Evolutionary Influences: Pre-Darwin Thinkers & Darwin's Theory

1. Ch.10: Principles of Evolution

2. People Who Influenced Darwin

3. Before Darwin • Most people believed that the Earth was only a few thousand years old, and that it was unchanging • Around the 1700s, these ideas began to change

4. Hutton & Lyell • Believed that geologic features of Earth must have taken a long time to form, therefore Earth must be much older than a few thousand years • Also believed that Earth is and has always been changing • Darwin figured that since the Earth is changing maybe living things change as well

5. Lamarck • 1st to come up with a hypothesis about how organisms evolve • Believed that body structures would become larger or smaller due to use or disuse during an organism’s lifetime, & that those acquired traits could be passed to offspring • His hypothesis was wrong, but he was correct in that organisms do adapt to their environments

6. Malthus • Malthus was an economist who said that the human population was growing faster than the food supply, so eventually resources would run out • Darwin believed that this applied even more strongly to plant and animal populations, since they reproduce so much faster than humans

7. Section 2: Darwin’s Observations

8. Variation • Variation is the difference in the physical traits of an individual from those of others • Examples: • Tortoises who live on islands where vegetation is high have high shell edges and long necks to reach food & those who live on islands with low vegetation have short necks & legs • Finches have beaks that matched the food that they eat

9. Adaptation • An adaptation is a feature that allows an organism to better survive in its environment • Adaptations can lead to genetic change in a population over time

10. Darwin’s Evidence • Fossils Darwin found looked similar to living species, suggesting that they could be the ancestors of modern species • Darwin also found fossils of marine organisms in the mountains, suggesting that geologic change was occurring on Earth

11. Section 3: Theory of Natural Selection

12. Artificial Selection • Natural variation exists in all populations & some variation is heritable, meaning it can be passed from one generation to the next • For 100s of years, humans have been using artificial selection - the process by which humans change a species by breeding it for certain traits • Darwin believed that a process similar to artificial selection could happen in nature

13. Darwin Publishes his Theory • Over 20 years after Darwin’s voyage on the Beagle, he received a short essay from Alfred Russel Wallace that summarized all of Darwin’s thoughts about evolution. • This prompted Darwin to publish his own book called On the Origin of Species by Means of Natural Selection. • Natural Selection is the mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals

14. 4 Main Principles of Natural Selection 1.Variation - natural genetic variation exists in all populations 2.Overproduction - populations tend to produce more offspring than the environment can sustain, leading to competition for resources

15. 3.Adaptation - some variations allow an individual to better survive & reproduce • Fitness is a measure of the ability to survive and produce more offspring relative to other members of the population 4.Descent with modification - Over time, natural selection results in changes in a population, as only those with the highest fitness will pass on their genes

16. Natural Selection acts on Phenotypes • Natural selection doesn’t create new alleles, genetic mutations do • Natural selection can only act on traits that already exist in a population • As an environment changes, different traits become beneficial

17. Section 4: Evidence of Evolution

18. Darwin’s Evidence • The most important & convincing evidence of evolution comes from fossils, geography, embryology, & anatomy • Fossils - fossil organisms in lower, older layers of rock are more primitive than those in upper, newer layers; this supports descent with modification

19. Geography - Darwin observed that certain plants & animals in the Galapagos Islands were similar but not identical to mainland species • He hypothesized that some individuals from the mainland migrated to the islands & then adapted to each particular island

20. Embryology - similar features of embryos in very different organisms suggests evolution from a distant common ancestor • Ex. vertebrate embryos all have gill slits as embryos, but not as adults

21. Anatomy - comparing body parts of different species provides evidence of evolution • Homologous structures are features that are similar in structure but appear in different organisms & have different functions (suggest a common ancestor) • Analogous structures are structures that perform a similar function but are not similar in origin; they arise due to similar environmental challenges, not common ancestry

22. Structural Patterns & Evolutionary History • Structural patterns are clues to the history of a species • Vestigial structures are remnants of organs or structures that had a function in an early ancestor, but serve little or no function in the present • Ex. pelvic bones & hind limb bones in snakes • Ex. appendix & tail bone in humans

23. Section 5: Evolutionary Biology Today

24. Fossil Record • Paleontology was a new science in Darwin’s time • Our fossil record is incomplete, but it does support the theory of evolution • Many transitional fossils have been found that show the change in organisms over time

25. Molecular & Genetic Evidence • DNA Sequence Analysis - The more related two organisms are, the more similar their DNA will be. • Protein Comparisons - Molecular fingerprinting compares similarities among proteins of organisms. Species that have the same proteins most likely come from a common ancestor

26. Evolution Unites all Fields of Biology • All biological fields contribute to evolutionary theory • The theory of natural selection along with genetics is sometimes called the modern synthesis of evolutionary theory • The basic principles of evolution are used in many scientific fields such as medicine, geology, geography, chemistry