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Chapter 4

BIOL 180 Chapter 4: Reading 4-3

6 Pages

Course Code
BIOL 180
H E R R O N, J O N

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BIOL 180 - Reading 4-3: 22.5 Debunking Common Myths about Natural Selection and Adaptation: Intro - After more than two thousand years of belief in typological thinking , the scale of nature, ,and goal-oriented evolution, a great deal of cultural inertia has fostered myths about evolution by natural selection Natural Selection Does Not Change Individuals: During the process of natural selection, individuals do not change - only the population does. During the drought, the beaks of individual finches did not become deeper. Rather ,the average beak depth in the population increased over time because deep-beaked individual survived and produced more offspring than shallow- beaked individuals did Natural selection acted on individuals, but the evolutionary change occurred in the characteristics of the population When mutant alleles increase in frequency in the population over time, the average characteristics of the population change Natural Selection Is Not “Lamarckian” Inheritance - There is a sharp contrast between evolution by natural selection and evolution by the inheritance of acquired characters - the hypothesis promoted by Jean-Baptiste de Lamarck Lamarck proposed that 1. Individuals change in response to challenges posed by the environment 2. The changed traits are then passed on to offspring Key claim is that the important evolutionary change occur in individuals In contrast, Darwin realized that individuals do not change when they are selected. Instead they simply produce more or fewer offspring than other individuals do. When this happens, alleles found in the selected individuals become more or less frequent in the population Darwin was correct: There is no mechanism that makes it possible for natural selection to edit the nucleotide sequence of an allele inside an individual. An individual’s heritable characteristics don’t change when natural selection occurs. Natural selection sorts existing variants - it doesn’t change them Acclimatization Is Not Adaptation: The issue of change in individuals is tricky because individuals often do change in response to changes in the environment. If you were to travel to the Tibetan Plateau in Asia, your body would experience oxygen deprivation due to the low partial pressure of oxygen at high elevations. As a result, your body would produce more of the oxygen-carrying pigment hemoglobin and more hemoglobin-carrying red blood cells Your body does not normally produce more red blood cells than it needs, because vicious (thick) blood can cause a disease - chronic mountain sickness - that can lead to heart failure The increase in red blood cells in an example of acclimatization Acclimatization - a change in an individual’s’ phenotype that occurs in response to a change in natural environmental conditions. When this process occurs in study organisms in a laboratory, it is called acclimation Phenotypic changes due to acclimatization are not passed on to offspring, because no alleles have changed As a result, acclimatization does not cause evolution Adaptation vs Acclimatization Example: In contrast, populations that have lived in Tibet for many generations are adapted in this environment through genetic changes Among native Tibetans, an allele that increase the ability of hemoglobin two hold oxygen has increased to high frequency. In populations that do not live at high elevations, this allele is rare or nonexistent Common Misconceptions, Corrected Misconception Example “Evolutionary change occurs in organisms” Correction: Natural selection just sorts existing variants in organisms; it doesn’t Selection does not cause neck length to increase in individual giraffes, only in change them populations Evolutionary change occurs only in populations Acclimatization doesn’t equal adaptation “Evolution is goal directed” Correction: Adaptations do not occur because organisms want or need them Roses cannot grow thorns on purpose to Mutation, the source of new alleles, deter herbivores occurs by change Evolution is not progressive Loss of traits that can be adaptive There is no such thing as a higher or lower organism “Evolution perfects organisms” Correction: Not all traits are adaptive Humans lack the ability to grow wings, Some traits cannot be optimized even though flight could be an adaptive due to fitness trade-offs trait Some traits are limited by genetic, historical, or environmental constraints Example: Adaptation has a different meaning in science than in everyday life For example, in 1953, a New Zealand mountaineer and Tibetan sherpa were the first humans to reach the highest mountain peak in the world, the summit of Mount Everest. Climbers must acclimatize slowly to extremely high altitudes to avoid “mountain sickness,” but sherpas also have adaptations to life at high altitudes - genetically determined characteristics that improve their ability to survive in them mountains Natural Selection Is Not Goal Directed: Adaptations do not occur because organisms want or need them Mutations Occur By Chance: Mutations are the source of new alleles, but mutations occur by chance and are random with respect to fitness A purposeful change of an organism “needing” a change is not true The mutations that created the mutant alleles in both examples occurred randomly, due to error in DNA synthesis, and they just happened to be advantageous when the environments changed There is no mechanism that enables the environment to direct which mistakes DNA polymerase makes when copying genes Evolution Is Not Progressive: People often think that evolution by natural selection is progressive - meaning organisms have gotten better over time It is true that groups appearing later in the fossil record are often more morphologically complex than closely related groups that appeared earlier For example,. flowering plants are considering more complex than mosses, but there is nothing predetermined or absolute about this tendency Complex traits are routinely
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