1. CHAPTER 13 How Populations Evolve
SSHS AP Biology

2. Clown, Fool, or Simply Well Adapted?
All organisms have evolutionary adaptations
Inherited characteristics that enhance their ability to survive and reproduce
The blue-footed booby of the Galápagos Islands has features that help it succeed in its environment
Large, webbed feet help propel the bird through water at high speeds

3. A streamlined shape, large tail, and nostrils that close are useful for diving
Specialized salt-secreting glands manage salt intake while at sea

4. 13.1 A sea voyage helped Darwin frame his theory of evolution
EVIDENCE OF EVOLUTION
13.1 A sea voyage helped Darwin frame his theory of evolution
Aristotle and the Judeo-Christian culture believed that species are fixed
Fossils suggested that life forms change
This idea was embraced by Lamarck in the early 1800s

5. While on the voyage of the HMS Beagle in the 1830s, Charles Darwin observed
similarities between living and fossil organisms
the diversity of life on the Galápagos Islands, such as blue-footed boobies and giant tortoises
Figure 13.1A

6. The voyage of the Beagle
Great Britain
Europe
North America
Pacific Ocean
Atlantic Ocean
Africa
Galápagos Islands
Equator
South America
Australia
Andes
Cape of Good Hope
Tasmania
Cape Horn
New Zealand
Tierra del Fuego
Figure 13.1B

7. Darwin became convinced that the Earth was old and continually changing
He concluded that living things also change, or evolve over generations
He also stated that living species descended from earlier life-forms: descent with modification

8. 13.2 The study of fossils provides strong evidence for evolution
Fossils and the fossil record strongly support the theory of evolution
Hominid skull
Petrified trees
Figure 13.2A, B

9. Fossilized organic matter in a leaf
Ammonite casts
Fossilized organic matter in a leaf
Figure 13.2C, D

10. Scorpion in amber
“Ice Man”
Figure 13.2E, F

11. Many fossils link early extinct species with species living today
The fossil record shows that organisms have appeared in a historical sequence
Many fossils link early extinct species with species living today
These fossilized hind leg bones link living whales with their land-dwelling ancestors
Figure 13.2G, H

12. 13.3 A mass of evidence validates the evolutionary view of life
Other evidence for evolution comes from
Biogeography
Comparative anatomy
Comparative embryology
Human
Cat
Whale
Bat
Figure 13.3A

13. Molecular biology Human Rhesus monkey Mouse Chicken Frog Lamprey
Last common ancestor lived 26 million years ago (MYA), based on fossil evidence
80 MYA
275 MYA
330 MYA
450 MYA
Figure 13.3B

14. 13.4 Darwin proposed natural selection as the mechanism of evolution
DARWIN’S THEORY AND THE MODERN SYNTHESIS
13.4 Darwin proposed natural selection as the mechanism of evolution
Darwin observed that
organisms produce more offspring than the environment can support
organisms vary in many characteristics
these variations can be inherited

15. Darwin saw natural selection as the basic mechanism of evolution
Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted
Darwin saw natural selection as the basic mechanism of evolution
As a result, the proportion of individuals with favorable characteristics increases
Populations gradually change in response to the environment

16. Darwin also saw that when humans choose organisms with specific characteristics as breeding stock, they are performing the role of the environment
This is called artificial selection
Example of artificial selection in plants: five vegetables derived from wild mustard
Figure 13.4A

17. Example of artificial selection in animals: dog breeding
English springer spaniel
German shepherd
Yorkshire terrier
Mini-dachshund
Golden retriever
Hundreds to thousands of years of breeding (artificial selection)
Ancestral dog
Figure 13.4B

18. Thousands to millions of years of natural selection
These five canine species evolved from a common ancestor through natural selection
African wild dog
Coyote
Fox
Wolf
Jackal
Thousands to millions of years of natural selection
Ancestral canine
Figure 13.4C

19. 13.5 Connection: Scientists can observe natural selection in action
Evolutionary adaptations have been observed in populations of birds, insects, and many other organisms
Example: camouflage adaptations of mantids that live in different environments
Figure 13.5A

20. Insecticide application
The evolution of insecticide resistance is an example of natural selection in action
Insecticide application
Chromosome with gene conferring resistance to insecticide
Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow
Survivor
Figure 13.5B

21. 13.6 Populations are the units of evolution
A species is a group of populations whose individuals can interbreed and produce fertile offspring
Human populations tend to concentrate locally, as this satellite photograph of North America shows
The modern synthesis connects Darwin’s theory of natural selection with population genetics
Figure 13.6

22. 13.7 Microevolution is change in a population’s gene pool over time
A gene pool is the total collection of genes in a population at any one time
Microevolution is a change in the relative frequencies of alleles in a gene pool

23. 13.8 The gene pool of a nonevolving population remains constant over the generations
Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool
To test this, let’s look at an imaginary, nonevolving population of blue-footed boobies
Webbing
No webbing
Figure 13.8A

24. We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists
Phenotypes
Genotypes WW Ww ww
Number of animals (total = 500)
320
160 20
Genotype frequencies
320/500 = 0.64
160/500 = 0.32
20/500 = 0.04
Number of alleles in gene pool (total = 1,000)
640 W
160 W w
40 w
Allele frequencies
800/1,000 = 0.8 W
200/1,000 = 0.2 w
Figure 13.8B

25. Recombination of alleles from parent generation
W sperm
p = 0.8
W egg
p = 0.8
SPERM
EGGS WW
p2 = 0.64
w sperm
q = 0.2
w egg
q = 0.2 WW
qp = 0.16 Ww
pq = 0.16 ww
q2 = 0.04
Next generation:
Genotype frequencies
0.64 WW
0.32 Ww
0.04 ww
Allele frequencies
0.8 W
0.2 w
Figure 13.8C

26. 13.9 Connection: The Hardy-Weinberg equation is useful in public health science
Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population
Example: phenylketonuria (PKU)

27. 13.10 Five conditions are required for Hardy-Weinberg equilibrium
The population is very large
The population is isolated
Mutations do not alter the gene pool
Mating is random
All individuals are equal in reproductive success

28. 13.11 There are several potential causes of microevolution
Genetic drift is a change in a gene pool due to chance
Genetic drift can cause the bottleneck effect
Original population
Bottlenecking event
Surviving population
Figure 13.11A

29. or the founder effect
Figure 13.11B, C

30. Gene flow can change a gene pool due to the movement of genes into or out of a population
Mutation changes alleles
Natural selection leads to differential reproductive success

31. 13.12 Adaptive change results when natural selection upsets genetic equilibrium
Natural selection results in the accumulation of traits that adapt a population to its environment
If the environment should change, natural selection would favor traits adapted to the new conditions

32. 13.13 Variation is extensive in most populations
VARIATION AND NATURAL SELECTION
Variation is extensive in most populations
Phenotypic variation may be environmental or genetic in origin
But only genetic changes result in evolutionary adaptation

33. Many populations exhibit polymorphism and geographic variation
Figure 13.13

34. 13.14 Connection: Mutation and sexual recombination generate variation
Parents A1 A1 A2 A3
MEIOSIS A1 A2 A3
Gametes
FERTILIZATION
Offspring, with new combinations of alleles A1 A2 A1 A3
and
Figure 13.14

35. 13.15 Overview: How natural selection affects variation
Natural selection tends to reduce variability in populations
The diploid condition preserves variation by “hiding” recessive alleles
Balanced polymorphism may result from the heterozygote advantage

36. 13.16 Not all genetic variation may be subject to natural selection
Some variations may be neutral, providing no apparent advantage or disadvantage
Example: human fingerprints
Figure 13.16

37. 13.17 Connection: Endangered species often have reduced variation
Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment
Studies have shown that cheetah populations exhibit extreme genetic uniformity
Thus they may have a reduced capacity to adapt to environmental challenges
Figure 13.17

38. 13.18 The perpetuation of genes defines evolutionary fitness
An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals
Production of fertile offspring is the only score that counts in natural selection

39. 13.19 There are three general outcomes of natural selection
Original population
Frequency of individuals
Phenotypes (fur color)
Original population
Evolved population
Stabilizing selection
Directional selection
Diversifying selection
Figure 13.19

40. 13.20 Sexual selection may produce sexual dimorphism
Sexual selection leads to the evolution of secondary sexual characteristics
These may give individuals an advantage in mating
Figure 13.20A, B

41. 13.21 Natural selection cannot fashion perfect organisms
This is due to:
historical constraints
adaptive compromises
chance events
availability of variations

42. Connection: The evolution of antibiotic resistance in bacteria is a serious public health concern
The excessive use of antibiotics is leading to the evolution of antibiotic-resistant bacteria
Example: Mycobacterium tuberculosis
Figure 13.22