The Theory of Evolution

1
TheTheory of Evolution
2
Darwins Theory of Evolution

1. Natural Selection
2. Origin of Species

3
Darwins Ideas

• Natural Selection
• A process in which some individuals have
  genetically-based traits that improve survival or
  reproduction
• Thus, they have more offspring surviving to
  reproductive age than other individuals.

4
Basic requirements of Natural Selection

• There is variation/diversity in traits.
• There is differential reproduction.
• Since the environment can't support unlimited
  population growth, not all individuals get to
  reproduce to their full potential.
• There is heredity.

                            
5
What is the general way we refer to those who
survive?

• Fitness
• An individuals success at reproducing
• (the more offspring the individual leaves, the
  higher its fitness).
• Fitness is dependent upon a particular phenotype
  that individual has.
• Phenotypes are in turn dependent upon that
  individuals genotype.

Is this phenotype always the biggest, fastest and
strongest?
6
Lets explore this Cartoon to find out

• Take a minute to read the cartoon that was just
  handed out.
• When you are through reading the cartoon, turn it
  over to indicate that you have read it.

Based upon your reading, does fitness always
mean the biggest, fastest and strongest?
No. The fit cricket has adapted a strategy for
reproducing without the cost.
7
Misconceptions about Natural Selection
Mechanism 4. Natural Selection

• It is not Survival of the Fittest really it is
  Survival of the fit enough
• Recessive alleles for disease can stay unnoticed
  in a population
• Organism does not choose
• Perfection is not obtained

       
                                  

                                  
8
Adaptations

• Adaptations
• A behavior or a physical feature that enables an
  organism to survive

Kingsnake harmless (uses mimicry)
Echo-location
Venomous Coral Snake
9
Breeding Bunnies

• Lets re-explore the concept of natural selection
  with our bunnies!

10
How did we measure the changing population in the
breeding bunnies lab?

• Changes in gene frequency in a population from
  one generation to the next
• Over time, the allele frequency for fur
  _____________ while the allele frequency for
  hairless _____________
• This change in frequency is evidence of
  small-scale evolution microevolution

increased
decreased
11
Origin of Species

• Common Ancestry
• All life forms share a common ancestor
• We are all in the same tree of life

12
Macroevolution

• Large-scale evolution
• The descent of different species from a common
  ancestor over many generations.

For macroevolution to occur, two populations must
be reproductively isolated (or separated) from
one another
The two populations of beetles are eventually
considered different species, but they originated
from a common ancestor descent with modification
13
What is a species?

• Two populations that can mate and produce fertile
  offspring.

14
How does this descent with modification happen?

• Mutation
• A change in a DNA sequence
• usually occurring because of errors in
  replication or repair.
• Mutation is the ultimate source of genetic
  variation.

15
How does this descent with modification happen?

• Migration
• Individuals from one group move into another
  group.
• Makes certain genes more frequent in the
  population.

gene flow
16
How does this descent with modification happen?

• 3. Genetic Drift
• In each generation, some individuals may, just
  by chance, leave behind a few more descendents
  (and genes, of course!) than other individuals.

                                                                                     
17
Examples of Genetic Drift

• Population Bottleneck
• An event in which a populations size is greatly
  reduced

Northern Elephant Seal
Event that causes the population to be reduced in
size
Initial Diverse Population
Final population
Cheetah
18
Examples of Genetic Drift

• Founder Effect
• Changes in gene frequencies that usually
  accompany starting a new population from a small
  number of individuals.

19
Driftworm Activity

• Put your IntNB to the side, and get out
• Your colored pencils and
• The driftworm worksheet
• Color in Generation 0 of your driftworms

20
Driftworm Activity

• Each of these worms reproduces asexually
• The population size is constant
• The generations do not overlap
• These are haploid organisms

21
Driftworm Activity

• Follow along the directions on this website
• http//www.biology.arizona.edu/evolution/act/drift
  /manual.html