Download Natural Selection

Comparing Artificial,
Natural, and Sexual
Selection
Evolution
 A change in species over time
 But how does this happen? – 3 ways
 Artificial Selection
 Natural Selection
 Sexual Selection
Artificial selection
•
Variation exists naturally in a population
•
Humans select the variations (traits) we found useful
“descendants” of wild mustard
Selective Breeding
Humans create the
change over time
“descendants” of the wolf
Natural Selection
 Three things needed
 A big, diverse population with heritable adaptations
(variation of traits)
 Variations ultimately caused by mutation
 More born than survive: selection pressures that favor
some individuals over others
 Examples
 Predation – may favor those who run faster
 Disease – may favor those with better immune systems
 Competition for resources (food, water, space, etc) – may
favor those who are bigger/stronger/smarter
 Time
 Many generations needed to pass on traits
Natural Selection
Sexual Selection
 Instead of traits that help survival, they
are traits to help reproduce
 Usually hurts ability to survive
 Two types
 Male competition
 Weapons for combat
 Large Size
 Female (mostly) choice
 Looking fancy
 Causes males and females to look very different
Sexual Selection
 Male Competition
 Female Choice
Sexual vs. Natural
Selection
http://www.youtube.com/watch?v=RxHdzw7E0wU
Fitness
 The ability to survive AND reproduce
 Used to describe Natural and Sexual selection
 Survival of the Fittest
 Basic idea of evolution by natural selection
 The organisms that can survive and reproduce the most
successfully pass on their adaptations
Selection gone bad!
Unexpected
consequences of:
Pesticide Resistance
Antibiotic
Resistance
Resistance
Spray the field, but…
insecticide didn’t
kill all individuals
variation
resistant survivors
reproduce
resistance is inherited
insecticide becomes less
& less effective