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Chapter 11

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Western University
Biology 1225
Michael Butler

Chapter 11 Evidence of Evolution Pg. 190 - Darwin’s observations of the natural world led him to propose that evolution could occur by way of a process called natural selection. - There is mow much evidence in support of evolution that comes from fossils, the geologic record and radioactive dating of rocks. - Further evidence comes from comparative studies of anatomy and biochemistry of different lineages that have helped us to identify patterns of change through time. - NATURAL SELECTION ONLY ACTS ON A TRAIT IF IT IS INHERITABLE. What DOES the SELECTING of traits that will pass into the next generations in the greatest frequency?? – the ENVIRONMENT - individuals show variation and the environment selects the most FIT. The most fit individuals in evolutionary terms, in natural selection terms – are simply those that leave the most fertile offspring, no matter how healthy an individual might be during its life or how long it lives, it is how many fertile offspring that individual contributes to the next generation that counts, in evolutionary terms fitness means reproductive success. Another important point to note is that while natural selection certainly acts on an individual, it is actually POPULATIONS that evolve, evolution is a population based theory. 1 11.2 Early Beliefs, Confusing Discoveries biogeography – study of patterns I the geographic distribution of species and communities mass extinction – Simultaneous loss of many lineages from Earth comparative morphology – the scientific study of anatomical patterns in body plans fossil – physical evidence of an organism that lived in the ancient past 1. Expeditions by nineteenth century explorers yielded increasingly detailed observation of nature. 2. Geography, biogeography, and comparative morphology of organisms and their fossils led to new ways of thinking about the natural world. Take Home Message How did observations of the natural world change our thinking in the nineteenth century? 3. Increasingly extensive observations of nature in the nineteenth century did not fit with prevailing belief systems 4. Cumulative findings from biogeography, comparative morphology ad geology let naturalists to question traditional ways of interpreting the natural world. 2 11.3 A flurry of New Theories pg 192 lineage – line of descent evolution – change in a line of descent (lineage) adaptation – (adaptive trait) – A heritable trait that enhances an individual’s fitness in a particular environment artificial selection – process whereby humans alter traits of a domestic species by selective breeding over generations fitness – degree of adaptation to an environment, as measured by an individual’s relative genetic contribution to future generations. In other words how many fertile offspring . natural selection – differential survival and reproduction of individuals of a population based on differences in shared, heritable traits. Driven by environmental pressures. 1. Prevailing belief systems may influence interpretation of the underlying cause of a natural event. 2. Nineteenth century naturalists attempted to reconcile traditional belief systems with physical evidence of evolution, or change in a lineage over time. 3. Humans select desirable traits in animals by selective breeding, or artificial selection. 4. Charles Darwin and Alfred Wallace independently came up with a theory of how environments also select traits, stated here in modern terms: A population tends to grow until it exhausts environment resources. As that happens competition for those resources intensifies among the population’s individuals 5. Individuals with forms of shared, heritable traits that make them more competitive for the resources tend to produce more offspring. 6. Thus adaptive traits (adaptations) that impart greater fitness to an individual become more common in a population over generations. 3 7. The process in which environmental pressures result in the differential survival and reproduction of individuals of a population is called natural selection. 8. It is one of the processes that drives evolution. Take Home Message How did the way that naturalists thought about the history of life change in the nineteenth century? 1. Evidence found in the 1800s led to the idea that Earth and the species on it had changed over very long spans of time. This idea set the stage for Darwin’s theory of evolution by natural selection 2. Natural selection is a process in which individuals of a population survive and reproduce with differing success depending on the details of their shared heritable traits. 3. Traits favoured in a particular environment are adaptive. An adaptive trait increases the chances that an individual bearing it will survive and reproduce. 4 Principles of Natural Selection, in Modern Terms Fig. 11.1 page 195 Observations about populations - Natural populations have an inherent reproductive capacity to increase in size over time - As a population expands, resources that are used by its individuals (such as food and living space) eventually become limited - When resources are limited, the individuals of a population compete for them Observations about Genetics - Individuals of a species share certain traits - Individuals of a natural population vary in the details of those shared traits - Shared traits have a heritable basis, in genes. Slightly different forms of those genes (alleles) give rise to variation in shared traits Inferences - A certain form of a shared trait may make its beare
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