Transcript Evolution - Mrs. Zedan's Science

16.1-16.4 / 17.1-17.2/19.2
Darwin’s Voyage of Discovery
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Born in England in 1809 and grew up in a time
when scientific views were beginning to shift.
Sailed on the HMS Beagle for a 5 year journey.
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Goal was to map South America and collect
specimens.
This trip led him to develop his theory of
biological evolution which explains how modern
organisms evolved over long periods of time
through descent from common ancestors.
 As Darwin traveled he noticed three
patterns of biological diversity:
 Species vary globally
 Species vary locally
 Species vary over time
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Noticed similar flightless
birds (Rhae, Ostrich, and
Emu) each living in similar
habitats in three different
continents. These three
are now categorized under
the term Ratite.
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However there were species that were not
found in the same habitats across the globe
(kangaroos, rabbits, and other species).
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Noticed that tortoises shell shape varied based
on which Galapagos Island they lived on.
Noticed that in South America that different
species of Rheas lived in drastically different
conditions of grasslands.
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Noticed there was a wide variety of small brown
bird on the Galapagos Islands as well. He would
later recognize them to be finches and the
variation in their beaks would be a basis for a
major set of evidence of change over time.
Populations evolved to better suit their
eating/tool needs.
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Darwin was an avid fossil
collector and he noticed
that some fossils of
ancient / extinct animals
were similar to living
species.
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Example: The Glyptodont
(extinct) at 3m in length and
the Armadillo at 0.5m in
length both are versions of
each other and are found in
the same area. Made him
wonder what is the
connection?
 Darwin’s theory of Evolution arose from his
careful documentation of species on his travels
and how there were species of organisms that
were similar to others in the world but that
particular species was found NO WHERE ELSE.
The evidence suggested that species are not
fixed and that they could change by some
natural process called evolution.
Ideas that shaped Darwin’s thinking
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In Darwin’s day though evidence was being
discovered and ideas were changing many
Europeans believed that Earth was only a few
thousand years old. Many scientists along with
Darwin played important roles in bringing
evidence to light.
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He was a geologist so he studied
geologic structures (mountains,
valleys, layers of rocks, etc.)
Discovered connections
between geologic processes and
geologic features.
How is it possible that all the
geologic features could have
possibly formed in thousands of
years? Mountains, valleys,
rivers, uplift, tilting, etc….
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Found it would take a long period of time for
certain formations to form and created a
concept called deep time.
The concept of deep time said that our
Earth’s history is so long that our human
minds cannot properly imagine it.
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Published his work in 1785: Theory of the
Earth; or an Investigation of the Laws
observable in the Composition, Dissolution,
and Restoration of Land upon the Globe.
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He broke all the molds by proposing that
the center of the earth was hot/ molten
which helped to create new rock and form
processes on land.
 His ideas were not accepted readily by
many groups. (Neptunists,
Catastrophists, etc.)
Discovered that the
geological process
going on were always
going through regular
cycles of destruction
and rebuilding.
 Is famous for the idea of
uniformitarianism.
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He was insistent that
the processes for the
Earth are uniform
throughout history and
what occurred in the
past will keep occurring
into the future.
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Published his work in 1830:
Principles of Geology
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The combination of Hutton
and Lyell’s work created
what is now known as the
rock cycle.
Darwin read his book and
connected Lyell’s ideas of
geological processes to those
occurring in things that are
living.
 Darwin experienced an
earthquake which displaced sea
life over 3m and showed him
how the geology can change
and the organisms with it.
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He was suggesting the
change of species before
Charles Darwin was born.
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Thought all organisms
strived to become more
perfect.
Two main ideas:
 He suggested the
organisms could change
during their lifetimes by
selectively using or not
using various parts of
their bodies.
Two main ideas:
 He also suggested that
individuals could then
pass these acquired
traits on to their
offspring, enabling
species to change over
time.
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Ex: By not using
features (ex: wings)
they would over time
become smaller and
useless. Flying birds
would then would be
land or water bound.
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Ex: If a bird needed
longer legs to wade in
deep water they could
make an effort to stretch
them to make them
longer.
Evaluating his thinking
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Organisms don’t have the drive to be perfect.
They just want to survive!
Evolution does not mean that a species
becomes “better” and it doesn’t progress in a
predetermined direction.
Also traits acquired during ones lifetime ( a
broken wing which becomes useless) cannot be
passed on to offspring.
 Published his work in 1809 the year that
Darwin was born.
 While the basis of many of his ideas of
evolution were wrong his thought process
was true in explaining that there was a
link between environment and body
structures. This paved the way for future
scientists like Darwin.
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He noted that when human populations grew
out of control that there was a limitation of
space/resources and it required there be a
population of people in poverty who would not
have access to resources.
Only the strongest were surviving because if
left unchecked there would not be enough
living space for everyone and definitely not
enough resources
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He claimed their were two types of checks
that hold populations within resource limits:
 Positive Checks (raise the death rate)
▪ Ex: famine, war, disease
 Preventative Checks (lower the birth rate)
▪ Ex: birth control, postponing marriage,
celibacy, using moral constraint to not
have children until you could support
them.
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Though he was deemed to be insensitive to
the poor he merely was looking at methods by
which to reduce the immense amount of
poverty as seen in large cities (particularly
England).
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Darwin applied this to living organisms as well.
Organisms like trees and oysters can produce
thousands to millions of eggs/seeds per year.
What if all those seeds/eggs survived to
produce that organism?
They would overrun the world so there needs
to be some level of balance of the population.
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In this type of selection nature provides the
variations, and humans select (and breed)
those they find useful.
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Darwin did this with pigeons and was able to
create what he called fancy pigeons.
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Where else do we see artificial selection?
 Dogs, horses, farm animals, etc. It is everywhere
around us!
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This led Darwin to think about natural variation
in the wild and how it provided the raw
materials for evolution.
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On p. 459 there is a great timeline of scientists
Darwin Presents His Case
Based on his experiences in travel, and research of
other scientists’ data, he created a draft of his
thoughts on natural selection but he waited 20
years to publish it! Why so long?
 Because he saw the backlash that other scientists
received for their ideas so he decided to wait and
gather more evidence to support his ideas. What
finally forced him to publish his work on evolution
(On the Origin of Species)?
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Another scientists, Alfred Russell Wallace,
was about to publish a book with the same
thoughts as Darwin. He didn’t want to lose
his credit so he was forced to publish early.
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Based on reading Malthus he explains that if
there are more organisms born then the
environment can provide space/food for
some will live while others will die. This
brings up the important question of who
survives and who doesn’t? Darwin states
that those overall suited for their
environment (the fittest) will survive.
 The more fertile the environment the
more organisms it can hold (Harsh
desert vs. thriving jungle)
Due to sexual reproduction all offspring
will be genetically different and will
provide genetic variations into a
population. Those variants that are
better suited for their environment will
survive.
 Those that survive will then pass on those
better suited traits onto their offspring.
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Any heritable characteristic that
increases an organism’s ability to survive
and reproduce in its environment is
called an adaptation; coloration, claws,
wings, camouflage, mimicry, etc
Darwin used the term “fitness” to give a
level to how well suited an organism was
for its environment.
 Those with high fitness are well suited to
their environment and can survive and
reproduce at high rates.
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However those with low fitness are not
suited to their environment and
reproduce at very low levels. (few
offspring is bad!)
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Question: If an organism produces many
offspring, but none of them reach maturity, do
you think the organism has high or low
fitness? Explain why.
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Answer: Low fitness because it needs to be
able to reproduce and have those offspring
survive to keep the species lineage going.
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He summed up all of this with his term survival of
the fittest where survival means having the ability
to pass on your genetics and adaptations to future
generations.
 In natural selection the environment
influences fitness.
 Natural selection occurs when:
 More individuals are born than can
survive.
 There is natural heritable variation.
 There is variable fitness among
individuals.
Those with the highest fitness will adapt
and survive and those with the lowest
fitness will die off.
 Natural selection only works for heritable
traits. Note that this is not the ONLY
mechanism driving evolution… more to
come!
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He proposed that over time new species
form that are modified forms of their
descendents.
 He used evolutionary trees to show how
different species came from one original
descendent. According to this principle
all organisms are descended from ancient
common ancestors.
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Evidence of Evolution
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Evolution = fact
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The mechanism of how organisms
change over time = theory (it is
testable/falsifiable)
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Also evolution is not about perfection it
is about survival
 Biogeography is the study of where
organisms live now and where they lived
in the past.
 The patterns formed in the distribution of
living and extinct species tell us how
modern organisms evolved from their
ancestors. (movement, environment,
etc.)
 Many newly discovered fossils, are
filling in the fossil record, and
helping to complete the tracing of
evolution of living species from
extinct ancestors.
A clue to
common descent
from an ancient
ancestor.
 Common
structure, but
NOT common
function.
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This is synonymous (similar in definition to) divergent
evolution.
 Divergent evolution is the accumulation of differences
between groups which can lead to the formation of new
species, usually a result of diffusion of the same species
to different and isolated environments which blocks the
gene flow among the distinct populations allowing
differentiated fixation of characteristics through genetic
drift and natural selection.
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This is not a form of common descent.
Body parts that share common function,
but NOT structure.
 Ex: wing of a bee vs. wing of a bird. Both
fly, but they are not built nearly the same.
Both acquired the wing to help with flight.
This is synonymous with convergent
evolution.
 Convergent evolution describes the
acquisition of the same biological trait in
unrelated lineages.
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Structures that are passed from
generation to generation but have no
functional use.
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Why do organisms keep these if they are not
of use?
Scientists are not 100% sure but the current
theory is that the presence of the structure
does not hurt the organisms fitness level for
survival and therefore natural selection
doesn’t act quickly to eliminate it.
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Study of looking at embryos!
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In this picture the top row is the actual organism where
the bottom row is an artistic rendering pointing out
significant features. How are the different pictures
across the top similar? How are they different?
Do you think they all come from the same lineage of
organism? Why or why not?
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From left to right they are the following
organisms: Salamander, Human, Rabbit,
Chicken, and Fish
The strongest evidence for descending
from a common ancestor is based on
genetics.
 The Human Genome Project has coded
the genetics of a vast number of
organisms and guess what? We are all
VERY similar.
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To the point where the genetic code is
nearly identical in almost all organisms
(bacteria, yeasts, plants, fungi, and
animals). There must have been a
common ancestor at one point in order
for this to happen.
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Evolution, in genetic terms, involves a
change in the frequency of alleles in a
POPULATION over time.
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If the frequency of an allele is increasing or
decreasing it means that a population is
evolving. Judged by looking at the gene
pool of populations genes.
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Natural Selection happens to individuals,
but the changes that it causes in the
allele frequency shows up in the
population as evolution.
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IMPORTANT: The smallest unit that can
evolve is a population, NOT individuals.
Mutations (change in DNA sequence)
Genetic Recombination in Sexual
Reproduction (passing from parents to
offspring)
3. Lateral Gene Transfer (important for
single celled organisms where they
swap genes through plasmids)
1.
2.
Single Gene traits are much more simple
as they only involve one gene and can
lead to allele frequency changes faster.
 Polygenic Traits require more than one
gene and therefore take a much longer
time to affect the allele frequency.
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Stabilizing
selection- natural
selection that favors
the average
individuals in a
population. (Average
birth mass of baby
survives!)
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In this the extremes
will die out.
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Individuals with either
extreme of a trait’s
variation are selected
for survival.
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The average
phenotype tends to be
eliminated. (small and
large beak size survives
if small/large seeds are
in abundance)
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natural selection that favors one of the extreme
variations. (woodpecker with longer beak survives
since it can get food easier from tree)
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Geographic Isolation: physical barriers may
prevent this reproduction from happening. A
volcano eruption or a river may isolate a species.
Therefore, a new species may evolve. These new
organisms adapt to their new environment and
start their own gene pools.
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Reproductive Isolation: Different mating times
and the ability to fertilize an organism of the same
species could also result in speciation. NOTE:
speciation means to form a new species.
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Nondisjunction: Changes in chromosome number
can also cause speciation, which is seen in wheat
and apples.
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Speciation can occur quickly or slowly
 Gradualism- species originate through a
gradual change of adaptations slowly.
 Punctuated equilibrium- speciation occurs
quickly in rapid bursts due to changes in
geography, climate, predators.
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*****Both views are supported by fossil
evidence*****
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Background extinction is coined
“business as usual” extinction because
there is a natural competition of
evolution and survival over a longer
period of time.
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Whereas Mass extinction is a relatively rapid
extinction where entire ecosystems vanish,
whole food webs collapse, species go extinct
due to food loss, and the process of natural
selection just cannot compensate quickly
enough.
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What can cause these extinctions?
 Asteroids, global climate change, volcanoes, moving
continents, and changing sea levels.
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After this many species go extinct which leaves
space for other species to take over. This
rebuilding can take anywhere from 5 to 10
million years.
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This is the process by which a single
species or a small group of species evolve
over a relatively short period of time into
several different forms that live in
different ways.
 This is what Darwin discovered in the finches
on Galapagos Island.
 After the dinosaurs went extinct an
adaptive radiation occurred which
brought a large variety of organisms
into the population.
 When two different species are so
closely linked that they evolve
together.
Ex. of a GOOD relationship: Flowers and
Pollinators
 Flowers need to pollinate and pollinators (ex:
bees, moths, etc.) want the nectar inside the
flower. Pollinators will adapt to best retrieve the
nectar and in turn by more pollinators being able
to get the nectar the flower will pollinate more
often.
Ex. of a BAD relationship: Plants and Herbivores
 Herbivores like to eat plants. Over time plants
have evolved bad-tasting or poisonous
compounds that keep herbivores from eating
them. In response the herbivores will adapt to be
able to be resistant to such poisons (or even be
able to store it in their tissues to ward off
predators). And so the cycle continues.
Ex. of a BAD relationship: Plants and Herbivores
 NOTE: this relationship that has caused plants to
be so poisonous has created some of the most
powerful natural poisons used by humans.