UN9F38~0

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Grade 11 University Biology – Unit 3 Evolution
Artificial Selection versus Natural Selection
Section 7.2 Pages 305-311
Artificial Selection
 Selective pressure exerted by humans on populations to “improve” or modify
particular and desirable traits
 Selective breeding in farm animals and crops (genetics)
 Breeding for selective qualities or purebred cats and dogs
Natural Selection
 Process by which characteristics of a population (…not individuals…) change
over many generations as organisms with heritable traits (i.e., passed down in
genes) survive and reproduce passing the favourable traits to their offspring
Darwin observed….
 Every generation produces more offspring than can survive given the limitation of
resources
 Individuals within a species vary in many ways…and some of the variation is
inherited
 Individuals with traits that enabled them to survive would likely have more
offspring with these favoured traits…and as such, the traits are passed on
(Survival of the Fittest)
 Processes for change are slow, gradual and random
“Evolution?”
 Darwin did not use the term “evolution.” Rather, he used the expression
“Descent with Modification.” Why? Evolution implies progress. Darwin observed
that evolution via Natural Selection has no set or predetermined direction. As
well, it may not demonstrate progress.
Factors needed for Natural Selection to occur
 Variation in characteristics
 Differences in survival and reproduction (i.e., fitness)
 Heritability of characteristics from parent to offspring
Key Difference
 In Natural Selection, it is the environmental conditions that determine which
individual traits in a population are selected for…there is no human pressure or
involvement.
Consequences of Artificial Selection
Pro
Crops – Increased nutritional value
Con
Crops – may not tolerate poor soil
quality…limited locations to farm
To protect against genetic disasters, gene banks have been established. Gene banks
contain populations of early ancestors of modern plants. Our most important food
plants come from wild ancestors with genetic combinations that allowed them to survive
and reproduce successfully in their environments.
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