EvolutionEvolution

BiologyMrs. Zuck

Evolution by Natural SelectionEvolution by Natural Selection Organisms tend to be well suited to where

they live and what they do. How do they become so well suited? Charles Darwin observed that organisms in a

population differ slightly from each other in form, function and behavior

New genes/traits arise from random mutations. Most are either Neutral (no effect), or

disadvantageous (decrease an organism's chance for survival).

Natural SelectionNatural Selection

Darwin’s term to describe the unequal survival and reproduction that results from the presence or absence of particular traits Over many generations natural selection

causes the characteristics of populations to change.

Evolution: change in genetic characteristics of a population from one generation to the next

Darwin & Natural SelectionDarwin & Natural Selection

•Darwin was a Naturalist aboard an exploration ship called the HMS Beagle.•Collected and catalogued biological specimens for return to England.

The Voyage of the BeagleThe Voyage of the Beagle

Darwin & EvolutionDarwin & Evolution Natural selection:

Based on following premises: There are not enough resources for all

organisms to survive. Some organisms are more "fit" to survive. Fitness refers to: The ability of an organism to survive in its

environment. The ability of an organism to survive long

enough to reproduce. Natural pressures "weed-out" those individuals

"less fit" to survive. Thus changing a species over time.

Natural Selection : The Peppered Moth:Natural Selection : The Peppered Moth:

The peppered moth is a species of moth which uses camouflage against tree bark to avoid being eaten by birds. It is normally a light grey color.

During England's industrial revolution, pollution caused a darkening of the bark of the trees.

There was a natural variation in moth coloration with some being darker than others.

Those moths of a lighter color, were easier to spot and eat by birds. And were eaten at a faster rate.

The survivors tended to be darker, and when they mated, their offspring tended thus to be darker also.

Over time, this resulted in the species becoming darker in color.

Nature SelectsNature Selects

Darwin proposed that nature selects for certain traits that are more favorable to survival and reproduction Adaptation: an inherited trait that increases an

organism’s chance of survival and reproduction in certain environment.

Directional Selection:Directional Selection:

Eliminates one extreme variation from an array of possible phenotypes. Results in a shift towards the other extreme.

Stabilizing Selection:Stabilizing Selection:

Selection acts to eliminate both extremes of an array of phenotypes. Results in an increase in individuals exhibiting an intermediate phenotype.

Disruptive SelectionDisruptive Selection

Selection acts to remove the intermediate phenotypes favoring the extreme phenotypes:

How evolution worksHow evolution works

1. Organisms produce more offspring than can survive

2. The environment is hostile and contains limited resources

3. Organisms differ in the traits they have

4. Some inherited traits provide organisms with an advantage

5. Each generation contains proportionately more organisms with advantageous traits.

CoevolutionCoevolution

The process of two species evolving in response to long term interactions with each other

Artificial SelectionArtificial Selection

Selective breeding of organisms by humans for specific characteristics Examples: fruits, grains, vegetables, domestic

dogs and other animals

Evolution of ResistanceEvolution of Resistance

Sometimes humans cause populations of organisms to evolve unwanted adaptations. Resistance: the ability of one or more

organisms to tolerate a particular chemical designed to kill it.