1. Evolution
The Process of Evolution (Variation, Heredity and Differential Reproduction)

2. Important things to recall
DNA
deoxyribonucleic acid, the macromolecule, composed of two polynucleotide chains in a double helix, that is the carrier of genetic information in all cells
Genes
Heredity unit containing specific genetic information. A gene can mutate to various forms called alleles.
Alleles
Any of the alternative forms of a given gene
Allele Frequency
The relative proportion of all alleles of a gene that are of a designated type.
DNA (gene) → RNA → protein → trait

3. Definition of Evolution
Any process of change over time.
Classically
A change in the relative frequencies of heritable traits within a population across generations.
Modern
A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations.

4. Classical Evolution
A change in the relative frequencies of heritable traits within a population across generations
Relative frequency:
50% Tall plants
50% Short plants
55 generations later
25% Tall plants
75% Short plants

5. Modern Evolution
A change in the distribution of relative frequencies of genes (which code for heritable traits) within a population across generations

6. Differential Survival of Traits
Differential survival of traits in a population means that some characteristics will become more frequent while others occur less or are lost.
There are four known processes that affect the survival of a characteristic; or, more specifically, the frequency of an allele:
Mutation – error in duplication
Genetic drift - stochasticity
Gene Flow – movement of genes from pop. to pop.
Natural selection
The production and redistribution of variation is produced by three of the four agents of evolution: mutation, genetic drift, and gene flow. Natural selection, in turn, acts on the variation produced by these agents.

7. Mutation occurs in the trait
Mutation directly changes gene frequencies
An example of a spontaneous mutation during the development of plant leaves
For evolution to occur via this mechanism, what has to be true of the mutation?
The mutation has to be heritable
The mutation of fruit flies with four wings is an inherited mutation

8. The population size is small
Genetic drift – random fluctuations in the allele frequencies
Only 5 of 10 plants
leave
offspring
Only 2 of
10 plants
leave offspring
Generation 1
p (frequency of R) = 0.7
q (frequency of r) = 0.3
Generation 2
p = 0.5
q = 0.5
Generation 3
p = 1.0
q = 0.0

9. Gene flow
Immigration or emigration occurs based on the trait

10. Microevolution
Microevolution is the occurrence of small-scale changes in gene frequencies in a population over a few generations, also known as change at or below the species level.

11. Mechanisms of Evolution (cont.)
Natural Selection
Natural selection, the last of the four forces, is based on three principles:
(a) there is VARIATION within a species and this variation is HERITABLE
(b) parents have more offspring than can survive
(c) surviving offspring have favorable traits
The mechanism by which it operates is termed survival of the fitter meaning differential mortality and fertility.
Differential mortality is the SURVIVAL rate of individuals before their REPRODUCTIVE AGE. If they survive, they are then selected further by differential fertility – that is, their total genetic contribution to the next generation.
VARIATION HERITABLE SURVIVAL TO REPRODUCE

12. Darwin’s Observations
Biogeography
It is the study of distributions of organisms, both past and present, and of related patterns of variation over the earth in the numbers and kinds of living things
Agriculture
Selective breeding
Fossils
Evidence of organisms no longer present
Evidence that many living organisms were not present in the past
Geology
New ideas about the age of the Earth via plate tectonics
Economics
Competition for resources and the effects of overpopulation

13. Evolution by Natural Selection (a mechanism of evolution)
Population level:
If variation exists and
If variation is heritable and
If differential reproduction (differential selection) exists
Then over time, those variations that enhance the ability of the organism to reproduce will increase in any population
Natural Selection leads to ADAPTATION

14. Adaptation
A biological adaptation is an anatomical structure, physiological process or behavioral trait that has evolved over a period of time by the process of natural selection that increases the likely hood of producing larger numbers of offspring or its reproductive success.
A heritable characteristic of an organism that helps it to survive and reproduce in a particular environment.

15. Adaptation vs. Acclimatization
Evolutionary biologists refer to an adaptation as a trait that evolved as the result of natural selection.
Physiologists use “adaptation” when they mean “acclimatization” –
A nerve “adapts” to a continual stimulus or
our eyes “adapt” to darkness
does not involve genetic change!

16. Adaptation refers to traits that are heritable
Acclimation: Changes in the structure or physiology of an individual over its lifetime
Examples:
Increasing muscle
mass via weightlifting
High altitude acclimation:
But, neither of these involves genetic change!

17. Human example of an adaptation: Sickle Cell Anemia
In North America, sickle cell anemia is uncommon and a disadvantage.
However, in other parts of the world, specifically areas where malaria is common, the occurrence of sickle cell anemia is greater.
Why?

18. Sickle Cell Anemia
Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.

19. Sickle Cell Anemia
Because the heterozygous (SS, Ss, ss) Sickle Cell Anemia genotype gives a higher resistance to malaria, however a homozygous genotype is still a disadvantage.
DNA (gene) → RNA → protein → trait

20. Flattened tail – aids in swimming
Long, sharp claws – Aid in clinging to rocks
Salt gland – Allows drinking of salt water
Diving adaptations. While diving they:
Reduce blood flow to body surface- helps retain heat
Lower metabolic rate – conserves O2

21. Imperfect Adaptations
trait
performance
fitness
fitness
trait
feeding
defense
thermoregulation
Multi-tasking may force an evolutionary compromise
Can’t simultaneously optimize distinct functions.

22. Adaptation – organisms are not perfectly adapted ( have to make due with your genetics)
Examples: panda thumb

23. All traits evolve from something else, so carry historical baggage thus can be “contrivances” (make do!)
Homologous structures which have a common origin.

24. Divergent Evolution
Divergent evolution is the process of two or more related species becoming more and more dissimilar.
The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees.
The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators.

25. Convergent Evolution
Convergent evolution is an evolutionary process in which organisms not closely related independently acquire some characteristic or characteristics in common, or the evolution of species from different taxonomic groups toward a similar form.
This usually reflects similar responses to similar environmental conditions.
Structures that are the result of convergent evolution are called analogous structures or homoplasies; they should be contrasted with homologous structures which have a common origin.

26. Wings