Docstoc

Darwin and Natural Selection

Document Sample
Darwin and Natural Selection Powered By Docstoc
					  Darwin and
Natural Selection
  born in Shrewsbury,
   England, in 1809

   studied medicine at
  Edinburgh University
 (1825-1827) where the
    sight of blood and
     surgery without
anesthetics repulsed him

  studied to become a
clergyman at Cambridge
 University (1827-1831)
                             After Cambridge,
                               Charles was
                            recommended for a
                           surveying trip on the
                               HMS Beagle.




 He sailed aboard the
  Beagle for 5 years,
working as a naturalist.
The Beagle sailed around the world.




This voyage lasted from 1831 to 1836.
At the time Darwin made
 his trip, the majority of
   people believed the
Earth and all of its forms
of life had been created
  only a few thousand
    years in the past.
   People also believed that the Earth had not
   changed during those few thousand years.

People also believed in fixity of species; in other
        words, species never changed.

                                       After careful
                                     observation and
                                       study of new
                                         scientific
                                       discoveries,
                                     Darwin began to
The first dinosaur to be described
scientifically was Megalosaurus by   think otherwise.
William Buckland in 1824.
   James Hutton         Darwin was influenced
                         by geologist James
The Father of Geology
                        Hutton’s writings that
                          described geologic
                        forces he thought had
                        changed and were still
                          changing the earth.


                        Hutton proposed that
                          the Earth had to be
                        much more than a few
                         thousand years old.
  Darwin was also
   influenced by
 geologist Charles
  Lyell who wrote
Principia Geologica.


Lyell’s book proposed
  that tremendous
 geologic processes
had shaped the Earth
   such as seen in
 volcanoes active in
      the present.
  On the voyage,       Patterns in the species
  Darwin noticed         suggested that the
that everywhere he      species had changed
 went, the animals    over time and had given
and plants differed   rise to new and different
       vastly.                 species.
 Many of Darwin’s
conclusions were
    based on
 observations of
  wildlife in the
Galapagos Islands.


   The Galapagos
Islands lie 500 miles
 west of Ecuador in
 the Pacific Ocean,
    directly on the
       equator.
                        “Galapagos” means turtle.
Darwin noticed on
   these islands,
there were several
 types of finches.
  In particular,
Darwin observed
 something odd
    about the
finches: they all
  looked like a
bird he had seen
  on the South
    American
    continent.
    Darwin wondered if the birds and other
   animals had been created to match their
environment, why didn’t these birds look like
 the birds of the African continent, since the
  environments of both the Galapagos and
             Africa were similar?
Darwin guessed that
  some of the birds
from South America
   migrated to the
    Galapagos.


Once on the islands,
the birds must have
 changed over the
       years.
                large ground
                    finch



                               woodpecker
                                  finch

 cactus finch




This would explain the numerous species of
              birds present.
           Darwin concluded:
Each species has descended, with changes,
       from other species over time.


        Darwin called this…

     Descent With Modifications

                 or



    (change in species over time)
              Darwin based his theory
              on his own observations
                 and the writings of
                  Thomas Malthus.

               Malthus was a British
                social scientist who
              made these observations
                  about humans:

People have more children than are
able to survive.

There are built-in population checks:
disease, famine, and war.
    Darwin extended these
  principles to biology, which
helped him form his theory of…




        …or Survival of the Fittest.
Darwin published his ideas in the book
On The Origin of Species by Means of
Natural Selection, or the Preservation of
Favoured Races in the Struggle for Life
Five basic components of
1. All species have genetic variation.
              Every species is different,
              even within itself.
              Look around you…are
              you all the same?
2. Organisms produce more offspring than can
survive. Many that survive do not produce
offspring.

The female green sea turtle lays a clutch of about
110 eggs. She may lay several clutches.




                      It is likely that less than 1%
                      of the hatchlings will ever
                      reach sexual maturity.
3. Since more organisms are produced than can
survive, there is competition (struggle for
existence).


Competition exists WITHIN and AMONG species.

       Within and Among Species for
              food              water

              shelter           space

         And Within a Species for
                        mates
The constant struggle for survival is affected by
short-term natural disasters. (drought, fires,
floods, snowstorms, hurricanes, and tornadoes)




The constant struggle for survival
is also affected by long-term
changes in the environment. (ice
ages, biome shifts, etc)
4. Survival of the fittest Some organisms are
more suited to their environment as a result of
variations in the species.

      Fitness: the ability of an individual to
survive and reproduce in its specific
environment. Fitness is a result of adaptations.

Individuals that are fit to their environment
survive and leave more offspring than those
who aren’t.

     He who spreads the most genes wins!
                                                1st
5. Decent with modification: Living species today
are descended with modifications from common
ancestral species that lived in the past.


          Characteristics of fit individuals
          increase in a population over time.

                  Over time, genes for less
             favored characteristics will be
             eliminated from the gene pool.

                  Example: giraffes and their
             increasingly longer necks.
    Natural Selection: Survival of the Fittest


An adaptation is any inherited characteristic (a
genetic variation) that can increase an
organism’s chance of survival.

     An the variation exists first. change
         organism does not
      because of need or desire to
        the environment changes.
     survive. The organism either
     already has the variation that
        a variation may give an advantage
      survive environmental change.
   toenables it to survive or it dies.
                Species
• A group of organisms that are closely
  related and naturally mate to produce
  fertile offspring.
                 Speciation
• The process by which new species form.
  – Separate populations of a single species often
    live in different environments
  – In each environment, natural selection acts on
    populations
  – If environments different enough, separate
    populations can become dissimilar
    Different genes favor survival in different habitats
  – As two groups become more different over
    time, they may be unable to breed= new
    species
               Speciation
• What keeps new species separate?
• Reproductive Isolation- two populations
  of the same species do not mate with each
  other- can be due to…
  – Geographic isolation
  – Temporal isolation
  – Physical differences
  – Hybrid sterility
Ex. Garter snakes- some live in water, some are
terrestrial

Ex. Courtship behaviors

Ex. Eastern spotted skunk (late winter) and
western spotted skunk (late summer)




Ex. Differences in blossoms attract different
pollinators

Ex. Gametes of red and purple sea urchins are
unable to fuse



Ex. Hybrid salamanders do not complete
development, those that do develop are frail

Ex. Donkey + horse = mule- sterile

 Ex. Even if the first generation of hybrids is viable
 and robust, subsequent generations are
 weak or sterile- rice
As the environment changes, organisms must
have variations that allow them to survive
(adapt) to those changes or die


If an entire population of
a species cannot adapt,
that species becomes
extinct.
Many scientists
 say that the
   earth is
  currently
experiencing a
mass extinction
    crisis.


 It is estimated that 1/5 or more of the world’s
 species will become extinct if the rainforests
 are destroyed.
    If we are in a period of mass extinction . . .
    What animals will your grandchildren be able
    to see in the wild?




   Visit the World                      Photos by MartinHarvey
Wildlife Fund website                   World Wildlife
for more information                    Fund International
   on endangered
       species.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:6/21/2012
language:
pages:34