1. Natural Selection and Evolution
Chapter 5

2. Origins of Life

3. I. How origins and adaptation are studied
A. Fossils
Fossil record is uneven and incomplete
Why? Some organisms left no fossils - some have decomposed and some are not yet found.
B. Also use :
chemical and radioactive dating
Ancient rocks
Ice cores
DNA from living organisms

4. II. Adaptations or adaptive traits
A. A heritable trait that enables organisms to better survive and reproduce under a given set of environmental conditions= Process of Adaptation
B. Selective pressure - a factor in a population’s environment that causes natural selection to occur.
C. Limits to adaptation
Traits have to be already present in gene pool

5. Limits to adaptation
Changes in environmental conditions can lead to adaptation only if the traits are already present in the gene pool
Because each organism must do many things
Adaptations are usually compromise
Even if a beneficial trait is present, the population’s ability to adapt is limited by its reproductive capacity
Adapt, migrate or die

6. III. Natural Selection
Natural selection occurs when some individuals have genetically based traits that cause them to better survive and produce offspring
Idea developed by Charles Darwin in “On the origin of the species by means of natural selection”
Darwin Finches of the Galapagos 

7. A. Darwinian Principles of Natural Selection as a Mechanism for Evolution
1. More individuals are produced than can survive
2. Individuals within a population vary
3. Those individuals with features best
suited to their surroundings are more
likely to survive and reproduce
4. Favorable features can be passed on to
their offspring, then the offspring will
more likely to survive and reproduce
in the same setting= Fitness

8. B. Types of natural selection
1. Directional natural selection - conditions shift so that individuals at one end of the normal range become more common than midrange forms - “it pays to be different”
Most common during periods of environmental change or when members of a population migrate to a new habitat with different environmental conditions.

10. Second type:
2. Stabilizing natural selection - eliminates individuals at both ends of the genetic spectrum and favors average genetic make-up
“it pays to be average”
Occurs when an environment changes little and members are well adapted to that environment.
Individuals with unusual alleles tend to be eliminated

12. Third type:
3. Diversifying/Disruptive natural selection - individuals at both extremes of the genetic spectrum are favored and individuals with normal traits are eliminated.
“It doesn’t pay to be normal”
Population is split into two groups
Occurs when there is a shift in food supply selected against average individuals

14. IV. Evolution
Biological Evolution - change in genetic make-up in a population through successive generations
POPULATIONS EVOLVE, INDIVIDUALS ADAPT, BY BECOMING GENETICALLY DIFFERENT.

15. THEORY OF EVOLUTION - all species descended from earlier, ancestral species
A. Microevolution
Small genetic changes that occur in a population
B. Macroevolution -
Long-term, large-scale evolutionary changes among groups of species - new species are formed from ancestral species and other species are lost through extinction.
Chromosome 17 contains Color Pattern Genes for Butterflies

16. C. Coevolution
Populations of two different species interact over a long time and changes in one gene pool lead to changes in the gene pool of another species

17. D. Convergence or Convergent Evolution
Species with similar niches tend to evolve similar traits that enable them to survive and reproduce even though they are in different parts of the world

18. V. How do new species evolve?
A. Speciation - two species arise from one
Usually takes place in two phases:
B. Geographic isolation -
Populations become separated for long periods of time
Migration to new area
Physical barrier such as a road
Earthquake
C. Reproductive isolation -
Mutation & natural selection act on isolated populations - called divergence - eventually cannot interbreed
Divergent evolution - arises from speciation
Usually takes tens of thousands of years

19. Speciation

20. D. Timing of Speciation and Evolution
Punctuated Equilibrium
Sudden bursts of rapid evolution (thousands of years)
Triggered by changes in the environment, such as climatic change
OR biological environment, such as introduction of a new predator
Gradualism
Slow development of a species over long periods of time (millions of years)
BOTH ARE SUPPORTED BY THE FOSSIL RECORD