1. Chapter 22: Decent with Modification: A Darwinian View of Life

2. Darwin introduces a Revolutionary Theory
A new era of biology began on November 24, 1859 the day Charles Darwin published On the Origin of Species by Means of Natural Selection

3. The Origin of Species
Focused biologists’ attention on the great diversity of organisms
Figure 22.1

4. Darwin made 2 major points in his book
Organisms presently inhabiting the Earth are descendants of ancestral species
Proposed a mechanism for the evolutionary process, natural selection

5. Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

6. The historical context of Darwin’s life and ideas
Figure 22.2
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Lyell (modern geology)
Darwin (evolution, nutural selection)
Mendel (inheritance)
Wallace (evolution, natural selection)
1750
American Revolution
French Revolution
U.S. Civil War
1800
1850
1900
1795
Hutton proposes his theory of gradualism.
1798
Malthus publishes “Essay on the Principle of Population.”
1809
Lamarck publishes his theory of evolution.
1830
Lyell publishes Principles of Geology.
1831–1836
Darwin travels around the world on HMS Beagle.
Darwin begins his notebooks on the origin of species.
1837
Darwin writes his essay on the origin of species.
1844
Wallace sends his theory to Darwin.
1858
The Origin of Species is published.
1859
Mendel publishes inheritance papers.
1865

7. Resistance to the Idea of Evolution
The Origin of Species
Shook the deepest roots of Western culture
Challenged a worldview that had been prevalent for centuries

8. The Greek philosopher Aristotle viewed species as fixed and unchanging (scala naturae)

9. Carolus Linnaeus (~1750)
Founder of taxonomy, classifying life’s diversity
Each species designed for a specific purpose

10. Study of fossils helped lay the groundwork for Darwin’s ideas
Remains or traces of organisms from the past
Usually found in sedimentary rock, which appears in layers or strata
Figure 22.3

11. Paleontology, the study of fossils
Largely developed by French scientist Georges Cuvier (~1800)
Cuvier opposed idea of gradual evolutionary change
Advocated catastrophism
each boundary in strata represents a catastrophe

12. Gradualism
Profound change can take place through the cumulative effect of slow but continuous processes

13. Geologists Hutton and Lyell (~1830)
Changes in Earth’s surface can result from slow continuous actions still operating today
Strong influence on Darwin’s thinking

14. Hypothesized that species evolve
Lamarck (~1800)
Hypothesized that species evolve
Through use and disuse and the inheritance of acquired traits
Mechanisms he proposed are
unsupported by evidence
Figure 22.4

15. As a boy and into adulthood, Charles Darwin
Had a consuming interest in nature
After receiveing his B.A. degree was accepted on board the HMS Beagle, which was about to embark on a voyage around the world

16. During his travels on the Beagle
Observed and collected many specimens of South American plants and animals
Observed various adaptations of plants and animals that inhabited many diverse environments

17. Darwin’s interest in the geographic distribution of species
Darwin’s interest in the geographic distribution of species
Kindled by the Beagle’s stop at the Galápagos Islands
Figure 22.5
England
EUROPE
NORTH
AMERICA
Galápagos
Islands
Darwin in 1840,
after his return
SOUTH
Cape of
Good Hope
Cape Horn
Tierra del Fuego
AFRICA
HMS Beagle in port
AUSTRALIA
Tasmania
New
Zealand
PACIFIC
OCEAN
Andes
ATLANTIC

18. Darwin reassessed observations after the voyage
Adaptation to the environment and the origin of new species as closely related processes

19. From studies made years after Darwin’s voyage
Biologists have concluded that this is indeed what happened to the Galápagos finches
Figure 22.6a–c
(a) Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp.
(c) Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground.
(b) Insect eater. The green warbler finch (Certhidea olivacea) uses its narrow, pointed beak to grasp insects.

20. Darwin’s finches Figure 1.23
Large ground finch
Small ground
finch
Geospiza
magnirostris
Seed eater
Sharp-beaked
ground finch
Camarhynchus psitacula
Green warbler finch
Large tree finch
Large cactus
Ground finches
Tree finches
Insect eaters
Bud eater
Warbler finches
Common ancestor from South American mainland
Gray warbler finch
Certhidea olivacea
Certhidea fusca
difficilis
Cactus flower eater
Geospiza scandens
conirostris
fortis
Medium ground
Geospiza fuliginosa
Mangrove finch
Cactospiza
heliobates
Cactospiza pallida
Woodpecker
Medium tree finch
Camarhynchus pauper
Small tree finch
Vegetarian finch
Camarhynchus parvulus
Platyspiza crassirostris
Cactus ground finch
Figure 1.23

21. Darwin quickly finished The Origin of Species
1844, Darwin wrote a long essay on the origin of species and natural selection
Reluctant to introduce
1858, Darwin received manuscript f/ Wallace
Theory similar to Darwin’s
Darwin quickly finished The Origin of Species

22. Darwin’s 2 main ideas Evolution explains life’s unity and diversity
Natural selection is a cause of adaptive evolution

23. Descent with Modification
Summarized Darwin’s perception of the unity of life
All organisms are related through descent from an ancestor that lived in the remote past

30. Wrong!!

31. Darwinian view: the history of life is like a tree
Figure 22.7
Hyracoidea
(Hyraxes)
Sirenia
(Manatees
and relatives)
Years ago
Millions of years ago
Deinotherium
Mammut
Stegodon
Mammuthus
Platybelodon
Barytherium
Moeritherium
Elephas
maximus
(Asia)
Loxodonta
africana
(Africa)
cyclotis

32. Natural Selection and Adaptation as per Ernst Mayr
3 inferences based on 5 observations

33. Observation #1: Population sizes increase exponentially
Figure 22.8

34. Observation #2: Nonetheless, populations tend to be stable in size
Observation #3: Resources are limited
Inference #1: Production of more individuals than the environment can support
Leads to a struggle for existence, with only a fraction of their offspring surviving

35. Observation #4: Population varies extensively in their characteristics
No two individuals exactly alike
Figure 22.9

36. Observation #5: Much of this variation is heritable
Inference #2: Survival depends in part on inherited traits
Individuals whose inherited traits give them a high probability of surviving and reproducing are likely to leave more offspring than other individuals

37. Inference #3: Unequal survival and reproduction
gradual change in a population, favorable characteristics accumulating over generations

38. Artificial Selection
Human modification over many generations by selection and breeding individuals w/ desired traits
Figure 22.10
Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower
cluster
Leaves
Cauliflower
and
stems
Broccoli
Wild mustard
Kohlrabi
Stem
Kale

39. Natural selection is differential success in reproduction
Results f/ interaction between individuals that vary in heritable traits and their environment

40. Natural selection  increase over time of adaptation to environment
Figure 22.11
(a) A flower mantid in Malaysia
(b) A stick mantid in Africa

41. Environment changes natural selection results in adaptation to new conditions

42. Darwin’s theory of evolution
Continues to be tested by how effectively it can account for additional observations and experimental outcomes

43. Differential Predation in Guppy Populations
Observation of natural selection
 adaptive evolution in guppy populations
Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
and measured the average age and size of guppies at maturity over an 11-year period (30 to
60 generations).
EXPERIMENT
Pools with killifish,
but not guppies prior
to transplant
Experimental
transplant of
guppies
Predator: Killifish; preys
mainly on small guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
Figure 22.12

44. Control Population: Guppies from pools with pike-cichlids as predators
RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
161.5
185.6
67.5
Weight of guppies
at maturity (mg)
Age of guppies
at maturity (days)
92.3
48.5
Control Population: Guppies
from pools with pike-cichlids
as predators
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
76.1
Males
Females
85.7
58.2
CONCLUSION
Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.

45. The Evolution of Drug-Resistant HIV
Use of drugs selects for chance mutations that are resistant to the drugs
Natural selection is a cause of adaptive evolution

46. Percent of HIV resistant to 3TC
Drug therapy f/ HIV
Using medications selects for resistant viruses
Patient
No. 1
Patient No. 2
Percent of HIV resistant to 3TC
Patient No. 3
Weeks
Figure 22.13

47. Bacteria and viruses evolve rapidly
 challenge to society

48. Evolutionary theory
Cohesive explanation for many kinds of observations

49. Homology
Similarity resulting from common ancestry

50. Homologous structures
anatomical resemblances that represent variations on a structural theme that was present in a common ancestor
Figure 22.14
Human
Cat
Whale
Bat

51. Comparative embryology
Anatomical homologies not visible in adult organisms
Figure 22.15
Pharyngeal
pouches
Post-anal
tail
Chick embryo
Human embryo

52. Vestigial organs
Remnants of structures that served important functions in the organism’s ancestors

53. Molecular Homologies
Genes that are shared among organisms inherited from a common ancestor

54. Anatomical resemblances among species
Reflected in their molecules, genes, and gene products
Figure 22.16
Species
Human
Rhesus monkey
Mouse
Chicken
Frog
Lamprey
14%
54%
69%
87%
95%
100%
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide

55. Biogeography
Geographic distribution of species
Important part of Darwin’s theory

56. Biogeography (cont)
Similar mammals that have adapted to similar environments, have evolved independently from different ancestors
Sugar
glider
AUSTRALIA
NORTH
AMERICA
Flying
squirrel
Figure 22.17

57. Succession of forms observed in the fossil record  consistent with other evolutionary evidence

58. The Darwinian view of life
Predicts that evolutionary transitions should leave signs in the fossil record
Fossils of many such transitional forms have been found
Figure 22.18

59. In science, a theory (e.g. evolution)
Accounts for many observations, facts, laws, and data and explains and integrates a great variety of phenomena

60. Darwin’s theory of evolution by natural selection
Integrates diverse areas of biological study and stimulates many new research questions