Chapter 3: Darwinian Natural selectionOverview |
The early evolutionists had discovered an important phenomenon. A growing body of facts indicated that both fossilized and living organisms had descended from a common ancestor. The evidence that Darwin amassed to support this hypothesis was indirect, but persuasive enough that scientific controversy over the pattern component of the theory of evolution had virtually ended by the mid-1870s. Thanks to Darwin and his intellectual forebears, evolution became a well-established fact.
Chapter 2 focused on the evidence for the pattern called descent with modification; this chapter introduces a process, called natural selection.
3.1 Artificial Selection: Domestic Animals and Plants To understand the mechanism of evolution in nature, Darwin studied the mechanism of evolution under domestication. That is, he studied the method plant and animal breeders use to modify their crops and livestock.
In section 3.1 of your textbook you can learn about Darwin’s favorite domestic Organism, the pigeon, and how breeders can artificially select for desirable traits in their plants and animals.
3.2 Natural Selection: Darwin’s Four Postulates Darwin realized that a process much like artificial selection happens in nature. His Theory of Evolution by Natural Selection holds that evolution is the logical outcome of four postulates, which Darwin laid out in his introduction to On the Origin of Species by Means of Natural Selection.
In section 3.2 of your textbook you will explore the support and evidence for each of the postulates.
3.3 The Evolution of Flower Color in an Experimental Snapdragon Population Kristina Niovi Jones and Jennifer Reithel (2001) wanted to know whether natural selection by bumblebees could influence the evolution of a floral trait controlled by alleles of a single gene. To find out, they established an experimental population of 48 snapdragons in which they made sure that Darwin’s postulates 1 and 2 were true. Then they monitored the plants and their offspring to see whether postulates 3 and 4, and the predicted outcome, were true as well.
In section 3.3 you will learn about their study design and the results of their interesting experiments.
3.4 The Evolution of Beak Shape in Galápagos Finches Peter Grant and Rosemary Grant and their colleagues have been studying several species of Galápagos finches continuously and on various islands in the Galápagos archipelago since 1973 (see Boag and Grant 1981; Grant 1981a, 1991,1999; Grant and Grant 1989, Grant and Grant 2000, 2002, Keller et al. 2001).
Turn to section 3.4 to learn about how Darwin’s postulates are tested using these remarkable species of finches as a model.
3.5 The Nature of Natural Selection Although the Theory of Evolution by Natural Selection can be stated concisely, tested rigorously in natural populations, and validated, it can be difficult to un-derstand thoroughly. One reason is that it is essentially a statistical process: a change in the trait distributions of populations. Statistical thinking does not come naturally to most people, and there are a number of widely shared ideas about natural selection that are incorrect.
In section 3.5 how about selection does and does not operate.
3.6 The Evolution of Darwinism Because evolution by natural selection is a general organizing feature of living systems, Darwin’s theory ranks as one of the great ideas in intellectual history. Its impact on biology is analogous to that of Newton’s laws on physics, Copernicus’s SunCentered Theory of the Universe on astronomy, and the Theory of Plate Tectonics on geology. In the words of evolutionary geneticist Theodosius Dobzhansky (1973),“Nothing in biology makes sense except in the light of evolution.”
Section 3.6 of your textbook explores the problems with the natural selection theory and why it took so long for it to become universally accepted.
3.7 The Debate over “Scientific Creationism” and “Intelligent Design Theory” Scientific controversy over the fact of evolution ended in the late 1800s, when the evidence reviewed in Chapter 2 simply overwhelmed the critics. Whether natural selection was the primary process responsible for both adaptation and diversity was still being challenged until the 1930s, when the works of the Modern Synthesis provided a mechanistic basis for Darwin’s four postulates and unified micro- and macroevolution. Evolution by natural selection is now considered the great unifying idea in biology. Although scientific discourse about the validity of evolution by natural selection ended well over a half-century ago, a political and philosophical controversy in the United States and Europe still continues (Holden 1995; Kaiser 1995).
Section 3.7 explores this debate and why is it occurring.