Transcript Evolution Mechanisms

MECHANISMS OF EVOLUTION
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
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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 = best adapted
Adaptations:
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Camouflage
Mimicry
Structure
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Different Teeth shapes for different foods
Beak shapes (as in lab)
Leaf color
Seed dispersal
Attractiveness for mate
Attractiveness for pollinators
Ability to withstand a freeze, or draught, or flood or …..
Can you come up with some?
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.
 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.
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
EVOLUTION IN ACTION: ANTIBIOTIC RESISTANCE
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Antibiotics kill bacteria
Bacteria usually reproduce by binary
fission, which is basically mitosis
=> 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.
EVOLUTION IN ACTION: PESTICIDE RESISTANCE
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The few insects of a species
that survive reproduce, passing
the survival genes down
Eventually, most of the
population is unaffected by the
pesticide
so that the pesticide eventually
is rendered useless,
and the insect population is
even stronger.
The arms race continues
EVIDENCE FOR EVOLUTION
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Fossils
EVIDENCE
coprolite
Mosquito in amber
Dino tracks - Utah
EVIDENCE FOR EVOLUTION
COMPARATIVE ANATOMY
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Homologous structures
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Similar structures with
different functions
EVIDENCE FOR EVOLUTION – COMPARATIVE ANATOMY
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Analogous structures
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Structures are different, but functions are similar
EVIDENCE: COMPARATIVE ANATOMY
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Vestigial structures – no longer needed
Snake pelvic bones
Goose bumps
Whale pelvic bones
EVIDENCE
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Embryonic comparison
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.
 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?
EVIDENCE – GEOGRAPHIC DISTRIBUTION
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Fossil evidence from different continents fit
together where continents fit together before
Pangea broke up
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 .5 BILLION YEARS (ABOUT 500 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
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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
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
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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
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
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