Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin observed that –organisms produce more offspring than the environment can support –organisms vary in many characteristics –these variations can be inherited Darwin, an English naturalist, proposed natural selection as the mechanism of evolution DARWIN’S THEORY AND THE MODERN SYNTHESIS

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted Darwin saw natural selection as the basic mechanism of evolution –As a result, the proportion of individuals with favorable characteristics increases –Populations gradually change in response to the environment

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment –This is called artificial selection –Example of artificial selection in plants: five vegetables derived from wild mustard Figure 13.4A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Example of artificial selection in animals: dog breeding Figure 13.4B German shepherdYorkshire terrier English springer spaniel Mini-dachshundGolden retriever Hundreds to thousands of years of breeding (artificial selection) Ancestral dog

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings These five canine species evolved from a single common ancestor species through natural selection Figure 13.4C African wild dog CoyoteFoxWolfJackal Thousands to millions of years of natural selection Ancestral canine

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Important terminology Variation – Having genotypic and phenotypic differences in any population Heritable – Any genetics that can be passed on to future generations Fitness – Success of an organism’s individual adaptations and natural selection – usually measured by ability to reproduce. Adaptation –traits that make an organism to thrive and reproduce in its environment.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 4 parts of Natural Selection

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms –Example: camouflage adaptations of mantids that live in different environments Scientists can observe natural selection in action Figure 13.5A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The evolution of insecticide resistance is an example of natural selection in action Figure 13.5B Chromosome with gene conferring resistance to insecticide Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow Survivor Insecticide application

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sometimes, natural viruses or bacteria attack a population, killing those that have susceptibility to disease, leaving only that that are resistant to survive and reproduce.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A species is a group of populations whose individuals can interbreed and produce fertile offspring –Human populations tend to concentrate locally, as this satellite photograph of North America shows The modern synthesis connects Darwin’s theory of natural selection with population genetics Populations are the units of evolution Figure 13.6

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Natural selection results in the accumulation of traits that adapt a population to its environment –If the environment should change, natural selection would favor traits adapted to the new conditions Because of this, it is populations, NOT individuals, that are theorized to evolve or change over time. Today, evolution is a term used to describe biological change over time. Adaptive change results when natural selection upsets genetic equilibrium

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings