Chapter 7

1. Chapter 7 Evolution and the Fossil Record

2. Chapter 7 - Guiding Questions • What lines of evidence convinced Charles Darwin that organic evolution produced the species of the modern world? • What are the components of natural selection? • What is the source of the variability that is the basis of natural selection? • What role does geography play in speciation? • What factors lead to evolutionary radiation? • Why is convergence one of the most convincing kinds of evidence that evolutionary changes are adaptive? • Why do species become extinct? • What is mass extinction? • In what ways can evolutionary trends develop?

3. Evolution Evolution • changes in populations, which consist of groups of individuals that live together and belong to the same species • a change in gene frequencies • populations evolve, not individuals • YOU can’t evolve! Extinct ground sloth (20 ft long)

4. Evolution Adaptations • specialized features of animals and plants (or any other organism) which perform one or more useful functions • allow that organism to excel in its environment • YOU can only modify characteristics over which your genes have control; e.g., tanning Cat skull Horse skull Venus Flytrap

5. Inefficient Evolution • can only operate by changing what is already present; • it’s the business of remodeling rather than new construction from scratch • e.g., to make a new structure, natural selection starts by modifying an already existing one • e.g., how could ‘night vision’ evolve?

6. Charles Darwin • 1831 • set sail on the Beagle • schooled in uniformitarianism • Lyell’s Principles of Geology • a keen observer of natural phenomena • 1859-On the Origin of Species by Natural Selection

7. Some of Darwin’s Observations • Rhea • large flightless birds • found only in South America • also found extinct, fossil forms • Some similarities but also obvious differences from ostrich (Africa) and emu (Australia)

8. More of Darwin’s Observations • sloths and extinct armadillos • unique to the Americas

9. More of Darwin’s Observations • Oceanic islands • many barren; Hawaii has no native snakes, frogs, FW fish, etc. • species must have originated elsewhere • Galápagos Islands • tortoises with shells unique on each island • shared a common ancestry • followed later by differentiation

10. Galapagos Islands Range from 3 to 5 my old

11. Galapagos Tortoises • 14 subspecies, 11 extant, several with very small populations • e.g., Lonesome George

12. Lonesome George Isla Pinta

13. Finches of the Galápagos • different beak types • slender-insectivorous • sturdy-seed crushing • woodpecker-like-tool user • differentiation based on lifestyle • curiously resemble a South American mainland finch Darwin’s Famous Finches

14. Adaptive Radiation of Darwin’s Finches

15. Feeding Adaptations of Ground Finches

16. Charles Darwin • Additional observations • Anatomical relationships • embryos of many vertebrates are quite similar, even superficially indistinguishable

18. Charles Darwin • Additional observations • Anatomical relationships • embryos of many vertebrates quite similar • homology • presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions

20. Charles Darwin • Additional observations • Anatomical relationships • embryos of many vertebrates quite similar • homology • presence in two different groups of animals or plants of organs that have the same ancestral origin but serve different functions • vestigial organs • organs that serve no apparent purpose but resemble organs that perform functions in other creatures

21. Pelvic structures in whales and snakes

22. Vestigial Structures

23. Theory of Evolution • Natural Selection- ‘survival of the fittest’ • the process that operates in nature but parallels the artificial selection by which breeders develop new varieties of plants and animals • success of an individual determined by advantages it has over others • survives to bear offspring with same trait

26. Antibiotic Resistant Bacteria

27. The Basis for Natural Selection • There is much variation between members of a species.

29. The Basis for Natural Selection • There is much variation between members of a species • Reproduction is way in excess of the number that the habitat can survive e.g., Robins

30. E.g., Robins

31. The Basis for Natural Selection • There is much variation between members of a species • Reproduction is way in excess of the number that the habitat can survive e.g., Robins 3. Differential reproductive success-those best adapted survive to reproduce the most

32. Will the all survive?

33. Theory of Evolution • Darwin didn’t have all the tools we have today to explain his idea. • Genetics was in its infancy—Mendel’s ideas, though contemporary with Darin, weren’t appreciated for decades. • Genes-hereditary factors • Particulate inheritance • Gregor Mendel’s idea that organisms retain identities through generations • Peas • No blending • Colors could be masked for generations

35. Theory of Evolution • Mutations • alteration of genes • provides for variability • very few are helpful • DNA • Deoxyribonucleic Acid • transmits chemically coded information • mostly found in chromosomes

37. Theory of Evolution • sexual recombination • each parent contributes one half of its chromosomes to offspring via a gamete • special reproductive cell containing one of each type of chromosome • female ovum/egg; male sperm • yields new combinations-e.g., my kids aren’t exact copies of me; genes of their mother and me are both present. • mutations increase variability—and we all have them! • gene pool • sum total of genetic components of a population or group of interbreeding individuals • you have only a small subset of the human gene pool • reproductive barriers limit the pool and keep species separate • speciation • origin of a new species from two or more individuals of a preexisting species

38. Reproductive Isolation Fall breeder Spring breeder

39. Origination • Evolutionary radiations • pattern of expansion from some ancestral adaptive condition represented by descendant taxa • adaptive breakthrough • appearance of key features that allow radiation to occur • fossil record documents patterns • E.g., Jurassic corals

40. Jurassic Corals

41. Origination • Rates of speciation • Galápagos Islands-formed millions of years ago • Lake Victoria • 13,000 years old • 497 unique species of cichlid fish, many with specialized adaptations • Molecular clock • assume average rate of mutation • determine pace of change • extrapolate timing of change

42. Convergence • Evolution of similar forms in two or more different biological groups • Marsupials and placental mammals • similar form • isolated, adaptive convergent evolution after initial divergence

43. Extinction • caused by extreme impacts of limiting factors • predation • disease • competition • pseudoextinction • species evolutionary line of descent continues but members are given a new name • high rates of extinction make useful index fossil • ammonoids

44. Extinction • rates • average rate has declined through time • mass extinctions • many extinctions within a brief interval of time • largest events peak at extinction of >40% genera • rapid increase (radiation) follows

45. Modern Mass Extinctions • fossil patterns reflected in modern • tropical species • large animals • loss of habitat • direct exploitation • likely replacement by opportunistic species

46. Evolutionary Trends • Cope’s rule • body size increases during evolution of a group of animals • structural limitations on size • specialized adaptations limit evolution • elephants • manatees

47. Evolutionary Trends Whales • terrestrial origin • 50 Ma • small (2 m) mammals with feet • marine adaptation • 40 Ma • lost hind limbs • no pelvic bones • up to 20 m

48. Phylogeny • Phylogeny • complex, large-scale trend within a branching tree of life • gradual large-scale change from one species to another is rare • e.g., Jurassic coiled oysters

49. Phylogeny • Axolotl • example of rapid speciation from parent species • parent is amphibious • offspring is aquatic throughout life after one simple genetic change

50. Phylogeny • rates • gradualistic model • very slow rates • punctuational model • rapid evolution with little change between steps • bowfin fish • little change in 60 m.y.