Download Natural Selection

Evolution by
Natural Selection
Change OVER TIME
What is evolution by natural
selection?
 Adaptations will spread throughout a
population (species) if:
 It helps an organism GET FOOD
 It helps an organism AVOID PREDATION
 It helps an organism ATTRACT A MATE
How does Natural Selection Work?
 Variations (DO NOT HELP YOU TO
SURVIVE…JUST A DIFFERENCE
AMONG ORGANISMS) exist in a
population…in here we have different eye
color…DOES EYE COLOR help you to:
GET FOOD?
AVOID PREDATION?
ATTRACT A MATE?
How does Natural Selection Work?
 Adaptations: THESE TRAITS DO HELP
YOU TO SURVIVE,
– Examples:
 A turtles shell
 Bright colors
 Rattle on a rattle snake
Natural Selection is a Theory.
What is a Theory?
 A theory is a well supported testable
explanation of phenomena that have
occurred in the natural world
 Some Common Theories Include:
 Gravity
 Evolution by natural Selection
Darwin’s Observations
 He was fascinated at how WELL ADAPTED
the animals were to the island!
 He noticed that many of the animals he saw
on the island closely resembled the animals
on the main land but were a BIT
DIFFERENT!
Natural Selection
 The Struggle for Existence…survival of the
fittest (fit-ability to survive and reproduce result of adaptations)!
 Members of the same species compete for
food, living space, and mates
 Those that are faster or better camouflaged,
ect are more likely to survive…sometimes
leading to new traits!
Darwin’s Theory of Natural Selection
1. Organisms overproduce offspring
2. No 2 organisms are exactly alike (So when
competition exists, some may win!)
3. The organism BEST ADAPTED to the new
environmental pressure will SURVIVE to
REPRODUCE (and pass on adaptation to
offspring)!
4. In time…(millions of year)…the traits in a
population will change (and may form new
species).