Evolution by Evolution by Natural SelectionNatural SelectionMrs. WilesMrs. Wiles

April 2009April 2009

Who was Charles Darwin?Who was Charles Darwin? Began as a medical Began as a medical

student but changed to student but changed to be a “naturalist,” or be a “naturalist,” or person dedicated to person dedicated to the study of nature.the study of nature.

Voyage on Voyage on The BeagleThe Beagle to study various to study various species.species.

Upon returning wrote Upon returning wrote The Origin of SpeciesThe Origin of Species

What did he say?What did he say?

1.1. OverpopulationOverpopulation: : Every population is Every population is capable of capable of producing more producing more offspring than can offspring than can survive. There are survive. There are limited resources.limited resources.

What did he say?What did he say?

2. 2. VariationVariation: Variation : Variation exists within all exists within all populations. Much populations. Much of it is inherited of it is inherited because it is because it is created by crossing created by crossing over during over during meiosis.meiosis.

What did he say?What did he say?

3. 3. SelectionSelection: In an environment, having a : In an environment, having a particular trait can make individuals more particular trait can make individuals more or less likely to survive and have or less likely to survive and have successful reproduction. So, some successful reproduction. So, some individuals leave more offspring than individuals leave more offspring than others.others.

4. 4. AdaptationAdaptation: Over time, those traits that : Over time, those traits that improve survival and reproduction will improve survival and reproduction will become more common.become more common.

Popular MisconceptionsPopular Misconceptions

1.1. ““Evolution says man came from Evolution says man came from monkey” WRONG! Darwin never said monkey” WRONG! Darwin never said that. Ever. All he said is that we are that. Ever. All he said is that we are related species.related species.

Popular MisconceptionsPopular Misconceptions

2. “Evolution says that Earth began with 2. “Evolution says that Earth began with the Big Bang” WRONG! Darwin never the Big Bang” WRONG! Darwin never said that either. Evolution DOES NOT said that either. Evolution DOES NOT address how the Earth began. Only address how the Earth began. Only what happened after that.what happened after that.

Darwin = Darwin = Big BangBig Bang

More Popular More Popular MisconceptionsMisconceptions

3. “Evolution is 3. “Evolution is justjust a theory” Recall that in a theory” Recall that in science theories have been tested and proven. science theories have been tested and proven. Yes Evolution is a theory and it has been Yes Evolution is a theory and it has been proven. (More on the proof to follow!)proven. (More on the proof to follow!)

Did you knowDid you know… Darwin never even used the … Darwin never even used the word Evolution in his book? He preferred word Evolution in his book? He preferred “Descent with Modification.” So what does that “Descent with Modification.” So what does that mean?mean?

Descent with Descent with Modification Modification

The The realreal definition of the word evolution: definition of the word evolution: organisms change over time into order to organisms change over time into order to adapt to a changing environment. This adapt to a changing environment. This change can been passed on to the next change can been passed on to the next generation.generation.

AKA AKA descent with modificationdescent with modification..

How do they do this? How do they do this? Natural SelectionNatural Selection

What is Natural What is Natural Selection?Selection?

Competition for resourcesCompetition for resources: there isn’t : there isn’t enough food for everyone, those who are enough food for everyone, those who are the best at getting the food survive and the best at getting the food survive and pass on their genes.pass on their genes.

Traits that make them better at getting Traits that make them better at getting food are food are adaptationsadaptations. .

Natural Selection is Caused Natural Selection is Caused by the Environmentby the Environment

Pressure from the limited environment Pressure from the limited environment causes individuals to causes individuals to adaptadapt..

Certain individuals are born with genes Certain individuals are born with genes that make them more fitted for their that make them more fitted for their environment. Those genes are passed environment. Those genes are passed on. on.

More favorable More favorable traitstraits emerge generation emerge generation after generation.after generation.

Natural Selection Example 1Natural Selection Example 1

A Gazelle on the African Plains runs A Gazelle on the African Plains runs faster than any other Gazelle in the faster than any other Gazelle in the heard. A Cheetah comes after the heard heard. A Cheetah comes after the heard for some dinner, who survives? The for some dinner, who survives? The Gazelle who runs faster than the others. Gazelle who runs faster than the others. The slow ones get eaten. The slow ones get eaten.

The Gazelle does not have to be faster The Gazelle does not have to be faster than the Cheetah, just faster than the guy than the Cheetah, just faster than the guy next to him.next to him.

Natural Selection Example 1Natural Selection Example 1

That Gazelle lives on That Gazelle lives on to reproduce and give to reproduce and give his offspring the fast his offspring the fast running gene. This is running gene. This is an adaptation.an adaptation.

This Gazelle has This Gazelle has better better reproductive reproductive fitnessfitness. It is more able . It is more able to reproduce and to reproduce and pass on genes.pass on genes.

Natural Selection Example 2Natural Selection Example 2

Male peacocks have bright colorful tails. Male peacocks have bright colorful tails. These tails enable them to attract female These tails enable them to attract female mates. The males with the biggest and mates. The males with the biggest and brightest tails mate with more females. brightest tails mate with more females. The females see the tails as a sign of a The females see the tails as a sign of a healthy male. healthy male.

Natural Selection Example 2Natural Selection Example 2

Therefore, males who have genes for Therefore, males who have genes for those bright tails will have more offspring those bright tails will have more offspring and pass on the bright tails to their and pass on the bright tails to their offspring. They have offspring. They have adaptedadapted..

This is evolution at work!This is evolution at work! The key is to The key is to successfully reproduce and pass on your successfully reproduce and pass on your advantageous genes to as many advantageous genes to as many offspring as possible.offspring as possible.