This document provides an introduction to evolution and natural selection. It explains that evolution is a change in allele frequencies over time, driven by genetic variation, environmental changes, and the struggle for existence. Natural selection leads to traits that aid survival and reproduction being passed on, potentially resulting in new species. While organisms cannot mutate fully formed body parts, small mutations over thousands of years can lead to new structures. Various events like natural selection, genetic drift, migration and geographic isolation can promote evolutionary changes in populations.

1. Unit 7:
Intro to Evolution
&
Natural Selection

2. (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.

3. (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.

6. (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.

8. (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

10. (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.

13. (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.

17. (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

18. (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

19. (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.

21. (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.

23. (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.

26. Natural Selection video
Hummingbirds
YouTube Video
Now Let’s Watch This Video…