Evolution Part I:
Charles Darwin is known as the
Father of Evolution.
What we know now seems like
common sense but in Darwin’s day,
it wasn’t.
So…..How did Darwin come up
with his new and radical ideas that
eventually led to the (controversial)
Theory of Evolution?
After studying at Cambridge, Charles was
recommended for a surveying trip on the
HMS Beagle.
He sailed around the world on the Beagle
for 5 years, working as a naturalist.
On the voyage,
Darwin noticed that
everywhere he went,
the animals and
plants differed vastly.
Yet, there were
similarities
Patterns in the species
suggested that the species
had changed over time and
had given rise to new and
different species.
Many of Darwin’s
conclusions were
based on
observations of
wildlife in the
Galapagos Islands.
The Galapagos
Islands lie 500 miles
west of Ecuador in
the Pacific Ocean,
directly on the
equator.
“Galapagos” means turtle.
Were the animals and plants created to match
their environment?
Then, why didn’t the Galapagos finches look
like the birds of the African continent, since
the environments of both the Galapagos and
Africa were similar.
Darwin guessed that
some of the birds
from South America
migrated to the
Galapagos.
Once on the islands,
the birds must have
changed over the
years because each
island was different
from the
others….landscape
and flora.
Darwin concluded:
Each species had descended, with changes,
from other species over time.
Darwin called this…
Descent With Modifications
or
(change in species over time)
The mechanism by which
evolution takes place.
…or Survival of the Fittest.
Five basic components:
1. All species have genetic variation.
Nature has to have some
variety in order to choose.
Look around you…are
you all the same?
2. Organisms produce more offspring than
can survive. Many that survive do not
produce offspring.
The female green sea turtle lays a clutch of about
110 eggs. She may lay several clutches.
It is likely that less than 1%
of the hatchlings will ever
reach sexual maturity.
3. Since more organisms are produced than
can survive, there is competition (struggle for
existence).
Competition exists WITHIN and AMONG species.
Within and Among Species for
food
water
shelter
space
And Within a Species for
mates
Short-term natural disasters can have large
impacts on competion. (drought, fires, floods,
snowstorms, hurricanes, and tornadoes)
Long-term changes in the
environment also affect survival. (ice
ages, biome shifts, global warming
etc)
4. Survival of the fittest Some organisms
are more suited to their environment as a
result of variations in the species.
Fitness: the ability of an individual to
survive and reproduce in its specific
environment. Fitness is a result of adaptations.
Individuals that are fit to their environment
survive and leave more offspring than those
who aren’t.
He who spreads the most genes wins!
1st
5. Descent with modification: Living species
today are descended with modifications from
common ancestral species that lived in the
past.
Characteristics of fit individuals
increase in a population over time.
Over time, genes for less
favored characteristics will be
eliminated from the gene pool.
Example: giraffes and their
increasingly longer necks.
Natural Selection: Survival of the Fittest
An adaptation is any inherited characteristic
(a genetic variation) that can increase an
organism’s chance of survival.
variation has
to already
exist.
Anthe
organism
does
not change
because of the need or desire to
If the environment changes.
survive. The organism is either
born
with the
that
the variation
mayvariation
give an advantage
to enables
survive environmental
change.
it to survive
or it dies.
Darwin published his
theory in the book
November 24, 1859
And that is why Darwin is the father of Evolution
• Camouflage
(Cryptic coloration)
• Mullerian Mimicry –untasty imitates untasty
….both benefit by making sure their
predators gets the point.
• Monarch and Viceroy Butterfly
• Batesian Mimicry – palatable (tasty) mimics
unpalatable (untasty)
• Coral vs. King Snakes: Red on yellow, kill a
fellow, red on black friend of Jack
• Warning Coloration (Aposematic coloration)
• Disruptive Coloration
• Counter Shading
• Eye spots
Things to remember:
a. Populations evolve, not individuals.
b. Natural selection is the mechanism of evolution.
c. Evolution occurs by chance (NOT GOAL ORIENTED).
d. Organisms are born with adaptations, they can’t
adapt because they need or want to
Part II
• Speciation
• Causes of evolution
• Rates of evolution
– An organism that has the potential to
interbreed in nature and produce viable,
fertile offspring that looks like their parents.
Speciation is the
creation of a new
species
Occurs when 2 pop.
are capable of
interbreeding but
have different
courtship rituals or
other reproductive
strategies that
involve behavior
Behavioral isolation
produced by
Behavioral differences
Speciation
results from
Reproductive Isolation
Two or more
species reproduce
at different times
results from
Isolating mechanisms
which include
Geographic isolation
produced by
Physical separation
Temporal isolation
produced by
Different mating times
which result in
Independently
evolving populations
which result in
Formation of
new species
Two pop. Are
separated by
geographic barriers
such as rivers,
mountains, or
bodies of water
A reproductive barrier is any factor that prevents two
species from producing fertile hybrids, thus
contributing to reproductive isolation.
•
•
•
•
•
Habitat/Geographical Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Causes of Evolution
1.
Mutations - random changes in genetic material at the level
of the DNA nucleotides or entire chromosomes
2.
Natural Selection - most important cause of evolution;
measured in terms of an organism's fitness
– The contribution an individual makes to the gene pool of
the next generation, relative to the contributions of other
individuals…the more fit, the more they contribute.
Modes of Selection (types of
natural selection)
a. Stabilizing Selection - average phenotypes have a
higher fitness over the extreme phenotypes
b. Directional Selection - phenotype at one extreme
has a higher fitness over the average and the other
extreme
c. Disruptive Selection - both extreme phenotypes
have a higher fitness than the intermediate
phenotypes
Modes of Selection
Original population
Evolved
Original
population population
Directional
Phenotypes (fur color)
Disruptive
Stabilizing
In this case, darker mice are favored
because they live among dark
rocks and a darker fur color conceals
Them from predators.
These mice have colonized a
patchy habitat made up of light
and dark rocks, with the result
that mice of an intermediate
color are at a disadvantage.
If the environment consists of
rocks of an intermediate color,
both light and dark mice will
be selected against.
Causes of Evolution
3. Mating Preferences - Organisms usually do not choose their
mates at random, thus the selection process can cause evolution
4. Gene Flow - Transfer of genes between different populations
of organisms. This situation leads to increased similarity
between the two populations (Tends to reduce differences
between populations over time)
5. Genetic Drift (Founder Effect & Bottleneck) - Situation that
results in changes to a population's gene pool caused by random
events, not natural selection. This situation can have drastic
effects on small populations of individuals. Common on islands.
Gene Flow
Genetic Drift
Founder Effect
Bottleneck Effect
RATE OF EVOLUTION
Part III:
Types of Evolution
Extinction
• 1. Divergent Evolution - Multiple
species of organisms descended from
the same common ancestor at some point
in the past.
– Method of evolution accounting for the
presence of homologous structures.
– Adaptive Radiation.
• Ex. Darwin’s finches
• 2. Convergent Evolution - Because
certain adaptations are more
advantageous in different environments,
unrelated organisms that live in similar
environments will have similar features
that perform similar functions.
– Method of evolution accounting for the
presence of analogous structures.
– Ex. Dolphins and shark
• 3. Coevolution –Organisms that are
closely connected evolve together.
– Method of evolution accounting for
specialists.
• Ex. Monarch butterfly and milkweed plants
• Insects and flowers
As the environment changes, organisms must
have variations (adaptations) that will
determine whether they can survive with the
changes or they can’t and they die.
If an entire species
cannot adapt, that
species will then
become extinct.
No More, Finished, ByeBye!
There have been at least 5 MASS extinctions
during Earth’s history where a huge % of the
living species were destroyed
At least one of these mass extinctions has
been attributed to meteor impact and it’s
consequences.
Many scientists
say that the
earth is
currently
experiencing a
mass extinction
crisis.
It is estimated that 1/5 or more of the world’s
species will become extinct if the rainforests
are destroyed.
Part IV:
Evidence of Evolution
• 1. Fossil Evidence:
– Paleontology - Study of Fossils
Fossil - preserved evidence of past life
– Fossil record: shows organisms that are no longer
living and how they changed over time.
a. Relative dating
– Which rock layer is the fossil found…If you know the
age of one, the rest of them are about the same age.
– Index fossils: wide range, short time period
b. Radioactive dating
– Measuring radioactive isotope vs. stable atom content
» Carbon 14
MORPHOLOGICAL
HOMOLOGY (similarities)
• 2. HOMOLOGOUS STRUCTURES
– Structures that are similar because they are
derived from a common ancestral structure
• A structure that serves the same
function in two taxa, but is NOT
derived from a common ancestral
structure is said to be an
ANALOGOUS STRUCTURE
•
3. Embryology (ontogenic)
Homology
As organisms develop, they go through many
stages that are similar to other organisms.
– The longer two organisms share developmental
stages, the more closely related they are to each
other.
• 4. Molecular Homology
-The comparison of different proteins
(amino acids) can show how closely related
species are to each other.
-The fewer differences in the genetic make-up, the
closer related they are.
Hybridization of DNA
can also show
evolutionary
relationships.
5. Vestigial Structures
• Structures that have marginal, if any, use to
the organisms in which they occur.
– Reduced in size.
– Derived from an earlier ancestor that did
use/need this structure.
6. Biogeography
• The study of the geographical distribution of
organisms.
– Species that are related to each other tend to live
near each other. (fossils of ancestors are present
too)
– As geography changes, populations are separated
or combined with new populations.
• Continent movement (collide and separate), rivers,
mountains, lakes, etc. separate populations
Cladograms
• Evolutionary biologists can use all
evidence to create a cladogram.
• A chart that shows the development of
particular traits and the evolutionary
relationships between different species.