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Biology
EVOLUTION
THREE TRENDS IN OUR TIMELINE
1.
Cluster of events at the more resent end of the timeline.
Few, widespread events at the deep time end of the timeline.
1.
Geological events preceded biological events.
1.
Plant events preceded animal events.
TIMELINE OF EARTH’S HISTORY
EARTH’S HISTORY ON A 24–HOUR CLOCK
BASIC TERMINOLOGY

Evolution – Change in the characteristics of a population over
many generations. It can NOT happen in one generation (that
would be a mutation).

Mutation – Sudden alteration in the genetic make–up
(chromosome structure or number) of one individual.

Variation – Difference between individuals.
HOW MANY MOTHS DO YOU SEE?
VARIATIONS

Some of Darwin’s sketches
of Finches while aboard the
beagle
 Note the variation in
beak size and shape
 How do you think these
variations helped the
finch?
VARIATIONS

Some of the Finch
specimens Darwin
collected.
 What other variations do
you see?
BASIC TERMINOLOGY

Adaptation – Inheritable and beneficial traits that better equip
an individual to survive in a particular environment.

Fitness – Ability of an organism to reproduce and pass it’s
genes on to the next generation. An animal with a higher
fitness will reproduce more than other animals in the same
environment.
ADAPTATIONS

A polar bear is well adapted
to life in the arctic.

What are some
adaptations?
ADAPTATIONS

A polar bear is well adapted
to life in the arctic.

What are some
adaptations?
 Thick fur and blubber to
stay warm
 White fur helps them to
camouflage
 Large feet acts like snow
shows for walking on ice
CHARLES DARWIN

Charles Darwin – Spent five years
aboard the HMS Beagle observing
a variety of species in a wide
variety of habitats.

Darwin observed that each type of
organism was well suited for the
environment in which it lived, yet
seemed to be related to other
organisms in other parts of the
world.

Published On the Origin of Species
in 1859 to explain his theory of
descent with modification.
WHERE DARWIN SPENT MOST OF HIS TIME
DARWIN LATER IN LIFE
WALLACE

Alfred Wallace – Published
his paper first, but is not
often recognized.
 Darwin’s theory was more
detailed.
 Darwin’s paper contained
more extensive evidence.
 Darwin proposed a
mechanism for change
over time.
NATURAL SELECTION

Natural selection – Mechanism used to explain the theory of
evolution.

Natural environmental pressures select the best adapted
individuals in a population to survive longer and reproduce
more. Thus, passing on their beneficial traits to the next
generation.

Examples of environmental pressures for a plant include
 temperature, sunlight, water, minerals in the soil

If the environment changes, other traits may be selected for.
BEAK VARIATIONS IN FINCHES
EVOLUTION BY NATURAL SELECTION
1)
The members of a population have heritable variations.
• size, coloration, strength, behavior
2)
In each population, many more individuals are produced each
generation than the environment can support.
3)
Some individuals possess adaptations that enable them to survive
and reproduce more than other individuals.
4)
An increasing number of individuals in succeeding generations
possess the adaptation.
5)
The result of natural selection is a population adapted to its local
environment.
NATURAL SELECTION STATED SIMPLY
1)
2)
3)
4)
5)
Variation within a population
Struggle for existence
Survival of the fittest
Descent with modification
Change over time