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Evolution – A scientific theory that states that
living species are descendants of ancestral
species that were different from present day
ones (the genetic changes in a population
over generations)
Scientific Theory – a well-supported
explanation for some aspect of the natural
world that includes many observations,
inferences, and tested hypotheses (it is not
“just an opinion or belief”)
◦ Main difference between scientific law and theory is
that a law says that something does occur while a
theory attempts to explain why it occurs.
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Like Darwin, he also believed populations change
over time
BUT, his beliefs are no longer supported
Lamarck’s ideas on evolution:
1.
2.
3.
Believed in Spontaneous Generation
Simple forms of life eventually develop into more complex
forms
Traits gained in life by experience or behavior could be passed
on to offspring
(Ex. Bodybuilder parents
Bodybuilder baby)
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Darwin was 22 years old when he sailed from
Great Britain on the H.M.S. Beagle.
He spent the voyage collecting thousands of
specimens of the fauna and flora, observing
various adaptations of organisms. He was
particularly struck by the uniqueness of the fauna
of the Galapagos Islands.
Eventually he released the book “On the origin of
Species by Natural Selection”.
◦ (He was not the first or only person to believe that life
changes over time, but he was the first to come up with
the correct method by which evolution occurs.)
(1) Descent with Modification
 Basically, the process of evolution
 Living species descended with changes
(modifications) from prior species
 Species must be able to change over time
 Ex. Darwin’s Finches
(will discuss later)
(2) Natural Selection “Survival of the fittest”
 The process by which organisms best suited
to the environment survive, reproduce, and
pass their genes to the next generation.
 Fitness -(1) Survive Longer, (2) Reproduce
More
(3) Pass on traits to next
generation
 Occurs in populations, not in individuals
◦ Note: It is not essential to survive longer. The
longer life simply gives more time to produce more
offspring. Ex. Evolution would favor someone who
was 20 and had 4 kids rather than someone who is
80 with 1 kid.
1.
2.
3.
4.
5.
Organisms produce more offspring than can
survive.
Genetic Variation - Individual organisms in a
population have slight variations or
adaptations.
Individuals struggle to survive, those with
adaptations best suited to the environment are
more likely to survive.
Survivors pass on genes for the adaptations to
their offspring.
Gradually, the population’s gene pool changes
and the population evolves.
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13 different species of finches on the
Galapagos Islands
Each species has a beak that is best adapted
for a certain kind of food that is found on the
different islands
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Beetles living on brown tree bark are either
brown or green.
Predator (bird) can more easily see green
beetles and will catch them more often than
brown.
Brown beetles live longer and produce more
offspring, to whom they pass the gene for
brown.
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Natural selection is an “editing” process, not a
creating one
If the environment changes and there is not a
suitable phenotype to survive in the new
environment then the species will go extinct.
There is no amount of “trying” that can help
you evolve.
Nature simply “selects” the greatest physical
traits to survive in different environments and
those are passed on.
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The next few slides are all species observed
by Darwin on the Galapagos Islands that led
to him create his theories of descent with
modification and natural selection.
Video
Video
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Lamarck
“Acquire” new traits
though use or disuse
“Acquired” traits are
passed on to offspring
Evironment creates a
need for certain
“acquired” traits
Eventually get a new
species
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Darwin
Inheritable traits
already exist
Organisms with “new”
and “different” trait can
pass it on to offspring
Certain traits are
“selected” by nature
because the organism
is better able to survive
Eventually get a new
species
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1) Directional Selection
Selection that favors one extreme phenotype
(physical type)
This causes this particular extreme
phenotype to become much more common
(the look of the population is pushed in 1
direction)
Ex. Peppered Moths
2) Disruptive Selection
 Selection that favors both extreme
phenotypes (physical type)
 This causes extreme phenotypes to become
much more common (the look of the
population shows extreme differences)
 Ex. Darwin’s Finches
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3) Stabilizing Selection
Selection against the extreme phenotypes
(physical type)
This causes average phenotype to become
much more common (the look of the
population is very similar and average)
Ex. Human weight at birth
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Artificial selection – Natural selection that
“isn’t natural”
◦ Several species have evolved in certain ways due to
the influence of humans.
◦ Ex. Dog breeding, Crops
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1) MUTATIONS!!
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Meiosis (and sexual reproduction) gives us variation in a
population that creates a range of phenotypes that can be
acted upon by natural selection.
Mutations can give rise to completely new characteristics.
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MUTATION: a change in a gene
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◦ Remember that a gene is enough DNA to control 1 trait
On the rare occasion when mutations produce favorable
traits, a population’s gene pool (all of the genes in a
population) is changed because of the introduction of this
new, favored trait. The population will then evolve through
natural selection to show a greater percentage of the new,
beneficial trait.
Two Types of Mutations:
(1) Changes in genes in somatic (body) cells:
can affect the organism itself, but cannot be
passed to sexually produced offspring.
(2) Changes in genes in gametes (egg and
sperm): do not affect the parent organism
itself, can be passed to sexually produced
offspring
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Mutations may result in a trait that improves an
organism’s chances for survival, so that organism
would be more likely to reproduce. Then the
favorable mutation would be passed on to
offspring.
This results in evolution.
Mutations occur very rarely (and are almost
always bad), so populations evolve slowly.
NOTE: EVEN THOUGH EVOLUTION GENERALLY
OCCURS SLOWLY…IT SOMETIMES CAN OCCUR
RAPIDLY IF THE NEW MUTATED TRAIT IS
STRONGLY FAVORED OVER ALLOTHER
PHENOTYPES PRESENT IN THE POPULATION
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2) Genetic Drift – changes in gene pool
due to chance (has greater effect on smaller
populations)
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Examples
◦ 1) Bottleneck effect – drastic decrease in population
size may leave only certain alleles available. These
alleles will quickly be perpetuated.
◦ 2) Founder effect –When a few individuals colonize
a new area (same reasoning as bottleneck)
 3)
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Gene flow
Introduction or exit of alleles in a population
whenever individuals enter or leave.
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Notice that all 3 causes for evolution
(mutations, genetic drift, and gene flow) all
have 1 similarity – they change the GENE
POOL of the population.
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1) Molecular Biology
All living things use DNA and RNA.
The genetic code amongst all living things is
universally the same. (In other words, the fact
that the RNA codon AUG gives the amino acid
MET in humans is seen in every other living
thing as well)
This fact more than any other (at least to me)
indicates that all living things originated from
a common ancestor.
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Molecular Biology – Continued
The closer 2 different species DNA is to one
another, then the closer those 2 are related.
Which 2 species are closer related?
Species A: AACTGGCTTA
Species B: AACTAACCCG
Species C: TACTGGCTTA
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The remains or traces of organisms that have
once lived on Earth.
Fossil Record: the history of life on Earth,
based on fossils that have been discovered
The fossil record shows how organisms have
changed over time and shows that the life on
Earth is about 3.5 billion years old.
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Extinctions occur when there are major
changes in the environment and species do
not have the adaptations to survive.
The fossil record helps scientists to discover
relationships between different groups of
organisms and determine common ancestors.
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The Earth is divided into
layers called strata.
Generally speaking, the
lower the strata = the
older the layer of Earth
(each new layer
becomes stacked on the
older layer below it)
This means if two
fossils are found, the
fossil found in the
lowest layer would be
the oldest
There are also
techniques for
determining the
absolute (or relatively
exact date) of a fossil’s
age
Convergent evolution –
process by which different
species evolve similar traits
(SAME FUNCTION, DIFFERENT
ANCESTOR)
Example: Birds, bats, and
moths have wings, but they
did not evolve from a recent
common ancestor.
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Caused by:
◦ living in similar habitats /
performing similar
functions
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Structures with closely related function but
do not come from the same ancestral
structure
◦ Same function, different structure
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Example: Birds, bats, and moths have wings,
but they did not evolve from each other.
Divergent evolution- build up of differences
between groups which can lead to the
development of a new species
 In other words, two different species that
evolved from the same ancestor.
 Caused by populations of the same species:
1. moving to two different environments or..
2. specializing in different areas of the same
environment
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Structures in different species that originated
from common ancestor
May have different function but similar
structure
Evidence for Evolution –
Vestigial structures – no longer have a use,
but may have had a use in evolutionary
history.
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Ex: human tail bone (coccyx) made of 4 fused
vertebrae that resemble the bones in an
animal’s tail.
Other examples: the appendix, and ear
muscles!
When two or more species have evolved
together, the situation is called coevolution.
Example:
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◦ Insects and Flowers
 Flowers provide food for insects. Insects take pollen
from one flower to the next so they can reproduce.
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Behavioral evolution -a behavior that is selected for
strongly enough that all organisms in a species exhibit
this behavior because of the survival or reproductive
advantages that behavior gives
Examples:
 The dancing of the blue footed booby may have seemed
peculiar to you, but the execution of this courtship ritual
determines whether or not they will reproduce.
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Migration is another example of a behavioral adaptation
that would be essential in the survival and ability to
reproduce (if you don’t migrate, you die) of a species.
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Sexual selection-form of natural selection in which
individuals with certain characteristics are more likely than
other individuals to obtain mates (leads to sexual
dimorphism – differences in males and females)
Physical Examples:
Feathers of a male peacock
Antlers of a male deer
Humans
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Behavioral Examples:
Darwin Beetles Darwin Beetle Video
Blue footed Booby
Humans
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