Download Natural Selection

OBJECTIVE: NATURAL SELECTION
ESSENTIAL QUESTION: HOW CAN A CHANGE IN THE ENVIRONMENT INITIATE
A CHANGE IN A POPULATION?
ARTIFICIAL SELECTION VS NATURAL SELECTION
 Artificial Selection: the process by which humans change a species by breeding it for
certain traits
 Natural Selection: a mechanism by which individuals that have inherited beneficial
adaptations produce more offspring than others.
4 PRINCIPLES OF NATURAL SELECTION
 Variation—the heritable differences or variations that exist in every population are the basis for natural selection.
Reasons for differences could be from differences inherited from parents or from genetic mutations.
 Ex: Some Jaguars may be born with slightly longer teeth due to natural variation in the population, some variations
are heritable
Can you give an example from Bird Beak Challenge?
4 PRINCIPLES OF NATURAL SELECTION
 Overproduction—while having many offspring raises the chance that some will survive it also increases
competition
 Ex: A jaguar produces many offspring but only a few will survive due to competition
Can you give an example from bird beak challenge?
4 PRINCIPLES OF NATURAL SELECTION
 Adaptation—Sometimes a certain variation allows an individual to survive better than the other organisms it
completes against. The more successful individuals are ‘naturally selected’ to live longer and to produce more
offspring, to which they will pass on these adaptations
 Ex :Jaguars with longer teeth are better able to eat shelled retiles. They will survive longer and leave more
offspring than jaguars that can only eat mammals.
Can you give an example from the Bird Beak Challenge?
4 PRINCIPLES OF NATURAL SELECTION
 Descent with modification—over time natural selection will result in species with adaptations that are well suited
for survival and reproduction in an environment. More individuals will have the trait in every successive
generation, as long as the environmental conditions remain beneficial for that trait.
 Ex: Because large teeth and jaws are heritable traits they become more common characteristics in the population.
Can you think of an example in the bird beak challenge?
OTHER MECHANISMS OF EVOLUTION
 Gene Flow—The movement of Alleles from one population to another.
 When an organism moves from one population to another its alleles are
added to the new population but removed from the population it came
from. Gene flow between neighboring populations keeps their gene
pools similar.
 The LESS gene flow between populations means that their will be MORE
genetic diversity
OTHER MECHANISMS OF EVOLUTION
 Genetic Drift—Changes in allele frequency due to
chance (occurs when populations becomes small) his
decreases genetic diversity in the population
OTHER MECHANISMS OF EVOLUTION
 TYPES OF GENETIC DRIFT
 Bottleneck Effect– Genetic Drift after an event greatly reduces the size
of a population.
 Founders Effect—Genetic Drift that occurs after a small number of
individuals colonizes another area.
OTHER MECHANISMS OF EVOLUTION
 Sexual Selection—Occurs when certain traits increase mating success.
 Intrasexual selection is sexual competition among males Example?
 Intersexual selection sexual competition between females and males Example?
Traits that increase mating success are not always good for natural selection adaptations