1. Evolution

2. Evolution = a change in gene frequencies in populations over time
Evolution explains
origin of species,
diversity of organisms and their relationships,
similarities and differences among species,
adaptation to the environment

3. CHARLES DARWIN AND THE ORIGIN OF SPECIES
Charles Darwin’s On the Origin of Species by Means of Natural Selection was published in 1859
co-presented with Alfred Wallace
Darwin’s 2 main points:
All organisms descended from ancestral species
Natural selection was the mechanism for change

4. Darwin’s Theory of Natural Selection
Darwin based his theory of natural selection on two key observations:
Overproduction
All species tend to produce excessive numbers
This leads to a struggle for existence
Individual variation
Variation exists among individuals in a population
Much of this variation is heritable

5. “Survival of the Fittest”
Inference: Natural Selection leads to differential reproductive success
Individuals best suited for the local environment leave more fertile offspring
Evolution is the accumulation of more favorable variants over time
Natural Selection operates at the level of the individual, NOT for the good of the species

6. Natural Selection in Action
Examples of natural selection include
Pesticide resistance in insects
The development of antibiotic-resistant bacteria
Kettlewell’s Peppered Moths
Figure 13.1
Insecticide
application
Chromosome with gene conferring resistance to insecticide
Survivors
Additional applications of the same insecticide will be less effective, and the frequency of resistant insects in the population will grow

7. Kettlewell’s Peppered Moths
Kettlewell studied the peppered moth (Biston betularia) from insect collections in England.
Birds ate moths that were easiest to find.
Selection for Light colored
moths in non-polluted areas
Selection for Black moths in
polluted areas

8. Three General Outcomes of Natural Selection
Directional Selection
Selects in favor of one or the other extreme
Diversifying Selection
Selects in favor of two extreme types
Stabilizing Selection
Selects in favor of intermediate type
1) Directional Selection
2) Diversifying Selection
3) Stabilizing Selection
Selects in favor of one or the other extreme
Selects in favor of two extreme types
Selects in favor of intermediate type

9. Patterns of Evolution Convergent Evolution
evolutionary change in two or more unrelated organisms that results in the independent development of similar adaptations to similar environmental conditions
Example: anteaters found in Australia, Africa, North and South America

10. Cactus-flower -eaters South American mainland
Patterns of Evolution
Divergent Evolution
occurs when a single group of organisms splits into two or more groups and each group evolves in increasingly different directions
Example: Darwin’s Galapagos Finches
Medium
ground
finch
Cactus
Small
tree finch
Woodpecker
Large
Large cactus
ground finch
Vegetarian
Mangrove
Green
warbler
Gray
Sharp-beaked
Seed-eaters
Cactus-flower -eaters
Bud-eater
Insect-eaters
Ground finches
Tree finches
Warbler finches
Common ancestor from
South American mainland
Figure 1.13

11. EVIDENCE FOR EVOLUTION
Common ancestry and descent with modification are found by studying:
The fossil record
organisms appear in a historical sequence
Biogeography
the geographic distribution of species
Comparative anatomy
comparison of structures in different species
Comparative embryology
comparison of structures that appear during development
Molecular biology
comparison of genes and proteins
(a) Chick embryo
Gill
pouches
Post-anal
tail
(b) Human embryo
(right) Comparative embryology of vertebrates supports evolutionary theory

12. Homologous structures
Homologous (also called “divergent”) structures have a similar anatomy due to common ancestry
Same form (function may or may not be the same)
Ex: forelimbs of vertebrates
Human write
Cat Walk
Whale Swim
Bat Fly

13. Analogous structures
analogous (also called "convergent") structures have evolved independently
Serve the same function in different species
Ex: wings of butterfly and bird
ButterflyFly
Bird
Fly

14. The Origin of Species
The biological species concept defines species as “groups of interbreeding natural populations that are reproductively isolated from other such groups”
(a) Similarity between different species
(b) Diversity within one species
Figure 14.4

15. Mechanisms of Speciation
The two modes of speciation are
Allopatric speciation
“other country”
Sympatric speciation
“same country”
Allopatric speciation
(b) Sympatric speciation
Figure 14.8

16. Allopatric Speciation
Members of a population become physically separated
The separated populations diverge, through changes in mating tactics or use of their habitat
They become reproductively separated such that they cannot interbreed and exchange genes

17. Viable, fertile offspring
Sympatric Speciation
a species splits into two due to reproductive isolation without any geographic separation
Reproductive isolation may be
Pre-zygotic
Post-zygotic
Figure 14.5
Individuals of
different species
Pre-zygotic
barriers
Temporal isolation: Mating or flowering occurs at different seasons or times of day
Habitat isolation: Populations live in different habitats and do not meet
Behavioral Isolation: Little or no sexual attraction between males and females
Mating
Mechanical isolation: Structural differences in genitalia or flowers prevent copulation or pollen transfer
Gametic isolation: Female and male gametes fail to unite in fertilization
Fertilization
(zygote forms)
Post-zygotic
Hybrid inviability: Hybrid zygotes fail to develop or fail to reach sexual maturity
Hybrid sterility: Hybrids fail to produce functional gametes
Viable, fertile offspring

18. Pre-zygotic barriers
Pre-zygotic barriers impede mating between species or hinder fertilization of eggs
Temporal isolation
Habitat isolation
Mechanical isolation
Gametic isolation
Behavioral isolation

19. Post-zygotic barriers
Post-zygotic barriers are backup mechanisms that operate should interspecies mating actually occur and produce hybrid zygotes
Hybrid inviability
Hybrid sterility
Horse
Mule (hybrid)
Donkey
Figure 14.7

20. Study Objectives
Define evolution and describe Charles Darwin’s contribution to the current Theory of Evolution.
Define natural selection and describe how natural selection works to change a population.
Describe some examples of natural selection, including Kettlewell’s study with the black and peppered moths.
Contrast directional, diversifying, and stabilizing selection.
Define convergent evolution and divergent evolution and give an example of each.
Describe five main lines of evidence in support of evolution.
Contrast homologous and analogous structures.
Define species.
Define speciation and describe two mechanisms by which speciation can occur (allopatric, sympatric).
Distinguish between pre-zygotic and post-zygotic barriers and describe ways in which sympatric populations can be reproductively isolated.