Natural Selection

1
Natural Selection

• Struggle for Existence
• Survival of the Fittest
• Descent with Modification
• Results of Natural Selection

2
Natural Selection

• Struggle for Existence members of each species
  compete regularly to obtain food, living space,
  and other necessities of life
• From Malthus work, Darwin concluded that high
  birth rates and a shortage of lifes basic needs
  would force competition for resources.

3
Natural Selection

• Survival of the Fittest some individuals are
  better suited for their environment than others
  those best suited will survive
• Fitness ability of an individual to survive and
  reproduce in its specific environment
• Result of adaptations
• Evolutionary Fitness organisms success in
  passing genes to the next generation
• Where fitness varies, natural selection can act.

• Adaptation any inherited characteristic that
  increases an organisms chance of survival
• Could be anatomical, behavioral, physiological
• Evolutionary adaptation any genetically
  controlled physiological, anatomical, or
  behavioral trait that increases an individuals
  ability to pass along its genes

4
Natural Selection

1. Descent with Modification every living species
   has descended, with changes, from other species
   over time

• Implies that all living organisms are related to
  one another
• Principle of Common Descent all species (living
  and extinct) were derived from common ancestors
• Allows for a single tree of life that links all
  living things

5
Result of Natural Selection

• changes in the inherited characteristics of a
  population
• These changes increase a species fitness in its
  environment.
• Acts on populations, not individuals. It is
  populations that evolve over time.

6
Summary of Darwins Theory of Evolution

• Individual organisms differ (variations exist in
  a population).
• Some of this variation is heritable.
• In nature, there is a tendency for
  overpopulation.
• Organisms produce more offspring than can
  survive. There is a high death rate.
• Only the organisms with the variations that are
  suitable to the environment survive.
• Organisms must compete for limited resources.
• Each unique organism has unique advantages and
  disadvantages in the struggle for existence.
• The organisms that survive get to reproduce and
  pass on their genes.
• The process of Natural Selection causes species
  to change over time.
• It is the population that changes to match the
  environment not individuals.
• Species alive today are descended with
  modification from ancestral species.