Download Natural Variation & Artificial Selection

Natural Variation &
Artificial Selection
Natural Variation & Artifical
Selection
• Darwin, through many observations, explained evolution
by natural variation
• In 1859, Darwin published “On the Origin of Species”
where he proposed his theory of evolution
• Natural variation – differences among individuals of a
species and is found in all types of organisms (inherited
traits)
• Breeders routinely used variations to improve crops and
livestock = selective breeding aka artificial selection
• Artificial selection – nature provided the variation among
different organisms, and humans selected those
variations they found useful
– Ex. Only cows that produce the most milk are bred
Evolution by Natural Selection
• Struggle for existence – members of each
species compete regularly to obtain food,
living space, and other necessities
Evolution by Natural Selection
(continued)
• Survival of the fittest – how well suited an
organism is to its environment
– Fitness – ability of an individual to survive and
reproduce in its specific environment
– Adaptation – leads to fitness – any inherited
characteristic that increases an organism’s
chance of survival – can be physical or
behavioral adaptations
Survival of the Fittest
(continued)
• Generation after generation, individuals
compete to survive and produce offspring
• Individuals with characteristics that are
NOT well suited to their environment die or
leave few offspring
• Individuals with characteristics that ARE
well suited to their environment survive
and reproduce most successfully
Natural Selection
• Takes place without human control or
direction
• Over time, natural selection results in
changes in the inherited characteristics of
a population
Insecticide application
Natural Selection
Chromosome with gene
conferring resistance
to pesticide
Survivors
Reproduction
Descent with Modification
• Over long periods of time, natural
selection produces organisms that have
different structures or occupy different
habitats. As a result, species today look
different from their ancestors.
• All living organisms are related to one
another through common ancestors =
common descent