Darwinian Revolution

Why was Darwin so revolutionary and why does he remain so? His breakthrough was not in introducing the idea of evolution, which had long been debated, but in proposing how evolution occurs. In this lecture, you survey these and other themes that are developed in the course.

This lecture examines the traditional worldview in the West, which was based on the biblical account of creation, fixed by one 17th-century scholar at 4004 B.C. An allied idea was the Great Chain of Being, pictured as an immutable scale of life forms from the most primitive to God himself.

You study three 18th-century thinkers: Benoît de Maillet, who estimated the cosmos to be billions of years old; Georges Buffon, who believed that living things descended from more primal forms; and Pierre Simon Laplace, who proposed a developmental theory for the formation of the solar system.

At the end of the 18th century, fossils were not necessarily regarded as actual remains of living things. You learn that they became central to the work of Georges Cuvier, who connected fossils to extinct species, which he believed had died out in violent catastrophes.

The idea of evolution was in the air by the early 19th century. This lecture looks at precursors to Darwin, including Jean-Baptiste Lamarck, who wrote a systematic account of the evolution of species over time and proposed that acquired characteristics can be inherited.

You investigate the dubious status of evolutionary ideas in the years before Darwin's book. Among the objections: Evolution challenged the Bible and lacked convincing empirical support. Some critics even classed evolution with fringe ideas such as Mesmerism and phrenology.

The young Darwin's intention to join the ministry was interrupted by an offer to travel around the world as a naturalist aboard HMS Beagle. The experience changed his life, giving him a growing conviction that species had altered over time, a conclusion he kept largely to himself.

Darwin spent two decades developing his theory of evolution through natural selection. You learn how he was rushed to publish prematurely by the independent discovery of the same principle by Alfred Russel Wallace. Yet Darwin's book, On the Origin of Species, is a masterful statement of his idea.

Even as Darwin's book stimulated greater acceptance of the idea of evolution, scientists criticized his specific mechanism, natural selection. This separation of the general notion of evolution from the means by which it occurs has permitted Darwinism to mean different things to different people ever since.

This lecture explores the religious response to Darwin's theory. Some argued that natural selection was tantamount to atheism, raising an issue that endures to the present day. Others reinterpreted natural selection to make it compatible with a belief in God. Still others completely separated science from religion.

Those who accepted evolution in the 19th century generally considered it a purposeful or goal-directed process, rejecting the random variation of natural selection. You explore how such an understanding influenced Herbert Spencer's social philosophy of the survival of the fittest.

You examine the difficulty that evolutionary theory faced in showing its compatibility with a theory of heredity. Darwin proposed a particulate theory of heredity, called pangenesis. Meanwhile, Gregor Mendel, an obscure Austrian monk, developed a powerful hereditary theory based on his experiments with pea plants.

In the early 1900s, Darwin's theory was in eclipse as its two fundamental tenets—selection and small variations—were rejected by a majority of scientists. You also see how Mendel's rediscovered work was interpreted as further evidence against natural selection.

This lecture discusses how developments in cell biology in the early 20th century clarified the process of heredity, showing that small changes in chromosomes were responsible for determining larger characteristics of organisms. This hinted that Darwin had been correct to focus on small continuous variations.

Darwin did not deal with the explosive issue of human evolution in Origin, but others were quick to see the implications of natural selection for the question of human origins. You learn how the discovery of Neanderthal remains and other human-like fossils fed the controversy.

This lecture investigates fact and fiction in the famous Scopes anti-evolution trial in 1925. Supposedly, teacher John Scopes was persecuted, attorney Clarence Darrow rose to Scopes's defense and defeated prosecutor William Jennings Bryan, and the anti-evolution movement was discredited. There are problems with all three statements.

Two controversies in the 20th century show the staying power of Lamarck's theory of inheritance of acquired characteristics. In Austria, biologist Paul Kammerer claimed that bodily changes in amphibians were heritable. In the Soviet Union, agronomist T. D. Lysenko made a similar claim about food crops.

You learn how the work of population geneticists, field naturalists, and paleontologists in the early 20th century led to an evolutionary synthesis that recognized Darwin's theory of natural selection as the major agent of evolution. Factors such as Lamarckian inheritance were rejected.

The new science of molecular biology added stunning evidence for Darwin's theory with the discovery of DNA as the carrier of genetic information. The decoding of DNA's double-helical structure by Francis Crick and James Watson shed new light on the origin of the minute variations responsible for natural selection.

This lecture examines the backlash against evolution by American evangelicals, who came up with increasingly sophisticated attacks on Darwinism to defend the biblical account of creation. Their tactics led to an alternative explanation of the origin of life, called "scientific creationism."

Altruistic behavior poses a problem for natural selection at the level of individuals. Therefore some scientists have theorized that selection acts on groups or even on individual genes. You investigate these proposals and also the field of sociobiology, which sees a Darwinian component to human social behavior.

You learn how evolution has inspired controversial ideas such as eugenics—the study of improving human heredity through controlled selective breeding. Eugenics led to restrictive marriage laws and forced sterilization in the United States and to mass euthanasia in Nazi Germany.

You see how the classical philosophical argument from design has been restyled "intelligent design" to attack natural selection, leading to a 2005 court case in Dover, Pennsylvania. The trial ended in an adverse ruling against a school that sought to teach intelligent design as an alternative to evolution.

In this final lecture, you take stock of the Darwinian revolution and some of the scientific, philosophical, and religious reactions to it. An analysis of these issues illuminates the difference between metaphysical beliefs and scientific explanations, and how they are inextricably linked when it comes to interpreting Darwin.