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 –c–changes in populations, which consist of groups of individuals that live together and belong to the same species –a–a change in gene frequencies –p–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 skullHorse 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 sloths and extinct armadillos –unique to the Americas More of Darwin’s Observations

9 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 More of Darwin’s Observations

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

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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

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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

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26 Antibiotic Resistant Bacteria

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

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29 The Basis for Natural Selection 1.There is much variation between members of a species 2.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 1.There is much variation between members of a species 2.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

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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

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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 Spring breeder Fall 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 –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.

51 Phylogeny Horses –increase in body size –evolved tall complex molars and single-hoofed toe –change driven by climate expansion of grasslands Dollo’s law –evolutionary transition from at least several genetic changes is highly unlikely to be reversed by subsequent evolution

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