EV: Natural Selection Lesson

You're a Natural!

So What is Evolution?

It means that a species or a population (not an individual) will change over time as traits are passed on from generation to generation.

Two Parts to the Theory of Evolution (proposed by Charles Darwin)

  1. Living things here today are descended from common ancestry.
  2. Natural selection is a process that occurs when living things with favorable (inherited) characteristics survive to reproduce, thereby passing on those beneficial characteristics.

What Darwin Said

Charles Darwin (1809-1882), developed the basis for the Theory of Evolution after traveling around the world on the H.M.S. Beagle.
Click through the notes below to learn more about Darwin and how this trip influenced his ideas about evolution.

Survival of the Fittest

Two ram fight for dominance to gain access to potential mates. The peacock flounder can change its pattern to camoflage. In both cases, the key to being fit is being able to reproduce and surviving a predator.

Types of Natural Selection

Types of Natural Selection

Stabilizing Selection

Directional Selection

Disruptive Selection

Graph showing before and after having similar peaks Graph showing before peaking to the left of after Graph showing before with two peaks on the outside of after's one peak

Favors the intermediate phenotypes.

Predators cannot catch the medium-sized lizards (they are the fastest), you would see fewer small and large lizards over time.

Favors one extreme or the other.

Giraffes with longer necks get more nutrients from higher vegetation. That trait increases in the population over time.

Favors extreme phenotypes.

For the shells, predators could see the pink shell but not the other two (they were camouflaged), and the frequency of pink shells decreased.

Natural Selection Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

Before You Go - You Need To Know

The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.

 

  1. Change over time is called: Evolution
  2. The 3 Types of Natural Selection are:
    • Stabilizing
    • Directional
    • Disruptive
  3. Charles Darwin proposed that Natural Selection was a way to explain evolution. 

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