1. Charles Darwin & Natural Selection

2. Charles Darwin -
English naturalist (1809 – 1882)
Travelled on the HMS Beagle
Observations of living things led to the concept of natural
selection.
Completed many studies in the Galapagos Islands.

3. Species – a group of organisms with similar
characteristics that can breed and produce
fertile offspring.
Speciation – the development of new species.
Mutation – any change or random error in the genetic code (DNA) of an organism.
Gene Pool – all of the genes present in a population.
Evolution – the concept of living things changing
over time.

4. Trials for Survival:
Competition for food and space.
Escaping from predators.
Finding mates.
Locating shelter.
Natural Selection – the process of change that allows some species to survive,
reproduce, and pass on their traits to the next generation.
* Based on “Survival of the Fittest”.
Not necessarily the biggest, fastest, strongest BUT those “best fit” for their
environment will survive and reproduce.

5. Major Components of Natural Selection
More organisms are produced than can
possibly survive. Ex. Sea turtles.
Organisms will compete for resources.
Ex. Food, mates, shelter.
There is variation amongst a species.
(Organisms of the same species differ from
one another).
4. Only those organisms “best fit” for their environment will survive & reproduce.

6. Physical Adaptations –the physical characteristics of the organism.
Organisms must adapt to their environment in order to survive.
Adaptations may be:
Physical, physiological, behavioral
Physical Adaptations –the physical characteristics of the organism.
Ex. 1: Teeth – shape indicates type of food consumed.
* Sharp & pointed – carnivores (tigers, sharks, alligators)
* Flat – herbivores (cows, elephants, goats)
* Combination – omnivores (humans)
Ex. 2: Camouflage – organisms blend in with their environment.
(Arctic fox, rattle snake, tree frog, parrot)
Ex. 3: Mimicry – organisms that look like other organisms for protection
from predators. (walking stick, viceroy butterfly,
scarlet king snake)
Ex. 4: Plants – many have fragrances, color, shapes, seed
design that enhance survival rates.

7. Physiological Adaptations – structural differences that enhance survival.
Ex. 1: Bats have sonar. The ability to detect distances by
bouncing signals off objects.
Ex. 2: Camels can go for days without water.
The ability to store water.
Ex. 3:
Whales and dolphins have adapting breathing so
they can remain under water for longer periods
of time.
Ex. 4: Some plants (mushrooms, poison oak & ivy) have chemicals that are
poisonous.

8. There are 3 fundamental kinds of natural selection.
Directional selection – when evolution of a species occurs in one direction.
Ex. Peppered moths –
* Original population of light color moths.
Industrial revolution covers trees with black soot.
* Light color moths are visible on trees and
eaten by birds. Do Not survive & reproduce.
* Black color moths blend in with trees, survive
& reproduce .
* Population has moved in one direction
to favor dark color.

9. 2. Stabilizing Selection – the average is favored to survive & reproduce.
Ex. Rabbits with different leg lengths and a fox.
Rabbits with short legs cannot run fast,
caught & eaten by fox.
Do not survive & reproduce.
Rabbits with long legs can run fast but cannot
get into rabbit hole quickly, caught & eaten by
fox. Do not survive & reproduce.
Rabbits with medium legs can run fast & get
into rabbit hole. Survive & reproduce more
medium length legged rabbits.

10. 3. Disruptive Selection – the extremes are favored to survive & reproduce.
Ex. Acorns of different sizes and squirrels.
Squirrels can easily find large acorns but
cannot carry away. Large acorns grow into
trees that produce large acorns.
* Squirrels cannot find small acorns. Small
acorns survive and grow into trees that
produce small acorns.
* Squirrels can find & carry away medium
acorns. Medium acorns do not survive.

11. Patterns of Evolution
Divergent Evolution –related organisms become less alike and diverge into new species.
* May occur due to:
Geographic Isolation – populations become physically separated by geography.
Ex. Population of squirrel that became isolated by the grand canyon diverged into two new species Populations can no longer interbreed as they are different species.
Adaptive Radiation – new populations evolve from
a common ancestor due to adaptations needed for
survival.
Ex. Hawaiian honeycreepers developed beaks
according to food sources.

12. C. Reproductive Isolation - when inter-breeding
organisms can no longer produce fertile offspring.
May be the result of geographic isolation
that has caused speciation.
Ex. Horse and donkey produce the mule.
2. Convergent Evolution
Non-related organisms develop similar characteristics.
Can often lead to mimicry.
Ex. Whales and dolphins adapted
to their marine environment.
* Now resemble fish with body shape,
flippers for fins. However, they are
mammals not fish.

13. Genetic Equilibrium – the genetic make-up of a population will remain
the same unless some external factor causes it to change.
A population in genetic equilibrium does not evolve.
Genetic equilibrium may be upset by:
Natural selection
Migration
Genetic drift Any change will result in evolution.
Isolation
Mutation

14. Migration – the movement of individuals into (immigration) and
out of (emigration) a population.
When individuals leave, they take
their genes out of the gene pool.
New individuals bring new genes
into the gene population.
Result = new gene pool
Genetic Drift – the change in gene frequency of a very small population
due to chance.
Ex. Population of 15 beetles – 14 black, 1 red.
If random mating occurs, it is possible
that the red beetle will not mate.
Trait for red beetles would be lost.