Evolution
A change in allele frequencies in a population, not individuals.
Result of inherited adaptations that enhance survival and reproduction of the organism in a particular environment.
Evolutionary Goal
To make organisms adapt to their environment and thus, increase diversity. Not trying to reach one top branch. It equals many branches.
Before Darwin
People believed
1. the earth was only 6000 years old
2. the earth and its organisms had not and would not change (i.e. extinction didn't occur_
3. all organisms were created at the same time
Charles (Chuck) Darwin
1809-1882
Did a round the world voyage
Two Important and Unexpected Patterns
1. Traits exhibited by species or different species
2. Resemblance between the fossils of extinct species and the living species in that same area
After Darwin
People believed
1. Organisms change over time
2. Some organisms have gone extinct
3. Earth is more than 6,000 years old
4. The geology of earth is not constant, but always changing
5 Primary Lines of Evidence
1. The Physical Record-physical evidence of organisms that lived in the past
2. Biogeography-patterns in the genographic distribution of organisms
3. Comparative anatomy and embryology-growth, development & body structures of major groups of organisms
4.
Fossils
Show:
1. change in species
2. similarities
Some still contain organic material, DNA, and even cells
Tiktaalik
Transitional form between fish and four legged land animals
Fossils Show
Younger rock layers lack fossils of modern life
Life has changed over time (# species, types)
Current organisms resemble earlier ones with changes
Biogeography
Shows:
>Older organisms gave rise to current organisms
>Continent positions have moved over time
>Structures have changed as the continents moved.
Homologous Bone Structure
An ancient ancestor was the first to have this bone structure; we all inherited it
Vestigial Structures
remnants of structures that may have had important functions in an ancestral species, but have no clear function in some of the modern descendants
Convergent Evolution
Analogous structures all developed from different original structures
Analogous Structures
>Different Ancestry
>Ancestral Form A, B, & C --> Similar Forms
Homologous Structures
>Common Ancestry
>Organisms that have a close genetic relationship with the same extinct species.
EX. Basic Form --> Evolved Form A, B, & C
Comparative Anatomy and Embryology
Suggests:
>A comparative common ancestor
-modification in structure has led to different functions
-modification of genes (i.e mutation) have let each species develop differently
Human vs Chimpanzee
Chromosomes:
>Chimps=48
>Humans=46
Common Ancestry
the closer they are, the more related
the farther apart they are, the more they are not related
Agents of Evolutionary Change
1. Mutation
2. Genetic Drift
3.Migration
4.Natural Selection
Mutation
-Ultimate source of all genetic variation (SOURCE OF NEW TRAITS AND NEW ALLELES)
-An alteration of the base-pair sequence of an individual's DNA (can't occur in junk DNA, has to be new)
-When this alteration occurs in a gene, the change in the DNA sequenc
Genetic Drift
Random change in allele frequencies purely by CHANCE.
Much greater in small populations than in large populations.
Two Cases: 1. Founder effect & 2. Bottleneck effect
Founder Effect
A new population with dominating features
>A small number of individuals may leave a population and become the founding members of a new, isolated population.
>The founders may have different allele frequencies than the original source population, particu
Bottleneck Effect
Genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions. Typically, the surviving population is no longer genetically representative of the original population.
Migration (Gene Flow)
May change allele frequencies.
The movement of some individuals of a species from one population to another.
Natural Selection
1. There must be variation for the particular trait within a population
2. That variation must be inheritable
3. Individuals with one version of the trait must produce more offspring than those with a different version of the trait.
Survival of the Fittest
>Reproductive success
>Fitness is the relative amount of reproduction of an individual with a particular phenotype, as compared with the reproductive output of individuals with alternative phenotypes
Natural Selection and Perfect Organisms
No such thing because:
1. Environments change quickly
2. There may be multiple different alleles fora trait each causing on individual to have the same fitness
3. Variation is needed as the raw material of selection
Other Types of Selection
-Artificial
-Directional
-Stabilizing
-Disruptive
-Sexual
Artificial Selection
A special case of natural selection, accept humans determine the selection. (ex. large milk producing cows)
Directional Selection
Individuals with one extreme from the range of variation in the population have higher fitness
>One side is favored
Ex. humans may choose only to mate cows that produce a lot of milk or only mate a turkey with large breasts)
Stabilizing Selection
Individuals with intermediate phenotypes are most fit.
>Both sides are pressured
(ex. a baby born with low birth weight will have complications but also a baby with high birth weight will also have complications)
Disruptive Selection
Individuals with extreme phenotypes experience the highest fitness, and those with intermediate phenotypes have the lowest
>Both sides are favored
Sexual Selection
ability to successfully obtain a mate
Sexual Dimorphism
differences in form between sexes of the same species
ex. Male: Larger, brighter, longer, sounds, etc. (for attraction)