1. Theory of Evolution
Natural Selection

2. Genetic variation is the driving force behind
evolution. There are many ideas of why populations
change overtime. These changes may be due to
mutation, movement of alleles between
populations, interbreeding, isolation, and natural
selection

3. Theories of Evolution
A. Jean Baptist Lamarck
Evolution occurs due to inheritance of ACQUIRED
TRAITS FROM A COMMON ANCESTOR, not from
changes in the environment
Idea that variation in a population is created by
experience
Ex. Individuals passed on to offspring body and
behavior changes acquired during life

4. What is wrong with this idea?

5. Theories of Evolution
B. Charles Darwin
2 Major Theories:
1. Descent with Modification: stated that ALL
new species were ALTERED DESCEDENTS of
OLDER ANCESTORS and arose from similar
geographic locations

6. 2. Natural Selection: proposes that NATURE or
environmental conditions DETERMINE and
individual’s CHARACTERISTICS, which in turn
leads to EVOLVING population over time

7. 4 Mechanisms of Natural Selection

8. o GENE VARIATION EXISTS WITHIN A POPULATION
Only if variation is
GENETICALLY BASED will
natural selection lead to
evolution
-MUTATIONS and
RECOMBINATION of
genes may produce
beneficial changes and
INCREASE gene variation
within a population

9. o INDIVIDUALS WITH MORE SUCCESSFUL TRAITS
WILL PASS TRAITS ON TO OFFSPRING
-in turn, will increase the
success of the
population

10. o INDIVIDUALS MOST ADAPTED TO THE ENVIRONMENT
WOULD GET THE BASIC RESOURCES FOR LIFE
-ADAPTATION: individuals response to
environmental pressures – may reduce
competition within a population

11. o INDIVIDUALS THAT ARE MOST “FIT” HAVE
GREATEST POTENTIAL TO REPRODUCE
SUCCESSFULLY AND INCREASE POPULATION
NUMBERS OVER TIME –”survival of the fittest”
-FITNESS: reproductive success of one individuals
genetic contribution to the next generation

12. Examples of “fitness”
• Bacterial resistance to antibiotics

13. • Pesticide resistant insects

14. • Skin color - melanin

15. Summing Up Natural Selection