Chapter 2 The Development of Evolutionary Theory Chapter Outline Brief History of Evolutionary Thought Natural Selection in Action Constraints on Nineteenth-Century Evolutionary Theory Opposition to Evolution Evolution A change in the genetic structure of a population. Also refers to the appearance of a new species. Often controversial, some religious views hold that evolutionary statements run counter to biblical teachings. Evolution Is a Theory The theory has been supported by a mounting body of genetic evidence. The theory has stood the test of time. The theory stands today as the most fundamental unifying force in biological science. Pre-scientific View In the middle ages, the predominant world was stasis, the world was fixed and unchanging. The great chain of being held that life was arranged from simplest to most complex. It was believed that the earth was “full” and nothing new could be added. The world was seen as the result of a grand design - God’s design. The Scientific Revolution Discovery of the new world challenged fundamental views about the planet. Exposure to new plants and animals increased awareness of biological diversity. The Scientific Revolution Copernicus challenged the idea that the earth was the center of the universe. Galileo’s work supported the idea that the universe was a place of motion. Keppler, Descartes and Newton established the laws of physics, motion and gravity. The Path to Natural Selection John Ray provided first definition of the concept of species and genus. Carolus Linnaeus developed system of classification and the basis for taxonomy. Comte de Buffon stressed the importance of change in the universe and the environment as an agent of change. The Path to Natural Selection John Baptiste Lamack was the first scientist to produce an explanation for the evolutionary process. Georges Cuvier introduced the concept of extinction and the theory of catastrophism. Charles Lyell developed the theory of uniformitarianism. Thomas Malthus wrote about relationship between food supply and population increase. Charles Darwin (1809-1882) Ideas were formed while serving as a naturalist on the voyage of the HMS beagle. Darwin saw the importance of biological variation within a species. Recognized the importance of sexual reproduction in increasing variation. By 1844, Darwin had complete the work that he would publish fifteen years later. Alfred Russell Wallace (1823-1913) A naturalist who worked in South America and Southeast Asia. Suggested species descended from other species and new species were influenced by environmental factors. Presented paper on evolution and natural selection to the Linnean Society of London jointly with Darwin. Processes of Natural Selection 1. 2. 3. Species can produce offspring at a faster rate than food supplies increase. There is biological variation within all species. In each generation, more individuals are produced than can survive. Processes of Natural Selection 4. 5. 6. Individuals that possess favorable traits or variations are more likely to survive and produce offspring. Environmental context determines whether a trait is beneficial. Traits are inherited and passed on to the next generation. Processes of Natural Selection 7. 8. Variations accumulate over long periods of time, so later generations may be distinct from ancestral ones. As populations respond to pressures over time, they may become distinct species, descended from a common ancestor. Evolutionary Change Through Natural Selection 1. 2. 3. A trait must be inherited to have importance in natural selection. Natural selection cannot occur without variation in inherited characteristics. Fitness is a relative measure that will change as the environment changes.