Transcript Evolution - Houston Independent School District

Notes: Evolution & Natural
Selection
Charles Darwin
His father was a wealthy doctor and wanted
Charles to become a doctor.
At age 16, he went to Medical
School.
In 1827, his father sent him to
become a priest.
In 1831, a friend asked him
to go on a ocean trip as
an unpaid naturalist.
Other Scientists and Evolution
ß Hutton- Geologist who studied how geological
forces shaped Earth
ß Earth processes happen very slowly
ß Earth must be older than a few thousand years
ß Lyell- Geologist who said that in order to
understand the past, we must observe how
geological processes shape the earth today. If
Earth can change over time, so must life.
ß Examples: volcanoes, earthquakes
Lamark was a French naturalist who…
ß Claimed that organisms tend to be complex and perfect
and are therefore unchanging.
ß Use and disuse- Lamark thought that animals could
change their bodies by using them in new ways.
Example: animals could use front limbs as wings and
develop flight.
ß Inheritance of acquired traits- Lamark though that all
changes could be inherited. For example, if you lift
weights, your children would inherit your muscles.
ß Lamark’s ideas are not scientifically accepted today!
Darwin’s Voyage on the HMS Beagle
The purpose of Darwin’s trip was to draw accurate
maps of the region. Darwin was to collect
specimens and document the plant and animal life.
Darwin’s original beliefs
Divine creation - each species was created
by God, unchanging and existing as it
was originally created.
However, on the voyage, his beliefs began
to change when he got to the Galapagos
Islands.
Darwin’s Finches
The finches showed convincing evidence
that species evolve.
Darwin was struck by the fact that the animals
of the Galapagos Islands resembled those of
the nearby coast of South America.
Darwin hypothesized that ancestors of the
Galapagos Islands must have migrated to the
island and the population slowly changed
after they arrived.
Darwin published his book in 1844:
On the Origin of Species by Means of
Natural Selection.
Darwin’s Theory of Natural
Selection
1.
2.
3.
4.
5.
There is variation within any species
All organisms tend to over-reproduce
There is a struggle for survival
The fittest survive
The environment determines who is
the fittest
1. Variation exists within every
population
1. Ladybugs have different spots
1. Variation exists within
every population
2. Zebras all have
different stripes
2. All species tend to produce more
offspring than they can SUPPORT
3. Frog eggs
1. Turtle eggs
2. Insect
eggs
4. Baby
mice
3. There is a Struggle for
Survival
1. To eat
2. To drink
3. Territory
4. To mate
4. The fittest will survive
4. The fittest will survive
Healthy or sick horse?
5. Nature (the environment) will
determine which organism is the
fittest to Survive
1. long neck giraffes survive over short neck giraffes.
Evidence of Natural Selection in
our lifetime
The Peppered Moth in England
Before the industrial
revolution
After the industrial
revolution
Explanation for the peppered moth
There was variation in the moth population to
begin with, some were black and some were
white.
This variation was due to random mutations.
Before the industrial revolution, the bark of the
tree bark was white in color.
The white moths then were
easily camouflaged,
survived, and reproduced.
Black moths were rare.
After the industrial revolution, the trees
became covered in soot/pollution from all of
the factories and the trees turned black.
Now the black moth
were easily camouflaged,
survived, and reproduced.
White moths were rare.
How does the peppered moth
illustrate natural selection?
There was variation in the population to begin
with (some white, some black).
Moths tend to over-reproduce.
Therefore there is a struggle for survival.
The fittest (those that were camouflaged the
best) survived.
The environment determined which moths were
the most fit.
How Do New Traits Appear?
ß Recall that all genes have at least 2 alleles
(forms)
ß All organisms have additional “invisible variation”
due to small biochemical differences
ß Mutations- Random mutations also occur as a
result of mistakes in DNA replication or due to
environmental factors.
ß Gene Shuffling- homologous chromosome pairs
move independently during meiosis- the 23
pairs in humans can produce 8.4 million
different gene combinations!
Natural Selection may lead to
Speciation
Speciation - the evolution of a
new species
The process of speciation
ß Geographic Isolation - when two
populations become isolated by a
geographic barrier such as mountains.
Geographic Isolation
ßReproductive Isolation - Sometimes
when populations have been separated
for a long, long time, they become so
different that they can no longer breed
and produce fertile offspring.
Same species now, but may become two different ones.
1. Horse and Donkey = Mule
Mule is infertile (can’t reproduce)
horse
donkey
mule
Lion and Tiger = Liger
Liger is often infertile (there have
been successful breedings)
2. The Kaibab and Abert Squirrels
Became reproductively isolated by huge mountains
3. Wood and Leopard Frogs
Wood frogs
Leopard frogs
Seem to be the same species, but they breed
at different times of the year.
ßSpeciation -When two populations
become so different that they can no
longer breed and produce fertile
offspring. They are then considered two
separate species.
Speciation in Finches
Types of Selection
ß Directional Selection- when individuals at one
end of the curve in a population have higher
fitness than in the middle or other end.
ß Example: Supply of small seeds is low, birds with
larger beaks can still feed, birds with smaller beaks
cannot. We will see higher numbers of birds with
larger beaks.
ß Disruptive selection- When individuals at the
upper and lower ends of the curve have higher
fitness than in the middle.
ß Example: If medium seeds are scarce, small and
large seeds are plentiful, birds with small or large
beaks will be most fit. Medium beaks will not be
as numerous.
ß Stabilizing selection- when individuals in the
center of the curve have higher fitness than
those at the ends.
ß Example: babies with very low birth rate may not
survive while very large babies may have trouble
being delivered. Average sized babies are most
fit.