-taught, he had always had an interest in natural history but not the funds to indulge it. Unhappy with what was essentially a dead-end job he managed to save enough money to fund a trip to South America, with the intention of collecting specimens and selling them to wealthy private collectors. This was a difficult life but Wallace was moderately successful. More importantly, he also attended various scientific meetings, published papers, and began corresponding with Darwin.
While on a major expedition to South-East Asia Wallace began to give serious consideration to how the species he was observing might have evolved. Like Darwin, he was influenced by the ideas on limits to population size developed by Malthus. Quite independently of Darwin, Wallace came up with the idea that the best-adapted organisms in a population would survive to breed, passing on their adaptations to their offspring. He worked this insight up into a paper that he sent to Darwin, asking for his comments and assistance in getting it published.
Online biography of
Alfred Russel Wallace available at
Online biography of
Malthus available at
The theory of evolution by natural selection
Darwin was shocked to receive Wallace's paper. He had been sitting on his theory for 25 years and here was another naturalist coming up with the same concept. Darwin felt that Wallace should have priority in publication, but was persuaded by his friends that he should produce a précis of his own work. The two documents were read together at a meeting of the Royal Society, but it is Darwin's contribution that we remember today. "On the Origin of Species by Means of Natural Selection, or the preservation of favoured races in the struggle for life" was published in 1859.
The following statements represent the heart of the theory of how species evolve by the process of natural selection, developed by Darwin and Wallace:
- Observation 1:
organisms of all species can produce so many offspring
that their population size would increase exponentially if all
individuals that are born reproduce successfully.
- Observation 2: populations tend to remain stable in
size, except for seasonal fluctuations.
- Observation 3: environmental resources are limited.
- Inference 1:production of more individuals than the
environment can support leads to a struggle for existence among
individuals of a population, with only a fraction of offspring
surviving each generation.
- Observation 4: individuals of a population vary extensively
in their characteristics; no two individuals are exactly alike.
- Observation 5: much of this variation is heritable.
- Inference 2: survival in the struggle for existence
is not random, but depends in part on the hereditary make-up of
the surviving individuals. Those individuals whose inherited characteristics
best fit them to their environment are likely to leave more offspring
than less-fit individuals.
- Inference 3: this unequal ability of individuals to
survive and reproduce will lead to a gradual change in a population,
with favourable characteristics accumulating over the generations.
Or, to put it another way:
- Natural selection = differential reproductive success.
- Natural selection occurs as a result of interaction between the environment and genetic variability in the population.
- The outcome of natural selection is the adaptation of populations to their environment.
The modern synthesis
A major problem for Darwin lay in the apparent lack of a mechanism by which features could be inherited. Gregor Mendel had developed his theory of heredity at much the same time as Darwin was grappling with the theory of evolution by natural selection. However, although Mendel published his findings, it seems that Darwin never read the paper. In fact, the significance of Mendel's work wasn't properly grasped until early in the 20th century.
Online biography for
Gregor Mendel available at
The "rediscovery" of Mendel's research led to the understanding of how various characteristics, coded for in an individual's DNA, could be passed on to successive generations. However, both Mendel and the early geneticists recognised only the classic "either/or" states of discrete characteristics. It seemed there was no way to explain how natural selection could operate on more subtle variations within a population.
It took the development of population genetics to reconcile Mendelism and Darwinism. As the name suggests, population genetics examines genetic variation within populations, not individuals, and allows an understanding of the relationship between this variation and natural selection.
The modern synthesis, a "comprehensive theory of evolution" (Campbell & Reece, 2002), was developed in the 1940s. It brings together information from the fields of population genetics, palaeontology, taxonomy, biogeography, and molecular biology. It "emphasises the importance of populations as the units of evolution, the central role of natural selection as the most important mechanism of evolution, and the idea of gradualism to explain how large changes can evolve as an accumulation of small changes occurring over long periods of time" (Campbell & Reece, 2002: 446). While modern evolutionary biology may see healthy debate over
some of the assumptions made by the modern synthesis, the underlying tenets of evolution set out by Charles Darwin remain secure.
Browne, J. (1995) Charles Darwin: Voyaging; Pimlico
Campbell, N. & J. Reece (2002) Biology (6th edition); Benjamin Cummings
Cobern, W. (1994) Point: belief, understanding, and the teaching of evolution Journal of Research in Science Teaching 31(5): 583-590
Cobern, W. (1995) Science education as an exercise in foreign affairs Science & Education 4: 287-302
Gribbin, J. (2002) Science: a History 1543-2001; Penguin
Keynes, R. (2002) Fossils, Finches and Fuegians: Charles Darwin's adventures & discoveries on the Beagle, 1832 - 1836; Harper Collins
van Oosterzee, P. (1997) Where Worlds Collide: the Wallace Line; Reed
Georges Louis Leclerc
Etienne Geoffroy Saint-Hillaire
Charles Robert Darwin
Alfred Russel Wallace