Chapter 24 - Chapter 24 Evolution by Natural Selection I II...

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Chapter 24: Evolution by Natural Selection I. Introduction a. Key Concepts i. Populations and species evolve—heritable characteristics change through time ii. Evolution: changes in allele frequencies over time iii. Natural selection: individuals with certain alleles produce the most surviving offspring in a population iv. Adaptation: genetically based trait that increases an individual’s ability to produce offspring in a particular environment (fitness) v. Evolution by natural selection is not progressive, and it does not change characteristics of the individuals that are selected—changes only characteristics of the population. Animals do not do things for the good of the species, and not all traits are adaptive. All adaptations are constrained by trade-offs and genetic and historical factors b. Special creation: species immutable—incapable of change, remaining unchanged since moment of creation c. Darwin proposed life on Earth was ancient and species change through time d. Theory: pattern (facts) and process (produces that pattern) II. 24.1: The Evolution of Evolutionary Thought i. Scientific revolution: overturns an existing idea about how nature works and replaces it with another, radically different, idea 1. Typological thinking: species are unchanging types and variations within species are unimportant or even misleading a. Plato: every organism an example of a perfect, unchanging essence, or type, created by God—key to understanding life: ignore shadows and focus on understanding each type of unchanging, perfect essence b. Aristotle: ordered types of organisms into linear scheme called great chain of being (ladder of life)—species organized into a sequence based on increased size and complexity, with humans at top 2. 1809: Jean-Baptiste de Lamarck proposed formal theory of evolution —idea that species change through time a. Initially based on great chain of being—simple organisms originate at base of chain by spontaneous generation, then evolve by moving up chain over time b. Progressive—always producing larger and more complex species c. Species change through time via inheritance of acquired characters developed in response to challenges of environment 3. Darwin and Wallace emphasized process responsible for change through time is based on variation among individuals in populations (individuals of the same species living in the same area at the same time) a. Darwin claimed that instead of being unimportant or an illusion, variation among individuals in a population was key to understanding nature of species b. Individuals with certain traits leave more offspring than others do
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4. Plato and followers emphasized existence of fixed types; evolution by natural selection is all about change and diversity III. 24.2: The Pattern of Evolution: Have Species Changed Through Time?
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Chapter 24 - Chapter 24 Evolution by Natural Selection I II...

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