Charles Darwin (PowerPoint) by wuyunqing


									There is variation among individuals
   of the same species,
   and therefore differential survival,
   with survival of only the fittest.
•   Human variation
    E.g. darker skin at the equator is a function
    of increased melanin in the skin for
    protection against the sun
    (environmental adaptation).

    Pale skin is an environmental adaptation to
    reduced sunlight at higher latitudes.
    Less melanin allows the sun in because sunlight
    promotes the production of vitamin D.
Human variation
E.g. Oriental eyes are genetic, due to a
relatively isolated gene pool (breeding
population) in the past 120 000 years in the
                               Lions Panthera leo

   Lions (Panthera leo) only mate with lions, and that makes
    them one species. They do not mate with other cats like
                tigers, leopards and panthers.

Tiger Panthera tigris   Leopard Panthera pardus Panther Puma concolor
              Genus: Equus
 Equus zebra (mountain zebra)
 Equus quagga (common zebra)
 Equus africanus (wild ass)

All of the horse type, thus the genus Equus,
but different enough to be divided into species.

Equus zebra        Equus quagga           Equus africanus
              Genus Equus
      Zebras do not mate with race horses.

      Different species cannot produce viable
      offspring if mated.

a mule is a cross between
a donkey (species) and a
horse (species).

A mule is always sterile
and cannot reproduce.
2. This infers a struggle for survival
   and competition between
   individuals of the same species.
4. There is a natural selection for
individuals with traits favoured in a
particular environment.
5. Traits are in the
   genes, so are
   inherited through
   sexual reproduction
   (male and female
   genes paired).
• New genetic combinations allow for
  variation, giving more chances to
  adapt to a changing environment.
6.   Offspring carry the
     advantageous feature and
     pass it on to their offspring.

     The result is a gradual
     genetic shift (evolutionary
     change) in the population
     as the trait is naturally
                                   e.g. better thermo-regulation in some lions
                                   living in extremely hot desert environments
 Genes are not the only factor that
 determine an organism’s appearance.

• Environmental influences: A person
  with a dominant gene for height could
  end up short due to poor diet and living

• Mutation: random change in an
  individual’s genes.
           E.g. of a useful mutation:
      A lamb born with short, bent legs that
        prevented it from jumping fences.
Used in breeding to establish short-legged sheep.

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