Natural Selection & Biological
Resistance
EVOLUTION UNIT
Natural Selection
 Natural Selection: a scientific theory that explains
the process of evolution
Principles of Natural Selection:
1. Variation exists within populations
2. Organisms compete for limited natural resources.
3. Organisms produce more offspring than can
survive.
4. Individuals with variations suitable for their
habitat survive and reproduce.
Natural Selection at Work
 Genetic variations that result in helpful traits can
increase an organism’s fitness.
 Fitness: the physical and behavioral traits that
allow an organism to survive and reproduce
https://www.youtube.com/watch?v=wrTXvrKBlbc
Pocket Mouse Video-Natural Selection
Pesticide Resistance
 Resistance: an organism’s ability to withstand a
harmful agent
 People develop chemicals called pesticides that kill
insects. Some insects have slight variations that
enable them to survive the pesticide. They are
pesticide-resistance. These organisms survive and
reproduce and pass that trait onto the next
generation of insects.
 Generation: one step in the line of descent of an
organism from parent to offspring
Health Issues-Malaria
 Mosquitoes became
immune to the DDT
(insecticide) spray
Antibiotic Resistance
 Antibiotic: a drug that is used to kill bacteria or
slow their growth
 Some bacteria in a population may have a trait that
makes them resistant to an antibiotic. Over time,
enough of these bacteria survive and reproduce. The
antibiotic becomes ineffective against the infection.
 Bacterial Resistance Animation:
https://www.youtube.com/watch?v=zjR6L38yReE
Viruses
 Not considered living, but
they do have the ability to
make new viruses through
replication.
 Virus can mutate when they
replicate. Therefore, an
organism that was immune
to the virus due to
vaccination may no longer
be protected after the
mutant virus is created.