Evolution
Early Evolutionists
Darwin's Theory
Agents of Change
Patterns of Evolution
Sources of Variation
Genetic equilibrium
Speciation
Natural selection
Mutations
Gene Flow
Genetic Drift
Nonrandom Mating
Stabilizing Selection
Directional Selection
Disruptive Selection
Sympatric Speciation
Adaptive radiation
Balanced polymorphism
Polyploidy
Hybridization
Reproductive Isolation
Pre-mating
Post-mating (prevents the formation of fertile offspring.)
Habitat isolation
Behavioral isolation
Mechanical isolation
Gametic isolation
Hybrid inviability
Temporal isolation
Hybrid Sterility
Hybrid Breakdown
Hardy-Weinberg Equilibrium:
No natural selection is occuring
No mutations are occuring
No gene flow is occuring
No genetic drift is occuring
Mating is random
George-Louis Leclerc de Buffon (1707-1788)
James Hutton (1726)
William Smith (1726-1797)
Jean Baptiste Lamarck (1744-1829)
First to propose that species change with time. His theory had 3 important ideas.
Use and disuse
Inheritance of acquired characteristics
He was among the 1st to propose that the species on Earth in the present were different from those long ago, although he still believed in creation.
He was an English surveyor who studied the distribution of fossils in various strata or layers. He found certain types of fossils always appeared in the same strata.
He was a geologist who proposed that the Earth was created through slow and gradual processes.
Darwin proposed that species can change over time, that new species come from pre-existing species, and that all species share a common ancestor.
Observation 1: Superfecundity
Observation 2: Population size tends to remain stable
Observation 3: Environmental Resources are limited
Inference 1: production of more individuals than environment cant support results in competition
Observation 4: Variation Exists
Observation 5: Variation is Heritable
Inference 2: Survival is not random but based on fitness of heritable traits.
Variations in the genetic makeup of populations is what drives evolution.
Random mutations are the key to the creation of new alleles. All other methods merely rearrange the existing alleles in the gene pool.
Sexual reproduction also facilitates variation in populations of organisms. Crossing-over, independent assortment of homologues, and the random joining of gametes are examples processes that promote variation.
Diploidy, the presence of two copies of each chromosome in a cell, also promotes variation.
Outbreeding, or mating with unrelated partners, increases the possibility of different combinations of alleles.
Balanced polymorphism encourages the existence of more than one allele for a certain gene because of the survival benefits of both alleles
In heterozygote advantage, the heterozygote with both the dominant and the recessive allele has a better chance of survival than both the homozygous dominant and homozygous recessive varieties.
Hybrid vigor
Describes the superior quality of offspring between two inbred strains of plants.
Genetic drift is the random increase or decrease of the occurrence of an allele in a population. Genetic drift is the most evident in small populations.
The founder effect is a type of genetic drift that occurs when the organisms in the founding group have different allele frequencies from the population they left. The resulting offspring will reflect the genetic makeup of the founders.
A population bottleneck is another type of genetic drift that occurs when the population undergoes a dramatic decrease in size.
This may lead to the removal of some alleles from the gene pool if all the carriers of that allele were wiped out.
Gene flow is the addition or reduction of alleles when individuals enter and leave the population.
Nonrandom mating occurs when individuals choose mates based on certain traits.
Sexual selection is when females choose males based on their appearance or their competence in some other area. Nonrandom mating also occurs when individuals choose mates from only nearby individuals.
Inbreeding is when individuals mate with relatives.
Sexual Selection
Artificial Selection
Sexual selection is the selection of a mate based on a trait.
In male competition the male that wins the contests of strength, agility, etc. mates with the female.
In female choice the female mates with the male that she prefers based on certain characteristics.
Artificial selection is a form of selection carried out by humans.
Stabilizing selection eliminates individuals with extreme or unusual traits.
Disruptive selection occurs when the environment favors extreme traits over common traits.
Directional selection favors traits at one extreme of the range of traits.
Habitat isolation occurs when the organisms do not encounter each other.
Temporal isolation occurs when the organisms mate at different times of the day.
Temporal isolation occurs when the organisms mate at different times of the day.
Mechanical isolation occurs when the male and female genitalia are physically incompatible.
Gametic isolation occurs when the male gametes cannot survive in the mating environment long enough to fertilize the female.
Hybrid inviability occurs when the zygote fails to develop properly and dies.
Hybrid sterility occurs when resulting offspring are unable to reproduce as adults.
Hybrid breakdown occurs when the hybrids produce offspring that have limited reproductive capacity.
Divergent Evolution
Convergent evolution
Parallel Evolution
Coevolution
Divergent evolution describes two or more species that evolved from a common ancestor.
Convergent evolution describes two or more unrelated species that have adopted similar adaptations to their environment.
Coevolution describes the evolution of one species in response to the evolution of another. Coevolution usually occurs in a predator-prey relationship.
Parallel evolution describes two or more species that have continued to evolve similar characteristics even after their divergence from a common ancestor.
Evidence of Evolution
Fossil Record
Biogeography
Embryology
Comparative Anatomy
Embryology has revealed that there are similar stages in development among related species. Most notable is the fact that gill slits and tails are found in fish, chicken, pig, and human embryos.
Homologous Structure
Analogous Structure
Biogeography has revealed that organisms in similar environments around the world tend to acquire the same adaptations for their survival. There may be no rabbits in Australia, but the Australian wallaby resembles rabbits in many ways.
The fossil record has revealed the extinction of certain species, the beginning of new species, and the evolution of other species.
Homologous structures in the forelimbs of various vertebrates support the concept of a common ancestor.
Analogous structures in organisms that live in similar environments (like fins whales and fish) support the concept that the environment affects the development of organisms.
Increase in Complexity
Inheritance of acquired characteristics incorrectly described how things like muscle mass could be passed onto offspring.
Use and disuse referred to how body parts of organisms grow stronger with use and atrophy with disuse.
Allopatric Speciation
Occurs when a population is divided by a geographic barrier. With no interbreeding occurring between the members of the separated populations, the genetic makeup of the two groups gradually changes through successive generations so that if the barrier were to be removed they would no longer be able to reproduce together.
Sympatric speciation occurs when a new species is formed without geographic isolation.
It is an example of sympatric speciation that occurs when members of a population only interbreed with other members that share a certain allele (i.e. fur color). Eventually, the gene pool is altered to the point that a new species is formed.
It is the possession of more than two sets of chromosomes and is common in plants.
This occurs when members of two different species have offspring that become different species.
Adaptive radiation is the sudden evolution of many species from a single ancestor.
Mutations are random changes in an organisms genetic code that may lead to the formation of a new allele. Most mutations, however, are harmful.
Nonrandom mating occurs when individuals choose mates based on certain traits.
Sexual Selection
Sexual selection is when females choose males based on their appearance or their competence in some other area. Nonrandom mating also occurs when individuals choose mates from only nearby individuals.
Inbreeding
Inbreeding is when individuals mate with relatives.
Hardy Weinberg: The allele frequencies are represented by the letter p and q. The frequencies of both alleles add up to 100%.
MacroEvolution
MicroEvolution
Microevolution happens on a small scale (within a single population)
Macroevolution happens on a scale that transcends the boundaries of a single species.
Examples include:
mosquitoes evolving resistance to DDT.
whiteflies evolving resistance to pesticides.
gonorrheal bacteria strains evolving resistance to penicillin
Examples include:
tetrapods, which are animals with four limbs.
the origin of mammals and the radiation of flowering plants.
Multiplication of the species.