Natural Selection

Natural Selection – “Survival of the Fittest”

• Survive : When things around you die and you remain alive

• Fitness: Any adaptation which enhances survival (Ex: Strength, Immunity, Mental Ability, Camouflage (ability to blend)

Charles DarwinBritish Naturalist

1809 -1882  

 I have called this principle, by which each slight variation, if useful,

is preserved, by the term Natural Selection.   

                                 —Charles Darwin from "The Origin of Species"

The Origin of Species through Natural Selection

                                                                            

Natural Selection

Factors of Evolution

• 1) Individual species vary.

• 2) Some variations are genetic

• 3) More individuals are produced than reproduce.

• 4) Organisms best adapted to their environment survive and pass on their traits to their offspring.

Ecological Niche

• Niche: The “place where and organism fits” in the world. An organism’s space in the environment

Competition:

• Competition: The struggle for food, space (territory) or reproduction

Predator – Prey relationship

• Predator : Organisms which stalk and eat another organism in order to stay alive.

• Prey: Organism which is eaten

Predator – Prey relationship

• Predator : Organisms which stalk and eat another organism in order to stay alive.

• Prey: Organism which is eaten

Reproduction

• Reproduction: Organisms which survive pass on their adaptation traits (fitness factors)

• Pass on favorable phenotypes.

Camouflage

• Organisms which blend into the environment have greater survival value

• 1) Cryptic coloration: Blend with background Katydid – leaves, Peppered moths – industrial melanism

Camouflage

• Organisms which blend into the environment have greater survival value

• 1) Cryptic coloration: Blend with background Katydid – leaves, Peppered moths – industrial melanism

Cryptic Coloration

Countershading

Camouflage

2) Warning coloration: Bright distinctive colors. Ex: California newt, Ladybugs – red; Bumble bee, wasp – banded warning

http://search.live.com/images/results.aspx?q=hornet&FORM=QBIR&mkt=en-US

Warning Coloration

http://upload.wikimedia.org/wikipedia/commons/9/9b/Flying_Vespula_vulgaris.jpg

Camouflage

3) Batesian mimicry: Where a palatable (edible) mimic resembles and unpalatable model.

Ex: Bumble bees – Robber flies (H-bee) ; Monarch vs Viceroy

Environment:

• Environment: Organism’s surroundings. Anything other than genes which influences the expression of traits (phenotype) Organisms either adapt, die, or leave new environments.

SunlightTemperaturePrecipitation

SoilPressurePollution

TidesSalinity

Environmental Factors

Mutations• Mutations: May be

caused by natural agents. Nearly always harmful. Raw materials upon which natural selection operates.

• Some make no difference

• Some are useful (to us).Ex: Ancon sheep, Seedless grapes, navel oranges, Delicious apples.

Mutations• Mutations: May be

caused by natural agents. Nearly always harmful. Raw materials upon which natural selection operates.

• Some make no difference

• Some are useful (to us).Ex: Ancon sheep, Seedless grapes, navel oranges, Delicious apples.

Environmental restraints

• Any factors which control the populations

Ex: Water in the desert, predators, disease, food source.

• Extinction: When all the species of a population die out

Factors of Evolution

• 1) Individual species vary.

• 2) Some variations are genetic

• 3) More individuals are produced than reproduce.

• 4) Organisms best adapted to their environment survive and pass on their traits to their offspring.

Evolution• Evolution: The process of

change over a long period of time producing varyingly different organisms.– Species: Genetically

diverse organisms that mate freely in nature and produce fertile offspring.

• genetically diverse – chromosomal differences between species (DNA)

Charles DarwinBritish Naturalist

1809 -1882  

 I have called this principle, by which each slight variation, if useful,

is preserved, by the term Natural Selection.   

                                 —Charles Darwin from "The Origin of Species"

                                                                            

Inheritable Mutations

Charles DarwinBritish Naturalist

1809 -1882  

 I have called this principle, by which each slight variation, if useful,

is preserved, by the term Natural Selection.   

                                 —Charles Darwin from "The Origin of Species"

On the Origin of Species through Natural Selection

The Wallace Line (or Wallace's Line) is a boundary that separates the zoogeographical regions of Asia and Australasia. West of the line are found organisms related to Asiatic species; to the east, mostly organisms related to Australian species. The line is named after Alfred Wallace.

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Charles DarwinBritish Naturalist

1809 -1882  

 I have called this principle, by which each slight variation, if useful,

is preserved, by the term Natural Selection.   

                                 —Charles Darwin from "The Origin of Species"

Factors of Evolution

• 1) Individual species vary.

• 2) Some variations are genetic

• 3) More individuals are produced than reproduce.

• 4) Organisms best adapted to their environment survive and pass on their traits to their offspring.

Natural Selection

Forms of Selection

1) Stabilizing – Selection is geared for the average individuals. Extremes are removed

2) Directional – Selection for the most beneficial trait for an environment

3) Disruptive – Selection for the two extremes of traits

Forms of Selection

• Stabilizing – Selection is geared for the average individuals. Extremes are removed

• Directional – Selection for the most beneficial trait for an environment

• Disruptive – Selection for the two extremes of traits

Forms of Selection

• Stabilizing – Selection is geared for the average individuals. Extremes are removed

• Directional – Selection for the most beneficial trait for an environment

• Disruptive – Selection for the two extremes of traits

Forms of Selection

• Stabilizing – Selection is geared for the average individuals. Extremes are removed

• Directional – Selection for the most beneficial trait for an environment

• Disruptive – Selection for the two extremes of traits

Evidence for Evolution

• Direct – Observable – If you could watch organisms change for several generations.

• Ex: Resistant bacteria and insects to antiobiotics and pesticides

Indirect Evidence

• Evidence from dead organisms or comparisons

A) Inheritance

• Artificial selection: Plant and animal breeders select what should live or die to suit specific purposes.

B) Geographic distribution

• Isolations of populations show distinct variations

• Isolation : Separation of populations by natural barriers

• Divergent populations: Formed by the splitting up of original species by some barrier

Allopatric speciation

• In allopatric speciation, an ancestral population is geographically isolated, resulting in the evolution of separate species largely due to genetic drift.

• The additive effect of differences due to genetic drift can eventually result in behavioral isolation (refusal to mate) if the two groups were to meet again in the future.

• If they refused to interbreed, they would be considered separate species.

Genetic Drift

• Random events which cause a change in allele (gene) frequency

Ammospermophilus leucurus – White tailed antelope squirrel

Ammospermophilus harrisi –Harris’s antelope

North RimSouth Rim

Allopatric speciation

• Allopatric speciation due to geographic separation of the Grand Canyon.Harris's antelope squirrel (Ammospermophilus harrisi) inhabits the canyon's south rim (left). Just a few miles away on the north rim (right) lives the closely related white-tailed antelope squirrel (Ammospermophilus leucurus). Another example is the Tassel-eared Squirrel, where Abert's Squirrel (Sciurus aberti) lives on the south rim and the Kaibab Squirrel (Sciurus aberti kaibabensis) lives on the north rim.

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Sympatric speciation• Sympatric speciation

involves speciation without a geographic barrier. 

• One example of sympatric speciation is polyploidy, found more often in plants. 

• Polyploidy occurs when a failure of meiosis increases the number of chromosome sets to 3N or more. At this point, the two "cousin" species can no longer mate with each other.

C) Reproductive Isolation

D) Fossils

• Remains of organisms from the past. Show the change of structure and from through time

• Presence of common patterns of structure.

• Ex: Bones in vertebrate forelimbs, wings, flippers – same bones

E) Homology

Homologous Structures in Vertebrates

Vestigial organs

• Lost function (organs)• Ex: Appendix; hind

limbs in whales, python; wings – kiwi, cormorant, penquin

Homology

• Divergence – Descendants are more different

• Convergence – Unrelated organisms – Analagous – similar characteristics in similar environment

F) Embryology

• Studies of early stages. Much like the evolutionary history of species

F) Embryology

• Studies of early stages. Much like the evolutionary history of species

G) Biochemistry

• Analysis of amino acid sequences. Different species have different sequences of Amino Acids in Cytochrome C (Electron transport chain proteins)

G) Biochemistry

• Similar DNA is found in the same species. Fewer DNA differences are found in closely related organisms

Hardy-Weinberg Principle

• Used to assess whether natural selection is occurring

• States that the frequencies of alleles and genotypes in a population will remain the constant from generation to generation provided only Mendelian segregation and crossing over occur

Hardy-Weinberg Principle

• Used to assess whether natural selection is occurring

• States that the frequencies of alleles and genotypes in a population will remain the constant from generation to generation provided only Mendelian segregation and crossing over occur

Hardy-Weinberg Principle• Conditions for Hardy-

Weinberg:

1) No mutations

2) Random mating

3) No natural selection

4) Extremely large population size

5) No gene flow ( movement of alleles into or out of population)

Hardy-Weinberg

Hardy-Weinberg• Under Hardy-Weinberg equilibrium, allele and genotype frequencies remain constant over generations. The allele frequencies are described by

• p + q = 1, where p is the dominant allele frequency and q is the recessive allele frequency. • The genotype frequencies are described by p2 + 2pq + q2 = 1, where p2 and q2 are frequencies of the homozygous genotypes and 2pq is the frequency of the heterozygous genotype.

Hardy Weinberg

p = the frequency of the dominant allele (represented here by A)q = the frequency of the recessive allele (represented here by a)

For a population in equilibrium:

p + q = 1.0 ( the sum of the frequencies of both alleles is 100 %)(p + q)2 = 1

sop2 + 2pq + q2 = 1

The three terms of this binomial expansion indicate the frequencies of the three genotypes:

p2 = frequency of AA (homozygous dominant)2pq = frequency of Aa (heterozygous)q2 = frequency of aa (homozygous recessive)