This document summarizes the key components of biological evolution by natural selection: 1) Genetic variation within populations arises from mutations, gene flow, and sexual reproduction. 2) Variations must be heritable in order to be passed on to offspring. 3) Individuals with heritable traits that increase fitness, like survival and reproductive success, will pass their genes on more often. 4) Over time, natural selection leads populations to become better adapted to their environment as less fit individuals are less likely to survive and reproduce.

1. Biological Evolution by
Natural Selection
 Biology: Mr.
McFadden
 4-24-10
 Write the Red

2. Population
 a localized group of
individuals belonging to the
same species
Wildebeest

3. What is a species?
 Biological species concept
(Mayr): a population or group of
populations whose members have the
potential to interbreed and produce
viable, fertile offspring (genetic exchange
is possible and that is genetically isolated
from other populations)

4. Biological Evolution
What is needed:
1. Genetic Variation: Differences that occur
in a population between individuals.
3 Sources of Variation:
 Mutations are changes in
the DNA. A single mutation can
have a large effect, but in many
cases, evolutionary change is
based on the accumulation of
many mutations.
 Gene flow is any movement of
genes from one population to
another.
 Sex can introduce new gene
combinations into a population
during meiosis & fertilization.

5. Variation in
Phenotype
Fig. 18-2a, p.285

6. Variation in
Phenotype
Fig. 18-2b, p.285

7. Variation in Phenotype
Fig. 18-2c, p.285

8. Variation in Phenotype
Fig. 18-2d, p.285

9. Variation in
Phenotype
Fig. 18-2e, p.285

10. Variation in Phenotype
Variation can exist in:
•Form, Shape, or Color
•Speed, Intelligence, or Strength
•Behavior or senses
•Beak Size!!!
•The possibilities are endless…

11. 2. Heritability: This
variation can be passed to
offspring.

12. 3. Fitness: some individuals are better able to
survive and pass their genes to their offspring when
they reproduce.

13. 4. Natural Selection: Individuals that survive and
reproduce (highest fitness) are those with the genes
that are best adapted to their environment
(adaptation).

14. Selective Pressures:
o Environmental Change
i. Temperature or Habitat Change
ii. Earthquakes or Volcanoes

15. Selective Pressure Cont..
Predation

16. Selective Pressure Cont..
Limited Resources
i. Food, Water, and/or Habitat

17. Review of Biological
Evolution
1. Variation
2. Heritability
3. Fitness
4. Natural Selection

18. Review: Selective Pressures
 A pressure put on a species to survive
such as an environmental change,
predation, or limiting resources.
 Go to the following website to
complete the Planet Earth Evolution
“Mini Lesson”
 http://dsc.discovery.com/
convergence/planet-earth/video-
player/video-player.html

19. Your Task Today
 Using your Notes and the Planet Earth
Videos on Computers in the back,
prepare a “mini-evolution” lesson to
present to the class TODAY, with your
video.
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