1. The Theory of Evolution
Chapter 15
The Theory of Evolution

2. 15.1 Charles Darwin
Darwin developed the first theory on evolution, which is the basis for modern evolutionary theory
Darwin spent 5 years sailing around the world collecting organisms and fossils
His idea that species can change over time is based on his observations on the Galapagos Islands where many species were similar to species in other parts of the world, yet still unique

3. 15.1 Selection of Traits
Darwin bred pigeons and studied how traits were inherited from one generation to the next
He was able to breed for specific characteristics using artificial selection
He then hypothesized that desirable traits were bred into the population through natural selection
The organisms without the desirable traits were less likely to survive and pass on their traits
As a result, only the desirable traits got passed on

4. 15.1 Adaptations
An adaptation is any variation that aid’s an organisms chances of survival in its environment
Structural adaptations include any change to the physical appearance or body parts of an organism
These develop very slowly (over millions of years)
Examples include beak shape, neck length (giraffes), camouflage and mimicry
Mimicry is when one organism looks similar to another organism
Physiological adaptations are changes in the metabolic processes of an organism
They develop over fairly short time periods (a few generations)
Examples include antibiotic and pesticide resistance

5. 15.1 Evidence for Evolution Fossil Evidence
Fossils are used to examine physical similarities in organisms
Homologous structures are similar in function, arrangement or both between organisms with a common evolutionary origin
An example would be forelimbs of whales, crocodiles and bird wings
Analogous structures are similar in function between organisms that do not have a common evolutionary origin
An example would be bird and bat wings
Vestigial structures are those which probably used to serve a purpose but are no longer needed, yet still inherited
In humans, your appendix is a vestigial structure

6. 15.1 Embryology
An embryo is the earliest stage of growth and development for both plants and animals
Even though they develop into very different organisms, the embryos of fish, reptiles, birds and mammals are very similar, indicating that they may have had a common ancestor

7. 15.1 Biochemistry
Scientists often compare amino acid or DNA sequences of organisms
Organisms that have more in DNA or amino acid sequences in common are said to be more closely related in terms of biochemistry

8. 15.2 Genetic Equilibrium
Genetic equilibrium is a state where the genes in a population are the same over several generations
The combination of all the alleles of a population’s genes is called the “gene pool”
The percentage of any specific allele in the gene pool is called the allelic frequency
Any factor that changes the allelic frequency results in the process of evolution

9. 15.2 Mechanisms for Change
There are several factors that can cause changes within a population, some of which impact small, isolated populations such as islands, and others than impact larger populations
Mutations, genetic drift and gene flow can have a big impact on small populations
Genetic drift is the alteration of allelic frequencies by chance events
Gene flow is the movement of genes in and out of a population through migration

10. 15.2 Natural Selection There are 3 types of natural selection:
Stabilizing selection is natural selection that favors average individuals in a population
Directional selection is natural selection that favors one extreme of a trait
Disruptive selection is natural selection that favors both extremes of a trait

11. 15.2 Speciation
Speciation occurs when new species are produced because members of similar populations can no longer breed to produce fertile offspring
Geographic isolation occurs when a physical barrier divides a population and can lead to a new species
Reproductive isolation occurs when populations who used to interbreed no longer mate and produce fertile offspring
This can be because of genetic changes, such as polyploidy, or behavioral changes

12. 15.2 Patterns of Evolution There are 2 main patterns of evolution:
Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world and develop similar traits due to natural selection
Divergent evolution occurs when populations that were once similar become increasingly distinct as they adapt to different environments
Adaptive radiation is an example of divergent evolution
In adaptive radiation, one ancestral species evolves into many separate species to occupy different habitats