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Arches National Park
And who made this one???
Science is WHAT?? 3 min.
How did you get here?
• Let’s check someone’s family tree.
• Is this how you got here?
• Is there another way to answer the question?
• Has it always been answered this way?
• Pick another explanation from here.
The evolution of intelligent life on earth:
•Man learns to use
simple machines –
Part 1
Let’s listen to Ken Miller, an evolutionary
biologist from Brown University
• Go here to the 2006 Informal
Lectures and select section 2 – 6
(12 min.) or 9. Here he explains
why this is such an important
topic, and it all goes back to the
nature of what science is and
isn’t.
• On November 24, 1859, Charles Darwin published On
the Origin of Species by Means of Natural Selection.
• Darwin made two points in The Origin of Species:
• Today’s organisms descended from ancestral
species.
• They have changed over time.
• Natural selection is the mechanism by which these
changes occur.
Introduction
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
What evolution is NOT…
• Evolution is not the study of the ORIGIN of life
on earth,
• although
• This also involves evolution, in a sense, but an
evolution of chemicals. Let’s watch… if time.
4 min.
Why, why, why…
• Why would anyone, Darwin or otherwise, have
any reason to think that living things may have
changed as time has gone by?
• What evidence would make them think this?
• Let’s get our hands on some.
• Darwin’s views were influenced by fossils, the relics
or impressions of organisms from the past,
mineralized in sedimentary rocks.
• How do fossils form??? Check it out. 2m
• Such fossils were largely undiscovered
until the 1700’s.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.2 Fig. 22.4
• Paleontology, the study of fossils,
was largely developed by Georges
Cuvier, a French anatomist.
How can we use isotopes to tell
how old these fossils are? Let’s
do some math.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Fossils show a pattern of change that is supported by other evidence, like DNA comparisons.
• Special creation explanations state that life has not changed from the time of its creation.
• This is not what paleontologists actually observe. Life has changed a lot!!
• Here’s the scoop from some dino poop…
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• What are “transition fossils”?
• Here’s a whale of a tale… 1:20
• Now let’s take a closer look.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.17
And here is Archeopteryx, still the king of
transition fossils. New video from HHMI 18:00
And here is the hoatzin, a modern bird with
claws on its wings, like Archeopteryx!
• What’s the best explanation? That is why this is
evidence for how evolution works!
Wrap it up
• Let’s revisit this science and religion issue
(notice I didn’t say “science vs. religion”) one
more time. 4:00 Can there be another
explanation for what you just heard? Can
science and intelligent design coexist?
• Here is the short version of animal evolution.
Quick fossil summary
• Fossils show us two things
• Change has happened. Living things are not like they
used to be. Evolution has occurred.
• In many cases, the fossil record tells us exactly what
kind of changes have occurred, as in those transition
fossils.
• Soooooooo, since the fossil record agrees with the
explanation for the history of life on earth that we call
the process of evolution, the fossil record qualifies as
proof that this process is how change comes about.
• When you see two people who look very much
alike, you assume they are related. The more alike
they look, the more closely related you think they
are.
• Why does your mind come to this conclusion?
• And do you have the same thoughts when you look
at your dog?
• A pine tree? The mold on your shower curtain?
2. Homology - similarity suggests
relatedness; the study of real estate
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• Similarities in characteristics resulting from
common ancestry is known as homology.
• There are three main categories of similarities:
• Big structures like arms and legs.
• The way that a thing develops after it is
conceived.
• Little structures (molecules) like DNA and
ATP and the reactions they are involved in.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• For example, the forelimbs of human, cats, whales,
and bats share the same skeletal elements, but
different functions because they diverged
from the ancestral tetrapod forelimb.
• Homologous structures. Classic example.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.14
• The whale’s flipper is not a new
structure, it is a remodeled leg.
• Tinkering?
• Such structures are often not perfect.
• How good are your knees and
back??
• How about a plant example??
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Vestigial organs are great proof.
• For example, the skeletons of some
snakes and of fossil whales retain
vestiges of the pelvis and leg bones of
walking ancestors.
• Do you have any vestigial structures?
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• Sometimes, homologies that are not obvious in
adult organisms become evident when we look
at embryonic development.
• Hey swimmers, have you ever wished that
you had gills?
• Let’s look at some neat video of embryonic
development. 5:00
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• And how about molecules???
• Do you have any molecules that
are homologous to chemicals in
related organisms?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• If two species have genes and proteins
with sequences that match closely, the
sequences have probably been copied
from a common ancestor.
• Comparing chemicals agrees with fossil
and other evidence in terms of how the
history of life has played out.
• How about a worksheet??? A
cladogram? Now the whale activity!
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
3. Actual documented examples of
evolution happening in a short time.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The evolution of resistance to insecticides in hundreds
of insect species is a classic example of evolution by
natural selection in action.
• Is this “smoking gun” evidence???
Another example:
• The use of antibiotics has resulted in a
tremendous increase in the number of bacteria
which are resistant to their deadly action. This
is also a great example of why it is important
to understand how evolution works – it
allows to have a better chance to fight such
disease causers as this tuberculosis bacteria.
6:20
• Here’s another – experimental evidence! 5:40
• And another – Cats evolving before our eyes.
• Category 4: - the geographical distribution
of species - biogeography - first suggested
evolution to Darwin. “Where are the
rabbits?”, he once wondered while looking
out on the plains of Argentina.
• How do you catch a unique rabbit???
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• For example, while the sugar glider and flying
squirrel are similar, they are not closely related.
• The sugar glider from Australia is more closely related to
other marsupial mammals from Australia than to
the flying squirrel, a placental mammal from North
America. What’s the best explanation???
• The resemblance
between them is an
example of
convergent
evolution.
• Divergent???
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.15
Here’s what the Line means
• He noticed that organisms on one side of the line
were totally different than those on the other side,
even on islands that were only 20 miles apart. He
hypothesized that islands on each side must have
been connected in the past. Most notable were
big placental mammals on the west side of the
line and marsupials on the east.
• The best explanation for why this is is the
evolutionary one, thus this is support for that
explanation/theory.
That evolution occurs, then, is proven by
four great categories of evidence:
• The fossil record.
• Similarities in different existing organisms that suggest descent from common ancestors.
• Actual, documented examples, such as resistence in insects and bacteria, as well as long term studies such as one on Darwin’s finches that is ongoing.
• Biogeography
• James Hutton, a Scottish geologist, proposed a theory of
gradualism.
• Later, Charles Lyell, proposed a theory of
uniformitarianism.
Theories of geological gradualism helped
clear the path for evolutionary biologists
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Paleontology, the study of fossils, was largely
developed by Georges Cuvier, a French anatomist.
• Instead of evolution, Cuvier advocated
catastrophism.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• These ideas greatly influenced Darwin.
• First, if geological changes result from slow, continuous
processes, rather than sudden events, then the Earth
must be far older than the 6000 years assigned by
theologians from biblical inference.
• Second, slow and subtle processes persisting for long
periods of time can add up to substantial change.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• In 1809, Jean Baptiste Lamarck published a
theory of evolution based on his observations of
fossil invertebrates in the Natural History
Museum of Paris.
• Lamarck was convinced new forms evolved from
common ancestors, just like Darwin and many others
did. His work added much evidence to the fossil
record.
• But he missed the boat when he guessed the reason for
the change. Or did he?
Lamarck placed fossils in an evolutionary
context
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Central to Lamarck’s theory on why these
changes have occurred were the concepts of
use and disuse of parts and of inheritance of
acquired characteristics.
• He thought giraffes did what????
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• However, the reasons he gave for why things
change was off - there is no evidence that
acquired characteristics can be inherited.
• Acquired traits (e.g., bigger biceps, longer
necks) do not change the genes transmitted by
gametes to offspring.
• Or do they…? Science is at it again.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Charles Darwin (1809-1882) was born in western England.
• He studied to be a doctor.
• Then a clergyman.
Introduction
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwin received his degree in 1831.
• After graduation Darwin was recommended to be
the conversation companion to Captain Robert
FitzRoy, preparing the survey ship Beagle for a
voyage around the world.
• The world would never be the same.
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• Imagine the adventure of five years at sea.
1. Field research helped Darwin frame
his view of life
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Fig. 22.5
• Darwin noted that the plants and animals of
South America were very distinct from those
of Europe.
• Organisms from temperate regions of South
America were more similar to those from
the tropics of South America than to those
from temperate regions of Europe.
• Further, South American fossils more
closely resembled modern species from that
continent than those from Europe.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The origin of the fauna of the Galapagos, 900
km west of the South American coast,
especially puzzled Darwin.
• On further study after his voyage, Darwin
noted that while most of the animal species
on the Galapagos lived nowhere else, they
resembled species living on the South
American mainland.
• It seemed that the islands had been
colonized by plants and animals from the
mainland that had then diversified on the
different islands.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• While on the Beagle, Darwin read Lyell’s
Principles of Geology.
• Lyell’s ideas and his observations on the
voyage lead Darwin to doubt the
common view that the Earth was static
and only a few thousand years old.
• Instead, he was coming to the
conclusion that the Earth was
• (1) very old and
• (2) constantly changing.Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Finches became one of his famous examples.
• These are from Cornell’s Ornithology Lab.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 22.6
• Why did Darwin hesitate to publish his theories??
• Who was Alfred Wallace??
• Why is Darwin more famous??
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwinism has a dual meaning.
• It refers to evolution as the explanation for life’s
unity and diversity.
• It also refers to the Darwinian concept of natural
selection as the cause of organisms changing over
time..
On The Origin of Species has two main
points: evolution occurs, and natural
selection is its mechanism
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Central to Darwin’s view of the evolution of life
is descent with modification.
• All present day organisms are related through
descent from common ancestors, like whales
and hippos from Mesonychids.
• Descendents have modifications which have
allowed them to survive in their environments.
• The history of life is like a tree.
• Closely related species, the twigs of the
tree, shared the same line of descent until
their recent divergence from a common
ancestor.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 22.7
• This evolutionary tree of the elephant family is
based on evidence from fossils.
• Let’s practice some cladograms like this, if we
haven’t already.
• The second major point that Darwin
made is that natural selection is the
reason for changes.
• Ernst Mayr, an evolutionary
biologist, has dissected the logic of
Darwin’s theory into three inferences
based on five observations.
• (Be able to explain this logic)
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Observation #1:All species, not just ones like the fungus
below, have such great potential to reproduce. Examples?
• Observation #2: Populations tend to remain stable in size.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Observation #3: Environmental
resources are limited.
• Logical conclusion: 1, 2 and 3
lead to a struggle for existence.
Not all offspring are going to
make it.
Fig. 22.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• How about that essay by
Thomas Malthus in 1798.
•Jonathon Swift wrote a
famous reply to Malthus.
•Let’s look at some
population ecology…
• If B = D then there is zero population
growth (ZPG).
• Under ideal conditions, a population
grows slowly at first (the lag phase),
because there are few reproducing
individuals, then very rapidly.
• Exponential population growth is
said to be happening.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Typically, unlimited resources are rare.
• Population growth is therefore
regulated by carrying capacity (K),
which is the maximum stable
population size a particular
environment can support.
2. The logistic model of population growth
incorporates the concept of carrying
capacity
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• This is the pattern - lag, exponential growth, then a
limiting factor (food, space, water, pedators, etc.)
slows it down to logistic growth and keeps the
population around the carrying capacity.
Fig. 52.11
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Observation #4: Great variety exists.
• Observation #5: Much of this variation is heritable.
Fig. 22.9
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Logical conclusion #2: Survival in the struggle for
existence is not random, but depends in large part
on what traits an individual has.
• Those individuals whose inherited characteristics best fit
them to their environment are likely to leave more
offspring than less fit individuals.
• Logical inference #3: This unequal ability of
individuals to survive and reproduce will lead to a
gradual change in a population, with favorable
characteristics accumulating over the generations.
If only redheads were allowed to have more than
one child, what would you notice as time passed?
• Is Michael Phelps the most “fit”?
• Does it mean Ultimate Fighting???
• Could more subtle and passive factors be involved?
How about that “Survival of the Fittest” thing?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwinian fitness is the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
• So who is most fit - ?
•
• Fitness = reproductive success.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwin fooled around with pigeons!!!
How did this influence him???
Fig. 22.11
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwin’s ideas can be summarized in three points.
• Natural selection is differential success in reproduction
(unequal ability of individuals to survive and reproduce).
• Natural selection occurs through an interaction between
the environment and the variations among the individual
organisms making up a population.
• The product of natural selection is the adaptation of
populations of organisms to their environment, they didn’t
TRY to make it happen.
• More redheads is a product of their being selected to
reproduce more.
• For example, related species of insects called
mantids have diverse shapes and colors that evolved in
different environments.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.10
What separated Darwin from others is
his conclusion that variations occur
• AT RANDOM!!!
• Not because of a desire or a need, and not because of a special creation of a mystical nature (a supernatural explanation).
• Given enough time, he argued, random changes acted on by the selection process can result in magnificent adaptations, possibly appearing to be the result of some intelligent design. Monkeys with typewriters?
• If the design is indeed intelligent, he argued, it came about through the process of natural selection, not supernaturally, but naturally. This, he argued, was the creator’s method! Science can explain this – the HOW.
• In each generation, environmental factors favor
some variations over others.
•An organism receives variations from its parents
randomly. The selection process itself, however, is
not random at all.
•It depends on how a trait fits in with its environment.
• This increase in the frequency of the
favored traits in a population is how
the population changes; it is, by
definition, evolution.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Darwin envisioned the diversity
of life as evolving by a gradual
accumulation (Hutton’s idea) of
minute changes through the
actions of natural selection
operating over vast spans of
time (Lyell and the geologists’
idea).
The process of Natural Selection in a nutshell:
• More things are born than can live to reproduce, because the earth’s resources are not infinite. This creates competition –Darwin’s “struggle to survive”.
• These organisms have differences that are heritable. These variations occur by chance; they are random.
• Some of these variations are adaptive, they “match up” with aspects of the environment (selection pressures) that allow those that have them to reproduce more. This “match up” is not at all random.
• The average characteristics of a group are those that have been passed on more (selected for) and the group changes as this process continues.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• While natural selection involves interactions
between individual organisms and their
environment, it is not individuals, but
populations that evolve. Individuals do what?
• Populations are defined as a group of interbreeding
individuals of a single species that share a common
geographic area. Example?
• Evolution is measured as the change in relative
proportions of variation in a population over a
succession of generations (longer average neck
length as time goes by - not for each giraffe, but for
the group as a whole).
Bottom Line:• Groups of organisms (populations) change their
average characteristics (evolve) as a result ofgoing through this process by which the characteristics which lead to reproductive success (are adaptive) get passed down more often.
• They don’t change because they need to, want to, or have to so that they can survive. If they could do this, no populations would ever become extinct.
Here, I think, is what leads to many
misconceptions…
• We commonly say that organisms adapt to their
environment. Biology textbooks even list this as a
characteristic of life – the ability to adapt to its
environment, along with metabolism, growth,
reproduction, etc.
• When people first start to learn this, they seem to
naturally infer that the organisms are DOING this
“adapting” thing themselves, just like they DO
metabolism, growth, reproduction, etc. Can you
understand that living groups become adapted by having
the process happen to them, not by doing it??
If YOU are asked to explain Natural Selection:
• Explain that these three facts set the table for the process to occur:
1. More things are born than can live to reproduce.
2. The earth’s resources are not infinite.
3. These organisms have differences that are heritable. These variations occur by chance; they are random.
Then explain the result when the situation is as described above:
• Some of the variations “match up” with aspects of the environment (selection pressures) that allow those that have them to reproduce more. This is not at all random.
• As the generations go by, more and more individuals have the adaptive traits passed to them, and in this way the average characteristics of the group change – the group evolves.
So don’t use the terms…“need to”, “want to” or “have to” to explain why populations evolve, and don’t say that things change “so that” they can survive, live, eat the leaves from the tops of trees, etc.
• This is called Lamarckian thinking.
• All these terms suggest organisms change on purpose, either by their own will or that of a higher power. Neither explanation holds up to scientific scrutiny. If a higher power is at work (a religious question), it is working through the process of natural selection.
• Let’s watch an example, rock pocket mice. (11 min.).
• And now – a worksheet!
• Arguments by individuals dismissing the Darwinian view as “just a theory” suffer from two flaws.
• First, it fails to separate Darwin’s two claims: (1) that modern species evolved from ancestral forms and, (2) that natural selection is the main mechanism for this evolution.
• The conclusion that life has evolved is supported by an abundance of evidence, as we have seen.
• This is fact, not theory. The theory explainsthese facts.
4. What is theoretical about the Darwinian
view of life?
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The “just a theory” arguments concern only
Darwin’s second point, his theory of natural
selection as the reason for the fact of evolution.
• Here lies the second flaw, as the term theory in
colloquial use is closer to the concept of a “hypothesis”
in science.
• In science, a theory is more comprehensive than a
hypothesis.
• A theory, such as Newton’s theory of gravitation or
Darwin’s theory of natural selection, accounts for many
facts and attempts to explain a great variety of
phenomena and is supported by a great deal of
evidence. (Notice I didn’t say “proven”).
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• By attributing the diversity of life to natural causes
rather than
to supernatural
creation, Darwin
gave biology a
sound, scientific
basis.
• As Darwin said,
“There is grandeur
in this view of life.”
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.18
A population of termites initially consists of
darkly colored and brightly colored members. After several
generations, the termite population consists almost entirely of
darkly colored members because the brightly colored
termites are easier for a predatory species of insectivores to
locate. This situation is an example of :
A. The evolution of a new species
B. Natural selection
C. Artificial selection
D. Adaptive radiation
Scientists use the similarities and differences among
species to determine how they are related. Which of
the following is NOT used by scientists to determine
relationships among species?
A. Analogous structures
B. Vestigial structures
C. Cellular structures
D. Homologous structures
Many species of animals use hemoglobin to transport oxygen
from their lungs to their cells, but they have some differences
in their hemoglobin molecules. The hemoglobin molecule in
humans is very similar to the hemoglobin in gorillas, and very
different from the hemoglobin in mice. Which inference is
best supported by these observations? A. Gorillas are closely related to mice, but humans are not
B. Humans and gorillas are closely related to each other but not to mice
C. Large animals need a specific kind of hemoglobin to transport oxygen throughout their large bodies
D. Humans and gorillas have similar hemoglobin because they are adapted to eat similar foods
For centuries, dog breeders have chosen to breed particular dogs to pass
on, or even enhance, desirable traits. This is an example of:
A. Speciation
B. Artificial selection
C. Natural selection
D. Sexual selection
How is natural selection in the evolution
of long necks in giraffes best explained?
A. Shorted-necked giraffes were killed by long-
necked giraffes
B. B. Giraffe necks grew longer because of the
bone structure of the animals.
C. Giraffes with longer necks survived because
they were better suited to the environment
D. Long-necked giraffes mated only with other
long-necked giraffes
Of the following, which best illustrates natural
selection?
A. An organism with favorable genetic variations
will tend to survive and breed successfully
B. A population monopolizes all of the resources in
its habitat, forcing other species to migrate
C. A community whose members work together
utilizes all existing resources and migratory routes
D. The largest organisms in a species receive the
only breeding opportunities
If a paleontologist finds fossils of many different species existing in
the same area at approximately the same time, the paleontologist
can conclude that the ecosystem in this area had a high degree of:
A. Climatic variation
B. Episodic speciation
C. Biological diversity
D. Geographic isolation
Which of the following is true, because of
comparative embryology?
• A. a frog embryo resembles an adult frog.
• B. Both turtle and human embryos have a tail.
• C. the embryos of all animals appear different.
• D. male and female eagle embryos have wings.
Within a species of fish, variations exist in color, size & the
speed at which individuals can swim. Which variation would
be the least likely to be passed on to future generations of the
species?
• A. color of marking which aid in camouflage
• B. reproduction by laying large numbers of
eggs
• C. swimming speed which is less than that of
predators
• D. size which enables hiding among small
rocks & in rock crevices
Which of the following statements about natural
selection is true?
• A. Natural selection works on individuals,
rather than a population of organisms
• B. All organisms within a species are
genetically identical.
• C. Offspring can inherit traits of an organism
which that organism develops during its life
• D. Organisms which survive to reproduce can
pass favorable variations on to offspring
A population of termites initially consists of
darkly colored and brightly colored members. After several
generations, the termite population consists almost entirely of
darkly colored members because the brightly colored termites are
easier for a predatory species of insectivores to locate. This
situation is an example of :
A. The evolution of a new species
B. Natural selection
C. Artificial selection
D. Adaptive radiation
For centuries, dog breeders have chosen to breed particular
dogs to pass on, or even enhance, desirable traits. This is an
example of:
A. Speciation
B. Artificial selection
C. Natural selection
D. Sexual selection
What 2 processes result in variations that commonly
influence the evolution of sexually reproducing species?
• A. mitosis and natural selection
• B. extinction and natural selection
• C. mutation and genetic recombination
• D. environmental selection and selective
breeding
How is natural selection in the evolution of
long necks in giraffes best explained?
A. Shorted-necked giraffes were killed by long-
necked giraffes
B. B. Giraffe necks grew longer because of the
bone structure of the animals.
C. Giraffes with longer necks survived because
they were better suited to the environment
D. Long-necked giraffes mated only with other
long-necked giraffes
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