Unit 7: Intro to Evolution

&Natural Selection

(1) What is Evolution?

• A change in the allele frequency of a population of living things, over a period of time.– “Allele Frequency” = How often a certain trait

shows up in the population.

• Causes for Evolution:– Genetic variation amongst the population.– Changes in the environment/resources.– Changes in sexual preference.– The dying/extinction of certain populations.

(2) Genetic Variation in the Population

• There must be variety / diversity for evolution.

• Genetic Variation / Diversity Organisms inherited different variations of traits, giving them different strengths and weaknesses.

• Genetic Variation allows for some individuals to succeed + survive.

(3) The Struggle for Existence

• Living things are always competing to stay alive AND pass on their genes:– Limited food– Limited water– Limited shelter– Changes in climate, disease transmission, etc.

• Those who can survive and reproduce during tough times are best suited/adapted to their environment.

(4) What does it mean to Adapt?

• Evolutionary Adaptation: Having the traits necessary to remain living and sexually attractive during times of change.

• It does NOT mean:To change/grow body parts so that you can

(5) What is Natural Selection?

• As the environment changes, certain characteristics amongst living things will help them to survive (Survival of the Fittest).

• If you don’t have these characteristics, you will most likely die, or at least not reproduce.

(6) The End Result of Natural Selection

• There will be a change in the allele frequencies in the population.

• Could produce a new species (a group of organisms that can only reproduce with each other).

• Example:– Start with a population of large lizards.– Decrease in climate oxygen and available food + water.– Larger lizards do not survive during the change.– End with a population of smaller lizards.

(7) What About Mutations?

• Organisms CANNOT mutate whole, fully functioning body parts.

• Organisms can pass on small body mutations, over thousands of years, leading to the development of a new body part.

• Mutations can either hurt, or provide an advantage to individuals during times of change.– Both = Evolution

(8) Events Driving Evolution

• All evolutionary changes are still driven my natural selection.

• There are different events that can promote evolution:– Basic Natural Selection– Mutations– Genetic Drift– Genetic Migration– Geographic Isolation

(9) Genetic Drift

• The random removal of certain traits (alleles) from a population.

• “Wrong Place, Wrong Time.”

• Example:– You cut your grass and accidentally kill a bunch of

yellow lady-bugs.– The frequency of yellow lady-bugs decreases.– There’s now an increase in the # of red lady-bugs.– Accidental evolution.

(10) Genetic Migration

• When organisms with different traits move into new regions and populations, and reproduce with the original organisms.

• Example:– Yellow lady-bugs fly into a population of red lady-

bugs.– They reproduce, and produce some yellow

offspring.– Now there’s a higher frequency of yellow in the

population.

(11) Geographic Isolation

• When a diverse population is separated and isolated by some geographic barrier (land, water, climate).

• Example:– A population of red and yellow lady-bugs is

separated by a newly formed river.– On one side there end up being mostly red bugs.– On the other side there end up being mostly yellow

bugs.– There are new allele frequencies on each side.

Natural Selection video

Hummingbirds YouTube Video

Now Let’s Watch This Video…