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Mechanisms for Evolution
After the voyage…

Darwin observed that all individuals struggled…


Predation
Competition for:
• Food
• Space
• Mates
• shelter
Finding mates
Food
Shelter
Predators
Space
Darwin observed…

Overproduction


Genetic Variation


Within populations, individuals have different traits
Struggle to survive


More offspring produced than can survive
Must compete for existence
Differential reproduction

Not everyone has an equal opportunity to reproduce.
Those with best adaptations are most likely to survive
and reproduce
“Descent with Modification”
species – living and extinct –
descended through reproduction from
preexisting species (genetic information
passed down from generation to
generation)
 Every
A
species must be able to change over
time (modify) in response to the changes
in their environment
How Natural Selection works…

In any population, individuals have traits, many
of which show variation.

Traits that are determined by genes are
heritable.

Advantageous traits benefit an organism and
allow it to leave more offspring—this is natural
selection.

Advantageous traits become more common in a
population, resulting in adaptation of the
species in response to its environment.
What is an adaptation?

An adaptation is a structural(physical) change in
DNA or behavior that helps a living thing survive
and reproduce in its environment.

Examples: The shape of a bird’s beak or the color of
an animal’s fur.
Types of Adaptations
 STRUCTURAL
 (physical)



Mimicry
Camouflage
Protective Coloration
 BEHAVIORAL
•
•
Hibernation
Move in groups
 PHYSIOLOGICAL

Changes in metabolic
processes
ie. Pesticide-resistance
in insects
Examples of Adaptations

The shape of an
animal’s teeth is
related to its diet.


Herbivores, such as
deer, have many
molars for chewing
tough grass and
plants.
Carnivores, such as
lions, have sharp
canines to kill and tear
meat.

Animal Defense
Some animals use
these methods of
defense to protect
themselves:

Camouflage
Blend with environment

Mimicry
Look like other species
Bright colors
• warning

“Hair” projections
• Cause harm/ pain
Adaptation Applications: Lions
 Why
are the eyes of a lion set in front of
the head rather than on the sides?
 Answer:
Eyes in front of the head allow for
depth perception and ability to judge
distances when hunting.
Adaptation Applications: Giraffe
 How
are their long necks adapted to their
lifestyle?
 Answer:
The extra length is
thought to have evolved to
help the giraffe spot predators
and other giraffes in the
distance. Interestingly, giraffes
and humans have the same
number of vertebrate in their necks.
How are plants adapted to their
environment?
 Each
biomes plant adaptations
This cactus displays
In the autumn,
desert adaptations: it has
deciduous trees drop
spines rather than leaves
their leaves to
and it stores water in its
minimize water loss.
stem.
In floating plants, chlorophyll is
restricted to the upper surface.
Note the green color on the top of
the leaves and the reddish
underside.
Soft stems enable
prairie grasses to
bend in the
wind. Narrow leaves
minimize water loss.
How are adaptations &
evolution related?
 Adaptations
allow the species to change
over time – a process we call evolution.
From the variation present in the
population, the variant selected for
depends on the selective pressures that
the species encounters in its environment.
What is a selective pressure?
A
driving force of evolution and natural
selection, ANY force that shapes/changes
organisms within a given environment is a
SELECTIVE PRESSURE.
 Can be caused by:
mutation, natural selection, genetic drift
 Possible selective pressures:
available prey/food; predators;
environmental stress; competition w/ others
Some basic definitions to
understand a theory…
 Fact:
an observation that has been
repeatedly confirmed
 Law: a general description about how the
physical world behaves
 Hypothesis: a testable statement that can
be used to build inferences and
explanations
All contribute to…
 Theory:
a well-substantiated explanation
that incorporates facts, laws, inferences
and tested hypotheses.
In science, you don’t get any better
than a theory.
What is evolution?
Let’s start by seeing what evolution is not.
Old Theories of Evolution
 Things
change because organisms want
or need them to!
Jean Baptiste Lamarck (early 1800’s)
“The inheritance of acquired characteristics”
What does this Mean?
According to Lamarck:
A giraffe acquired its long
neck because its
ancestor stretched
higher and higher into
the trees to reach leaves.
The animal’s increasingly
long neck was passed on
to its offspring.
So…what IS evolution?
A basic definition…
“…evolution can be precisely defined as
any change in the frequency of alleles
within a gene pool from one generation to
the next."
- Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers,
p.974
What does this mean?

Evolution is a change in
the number of times
specific genes that code
for specific characteristics
occur within an
interbreeding population.
Individuals don’t evolve,
populations do!
Types of Evolution
 Divergent
Evolution
Many species evolve from a
common ancestor.
 Populations
change as
they adapt to different
environmental
conditions, eventually
resulting in new species.
Convergent Evolution

Fast swimmers such as tuna
(a fish), penguin (a bird), and
seal (a mammal) all have
streamlined bodies.
 They evolved independently but
made similar adaptations in
form to perform the same
function of moving through
water.
 Similar adaptations among
unrelated organisms to similar
environments is called
convergent evolution.

These honeycreepers, evolved from a single
ancestral species that lived on the Hawaiian
Islands long ago.

When an ancestral species evolves into a group
of species to fit a number of diverse habitats, the
result is called ADAPTIVE RADIATION.

Adaptive radiation is a type of divergent
evolution, which occurs when populations
change as they adapt to different environmental
conditions, eventually resulting in new species.
Adaptation Games
 Animal
Adaptations Game
 Harcourt animal adaptation game