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Natural Science - Year II

Unit 43: Darwin and Natural Selection

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History Weblecture for Unit 43


This Unit's Homework Page History Lecture Science Lecture Lab Parents' Notes

History Lecture for Unit 43: Darwin and Natural Selection

For Class
Outline/Summary

Challenge: Before you read the history and science weblectures and the external sites for this unit, write down your definition of the term "species". Be very specific, and give at least one example. Do not look up a dictionary definition: this is about your current understanding of the term, which influences what you read. You do not need to show this definition to anyone.

Then, as you read the material in the weblectures and assigned sites, consider how others use this term. Are all of the people you read below use the term in the same way? Do you use the term the same way a modern biologist would (see the science lecture)?

Evolution Theory

Any explanation of living matter has to address two major questions:

  • Why do all organisms share certain characteristics and structures?
  • Why do individual organisms differ from one another?

Creation stories from different cultures address this problem in different ways. Chinese stories attribute the creation of animals to a deity called Nuwe (usually but not always represented as female), who restores life to earth each time a calamity wipes it out: in this view, there is not one creation of living things but many. The Babylonians and Egyptians held a belief similar to that of other Mesopotamian cultures, including the Hebrews, that the most powerful of Gods had created animals and men at some single point of time in the past.

Read the first chapter of Genesis and the story of creation as translated from the Hebrew in the King James Version.

  • What ideas or concepts are mentioned but not explained in this version of the story? (e.g., what does the writer of Genesis mean by "firmament"?)
  • What is the order of creation -- what does God create first, then second? Keep this in mind as you look at the order in which evolutionists think life developed on earth.
  • What purpose does God have in creating the earth, living creatures, and humankind?
  • How does that purpose affect the way we view ourselves?
  • How does that purpose affect the way in which we view nature and other living things?
  • Is the purpose of life a concept that is susceptible to scientific investigation?

Charles Darwin (1809-1882)

Charles Darwin's theories are so controversial that it is difficult to find a website biography that doesn't "spin" the story one way or another. I'm resorting to the Wikipedia article, since it is juried and tends to be relatively detailed and for the most part, objective. As you read this material (and this applies not just to Darwin, but any controversial material), try to differentiate between what the historical person actually says (primary material), and what other people say about him (secondary material). Real people grow as they discover new informtion or realize the implications and (often unintended) results of their theories or actions. Over the course of his lifetime, Darwin's views changed significantly as he studied new examples of the diversity of life forms, and considered his own work and the response or criticims others raised.

Read sections 1.1-1.6 of the Wikipedia biography of Charles Darwin.

  • Who were some of the people who influenced Darwin in his pursuit of knowledge about nature?
  • How did Darwin make a living or pay for his scientific investigations?
  • What did Darwin observe during his trip on the H.M.S. Beagle that puzzled him?
  • What were the accepted ideas about species at the time Darwin tries to explain the observations he made on his trip?
  • What observations led Darwin to challenge the accepted ideas about species?
  • How did Darwin communicate his findings and theories to the scientific societies in England?
  • How was Darwin influenced by Alfred Russel Wallace's work?
  • How was Darwin influenced by Thomas Malthus' work?
  • Challenges for putting this information together with what you (should) already know. The answers to these questions are not in the Wikipedia article, but in other material we've already covered.
    • What is materialism (recall our study of early Greek theories of matter!)? How would a radical materialist explain a natural event?
    • What were Lamarck's ideas? Did Darwin eventually agree with them or refute them?
    • What was the debate between Neptunism and Plutonism? How do modern geologists resolve this debate?
    • Why was Darwin's discovery of fossil bones near Punta Alta significant? Whose theory was challenged by this discovery?

Charles Darwin was educated as a doctor, but his abiding interest was in natural history (another term used for science), and he accepted an invitation to accompany the H.M.S. Beagle during its surveying expedition. For five years, Darwin observed and noted the similarities and differences of species on both coasts of South America and many Pacific islands. He read the works of Charles Lyell on the principles of geology, in which Lyell proposed a scale of time going back some 3.8 billion years to account for the fossils in the different geological strata. Darwin also read the works of Thomas Malthus, an English philosopher who observed that populations increase geometrically, while food supplies generally increase arithmetically.

In a geometrical progression, the numbers go up by powers, for example, the common series in which the current number is doubled to get the next:

1, 2, 4, 8, 16.

In a related arithmetic series, the next number in the series is two more than the current one:

1, 3, 5, 7, 9

Note that while the first three numbers of the arithmetic series are equal to or larger than the corresponding step of the geometric series, by step five the geometric series is significantly ahead of the arithmetic one.

If this were Malthus' population and food series, then by step four, things would be getting a little tight, and by step five, half the population would be starving.

Malthus predicted that populations imposed controls on themselves: when the population radically outstripped the food supply, famine, war, or disease would occur and reduce the population to a level which could be supported by the environment.

Darwin interpreted these ideas in light of the animals he had observed. So many of them seemed specially suited for their particular "niche" in their environment. Species of finches which were otherwise very similar had slightly different beaks and used different food sources, so that all species of finch could live in the same area without competing for precisely the same food sources. Darwin concluded that under circumstances where species were in competition, those which were best adapted to the environment would survive and reproduce, while those with less favorable characteristics would loose the competition and gradually die out.

While Darwin observed the species of South America, the English naturalist Alfred Russell Wallace observed the species of southeastern Asia. Darwin became aware of Wallace's work and ideas, at the same time that his own friends were urging him to publish his theories (and take the credit for coming up with it first). In stark contrast to the Newton-Leibniz controversy over the discovery of calculus, Darwin took the bold course of publishing his own and Wallace's work together, and each acknowledged the other's hard work on the simultaneously "discovery" of natural selection.

In 1859, Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

First edition of Darwin's work (Museum of Natural Philosophy, Paris).
© 2007 Christe Ann McMenomy

It was followed by Lyell's The Antiquity of Man in 1863, which argued on the basis of fossilized tools that humans must have existed in very early prehistoric times, and by Thomas Huxley's Man's Place in Nature, which tried to show that human anatomy was closely related to apes. Darwin's final work, The Descent of Man (published in 1871) presented evidence Darwin had gathered to support the claim that humans had descended (or evolved) from lower forms of life.

The implications of this final theory propelled the controversy over the acceptance of evolution theories out of scientific circles and into the general population. For many, the debate focussed on one question: If the development of the human species can be explained in purely mechanical terms, what justifies the special place of humans as stewards of creation or God's place as the Divine Creator? We'll look at some of the reaction to Darwin's theory in the next unit.

Study/Discussion Questions:

  • What key phenomena is Darwin trying to explain?
  • What are the main points of the controversy surrounding evolution theory?

Further Study/On Your Own