Natural Selection• Developed by Charles Darwin in

1859• Mechanism by which better

adapted organisms survive to produce a greater number of viable offspring

• Improve chances of survival• Variation

– Individuals in a population vary in phenotype which also means their genotype

– Some variations are better suited for survival and are inherited

• Overproduction – Populations tend to produce

more offspring than are needed

Neo-Darwinism• Refined version Darwin’s

theory• Combines Mendel’s

genetics • Evolution is driven by

chance• 2 ways– Small scale mutations

(single nucleotide polymorphisms)

– Large scale mutations (recombination)

• Creates new DNA by lucky accidents

Gene Pools • Total genetic information (alleles) in the gametes

of all individuals in any given population

Population• Group of organism’s of one species that

interbreed and live in the same place at the same time

Factors that Affect Gene Pools • Mutation • Emigration • Geographical Barriers • Non-Random Mating • Genetic Drift – Bottleneck effect,

founder effect • Gene Migration • Speciation • Selection Pressure • Adaptive Radiation

Factors Contribute to Fitness of Individual • Fitness– Measure of how well suited

an organism is to survive in its habitat and its ability to maximize the numbers of offspring surviving to reproductive age

– How successful an organism is at passing on its genes

– Natural selection tends to lean towards individuals who have specific traits that favour them in the environment

Allele Frequency (Gene Frequency) • Proportion of a particular allele (variant of a gene) among all

allele copies in a specific gene pool • Hardy-Weinberg principle is used to determine allele

frequency: • p² + 2pq + q² = 1– “p” and “q” represent frequency of alleles – “p” added to “q” always equals one (100%)

Mutation• Random occurrences which change the genome of the

organism• Increase genetic diversity • Advantageous mutations are favoured by natural selection• Disadvantageous mutations are phased out

Geographical Barriers• Isolates the gene pool and

prevents regular gene flow between populations

Non-Random Mating• Members of gene pool

seek out particular phenotypes increasing frequency of particular alleles

• Decreases genetic diversity • Also known as selective

breeding – Humans breed livestock

and plants for particular traits (favourable)

– Can lead to in-breeding depression caused by deleterious recessive alleles (cause abnormalities or death)

Genetic Drift • Species of same population split

into groups• Geographical barriers do not

allow members of same gene pool to reproduce with one another increasing genetic diversity

• Founder Effect– New population is started by few

members of original population – Contains reduced genetic

variation – Non-random samples of genes

• Bottleneck Effect – Population size is reduced for at

least one generation – Reduces genetic variation

Gene Migration• Immigration

– Populations gain alleles from other gene pools

– Dependent on difference in allele frequencies between gene pools

• Gene Flow– Members from one gene

pool mate with members of another gene pool leading to alteration of allele frequencies

• Emigration – Population loses alleles

from gene pool

Speciation• Genetic variation among population is so different

that members can no longer reproduce with one another

• New species is formed

Selective Pressure • Environmental factors reducing reproductive

success among members of a population • Contribute to evolutionary change or extinction

through process of natural selection • Include– Competition, predation, disease, parasitism, land

clearance, climate change, pollutants

Antibiotic Resistant Bacteria• Microorganisms show resistance

to an antimicrobial drug that was originally effective for treatment

• Conjugation – Transfer of genetic material

between bacterial cells– Creates genetic diversity– Antibiotic resistance

Adaptive Radiation • Species from a common ancestor have successfully

adapted to their environment via natural selection • Less competition in population • New ecological niches established (organisms

function in environment)• Darwin’s finches

Types of Natural Selection• Occur with or without

environmental change• Effect a population• Stabilizing Selection– Constant environment– Maintain status quo

• Directional Selection – New variation arises in

constant environment • Disruptive Selection– Changing environment– Variations that result in

better fitness in environment are favoured

Stabilizing Selection• Favours the average

individuals in a gene pool• Selects against extreme

phenotypes of gene pool• Favours majority of

population in gene pool• Diversity is decreased • Human birth weight• Infants with average birth

weight have increased chance of survival

Directional Selection• Favours one extreme phenotype

over another extreme phenotype• Phenomena is observed in

environments that have changed over time (climate change, food availability)

• Population bell curve shifts to left or right

• Fewer average individuals when compared to stabilizing selection

• Beak length of Galapagos finches • Influenced by human interaction

(hunting)

• Average individual in a population is not favoured

• Extreme phenotypes are observed

• Lead to speciation (new species)

• Diversity increased• Influence by human

interaction (environmental pollution)

• London’s peppered moths

Disruptive Selection

Sexual Selection• Special case of natural

selection• An organism’s ability

to successfully copulate with a mate

• Usually female chooses among males

• 2 ways – Female choice– Male competition

Female Choice• Intersexual selection between sexes • Females choose males based on specific

characteristics or behaviours

Male Competition• Intrasexual selection• Males compete against other males for territory

or mating rights with females • Lead to intense battles

Evidence of Evolution• Fossil record of change

in earlier species• DNA/protein

homologies• Geographic

distribution of related species

• Recorded genetic changes in living organisms over many generations

DNA/Protein Homologies• All living things on earth

share the ability to create complex molecules out of carbon and a few other elements

• All plants and animals inherit their specific characteristics from a combination of genes

• Protein is made from DNA made up mostly of only 20 kinds of amino acids