Download Natural Selection

Natural Selection:
the mechanism for evolution
Charles Darwin
(1809 – 1882)
I have called this principle,
by which each slight
variation, if useful, is
preserved, by the term
Natural Selection.
- from The Origin of Species
Darwin’s Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia.
The Voyage of the Beagle
Galapagos Islands
http://vimeo.com/17051816
• http://app.discoveryeducation.com/player/vi
ew/assetGuid/9E8DE1D4-BCBD-422CB307-E79CA309E95C
Natural Selection:
Nature acts as the “selecting”
agent.
 Organisms better adapted
(most “fit”) to the environment
survive and reproduce more
successfully.
STEPS of Natural Selection:
1. VARIATION - Individuals of a population vary
in their characteristics (different color, muscles,
eyesight, etc.)
HOW DOES THIS OCCUR??????
2. OVERPOPULATION – A population
produces more offspring than can survive
3. COMPETITION – Because of over
population, there is competition - “struggle
for existence” between organisms for food,
space, water, etc.
4. Heredity
“DIFFERENTIAL REPRODUCTIVE SUCCESS”
Individuals with best suited traits to the
environment are more likely to survive and
reproduce more offspring, passing the
helpful variations on in the population.
5. SPECIATION – over long periods of time,
variations accumulate and become so numerous that
the population represents a new species.
Artificial Selection
• Humans “select” which organisms breed
(humans act as selecting agent instead of nature)
Selection Pressures
Factors that cause “selection” to occur:
• Amount of food available
• Water
• Shelter
• Predation (predators hunting a population)
• Disease
• Humans…?
• Evolution is the progressive change in
populations of organisms over time
through the process of natural selection.
• It explains how biodiversity is achieved.
How does evolution really work?
Video and Questions:
http://www.pbs.org/wgbh/evolution/educators/cou
rse/session4/explore_a.html
Evolution of Camouflage Video:
http://www.pbs.org/wgbh/evolution/educators/cou
rse/session4/explore_b.html
http://app.discoveryeducation.com/player/view/assetGuid/12302FAB-8366-4FCEBF17-7A75F5700B4D