Darwin's Theory of Natural Selection: Evolutionary Concepts and Evidence

1. Chapter 15 Evolution 15-1 Darwin’s Theory of Natural Selection

2. Charles Darwin1809-1882 • As a boy liked nature study • Flunked out of med school • Theology degree from Christ College, Cambridge • Became minister Church of England • 1831 job as naturalist on HMS Beagle • 5 year world voyage to chart coasts

3. Unique Galapagos Islands • 1000 km off west coast of South America • Unique species animals, similar to S.A. but not exact • Unique species animals on each island, similar to S.A. and each other but not exact

4. Darwin’s Finches • Especially interesting is the number and variety of these birds • Each island had own variety dependent on the food source

6. Darwin’s Influenced by: • Thomas Malthus: human species grows faster than food supply; competition for food, space, mates, shelter; struggle to survive • Pigeon breeding: found individual variation, could breed desirable traits into a population (artificial selection) • His 13 children: found individual variation • 22 years of study after HMS Beagle to formulate his ideas

7. Darwin’s Influenced by: Charles Lyell: Geologist proposed theory of uniformitarism. Geological process are so uniform that their rates and effects must balance out over time. Example mountain uplift balanced by erosion. Darwin took from it that geological processes are slow and continuous meaning that the Earth is very old.

8. Darwin’s Influenced by: Lamarck Theory of Evolution (1809) Saw fossils like an escalator, evolution driven by more and more complex organisms (perfection). Use and disuse idea: the more you use a part the better (adaptation) it gets. Acquired traits: what you get during your lifetime gets passed to your offspring. He was WRONG!

9. Natural Selection • Is a mechanism for change in a population • Groups NOT INDIVIDUALS evolve • Occurs when organisms with certain variations survive, reproduce, and pass their variations onto the next generation

10. Individuals in a population have variations D. Overtime, individuals with helpful variations make up more and more of the population Organisms produce more offspring than can survive Individuals with certain helpful variations survive in their environment, reproduce, and pass helpful variation on to offspring Theory of Natural Selection (old)

11. 15.1 Darwin’s Theory of Natural Selection Natural Selection (NEW) • Individuals in a population show variations. • Variations can be inherited. • Organisms have more offspring than can survive on available resources. • Variations that increase reproductive success will have a greater chance of being passed on.

12. Origin of Species by Means of Natural Selection By Charles Darwin Published in 1859

13. Other’s Ideas on Evolution • Alfred Wallace: had same ideas about natural selection as Darwin, but Darwin published first (both presented their ideas in 1858 at a scientific meeting) • Genetics has changed ideas about evolution; now we measure frequency of allele in gene pool • Gene pool: all the genes of a population

14. Chapter 15 Evolution 15-2 Evidence of Evolution

15. Evolution and Natural Selection • Darwin’s theory of natural selection is not synonymous with evolution. • It is a means of explaining how evolution works. • The theory of evolution states that all organisms on Earth are related; share a common ancestor.

16. Evidence for Evolution • Fossils • Anatomy • Embryology • Biochemistry • Geographic Distribution • Adaptations

17. 1. Fossils • Record of early life • Ancestors of whales were dog sized land animals • Record is incomplete

18. 2. Anatomy • Homologous structures: similar arrangement or function or both Evidence that organisms evolved from a common ancestor (Analogous structures: body parts do not have common evolutionary origin but have similar function)

19. Homologous Structures

20. 2. Anatomy B. Vestigial structures: body part that has no function today but probably did in ancestor eyes of blind mole rat eyes of blind cave fish wings of flightless birds human appendix, little toe, muscles to move ears…

21. 3. Embryology • Embryo: earliest stage of growth and development • Similarities for all vertebrates • Tail • Gill slits Suggest a common ancestor Gill slits tail

23. 4. Biochemistry • Comparison of DNA, RNA, and/or proteins • Newest RNA evidence is that there are three types (Domains) of organisms Eukarya Eukaryote Protista Fungi Plants Animals Archae Prokaryote Archaebacteria Eubacteria Prokaryote Eubacteria Ancestral Prokaryote

24. 5. Geographic Distribution • The distribution of plants and animals that Darwin saw first suggested evolution to Darwin. Rabbit Mara

25. 5. Geographic Distribution • Patterns of migration were critical to Darwin when he was developing his theory. • Evolution is intimately linked with climate and geological forces. • Biogeography is the branch of science that studies the world distribution of organisms.

26. 6. Adaptations Any variation that helps an organisms’ chance for survival • Structural Adaptations: can take millions of years mimicry: enables one species to resemble another species; harmless look like harmful all harmful look alike

27. 6. Adaptations • Structural Adaptations camouflage: enables species to blend in with surroundings so that they are not easily found by predators

28. 6. Adaptations B. Physiological adaptations: takes shorter time Changes in organisms metabolic processes (function) antibiotic resistant bacteria pesticide resistant insects (head lice) herbicide resistant weeds

29. 6. Adaptations • Not all features of an organisms are necessarily adaptive. • Example: helplessness of human babies. • Human babies are born at a much earlier stage of development than other mammals. This is probably not an adaptation but a consequence of the larger brains and upright posture of humans.

30. Chapter 15 Evolution 15-3 Shaping Evolutionary Theory

31. Population Genetics and Evolution • Darwin knew NOTHING about genes, never read the work of Mendel even though they lived about the same time • Darwin: 1809-1882 • Mendel: 1822-1884

32. Populations NOT individuals evolve • Individuals can’t change their genes, can’t change their genotypes and can’t change their phenotypes or trait • Individuals can only respond to their environments as their genes allow

33. Natural Selection acts on Phenotypes • If an individual has a phenotype that is poorly suited to their environment, the individual organism may not survive • and/or may not reproduce to pass their genes on to the next generation

34. Natural Selection acts on Phenotypes • Each member of a population has the genes that characterize the traits of the species • All the genes (and alleles) of individuals make up the gene pool of the population • Evolution occurs as a population’s genes and their frequencies change over time

35. Allelic Frequency • Allelic frequency: % of any specific allele • = Number of specific allele Total number of alleles • Can change over time or stay the same

36. Hardy-Weinberg Principle • Hardy-Weinberg principlestates that when allelic frequencies remain constant, a population is in genetic equilibrium.

37. Hardy-Weinberg Principle • Equation: p2 + 2pq + q2 = 1 and p + q = 1 • This equation allows us to determine the equilibrium frequency of each genotype in the population. • Homozygous dominant (p2) • Heterozygous (2pq) • Homozygous recessive (q2)

39. Genetic Equilibrium • Frequency of alleles stays the same over many generations • Not evolving • Phenotypes remain the same too

40. Changes in Genetic Equilibrium • Mutations • Genetic Drift • Gene Flow • Nonrandom mating • Natural Selection

41. 1. Mutations • Caused by environmental factors like radiation and chemicals • Caused by random chance • Some mutations are lethal and quickly eliminated • Some mutations are helpful (useful) and new allele or gene becomes part of the population’s gene pool

42. 2. Genetic Drift • Alteration of allelic frequency by chance events • Small populations that become isolated by natural events can evolve differently • Bottleneck effect: disasters such as earthquakes, floods kill victims unselectively • Founder effect: few individuals colonize an isolated area (Darwin’s finches)

43. 3. Gene Flow • Movement of individuals into or out of a population • When individuals immigrate or emigrate their genes go with them • Example: westward expansion in the US

44. 4. Nonrandom mating • Usually organism mate with those in close proximity. (May result in inbreeding). • Usually organisms mate with those of the same or similar phenotype.

45. 5. Natural Selection • Acts on variation • Some variations increase or decrease an organism’s chance for survival • Variation can be inherited and are controlled by alleles

46. 5. Natural Selection • Four Types of Natural Selection that act on variation • Stabilizing Selection • Directional Selection • Disruptive Selection • Sexual Selection

47. Stabilizing Selection • Favors average • Reduces variation • Example: Large spiders easy to see and be eaten while small spiders have a hard time getting food

48. Directional Selection • Favors one extreme • Can lead to rapid evolution • Example: Over time there were more and more darker colored Peppered Moths in the industrial area of England in the 1800’s

49. Disruptive Selection • Both extremes are favored • Average (mean) disfavored • Leads to the evolution of two species • Example: Light yellow butterfly overtime becomes either nearly white or orange

50. Sexual Selection • Sexual selection operates in populations where males and females differ significantly in appearance. • Qualities of sexual attractiveness appear to be the opposite of qualities that might enhance survival. • Example: tail of male peacocks, while beautiful, makes the organism a greater target for predators.