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Natural
selection
and
evolution
Chapter 3.
What is Evolution?
It’s a gradual change in a species over time.
Fossils and evolution:
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We have already learnt that fossil
evidence has convinced scientists that
creatures have evolved form one to
the other; not that we have to accept
this as truth….but learn their evidence
and consider their theory.
Review your previous notes if you
need to! We look at some more
evidence soon!???
Background History:
Charles Darwin:
Explorer on a observation trip aboard
the HMS Beagle in the Galapagos
Islands.
He found a variety of species similar
to those found in South and Central
America and some completely new.
Darwin came up with the theory of
Natural Selection
Natural Selection: means that organisms
with traits best suited to their environment are
more likely to survive and reproduce.- this is
affected by the environment-or selective
pressures
This could be temperature, water availability,
predation or disease amongst others
“Survival of the Fittest”
1. Organisms produce more offspring
than can survive.
2. Variations are found among individuals
of a species.
3. Variations are passed on to offspring.-via
the genes
4. Some variations allow members of a
population to survive and reproduce
better than others- peppered mothsRead from pg 80 to students.
Over time, offspring of individuals with
helpful variations make up more and
more of a population.
Variations: an inherited trait (change in
the DNA) that makes an individual
different from other members of the same
species.
Could be colour, shape, behaviour or
chemical makeup
• Bacteria- as you know these are
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•
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single celled organisms and many can
cause disease.
It was found by Alexander Fleming that
fungus can produce natural chemicals
that kill bacteria.
These were called antibiotics
1st was penicillin
The practice of using antibiotics has
become widespread and bacteria in
some instances have become immune
to them via natural selection.
• As bacteria can reproduce every 20
mins it is easy for the “adapted or
selected ones” to produce lots of
themselves quickly creating a whole
new species that can be resistant to
the antibiotics.
• Some bacteria like golden Staff are
resistant to many antibiotics and this
causes lots of concern for doctors.
1st….some definitions to know
• Species- when the organisms are alike
physically and can breed and produce
fertile offspring
• DNA is also used to identify species –
DNA codes for genes which code for
proteins-identical proteins should mean
identical genes and therefore same
species.
• This is useful in fossil DNA to determine
ancestry.
Speciation•
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This is when one species splits into two or more
species- not a whole new creature…just a different
type i.e different type of bird like a different
coloured parrot that can’t any longer breed with
the other colour one to produce a fertile
offspring/baby.
Speciation means greater biological diversity or
more variation in the ecosystem or variety of
organisms.
It occurs in 3 steps –variation, isolation and
selection
Variation:
• Must be variation in a population
• The genes or attributes most suited will be selected
and those organisms will survive a given environment
Isolation:
• Next the “ different variety of organisms must be
isolated or separated from their relatives “
• This occurs physically first-i.e a flood separates two
groups, and they continue to develop differently
according to selective pressures in each of their new
environments.
• These physical separtors are called geographical
barriers and could also include temperature, currents
mountain ranges rivers etc.
Selection-speciation:
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Once isolated the barriers prevent cross
breeding
And as stated the organisms continue to
adapt and change often through mutations of
the DNA to the new environments via natural
selection
Changes in courtship behaviour, breeding
seasons, etc. all lead to a new species being
formed.
Evolution can happen
in two ways:
1. Gradualism - a
slow steady
process where you
can see different
forms of the new
species. Minor
changes happen
Example: horse
2. Punctuated
Equilibrium happens quickly .
Sometimes
intermediate species
are not there.
• Species branch off
and evolve
simultaneously.
Example: elephants
Practical pg 84 natural selection
Branching Diagram Essential Questions:
1. Give a brief description of the
evolutionary changes that occurred in
the organism.
2. During which time period did the fossils
differentiate into two branches? How did
you know to branch off?
3. Explain how the chart illustrates both
punctuated equilibrium and gradualism.
1. Fossil Record
Oldest fossils
are at the
bottom
Newest at the
top
2. Homologous Structures- Comparative
anatomy- body parts that have the same
number of bones, muscles or blood vessels.
3. Vestigial Structures - a body part that
doesn’t seem to have a function at this time.
Example
Pelvic
bone in
whales
4. Embryology- studying organisms at
the very early stages of development to
see how they are the same.
Show overhead
5. DNA - Organisms that have close
relatives have similar DNA. Example:
dogs are the closest relative to bears.
Human Evolution- students to read copy
of text book page
Practical pg 98/99