Unit 3 Exam Study Guide Notes Chapter 22 Descent with Modification Evolution descent with modification a change in genetic composition of a population from generation to generation Can view evolution in two related but different ways 1 Pattern evolutionary change is revealed by data from a range of scientific disciplines 2 Process mechanisms that produce the observed pattern of change 22 1 The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species I Scala Naturae and Classification of Species Life forms could be arranged on a ladder or scale of increasing complexity later called the scala naturae II Ideas About Change over Time Strata new layers of sediment that cover older ones and compresses them into superimposed layers of rock Catastrophism the principle that events in the past occurred suddenly and were caused by mechanisms different from operating in the present Uniformitarianism states that mechanisms of change are constant over time same geologic processes are operating today as in the past and at the same rate 22 2 Descent with modification by natural selection explains the adaptations of organisms and the unity and diversity of life I Darwin s Research A Darwin s Focus on Adaptation Adaptations inherited characteristics of organisms that enhance their survival and reproduction in specific environments Began to perceive adaptation to the environment and the origin of new species as closely related processes Natural Selection a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits II The Origin of Species A Descent with Modification by natural selection basic principles Unity in Life organisms share many characteristics Darwin attributed the unity of life to the descent of all organisms from an ancestor that lived in the remote past The Diversity of Life over long periods of time descent with modification eventually led to the rich diversity The match between organisms and their environments depending on a species habitat they accumulate diverse modifications or adaptations that fit them to specific ways in life B Artificial Selection Natural Selection and Adaptation Artificial Selection the selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits As a result offspring bear little resemblance to their wild ancestors Observation 1 Members of a population often vary in their inherited traits Observation 2 All species can produce more offspring than their environment can support and many of these offspring fail to survive and reproduce Inference 1 Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals Inference 2 This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations An organism s heritable traits can influence not only its own performance but also how well its offspring cope with environmental challenges When such advantages increase the number of offspring that survive and reproduce the traits that are favored will likely appear at a greater frequency in the next generation Over time this process will increase the frequency of individuals with favorable adaptations and hence refine the match between organisms and their environment C Natural Selection A Summary A process in which individuals that have certain heritable traits survive and reproduce at a higher rate than other individuals because of those traits Over time can increase the match between organisms and their environment In an environment changes or if individuals move to a new environment natural selection may result in adaptation to these new conditions sometimes giving rise to a new species Individuals do not evolve it is the population that evolves over time Can amplify or diminish only those heritable traits that differ among the individuals in a population Which traits are favored depends on the context in which a species lives and mates 22 3 Evolution is supported by an overwhelming amount of scientific evidence I Direct Observations of Evolutionary Change Natural selection is a process of editing not a creative mechanism Depends on time and place it favors those characteristics in a genetically variable population that provide advantage in the current local environment II Homology Similarity resulting from common ancestry A Anatomical and Molecular Homologies Homologous structures structures in different species that are similar because of common ancestry Vestigial structures remnants of features that served a function in the organism s ancestors All forms of life use the same genetic language of DNA and RNA and the genetic code is essential universal Thus it is likely that all species descended from common ancestors that used this code B Homologies and Tree Thinking All life shares the deepest layer and each successive smaller group adds its own homologies to those it shares with larger groups Evolutionary tree a diagram that reflects evolutionary relationships among groups of organisms Hypotheses that summarize our current understanding of patterns of descent C A Different Cause of Resemblance Convergent Evolution Convergent evolution the independent evolution of similar features in different lineages distantly related organisms can resemble one another for a different reason Species that share features because of convergent evolution the resemblance is said to be analogous not homologous Analogous features share similar function but not common ancestry Homologous features share common ancestry but not necessarily similar function III The Fossil Record Documents the pattern of evolution showing that past organisms differed from present day organisms and that many species have become extinct Show the evolutionary changes that have occurred in various groups of organisms Sheds light on the origins of new groups of organisms Shows that over time descent with modification produced increasingly large differences among related groups of organisms ultimately resulting in the diversity of life we see today Biogeography The geographic distribution of species Influenced by many factors including continental drift the slow movement of Earth s continents over time Pangaea all of Earth s landmasses into a single large
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