Artificial and Artificial and Natural SelectionNatural Selection

Angela Gula & Audrelyn Angela Gula & Audrelyn WatkinsWatkins

Artificial SelectionArtificial Selection

Human intervention in animal or Human intervention in animal or plant reproduction to ensure that plant reproduction to ensure that certain desirable traits are certain desirable traits are represented in successive represented in successive generations.generations.

Examples?Examples?

The Theory of Natural The Theory of Natural SelectionSelection

Originally presented in Originally presented in The Origin of The Origin of SpeciesSpecies in 1859. in 1859.

The theory of natural selection was The theory of natural selection was not accepted by the scientific not accepted by the scientific community until 60 years later.community until 60 years later.

Today, natural selection is Today, natural selection is considered one of the most considered one of the most important causes of evolution.important causes of evolution.

What leads to natural What leads to natural selection?selection?

1.1. Variation of individuals in the Variation of individuals in the populationpopulation

2.2. Inheritance of variationInheritance of variation

3.3. OverproductionOverproduction

4.4. Non-random Survival and Non-random Survival and ReproductionReproduction

VariationVariation

Take a look around—individuals Take a look around—individuals within populations vary.within populations vary.

Similar variations occur in plant Similar variations occur in plant populationspopulations Some plants bloom sooner than otherSome plants bloom sooner than other The amount of caffeine produced in the The amount of caffeine produced in the

seeds of a coffee bean variesseeds of a coffee bean varies Each different type of individual in a Each different type of individual in a

population is termed a population is termed a variantvariant..

Inheritance of VariationInheritance of Variation When When TheThe Origin of SpeciesOrigin of Species was written, was written,

Darwin did not understand the process of Darwin did not understand the process of inheritance.inheritance.

Darwin hypothesized that offspring tend to Darwin hypothesized that offspring tend to have the same characteristics as their have the same characteristics as their parents.parents.

Until Gregor Mendel’s work on inheritance Until Gregor Mendel’s work on inheritance was accepted, there was controversy over was accepted, there was controversy over this component of natural selection.this component of natural selection.

Now understood, natural selection operates Now understood, natural selection operates on genetic variation that can be passed from on genetic variation that can be passed from one generation to the next.one generation to the next.

OverproductionOverproduction

The capacity for reproduction The capacity for reproduction outstrips the resources of the outstrips the resources of the environment.environment.

Therefore, many individuals do not Therefore, many individuals do not survive to reproductive maturity.survive to reproductive maturity.

Non-random Survival and Non-random Survival and ReproductionReproduction

The subset of individuals that survive The subset of individuals that survive long enough to reproduce is not long enough to reproduce is not arbitrary.arbitrary.

Some variants in a population have a Some variants in a population have a better likelihood of survival and better likelihood of survival and reproduction.reproduction.

This is known as This is known as fitnessfitness.. Traits that increase an individuals fitness Traits that increase an individuals fitness

in that particular environment are in that particular environment are adaptations.adaptations.

So….What does it mean?So….What does it mean?

If the four underlying observations If the four underlying observations Darwin made are true, what can we Darwin made are true, what can we infer?infer?

Types of Natural Types of Natural SelectionSelection

Directional Selection—when an extreme Directional Selection—when an extreme phenotype is favored and the distribution phenotype is favored and the distribution shifts in that direction. (peppered moth, shifts in that direction. (peppered moth, bacteria resistance, pesticide resistance)bacteria resistance, pesticide resistance)

Stabilizing Selection—occurs when an Stabilizing Selection—occurs when an intermediate phenotype is favored. (birth intermediate phenotype is favored. (birth weight in humans)weight in humans)

Diversifying Selection—two or more Diversifying Selection—two or more phenotypes are favored over any phenotypes are favored over any intermediate phenotype. (Sickle-cell anemia)intermediate phenotype. (Sickle-cell anemia)

Graphic Representation of Graphic Representation of Selection TypesSelection Types

A. ________________ B. ________________ C. ________________

Addressing Addressing MisconceptionsMisconceptions

Three dreaded words…Three dreaded words…TryTry

IndividualIndividuals or s or populatiopopulations can try ns can try to evolve, to evolve, but it but it won’t won’t work!work!

www.evolution.berkley.edu

Three dreaded words…Three dreaded words…NeedNeed

Natural Natural selection selection cannot cannot provide provide what an what an organism organism needs.needs.

www.evolution.berkley.edu

Three dreaded words…Three dreaded words…WantWant

IndividuaIndividuals or ls or populatiopopulations ns cannot cannot control control what what they they want.want.

The lifetime problem…The lifetime problem…

Natural selection acts on the Natural selection acts on the inherited traits.inherited traits.

Individuals cannot change within Individuals cannot change within their lifetime in order to survive their lifetime in order to survive environmental changes.environmental changes.

Good, Better, Best…Good, Better, Best…

Natural selection does cause Natural selection does cause populations to become better fit to populations to become better fit to the environment, BUT…the environment, BUT…

The result of that process is not The result of that process is not necessarily a “better” organism.necessarily a “better” organism.

The Predetermined GoalThe Predetermined Goal

Natural selection does not occur Natural selection does not occur with a goal in mind; instead, it is with a goal in mind; instead, it is situational.situational.

Consider:Consider: Environmental conditions—drought, Environmental conditions—drought,

temperature change, food availability, temperature change, food availability, etc.etc.