Natural Selection & Evolution

I. Natural Selection & Charles Darwin Due to earth’s long history; life is thought to have evolved over time Charles Darwin (1819-1882) an English scientist considered the founder of the evolutionary theory

Darwin studied many forms of life through the voyage of the Beagle Galapagos Islands was where Darwin studied a majority of the organism

Darwin's many observations led him to the idea that species slowly change over time (Gradualism) Darwin's comparison of the animals of South America and the Galapagos Islands caused him to conclude that adaptation to the environment can cause diversification, including origin of new species

The Galapagos Islands: Volcanic islands off the South American coast Island species varied from the mainland species, and from island-to-island Each island had either long or short necked tortoises depending on the island's vegetation

The Galapagos Islands: Finches on the Galapagos Islands resembled a mainland finch, but there were more types Bill shapes are adaptations to different means of gathering food.

Galapagos finch species varied by nesting site, beak size, and eating habits

Darwin's Theory of Evolution: An adaptation is a trait that helps an organism be more suited to its environment Darwin decided adaptations develop over time Natural selection was proposed by both Alfred Russell Wallace and Darwin as a driving mechanism of evolution

Natural Selection: Natural Selection – a mechanism for change in a population where favorable conditions for a particular environment which help organisms, survive, reproduce and pass on these variations. This is also known as “Survival of the Fittest”

There is a variation in Traits. Green beetles tend to get eaten more often therefore lessen their chances to reproduce. The Brown Trait is an advantage therefore allows more brown beetles to be produced

Artificial Selection - a technique in which a breeder selects the particular traits Pigeon breeding experiments helped him to further study his theory of evolution This was an example of Artificial Selection

Adaptations: Mimicry – structural adaptation that provides protection. Allows a harmless species to resemble a harmful species. This caterpillar protects itself by mimicking a snake

Adaptations: Camouflage – structural adaptation that enables an organism to blend in with it’s surroundings Katydids camouflage into a variety of environments

Adaptations: Structural adaptations can occur over many generations Physiological adaptations can occur very rapidly (organisms adjusting to the changes of environment) Eg: tanning of skin when exposed o sun/ formation of callouses on hands/ change color of coat because of temperature

Evidence of Evolution Fossils show changes which have occurred over time: Homologous Structure – modified structure similar in structure and function. (PAP p.384/ p.401) Vestigial Structure – structure which was once used in an ancestral organism, but looses function due to evolution. (mole eyes/ Whale pelvic bones/ ostrich wings) Analogous Structure – similar in function different in structure (Insect wings/Birds). Does not support common ancestry.

Bell Ringer 2: Define Phenotype. What provides evidence for evolution? What is shown/ expressed. (ex. Fur color) What provides evidence for evolution? Fossils….. What is an adaptation? Having favorable traits for the given environment/ Reproductive success

II. Mechanisms of Evolution Phenotypes may determine the success or failure of an organism If the phenotype is poorly adapted to it’s environment the organism my not survive, therefore not reproduce Acquired traits are cannot be passed on

Genetics Determines Evolution: Gene Pool – All the alleles in a populations genes. In other words every form of a trait Allelic Frequency – the % of any specific allele w/in a gene pool

Statsis (Genetic Equilibrium) – allele frequency remains the same over generations Populations in genetic equilibrium are not evolving Factors that affects genes can affect equilibrium 1. Mutations [negative, positive] Negative more than likely causes death Positive may be beneficial

2. Genetic Drift – alteration of allelic frequencies by chance events

3. Gene Flow – transfer of alleles from one population to another population through immigration of individuals . This disrupts allele frequency.

Trait Variations – differences in Organisms Genetic Variation/ Diversity: Increases an organisms chance of survival Inherited and controlled by alleles Allelic frequencies in a populations gene pool will change due to natural selection

3 Types of Natural Selection that Act on Variation: 1. Stabilizing – natural selection that favors average individuals Spiders and Body Size ____Before ____After

Types of Natural Selection that Act on Variation: 2. Directional selection – natural selection that favors an extreme form of a trait

Types of Natural Selection that Act on Variation: 3. Disruptive selection – individuals w/ either extreme form of a trait

The Evolution of Species: Species – organisms that look alike can interbreed to produce fertile offspring Speciation – evolution of a new species, where members of similar populations no longer interbreed to produce fertile offspring

Physical Barriers Cause Speciation: Geographic Isolation – a physical barrier divides a population

Reproductive Isolation – the inability of organisms to mate and breed fertile offspring -Genetic material becomes so different fertilization can not occur -Behavior mating seasons are different

Different Theories: Gradualism – idea that species originate through a gradual change of adaptations Punctuated Equilibrium – idea that species originate in rapid bursts followed by long period of genetic equilibrium

Speciation: Sympatric Speciation: Is the process through which new species evolve from a single ancestral species while inhabiting the same geographic region.

Allopatric Speciation: occurs when the same species become isolated from each other. This can be the result of geographical changes such as mountain formation, island formation, or large scale human activities (for example agricultural and civil engineering developments).

Allopatric speciation due to geographic separation of the Grand Canyon 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.

Patterns of Evolution Adaptive Radiation – ancestral species evolves into an array of species to fit a particular environment.

Convergent vs. Divergent Evolution: Convergent Evolution: two completely different species look similar and have very similar traits because of their environment. Divergent Evolution: speciation occurs because of different environmental settings. They “diverge!” (move in different directions)