2. Patterns of Evolution / Descent with Modification
Chapter 23 / 19

3. Evolutionary Theories
Widely used to interpret the past and present, and even to predict the future
Reveal connections between the geological record, fossil record, and organism diversity

4. Geological Discoveries
Similar rock layers throughout world
Certain layers contain fossils
Deeper layers contain simpler fossils than shallow layers
Some fossils seem to be related to known species

5. Fossils Recognizable evidence of ancient life What do fossils tell us?
Each species is a mosaic of ancestral and novel traits
All species that ever evolved are related to one another by way of descent
The fossil record indicates that there have been great changes in the kinds of organisms on Earth at different points in time

6. Few individuals have fossilized, and even fewer have been discovered
The fossil record is biased in favor of species that
Existed for a long time
Were abundant and widespread
Had hard parts 6

7. Radiometric Dating
Radiometric dating

8. How Rocks and Fossils Are Dated
Sedimentary strata reveal the relative ages of fossils
The absolute ages of fossils can be determined by radiometric dating
A “parent” isotope decays to a “daughter” isotope at a constant rate
Each isotope has a known half-life, the time required for half the parent isotope to decay 8

9. Radiocarbon dating can be used to date fossils up to 75,000 years old
For older fossils, some isotopes can be used to date volcanic rock layers above and below the fossil 9

10. Geologic Time Scale
Geologic time scale

11. PANGEA - Changing Land Masses
Drifting continents

12. Plate Margins
Plate margins

13. Evidence of Movement
Wegener cited evidence from glacial deposits and fossils
Magnetic orientations in ancient rocks do not align with the magnetic poles
Discovery of seafloor spreading provided a possible mechanism

14. Geologic Forces
Geologic forces

15. 19th Century - New Theories
Scientists attempt to reconcile evidence of change with traditional belief in a single creation event
Georger Cuvier
Paleontologist
speculated that each boundary between strata represents a catastrophe that destroyed many species 15

16. 19th Century – New Theories
James Hutton and Charles Lyell
geologists
perceived that changes in Earth’s surface can result from slow, continuous actions still operating today
Lyell further proposed that the mechanisms of change are constant over time
This view strongly influenced Darwin’s thinking 16

17. 19th Century - New Theories
Lamarck
hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics
The mechanisms he proposed are unsupported by evidence 17

19. DARWIN Galapagos Finches
Darwin observed finches with a variety of lifestyles and body forms
On his return, he learned that there were 13 species
He attempted to correlate variations in their traits with environmental challenges

20. Finches of the Galapagos Islands
Galapagos Finches
Finches of the Galapagos Islands

21. (a) Cactus-eater (c) Insect-eater (b) Seed-eater Figure 19.6
Figure 19.6 Three examples of beak variation in Galápagos finches
(b) Seed-eater 21

23. Darwin’s Theory
A population can change over time when individuals differ in one or more heritable traits that are responsible for differences in the ability to survive and reproduce.

24. Darwin’s Focus on Adaptation
In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes 24

25. Ideas from The Origin of Species
Darwin explained three broad observations about life
The unity of life
The diversity of life
The match between organisms and their environment 25

26. Descent with Modification
The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past 26

27. Artificial Selection, Natural Selection, and Adaptation
Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits
artificial selection
Darwin argued that a similar process occurs in nature
video 27

29. Cabbage Selection for apical (tip) bud Brussels sprouts Selection for
axillary (side)
buds
Broccoli
Selection
for flowers
and stems
Figure Artificial selection
Selection
for stems
Selection
for leaves
Kale
Wild mustard
Kohlrabi 29

30. Darwin drew two inferences from two observations Observation #1:
members of a population often vary in their inherited traits
Inference #1:
Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals
Survival of the Fittest 30

31. many of these offspring fail to survive and reproduce Inference #2:
Observation #2:
all species can produce more offspring than the environment can support
many of these offspring fail to survive and reproduce
Inference #2:
This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations 31

32. If some heritable traits are advantageous
Darwin was influenced by Thomas Malthus, who noted the potential for human population to increase faster than food supplies and other resources
If some heritable traits are advantageous
these will accumulate in a population over time
this will increase the frequency of individuals with these traits
explains the match between organisms and their environment 32

33. Natural Selection: A Summary
Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals
Over time, natural selection increases the match between organisms and their environment
If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species 33

34. Note that individuals do not evolve; populations evolve over time
Natural selection can only increase or decrease heritable traits that vary in a population
Adaptations vary with different environments 34

35. Natural Selection
A difference in the survival and reproductive success of different phenotypes
Acts directly on phenotypes and indirectly on genotypes

36. Variation in Populations
All individuals have the same genes that specify the same assortment of traits
Most genes occur in different forms (alleles) that produce different phenotypes
Some phenotypes compete better than others

37. Change over Time
Over time, the alleles that produce the most successful phenotypes will increase in the population
Less successful alleles will become less common
Change leads to increased fitness
Increased adaptation to environment

38. Comparative Morphology
Study of similarities and differences in body plans of major groups
Puzzling patterns:
Animals as different as whales and bats have similar bones in forelimbs
Some parts seem to have no function
Guiding principle:
When it comes to introducing change in morphology, evolution tends to follow the path of least resistance

39. Comparative Morphology Comparative pelvic anatomy

40. Morphological Divergence
Change from body form of a common ancestor
Produces homologous structures
show whale video

41. Morphological Convergence
Individuals of different lineages evolve in similar ways under similar environmental pressures
Produces analogous structures that serve similar functions

42. Morphological Convergence

43. NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel
Figure Convergent evolution
AUSTRALIA
Flying
squirrel 43

44. Comparative Development
Each animal or plant proceeds through a series of changes in form
Similarities in these stages may be clues to evolutionary relationships
Mutations that disrupt a key stage of development are selected against

45. Similar Vertebrate Embryos
FISH
REPTILE
BIRD
MAMMAL

46. Pharyngeal arches Post-anal tail Chick embryo (LM) Human embryo
Figure Anatomical similarities in vertebrate embryos
Chick embryo (LM)
Human embryo 46

47. Altering Developmental Programs
Some mutations shift a step in a way that natural selection favors
Small changes at key steps may bring about major differences
Insertion of transposons or gene mutations

48. Proportional Changes in Skull
Mutation and proportional changes

49. Comparative Biochemistry
Kinds and numbers of biochemical traits that species share is a clue to how closely they are related
Can compare DNA, RNA, or proteins
More similarity means species are more closely related

50. Comparing Proteins
Compare amino acid sequence of proteins produced by the same gene
Human cytochrome c (a protein)
Cytochrome c functions in electron transport
Deficits in this vital protein would be lethal
Identical amino acids in chimpanzee protein
Chicken protein differs by 18 amino acids
Yeast protein differs by 56

51. Sequence Conservation
Cytochrome C comparison

52. Nucleic Acid Comparison
Use single-stranded DNA or RNA
Hybrid molecules are created, then heated
The more heat required to break hybrid, the more closely related the species

53. Impacts, Issues Video
Measuring Time