1. Evolution
IB 5.4

2. Evolution: Introduction
• Evolution: cumulative change in the heritable
characteristics of a population
– Descent with modification
– Occurs in populations of a species, not an individual
– Result of different selection pressures
• Conditions necessary for change:
– Variation: Members of a species show variation
– Overproduction of offspring: Populations tend to
produce more offspring than the environment can
support
– Change in environmental conditions

3. Individuals who traits give
Variation of traits them higher probability of
within the surviving & reproducing
population leave more offspring
Unequal ability of
individuals to survive
& reproduce leads to
accumulation of
favorable traits in
Overproduction of Natural population
Offspring
Selection

4. Variation: Where does it come from?
• Sex!
• Meiosis: Genetic Variation
– Crossing Over
– Genetic Recombination
– Random Fertilization

5. Overproduction of Offspring
• What happens when there are
too many babies?

6. Overproduction of Offspring
What happens when there are too many babies?
Lots of resources Population reaches
available, populati carrying capacity of
on increases environment
Variation exists
within
population, so Population
Weaker me better than
others continues to
individuals increase, too
perish, don’t many individuals
pass on traits

7. Natural Selection
• Overproduction of
Offspring + Variation +
Inheritance +
Competition+ Time =
Natural Selection
Images taken from UC Berkley Evolution Site: http://evolution.berkeley.edu/evolibrary/article/bergstrom_02

8. Evidence for Evolution: Fossil Record
• Fossil record provides
history of life on earth
• Shows similarities and
differences & indicates
relatedness of present
day and extinct
organisms
• Indicate formation of new
species

9. Evidence for Evolution: Selective
Breeding
• Process of humans purposefully breed wild
organisms to produce offspring with most
desired traits

10. Evidence for Evolution: Homologous
Structures
• Many organisms share structural similarities
• Homologous Structures
• Analogous Structures

11. Evolution in Action: Example 1
• Stickleback Fish
in Loberg
Lake, Alaska
changed from
fully armored to
low armored in
13 generations
after
environmental
change (caused
by humans)
Source: http://www.nature.com/news/stickleback-genomes-reveal-path-of-evolution-1.10392

12. Evolution in Action: Example 2
• Antibiotic Resistant Bacteria
Images taken from UC Berkley Evolution Site: http://evolution.berkeley.edu/evolibrary/article/bergstrom_02

13. Evolution in Action: Example 3