There is variation among individuals

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• There is variation among individuals
• of the same species,
• and therefore differential survival,
• with survival of only the fittest.

2

• 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.
3

• 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
  East.

4
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
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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 quagga
Equus africanus
Equus zebra
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Genus Equus
Zebras do not mate with race horses. Different
species cannot produce viable offspring if mated.
e.g. a mule is a cross between a donkey
(species) and a horse (species). A mule is
always sterile and cannot reproduce.
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• This infers a struggle for survival
• and competition between
• individuals of the same species.

8

• 4. There is a natural selection for individuals
  with traits favoured in a particular environment.
  

9

• Traits are in the genes, so are inherited through
  sexual reproduction (male and female genes
  paired).

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• New genetic combinations allow for variation,
  giving more chances to adapt to a changing
  environment.

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• 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 selected.

e.g. better thermo-regulation in some lions
living in extremely hot desert environments
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• Genes are not the only factor that determine an
  organisms appearance.
• Environmental influences A person with a
  dominant gene for height could end up short due
  to poor diet and living conditions.
• Mutation random change in an individuals genes.
  

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E.g. of a useful mutationA lamb born with
short, bent legs that prevented it from jumping
fences. Used in breeding to establish
short-legged sheep.