14.3 Natural Selection the Mechanism for Evolution

1
14.3 Natural Selection the Mechanism for
Evolution

• 14.3

2
14.3 Darwin proposed natural selection as the
mechanism of evolution

• Population a group of individuals of the same
  species living in the same area at the same time.
• Darwins finches- isolated finches adapt to their
  local environment. (Differences in beaks)
• (13 species of finches unique to Galapogos
  Islands) Finch wkst.

3
How Can This be Explained? Darwins Explanation

• Descendants of the earliest organisms spread into
  various habitats over millions of years. In these
  habitats, they accumulated different
  modifications, or adaptations, to diverse ways of
  life. (Descent With Modification)
• Finches better suited for their environment
  survive better than others. The organisms that
  are better suited reproduce offspring that are
  also better suited. Less suited organisms die and
  do not reproduce. (Natural Selection)

4
Darwins Observations Leading to Natural Selection

• Overproduction of Offspring species produce
  more offspring than the environment can support
• 2. Leads to a Struggle for Existence
• 3. Many Variations within a population!
• (def.) Differences among members of the same
  species
• 4. Individuals with best suited traits survive,
  have reproductive success, and pass on their
  advantageous traits.

5
(No Transcript)
6
Natural Selection

• Natural Selection individuals with
  traits/adaptations well suited for an environment
  will be survive and produce more offspring than
  individuals without these traits.
• Over time, there will be a higher of
  individuals with this advantageous trait.
• Nature selects, not humans.

7
Natural selection Beetles with brown genes
escaped predation and survived to reproduce more
frequently than beetles with green genes, so that
more brown genes got into the next generation.
8
Natural selection acts on existing variation.

• Natural selection can act only on traits that
  already exist.
• Structures take on new functions in addition to
  their original function.

9
(No Transcript)
10

11
Artificial Selection vsNatural Selection

• Artificial selection selective breeding of
  domesticated plants and animals to produce
  offspring with genetic traits that humans value.
  
• Plant breeder-Improved grain production, disease
  resistance, or protein content.
• Animal breeder- temperament, coat, growth rate
• Different from natural selection because they are
  traits that humans choose, not nature.
• Artificial selection can produce a great deal of
  change in a much shorter time period

12
The Bottom line is.

• Natural Selection Nature chooses/selects and
  favors traits more suitable for their
• particular environment.
• Result? ? Evolutionary adaptation to
• the environment.

13
Pesticides- Natural Selection in Action

• Pesticide poisons used to kill insects that are
  pests in crops and homes.
• Initial pesticide spraying kills most of the
  insects. Those that survive have a mutation- a
  gene for pesticide resistance.
• Resistant survivors reproduce passing on the
  resistant gene.
• In each generation the number of resistant
  insects increases.
• Eventually that pesticide is ineffective.
• The population underwent evolutionary change.
• The pesticide does not create resistant
  individuals.
• The pesticide naturally selects for resistant
  insects that are already present in a population.