Evolution Biology Mrs. Zuck

Evolution 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 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 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 Beagle

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

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

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

How 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.

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

Artificial Selection  Selective breeding of organisms by humans for specific characteristics  Examples: fruits, grains, vegetables, domestic dogs and other animals

Evolution 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.