24 - Evolution by Natural Selection
Learning Objectives: Students should be able to ... • Define evolution, fitness, and adaptation using the biological definitions. • Describe the nature of the evidence regarding (1) whether species change through time and (2) whether they are related by common ancestry. • Assess whether Darwin's four postulates are true in any given example, explain to a friend why evolution must occur if all four are true, and explain whether evolution will occur if any of the four are not true. • Identify common misconceptions about evolution, and give examples to illustrate why they are not true. (For example: Is evolution progressive? Do animals do things "for the good of the species"? Does evolution result in perfection?) Lecture Outline • Evolution is one of the best-supported and most important theories in the history of science. • Evolution is one of the five attributes of life. • Evolution has both a pattern and a process. I. The Evolution of Evolutionary Thought A. Plato and typological thinking 1. Plato saw species as unchanging, perfect "types" created by God. 2. Plato thought individual variation was an unimportant deviation from the true "type." B. Aristotle and the great chain of being (scale of nature) 1. Aristotle, like Plato, thought species were unchanging types. 2. Aristotle thought species could be organized into a sequence or ladder of increasing complexity, with humans at the top. (Fig. 24.1) C. Lamarck and the idea of evolution as change through time 1. Lamarck noticed that organisms changed over time. 2. Lamarck thought animals progressed over time from "lower" to "higher" forms (like Aristotle's ladder) via inheritance of acquired characteristics. D. Darwin and Wallace and evolution by natural selection 1. Species change over time, but they do not "progress." 2. A species does not have a single true "type." 3. Individual variation is important; variation is what drives evolution. 4. This theory made predictions and was testable; that is, it was scientific. II. The Pattern of Evolution: Have Species Changed through Time? A. Two predictions of Darwin's theory: 1. Species change through time. © 2011 Pearson Education, Inc.
Freeman, Biological Science, 4e, Chapter 24
2. Species are related by common ancestry. B. Evidence of change through time 1. The fossil record and geologic time a. A fossil is any trace of an organism that lived in the past. (Fig. 24.2) b. The fossil record was initially organized based on the relative age of the fossils. c. The geologic time scale (1) Sedimentary rocks form layers over long times. These layers form in a chronological sequence (the geologic time scale). (2) From the number of layers and the time it takes to deposit each one, geologists realized that the Earth must be very old. d. Radiometric dating enables us to date rocks directly. (1) The Earth is 4.6 billion years old. (2) The earliest signs of life are in rocks that are 3.4−3.8 billion years old. 2. Extinction changes the species present over time. a. The fossil record shows that more than 99% of all the species that have ever lived are now extinct. (Fig. 24.3) b. This is evidence that the species composition on Earth has changed over time. 3. Transitional features link older and younger species. a. Law of succession: Fossils found in a certain geographic region frequently resemble the species currently living in that region. (1) This is evidence that the extinct species are related to existing species. b. Fossils with transitional features (traits intermediate between those of older and younger species) are compelling evidence that species change over time. Example: the fins-to-feet transition. (Fig. 24.4) 4. Vestigial traits are evidence of change through time. a. Vestigial traits are traits that have reduced or no function but are clearly related to functioning organs in related species. (Fig. 24.5) b. The existence of these traits...