Mechanisms of Change

1
Mechanisms of Change

• The following four processes are the basic
  mechanisms by which evolution occurs.
• Its not just one mechanism that Evolution thrives
  on..

2
Natural Selection
Imagine that green beetles are easier for birds
to spot (and eat). Brown beetles are a little
more likely to survive and produce offspring.
They pass their genes for brown coloration to the
their offspring. In the next generation, brown
beetles are more common than in the previous
generation.
3
Mutation/ Speciation

• A mutation could cause parents with bright green
  coloration to have offspring with a gene for
  brown. The genes for BROWN would then become more
  frequent in the population.

4
Genetic Drift

• Imagine that in one generation, two brown beetles
  happened to have four offspring survive to
  reproduce. Several green beetles were killed
  when someone stepped on them. The next
  generation would have a few more brown beetles
  than green (purely by chance)
• Over time, a series of chance occurrences of this
  type can cause an allele to become common in a
  population.
• Small Populations

5
Gene Flow (Migration)

• Some individuals from a population of brown
  beetles might have joined the population of green
  beetles. That would make the gene for brown
  beetles more frequent in the green beetle
  population.

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Ex of Gene FlowFounder Effect

• Allele frequencies change as a result of the
  migration of a small subgroup of a population.

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Example of Gene FlowBottleneck Effect

• The bottleneck effect is an event in which a
  populations size is greatly reduced.
• When this happens, genetic drift may have a
  substantial effect on the population. In other
  words, when the population size is radically
  reduced, gene frequencies in the population are
  likely to change just by random chance and many
  genes may be lost from the population, reducing
  the populations genetic variation.

8
Bottleneck Effect
9
Term to know Gradualism

• Changes in species occurring slowly and
  incrementally.

10
Ex Gradualism
11
Term to know Punctuated Equilibrium

• Long periods of little or no change interrupted
  by rapid and dramatic changes.

12
Punctuated Equilibrium
13
Non Evolution Artificial Selection

• Long before Darwin and Wallace, farmers and
  breeders were using the idea of selection to
  cause major changes in the features of their
  plants and animals over the course of decades.
  Farmers and breeders allowed only the plants and
  animals with desirable characteristics to
  reproduce, causing the evolution of farm stock.
  This process is called artificial selection
  because people (instead of nature) select which
  organisms get to reproduce.
• Dogs are artificially selected all the time

14
Evolution Vs. Genetic Equilibrium
Genetic equilibrium the situation in which
allele frequencies remain constant.

• Five conditions are required to maintain genetic
  equilibrium from generation to generation
• There must be random mating
• The population must be very large
• There can be no movement into and out of the
  population
• No mutations
• And no natural selection