1. Biology, 9th ed,Sylvia Mader
Chapter 17
Chapter 17
Darwin and Evolution
Darwin and Evolution

2. Outline History of Evolutionary Thought Darwin’s Theory of Evolution
Earth very old
Descend with change from a common ancestor
Adaptation to a changing environment
The Evidence of Evolution
Fossil
Biogeographical
Anatomical
Biochemical

3. Voyage of the HMS Beagle

4. Charles Darwin at 31

5. History of Evolutionary Thought
Prior to Darwin
View of nature determined by deep-seated beliefs
Held to be intractable truths
Biology thought had slowly begun to accept
Various ideas of evolution
Similarities between living things reflect recent common ancestry
Dissimilarities between living things reflect ancient common ancestry

6. Mid-Eighteenth Century
Taxonomy matured during mid-eighteenth century
Linnaeus believed in:
The fixity of species
That each species had:
An ideal structure and function, and
A place in the scala naturae (scale of complexity)
Count Buffon:
Wrote 44-volume catalog of all known plants and animals
Suggested descent with modification

7. Late Eighteenth Century
Cuvier:
First to use comparative anatomy to develop a system of classification
Founded Paleontology
Proposed Catastrophism
Local catastrophes in past had caused later strata to have a new mix of fossils
After each catastrophe, the region was repopulated by species from surrounding areas

8. Late Eighteenth Century
Lamarck:
First biologist to:
Propose evolution
Link diversity with environmental adaptation
Concluded more complex organisms are descended from less complex organisms
Proposed inheritance of acquired characteristics – Lamarckianism
Charles Lyell:
Earth is subject to slow but continuous cycles of erosion and uplift
Proposed uniformitarianism, rates and processes of change are constant

9. Evolutionary Thought before Darwin
Lamarck:
First biologist to:
Propose evolution
Link diversity with environmental adaptation
Concluded more complex organisms are descended from less complex organisms
Proposed inheritance of acquired characteristics – Lamarckianism

10. Formation of Sedimentary Rock
Charles Lyell:
Earth is subject to slow but continuous cycles of erosion and uplift
Proposed uniformitarianism, rates and processes of change are constant

11. Darwin’s Theory of Evolution
Geological observations consistent with those of Hutton & Lyell
Biogeographical observations:
The study of the geographic distribution of life forms on earth
Darwin saw similar species in similar habitats;
Reasoned related species could be modified according to the environment

12. A Glyptodont and a Giant Sloth

13. The Patagonian Hare, Dolichotis patagonium
Did the Patagonian Hare resemble a rabbit because the two types of animals were adapted to the same type of Environment?
Did the Patagonian hare have the face of a guinea pig because of common descent with guinea pigs?

14. Galápagos Islands Tortoises Finches
Darwin observed tortoise neck length varied from island to island
Proposed that speciation on islands correlated with a difference in vegetation
Finches
Darwin observed many different species of finches on various islands
Speculated they could have descended from a single pair of mainland finch

15. Galápagos Tortoises, Geochelone
Darwin observed tortoise neck length varied from island to island
Proposed that speciation on islands correlated with a difference in vegetation

16. Galápagos Finches Finches
Darwin observed many different species of finches on various islands
Speculated they could have descended from a single pair of mainland finch

17. Geology and Fossils
Darwin began to accept the idea that the earth is very old. And that there would be enough time for “descent with modification” to occur.
Darwin decided adaptations develop over time; he sought a mechanism by which adaptations might arise.

18. Natural Selection & Adaptation
Natural selection was proposed by both Alfred Russel Wallace and Darwin as a driving mechanism of evolution caused by environmental selection of organisms most fit to reproduce, resulting in adaptation.
Because the environment is always changing, there is no perfectly-adapted organism

19. Natural Selection & Adaptation
Individuals have heritable variations
More individuals produced each generation than environment can support
Some individuals have adaptive characteristics
Enables increased survival and reproduction
Increasing proportion of succeeding generations will have these characteristics
Populations become adapted to their local environment through change in individuals

20. Natural Selection Preconditions for Natural Selection
The members of a population have random but heritable variations.
In a population, more individuals are produced than will survive.
Some individuals have adaptive characteristics that enable them to survive and reproduce better. (Fitness)
Consequences of Natural Selection
An increasing proportion of individuals in succeeding generations have the adaptive characteristics. (Adaptation)
The result of natural selection is a population adapted to its local environment.

21. Variation in a Population

22. Organisms Have Variations
Darwin emphasized that individuals from a population vary in their:
Functional characteristics
Physical characteristics
Behavioral characteristics
Proposed that these VARIATIONS:
Are essential
Allow adaptation to the environment over time

23. Artificial Selection of Animals

24. Artificial Selection of Plants

25. Organisms Struggle to Exist
Malthus
Each generation has the same reproductive potential as the previous generation
Reproductive potential is greater than environment can support
Death, disease, and famine were inevitable if population were to have stability
Individuals experience a constant struggle for survival

26. Organisms Differ in Fitness
Fitness is the relative reproductive success of an individual
The most-fit individuals in a population capture a disproportionate share of goodies
Interactions with the environment determine which individuals reproduce the most
Adaptation
Changes that help a species become more suited to its environment
Product of natural selection

27. Transitional Fossils

28. Evidence for Evolution
Common Descent
“Descent with Modification”
The hypothesis of common descent is supported by many lines of evidence.
The more varied the evidence, the more certain it becomes.
Darwin synthesized much of the current data but biochemical research was yet to come.

29. Evidence for Evolution
Fossils Evidence
Biogeographical Evidence
Anatomical Evidence
Embryological development
Biochemical Evidence

30. The Evidence of Evolution: Fossil
Fossil Evidence
Fossils record the history of life from the past
Document a succession of life forms from the simple to the more complex
Sometimes the fossil record is complete enough to show descent from an ancestor

31. Evidence for Evolution
Fossils Evidence
The fossil record is the history of life recorded by remains from the past.
Fossils are at least 10,000 years old and include skeletons, shells, seeds, insects trapped in amber, and imprints of leaves.
The fossil record traces history of life and allows us to study history of particular organisms.
Fossil evidence supports the common descent hypothesis; fossils can be linked over time because they reveal a similarity in form, despite observed changes.

33. Evidence for Evolution
Fossils Evidence
Transitional forms reveal links between groups.
Caudipteryx is between dinosaurs and birds
This Chinese fossil shows some dinosaurs had feathers on arms, tail and probably body.
Advantages during running and escape gave rise to birds once lift-off occurred.
Eustheopteron is an amphibious-like fish
Seymouria is a reptile-like amphibian
Therapsids were mammal-like reptiles

34. Fraud!

35. Intermediate & Transitional Links
Charles Darwin acknowledged that the fossil record was a serious problem for his theory:
“By the theory of natural selection, all living species have been connected with the parent-species of each genus, by differences not greater that we see between the natural and domestic varieties of the same species at the present day… the number of intermediate and transitional links, between all the living and extinct species, must have been inconceivably great.”

36. Evidence for Evolution
Fossils Evidence
According to Darwin’s theory of evolution, all animals are descended from a common ancestor in the distant past. Supposedly, a single primitive species gradually diverged into two species, then those diverged over millions of generations to the point where we now see the major differences in body plans

37. Evidence for Evolution
Fossils Evidence
When we look at the fossil record we see that most of these major differences were present at the earliest appearance of animal life. Darwin himself knew this, and in The Origin of Species he called it a “serious” problem for his theory.

38. Evidence for Evolution
Fossils Evidence
Paleontologists James Valentine and Douglas Erwin wrote in 1987 that the Cambrian explosion “is real; it is too big to be masked by flaws in the fossil record.” And in 1991, Valentine and his colleagues wrote that the Cambrian explosion “was even more abrupt and extensive than previously envisioned.”

39. The Evidence of Evolution: Biogeographical
Distributions of plants and animals across earth
Consistent with origin in one locale and then spread to accessible regions

40. All of the marsupials in Australia presumably evolved from a common ancestor

41. Evidence for Evolution
Biogeographical Evidence
Physical factors, such as the location of continents, determine where a population can spread.
Marsupials arose when South America, Antarctica, and Australia were joined; Australia separated before placental mammals arose, so only marsupials diversified in Australia.
The distribution of organism on the earth is explainable by ASSUMING that related forms evolved in one locale. They then diversified as they spread out.

48. The Evidence of Evolution: Anatomical
Vertebrate forelimbs:
Homologous - All contain the same sets of bones in similar ways
Yet they are modified extensively to meet various adaptive needs
Darwin interpreted this as support for a hypothesis of common descent

49. Significance of Homologous Structures

50. The Evidence of Evolution: Anatomical
Homologous Structures:
Anatomically similar because they are inherited from a common ancestor
May be functionally similar or not
Analogous Structures:
Serve the same function
Not constructed similarly
Do not share a common ancestor
Vestigal Structures:
Fully-developed anatomical structures
Reduced or obsolete function

51. Vestigial Limbs in Whales

52. Arguments against Homology
1. If homology is defined as similarity due to common descent, then it is circular reasoning to use it as evidence for common descent.
Common Descent
Homology

53. Arguments against Homology
2. Biologist have known for decades that homologous features are NOT due to similar genes, so the mechanism that produces them remains unknown.
“Because homology implies community of descent from… a common ancestor it might be thought that genetics would provide the key to the problem of homology. This is were the worst shock of all is encountered…[because] characters controlled by identical genes are not necessarily homologous… [and] homologous structures need not be controlled by identical genes”
Gavin de Beers

54. Arguments against Homology
Homologous Structures can arise from different genes
In fruit flies
“even-skipped” gene – development of body segments. Not found in all other insects
“Sex-lethal” gene – sex determination in fruit flies but not other insects

55. Arguments against Homology
Non-homologous structures can arise from identical genes.
“Distal-less” gene – an appendage developmental gene found in:
Mice, spiny worms, Butterfly, sea urchins, velvet worm
Yet the appendages are not homologous either by similar structure or by common ancestry (descent)

56. The Evidence of Evolution: Anatomical
Embryological development
All vertebrate embryos have:
A postanal tail and
Paired pharyngeal (gill) pouches

57. Significance of Developmental Similarities
Embryological development
All vertebrate embryos have:
A postanal tail &
Paired pharyngeal (gill) pouches

58. Evidence for Evolution
Anatomical Evidence
Embryological development reveals a unity of plan.
During development, all vertebrates have a post-anal tail and paired pharyngeal pouches.
In fishes and amphibian larvae, the pouches become gills.
In humans, first pair of pouches becomes a cavity of middle ear and auditory tube; second pair becomes tonsils, while third and fourth pairs become thymus and parathyroid glands.
Above features are explained if fishes are ancestral to other vertebrate groups.

59. Haeckel’s Embryos – similarities in early embryos not only demonstrate that they are descended from a common ancestor, but also reveal what that ancestor looked like.
“The [human] embryo itself at a very early period can hardly be distinguished from that of other members of the vertebrate kingdom.” Since humans and other vertebrates “pass through the same early stages of development, … we ought frankly to admit their community of descent”
Charles Darwin, The Descent of Man

60. Contrary Evidence Embryological Development
Pharyngeal pouches (or folds) are never rudimentary gills in reptiles, birds or mammals.
British embryologist Lewis Wolpert:
“A higher animal, like the mammal, passes through an embryonic stage when there are structures that resemble the gill clefts of fish. But this resemblance is ILLUSORY and the structures in mammalian embryos only resemble the structures in the embryonic fish that will give rise to gills.”
The only way to see “gill-like” structures in human embryos is to read evolution into development.

61. Contrary Evidence Concerning Haeckel’s Embryos
Include ONLY those classes and orders closest to fitting Haeckel’s theory.
They distort the embryos they purport to show
(Most Seriously) they entirely omit earlier stages in which vertebrate embryos look very different.

62. Contrary Evidence Concerning Haeckel’s Embryos
Stephen Jay Gould, Natural History magazine March 2000
Gould acknowledged that Haeckel faked his drawings. “To cut to the quick of this drama, Haeckel had exaggerated the similarities by idealizations and omissions. He also, in some cases – in a procedure that can only be called fraudulent – simply copied the same figure over and over again.”

63. Contrary Evidence Concerning Haeckel’s Embryos
Stephen Jay Gould, (Natural History magazine, March 2000, pg. 45)
Gould acknowledged that Haeckel faked his drawings. “We do, I think, have the right to be both astonished and ashamed by the century of mindless recycling that has led to the persistence of these drawings in a large number, if not a majority, of modern textbooks. Atrocious!”

64. Biochemical Evidence Almost all living organisms:
Use the same basic biochemical molecules
Utilize same DNA triplet code
Utilize same 20 amino acids in their proteins
DNA base-sequence differences:
When very similar, suggest recent common descent
When more different, suggest more ancient common descent

65. Significance of Biochemical Differences

66. Review History of Evolutionary Thought Darwin’s Theory of Evolution
Earth very old
Descend with change from a common ancestor
Adaptation to a changing environment
The Evidence of Evolution
Fossil
Biogeographical
Anatomical
Biochemical

67. Biology, 9th ed,Sylvia Mader
Chapter 17
Ending Slide Chapter 17
Darwin and Evolution
Darwin and Evolution