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BIOLOGICAL EVOLUTION
EVOLUTION BY NATURAL SELECTION IS A THEORY
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A theory is an explanation for a large body of evidence
What other theories are there?
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Cell
Gravitational
Relativity
These are all based on lots of evidence
Cannot be proven
If new evidence contradicts theory, theory must be adjusted.
EVOLUTION BY NATURAL SELECTION IS A THEORY
Darwin's Theory of Evolution by Natural Selection
1.
More individuals are produced each generation than can survive.
2.
Phenotypic variation exists among individuals and the variation is heritable.
3.
Those individuals with heritable traits better suited to the environment will survive.
4.
When reproductive isolation occurs new species will form.
These are the basic tenets of evolution by natural selection as defined by Darwin. The
following is a quote from Darwin.
"Variation is a feature of natural populations and every population produces more
progeny than its environment can manage. The consequences of this overproduction is
that those individuals with the best genetic fitness for the environment will produce
offspring that can more successfully compete in that environment. Thus the subsequent
generation will have a higher representation of these offspring and the population will
have evolved."
Copyright © 1997. Phillip McClean
https://www.ndsu.edu/pubweb/~mcclean/plsc431/popgen/popgen5.htm
BACKGROUND TERMS
Members of
the same
species:
1. Can
reproduce in
a natural
setting
2. and produce
fertile
offspring
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APPLY SPECIES DEFINITION
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A horse and donkey can mate in
the barnyard to produce a mule.
The mule is a very strong,
hardworking animal (albeit
stubborn!), but alas,
mules cannot have babies.
Are horses and donkeys
members of the same species?
No – the mule cannot reproduce,
therefore is not fertile.
MORE SPECIES DEFINED
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Are all birds members of the
same species?
Think of the biggest and
smallest birds you can
imagine.
Certainly hummingbirds cannot
mate with ostriches!
MORE SPECIES DEFINED
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Are all domesticated dogs members of one
species?
Can all dogs mate (theoretically)?
Are all normal puppies fertile?
Yes. All dogs are members of one species:
Canis domesticus
MORE SPECIES DEFINED
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A lion and tiger can be
artificially mated
together in a zoo.
This produces a
“liger”
Are lions and tigers
therefore members of
the same species?
No, they didn’t mate
in a natural setting –
and never would –
they don’t even live on
the same continent!
EVOLUTION VOCABULARY
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Branching diagram (CLADOGRAM)
Shows changes in species over time
Each new branch represents a newly evolved
feature
CLADOGRAMS
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Which organisms have jaws?
Which organisms have claws or nails?
Is the salamander more closely related to the
perch or pigeon?
MORE CLADOGRAMS
Where in the image is now? Left, right, top or
bottom?
CLADOGRAM SHOWING FISH EVOLUTION
Where is the common ancestor?
CLADOGRAM OF DINOSAURS

If a line stops before the top, what does that mean?
CLADOGRAM SHOWING EVOLUTION OF BIRDS
FROM DINOSAURS
What is the common ancestor?
MORE CLADOGRAMS - SIDEWAYS
Where is NOW in these diagrams?
MECHANISMS OF EVOLUTION - VOCABULARY
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Evolution: changes in species over time
Speciation: the formation of new species
Gradualism: the theory that species changed very
gradually over time. Fossil evidence shows jumps,
but the hypothesis is that we simply haven’t found
the in-between fossils (missing links).
Punctuated equilibrium: The theory that species
are relatively unchanged for long periods, but then
go through sudden rapid changes and new
speciation, usually due to geographic isolation or
environmental pressures.
EVOLUTION - VOCABULARY
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Gradualism vs. punctuated equilibrium
MECHANISMS OF EVOLUTION
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Natural selection: (aka Survival of the Fittest)
The members of the species that are best
adapted to the environment will survive to pass
their genes on to the next generation.
The less well adapted will be more likely to die
before reproducing, reducing the proportion of
their particular set of alleles in their population.
The “environment selects” which members
survive.
MECHANISMS OF EVOLUTION
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Fittest doesn’t necessarily mean strongest or fastest
Competition is not usually direct
Fittest = produces most offspring that survive
Adaptations:
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Camouflage
Mimicry
Structure
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Different Teeth shapes for different foods https://www.youtube.com/
Beak shapes (as in lab)
watch?v=wNqiclBUxdY
Leaf color
https://www.yout
Seed dispersal
ube.com/watch?v
=kYIWZuFsb60
Attractiveness for mate
Attractiveness for pollinators
Ability to withstand a freeze, or draught, or flood or …..
Can you come up with some?
MECHANISMS - OVERPRODUCTION
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Many species purposely produce more
offspring than they know will survive
This introduces competition,
so that only the members with the best
adaptations survive and the less well adapted
die off.
The less adapted may have survived if they
didn’t have to compete with so many others
OVERPRODUCTION EXAMPLES
Frog
eggs
OVERPRODUCTION EXAMPLES
Maple seeds
OVERPRODUCTION EXAMPLES
EXAMPLES OF NATURAL SELECTION
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During an especially cold winter, the birds with
the most under-feathers (down) are more likely
to survive, while some the others will die off.
The “environment selects” the survivors, who
then pass on their genes to the next
generation.
EXAMPLES OF NATURAL SELECTION
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Slower sea turtles may be eaten by gulls before
fast ones, when trying to get to the ocean. The
fast ones pass their genes on to produce fast
offspring.
MECHANISMS OF EVOLUTION –
GENETIC VARIATIONS
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A strong species is one in which
there are many differences, or
variations, between individuals in
the population.
These variations allow
individuals to survive changes in
the environment, and multiple
situations.
Not all members survive, but the
species does.
MECHANISMS OF EVOLUTION –
VARIATIONS EXAMPLES:
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Ex: The faster turtles on land may attract more
attention from gulls, and may also be slower
swimmers. Slow, better camouflaged ones may
swim better and have higher chance of survival
from predators once in the water. Both
variations are important to the species.
MECHANISMS OF EVOLUTION –
VARIATIONS EXAMPLES:
 Not all members of a population are
susceptible to the same illnesses, or they
would all die from the same disease.
 THE SPECIES MOST LIKELY TO SURVIVE WILL
HAVE MANY VARIATIONS THROUGHOUT ITS
POPULATIONS
 Clones, which have identical genes, are all
strong in the same areas and weak in the same
areas. One event (drastic environmental
change, new germ, loss of particular food
source) could kill them all at once.
MECHANISMS OF EVOLUTION –
VARIATIONS EXAMPLES:
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Irish potato famine in 1843.
Due to LACK of variation
Cloned potatoes all succumbed to
one single fungus species, that
wiped out the whole potato crop
for two years, starving 1 million.
EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE
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Antibiotics kill bacteria
Bacteria usually reproduce by binary fission,
which is basically mitosis, a form of asexual
reproduction, producing
=> genetically identical offspring
But when the species is threatened, (as when
their environment changes with antibiotics)
they can swap DNA through a conjugal bridge.
EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE
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When bacteria
conjugate, this
introduces genetic
variation, and gives
the species a chance
to develop a variation
that does not get
killed by the
antibiotics
EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE
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So if you don’t finish all
your antibiotics, the
strongest few could be
left behind to multiply.
Then if you get sick again,
you will need a different,
stronger antibiotic to kill
the stronger bacteria.
The bacteria have
evolved, by natural
selection, to survive the
environmental pressures
in your body
EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE
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New species of bacteria evolve
every day
Forcing the medical profession
to constantly have to continue
to develop new drugs to kill
them
This “arms race” has led to
“super-bugs”
such as a new strain of TB that
is killing thousands and cannot
be treated with antibiotics.
http://www.cbsnews.com/news/animalantibiotic-overuse-hurting-humans/
EVOLUTION IN ACTION: PESTICIDE RESISTANCE
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The few insects of a species survive and reproduce, passing the survival genes down
Eventually, most of the population is unaffected by the pesticide
so that the pesticide is rendered useless,
and the insect population is even stronger.
The arms race continues
ARTIFICIAL SELECTION
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Humans, rather than environment, select which
traits to pass to next generation
ARTIFICIAL SELECTION
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Humans, rather than environment, select which
traits to pass to next generation
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How are antibiotic resistance and pesticide
resistance examples of artificial selection?
EVOLUTION OF POPULATIONS
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A population is all the members of the same species
in a particular area.
For example: the population of ground squirrels in
Arizona.
EVOLUTION OF POPULATIONS
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Before a new species is
created, the gene pool can
be sharply affected within a
certain population, until
some members of the
population can no longer
mate with other members.
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At that point, a new species
has been formed.
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Sometimes, the lines are
blurred for a while, with
hybrid populations existing
between the two new
species.
EVOLUTION OF POPULATIONS
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A gene pool consists of
all the genes, including
all the different alleles,
in a population
relative frequency of
an allele is the number
of times that allele
exists in a population
compared to other
alleles
EVOLUTION OF POPULATIONS – SELECTIVE PRESSURES
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Selective pressures
(things in the
environment that
cause the allele
frequencies to change)
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Directional selection
when individuals at
one end of the curve
have higher fitness
than individuals in the
middle or other end.
Entire curve shifts.
EVOLUTION OF POPULATIONS – SELECTIVE PRESSURES
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Stabilizing
Selection when
individuals near
the center of the
curve have higher
fitness than
individuals on
either end of the
curve.
EVOLUTION OF POPULATIONS – SELECTIVE PRESSURES
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Disruptive Selection
when individuals on
either end of the
curve have higher
fitness than
individuals near the
center of the curve.
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another example:
black or white snakes
in Sweden
EVOLUTION OF POPULATIONS – SELECTIVE PRESSURES
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EVOLUTION OF POPULATIONS
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Populations whose relative frequencies do not
change are said to be in Hardy-Weinberg
equilibrium
That is, these populations are not evolving.
Can this happen? Let’s see some of the things
that change the allele frequencies in
populations:
EVOLUTION OF POPULATIONS
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To be in Hardy Weinberg equilibrium, there must
be:
1.
2.
3.
4.
5.
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Perfect random mating
Large population
No members moving in or out of the population
No mutations
No natural selection (no selective pressures)
Is it possible to have all of these conditions met in
any population? What do you think?
http://ed.ted.com/on/AJ9YkpPL
EVOLUTION OF POPULATIONS – FOUNDER EFFECT
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Founder effect = a small starter population goes to
a new habitat. The gene pool for the new
population is very small.
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Migration to islands is a common example of this
MECHANISMS OF SPECIATION
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When members of a population become too different
from each other to mate successfully, reproductive
isolation has occurred.
What factors can cause this?
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Behavioral isolation – mating patterns are not recognized
Geographic isolation – no access to each other
Temporal isolation – mating times of year/day no longer
align. Also applies to flowering and pollination
http://www.hhmi.org/biointeractive/origin-specieslizards-evolutionary-tree (17 minutes)
EVIDENCE FOR EVOLUTION
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Fossils
EVIDENCE
coprolite
Mosquito in amber
Dino tracks - Utah
EVIDENCE - FOSSILS
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Relative Dating of fossils
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Most recent on top
Oldest on bottom
Relative Age of fossils is
determined by the location
the fossils were found
relative to each other
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Radiometric Dating
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Chemical sample taken
Number of radioactive
elements remaining in
sample gives specific age of
sample
Uses Half-life calculations
EVIDENCE FOR EVOLUTION
COMPARATIVE ANATOMY
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Homologous structures
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Similar structures with
different functions
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These show divergent
evolution
•
Organisms with common
ancestors have evolved
AWAY from each other, and
use their common structures
for different purposes
EVIDENCE FOR EVOLUTION – COMPARATIVE ANATOMY
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Analogous structures
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Structures are different, but functions are similar
This shows convergent evolution. Organisms with very
distant common ancestors evolve similar adaptations
to similar environmental pressures.
EVIDENCE – COMPARATIVE ANATOMY
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Organisms develop similar adaptations in
response to similar environmental conditions in
areas very far apart from each other
Another example of convergent evolution
EVIDENCE: COMPARATIVE ANATOMY
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Vestigial structures – no longer needed
Snake pelvic bones
Goose bumps
Whale pelvic bones
EVIDENCE – SIMILAR EARLY DEVELOPMENT
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Embryonic
comparison
comparing the early
development of
organisms shows
similarities
 A common ancestor
is evident
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EVIDENCE – GEOGRAPHIC DISTRIBUTION
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Fossil evidence from different continents fit
together where continents fit together before
Pangea broke up
EVIDENCE
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Biochemical comparisons
The more similar the DNA, the more recently two
species branched apart.
 Many other chemical processes are similar among
species, such as photosynthesis and cellular
respiration
 Soft tissue found inside fossilized dinosaur bones
was found to have strikingly similar protein
structures as those in chickens!
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Can you see it?
https://www.ted.com/talks/j
ack_horner_building_a_dinos
aur_from_a_chicken?languag
OVERVIEW OF EVOLUTION
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Earth formation 4.6 BYA
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Swirling ball of hot molten lava
Gravity pulls in heavy solid nickel core
Magma begins to cool into thin crust
Rain begins to fall
Harsh, hot, toxic, anaerobic (no free oxygen in atmosphere)
FIRST 4 BILLION YEARS
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First life: archaebacteria –
prokaryotes
 Don’t need oxygen
 Don’t produce oxygen
 thrive in harsh environments
like deep ocean vents & hot caustic puddles at
Yellowstone
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FIRST 4 BILLION YEARS
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Next life: photosynthesizing prokaryotes
Cyanobacteria
 Make oxygen – for a billion years
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FIRST 4 BILLION YEARS FROM PROKARYOTES TO EUKARYOTES
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Finally: single-celled eukaryotes
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(have nucleus and membrane-bound organelles)
Eukaryotic cell
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Endosymbiont theory = photosynthesizing prokaryotes
were absorbed by other bacteria to become the first
organelles - chloroplasts
FIRST 4 BILLION YEARS
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Soft-bodied Multi-celled
eukaryotes
Began as colonies of
single-celled organisms.
 Cells started to
specialize and organize
into multicellular
organisms
 No backbone yet
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•
•
•
•
jelly fish,
sponges,
Worms
seaweed
NEXT .54 BILLION YEARS (ABOUT 540 MY)
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Cambrian explosion
Adaptive radiation: rapid
speciation due to new
opportunities
Once life organized, and the
planet was a comfortable
living space, evolution
happened in leaps and
bounds,
with new species diverging,
rapidly filling every niche
EVOLVE HOW?
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Mutations introduce genetic variation
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Some good, improve survival, so get passed down
Mixing of genes through sexual reproduction
Genetic “drift”
Driven by Natural Selection
Punctuated equilibrium
 Gradualism
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Adaptive radiation
Remember…it took billions of years to get this
way!
EVOLUTION OF EVOLUTIONARY THEORY
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Spontaneous generation –
living things can arise from nonliving things
Based on pure observation
 Flies come from meat
 Bacteria comes from broth
 Frogs comes from rain!
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EVOLUTION OF EVOLUTIONARY THEORY
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Biogenesis – living things come from living
things
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Break down the term
•
•
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Bio = life
Gen = birth, origin
Francesco Redi 1668
•
Disproved spontaneous generation by setting up simple
experiment to show covered meat produces no flies
EVOLUTION OF EVOLUTIONARY THEORY
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Jean-Baptiste
Lamarck –
theory of
natural
selection:
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Organisms
can change
their genes
through their
behavior
These
changes can
be passed
down
EVOLUTION OF EVOLUTIONARY THEORY
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Charles Darwin - theory
of natural selection
HMS Beagle –
 voyage to Galapagos
Islands 1830’s
 Helped form ideas of
speciation by
geographic isolation
from observations of
species on mainland
verses different islands

LAMARCK OR DARWIN?
EVOLUTION OF EVOLUTIONARY THEORY
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How did life originate?
In the 1950’s, Stanley Miller
and Harold Urey created an
experiment to show how
organic compounds could be
created from the mixture of
compounds present on the
primitive earth.
https://biodeluna.wordpress.
com/2012/01/11/abiogene
sis-miller-urey-experiment4eso-videos/