Principles of Evolution:

1. Natural Selection

- Require a “struggle for existence”

- Occurs at individual level

- “nature” selects individuals to die or survive

- Traits better adapted for their environment become more common

2. Adaptation: any heritable characteristic which improves an organism’s chance of survival

- Does not arise in an individual

- Requires variation- Individuals selected

for/against based on their adaptations

3. Fitness: the ability of an organism to survive and reproduce- Measured by relative

contribution to gene pool

- Survival of the Fittest: individuals best adapted to the environment survive and reproduce

1. Variation: pheno/genotypic differences between members of the same species

2. Struggle for Existence: the competition for needed resources/reproduction

3. Fitness: the ability to survive and reproduce – based on genetic contribution to gene pool

4. Adaptation: inherited characteristics that improve an organism’s chances of survival

5. Survival of the Fittest: the organisms best adapted to their environmental conditions survive and reproduce

6. Natural Selection: organisms displaying the best adaptations/traits become more common over generations

Populations: units of evolution- Individuals do not evolve

in a lifetime-Nature selects some for

survival some for death based on traits

* Rate of evolution = change in certain allele prevalence

- Gene pool: collection of genes in a population at a given time

Mutation: change in nucleotide sequence of DNA- Typically harmless- If it affects protein =

harmful- Rarely beneficial- Leads to variations- Usually not heritable,

unless it happens in gametes

Evidence For Evolution:

1. Fossil Evidence

-Supports the theory – especially in aquatic organisms

-many holes still in the fossil record

2. Homologous Structures: similar structures with different functions/same embryological origin

3. Vestigial Organs: organs/structures which have lost function over geological time

4. Embryological Similarities: all vertebrates have similar embryological development

5. Radiometric Dating: the use of radioactive elements to calculate the age of geological substances• Half life: the length of

time required for half of the radioactive atoms in a sample to decay into non-radioactive atoms

• Ex: Carbon-14 decays to form carbon 12 (5730 years) – comparing the amount of C14 to C12 allows us to age samples

6. DNA similarities: genomic data indicate that all life forms are closely related to one another

Ex. Humans and Bananas share 50% of the same DNA

-Humans and Chimps= 98.5%

Types of Evolution:

Adaptive Radiation: process of a single species or small group evolving into a diverse group of organisms

Convergent Evolution: unrelated organisms come to resemble one another

Coevolution: process by which two species evolve in response to changes in each other

Gradualism: life is in a constant, small state of flux and small changes evolve slowly into large differences

Punctuated Equilibrium: life is stable, for long periods of time but is interrupted with periods of dramatic change

Speciation: creation of new species

Species: a group of individuals which bear similar characteristics, can breed with one another, and produce viable offspring

Two Types of Speciation:

1. Allopatric Speciation: a population is separated and their genes drift apart- Only occurs if

environmental differences are significant

- Genetic Drift: change in allele frequency in a population

2. Sympatric Speciation: new species arise in the same area

- Arises due to changes in sexual selection and habitat preference

Genetic Drift: in populations, one allele becomes more common in descendents