DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE

1. DESCENT WITH MODIFICATION: A DARWINIAN VIEW OF LIFE CHAPTER 22

2. Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago

3. HISTORICAL CONTEXT • Carl Linnaeus (1707-1778) – founder of taxonomy (scientific name) grouped similar species into same genus • Georges Cuvier (1769-1832) – catastrophism – different species in layered rock due to catastrophic events like floods

4. James Hutton (1726-1797) – gradualism – profound change is a cumulative product of slow but continuous process; ex. Rivers making canyons • Charles Lyell (1797-1875) – uniformitarianism – geological process have not changed throughout Earth’s history • Jean Baptiste Lamarck (1744-1829)- thought acquired characteristics can be passes on to offspring

5. Formation of sedimentary rock and deposition of fossils from different time periods

6. Strata of sedimentary rock at the Grand Canyon

7. Charles Darwin in 1859, the year The Origin of Species was published

8. CHARLES DARWIN (1809-1882) • Worked on the HMS Beagle in 1830’s • Observed and collected thousands of different species • Galapagos Islands (west of S. America) most interesting

9. The Voyage of HMS Beagle

11. Galápagos finches

12. “The Galápagos tortoise (or Galápagos giant tortoise), is the largest living tortoise, endemic to nine islands of the Galápagos archipelago. Adults of large subspecies can weigh over 300 kilograms (660lb) and measure 1.2 meters (4 ft) long. Although the maximum life expectancy of a wild tortoise is unknown, the average life expectancy is estimated to be 150-200 years.” Source: en.wikipedia.org/wiki/Gal%C3%A1pagos_tortoise

13. Darwin read Lyell’s Principles of Geology and felt age of earth was much older than previously thought • 1844 Darwin wrote essay on the origin of species • 1858 – Alfred Wallace sends manuscript to Darwin about Natural Selection

14. Lyell presented Wallace’s paper as well as Darwin’s 1844 essay to scientists • 1859 The Origin of Species published by Darwin • Descent with modification • Natural selection (the mechanism)

15. Descent with modification

16. DARWIN’S OBSERVATIONS • Individuals vary within a population • Traits inherited • All species are capable of overproduction • Many offspring do not survive

17. DARWIN’S INFERENCES • Individuals with inherited traits that give them a better chance of surviving and reproducing tend to leave more offspring than those without those traits • Unequal ability of individuals to survive will lead to favorable traits in populations over generations.

18. NATURAL SELECTION • A population evolves, not an individual! • Acquired characteristics may be adaptable but are not inherited!** • The environment does not create a best fit characteristic, but selects for it!

19. A few of the color variations in a population of Asian lady beetles

20. Artificial selection: diverse vegetables derived from wild mustard

22. Goldendoodle and a liger AP:April. 29, 2005 ST. THOMAS, Barbados - It's male.  But what is it?  A zonkey? A deebra?  That's the debate in Barbados since a zebra gave birth to a foal sired by a donkey.

23. EVIDENCE OF EVOLUTION • Biogeography – geographical distribution of species • Ex. Islands with similar species to mainland • Fossil record – transitional forms • Comparative Anatomy – homologous structures among different organisms

24. Vestigial organs –marginal, if any importance, remnants of structures that once served a function • Whale pelvis and leg bones and human appendix • Comparative Embryology – most vertebrates share common early development (gill slits) • Molecular Biology – similar overall DNA, similar proteins (ex. Cytochrome c)

27. Evolution of insecticide resistance in insect populations

28. Evolution of drug resistance in HIV

29. Homologous structures: anatomical signs of descent with modification

30. Molecular Data and the Evolutionary Relationships of Vertebrates

31. Different geographic regions, different mammalian “brands”

32. The evolution of fruit fly (Drosophila) species on the Hawaiian archipelago

33. A transitional fossil linking past and present

34. Left: Trilobite evolution Right: Whale evolution

35. THE EVOLUTION OF POPULATIONS Chapter 23

36. GENETIC VARIATION • Genetic variation that makes evolution possible • Mutations • Change in DNA sequences • Average 1 in 100,000 genes per generation • Sexual reproduction • Crossing over • Independent assortment • Fertilization

37. POPULATION GENETICS • Population – localized group of individuals belonging to the same species • Species – organisms that can interbreed and produce fertile offspring • Gene pool – total genes in a population • If all members of a population are homozygous for the same allele, that allele is fixed. • Gene frequency - two or more alleles for a gene, each having a relative frequency (proportion) in the gene pool

38. Example: • A = pink • a = white • 1000 plants = 200 white + 800 pink • 800 pink = 340(AA) + 460(Aa) • Find A’s frequency • From AA: 340 x 2 = 680 • From Aa: 460 x 1 = 460 • 680 + 460 = 1140 • 1140/2000 = .57 = .6 • The 2000 is total number of alleles for 1000 plants

39. Find a’s frequency • From aa: 200 x 2 = 400 • From Aa: 460 x 1 = 460 • 400 + 460 = 860 • 860/2000 = .43 = .4 • Find A’s frequency • 1- .4 = .6

40. HARDY-WEINBERG THEOREM • Frequencies of alleles and genotypes in a population’s gene pool remain constant over the generations unless acted upon by agents other than random sexual recombination • Hardy-Weinberg tells us what to expect if a population is NOTevolving!!

41. The Hardy-Weinberg Theorem

42. Random Gamete production

43. The Hardy-Weinberg theorem

44. EXAMPLE USING FLOWER POPULATION • Probability of picking 2 A from example • .6 x .6 = .36 • Probability of picking 2 a from example • .4 x .4 = .16 • Probability of picking Aa from example (aA or Aa) • (.4 x .6) + (.6 x .4 ) = .48

45. HARDY-WEINBERG EQULIBRIUM • The sexual process of meiosis and random fertilization maintain the same allele and genotype frequencies over generations. • In the example: • p = .6 = A • q = .4 = a • p + q = 1 • p = 1 - q and q = 1 - p p2 + 2pq + q2 = 1 (AA)+ (2Aa) + (aa) = 1

46. FIVE CONDITIONS FOR H-W • Very large population size • No gene flow (genes entering or leaving a population) • No net mutations • Random mating • No natural selection These mean NO EVOLUTION!

47. MICROEVOLUTION • Microevolution – generational change in a population’s frequencies of alleles or genotypes

48. FIVE AGENTS OF MICROEVOLUTION • Genetic Drift – rapid changes in a gene pool of a small, isolated population due to chance • Flip coin 10 times: may get 7 heads and 3 tails • Flip coin 1000 times: unlikely to get 700 head and 300 tails

49. Genetic drift

50. Two conditions that lead to genetic drift • Bottleneck Effect – genetic makeup of a small surviving population is unlikely to be representative of original population • Northern elephant seals nearly extinct due to hunting in late 1890’s which caused little genetic variation at 24 different loci