Evolutionary Path: From Pre-Scientific Views to Modern Theories

1. Chapter 2 Development of Evolutionary Theory • Brief History of Evolutionary Thought • Natural Selection in Action • Constraints on Nineteenth-Century Evolutionary Theory • Opposition to Evolution

2. Evolution A change in the genetic structure of a population. Also refers to the appearance of a new species.

3. Pre-scientific View • Predominant world view throughout the middle ages was stasis, the idea that the world was fixed and unchanging. Also calledFixity of Species. • The Great Chain of Being held that life was arranged from the simplest to the 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 - that is, God’s design. Also called Teleology.

4. The Scientific Revolution • The discovery of the new world challenged fundamental views about the planet. • Exposure to new plants and animals increased the awareness of biological diversity. • Copernicus challenged the idea that the earth was the center of the universe. • Galileo’s work further supported the idea that the universe was a place of motion rather than fixity and solidified use of scientific method in research. • Keppler, Descartes and Newton established the laws (theories?) of physics, motion and gravity.

5. The Path to Natural Selection • John Ray provided the first definition of the concept of species and genus (groups of interbreeding organisms and related such groups). • Carolus Linnaeus developed a system of classification and laid the basis for taxonomy and binomial nomenclature used today. • Comte de Buffon stressed the importance of change in the universe and recognized the environment as an agent of change.

6. The Path to Natural Selection • John Baptiste Lamarck was the first scientist to produce an explanation for the evolutionary process, called Use-Disuse or Inheritance of Acquired Characteristics • Georges Cuvier introduced the concept of extinction and the theory of catastrophism. • Charles Lyell developed the theories of uniformitarianism and deep time. • Thomas Malthus wrote about the relationship between food supplies and population increase.

7. Charles Darwin (1809-1882) • Many of Darwin’s ideas were formed while serving as a naturalist on the voyage of the HMS beagle. • Darwin saw that biological variation within a species was critically important. • Darwin recognized the importance of sexual reproduction in increasing variation. • By 1844, Darwin had complete the work that he would publish fifteen years later.

8. Darwin’s Finches

9. Alfred Russell Wallace (1823-1913) • Wallace was a naturalist who worked in South America and Southeast Asia. • Wallace published an article suggesting that species were descended from other species and new species were influenced by environmental factors. • The coincidental development of evolution by natural selection by both Darwin and Wallace was resolved with the joint presentation of their papers to the Linnean Society of London.

10. Processes of Natural Selection • 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. • Individuals that possess favorable traits or variations are more likely to survive and produce offspring than those who do not.

11. Processes of Natural Selection • The environmental context determines whether or not a trait is beneficial. • Traits are inherited and passed on to the next generation. • Over long periods of time, variations accumulate so that 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.

12. Evolutionary Change Through Natural Selection • 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. See Peppered Moths for an example of this in action.

13. Peppered Moths & Industrial Melanism • Until the mid-nineteenth century, peppered moths, Biston betularia, had mostly light-colored wings. • Later, darker individuals became predominant. • Industrial smog helped turn tree trunks dark. • Contrasting colors between trunk color and moth color led to differential predation by birds. • Mutations and chance continued to create or permit survival of SOME lighter moths, though. • As pollution controls increased, frequencies reversed again.

14. Peppered Moths

15. Challenges to Darwin • Evolution not solidly demonstrated • There are no fossil intermediates • Intelligent design • Evolution violates Second Law of Thermodynamics • Proteins too improbable • Natural selection does not imply evolution • Irreducible complexity argument