235evolution Gives our Biodiversity7© Kendall Hu.docx

235
evolution Gives our
Biodiversity
7
© Kendall Hunt Publishing Company
eSSentiALS
Bats evolved echolocation to prey on insects
such as moths
Island without moths; Ecosystem low in diversity…today
Father and Son Sailing
The island once had many moths
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236 Unit 3: We Are Not Alone!
the Case of the Quiet island
I was a young student studying biology in Wales when I talked
with my father into sail-
ing with me. I had seen my friend sail a small boat earlier in the
season, and it looked
fairly easy. So my father and I set off to visit an island that our
family once vacationed
on when I was a child. The wind was at our backs, so we zipped
along toward the island
with ease. I thought, “I should buy a sailboat and make this my
new hobby; I am really
great at sailing.”
We docked the boat within a few minutes and began walking the
island. It was just
a few miles around On an earlier trip I had noticed that the
island had many different
creatures – plants, birds, bats, and lots of moths, one of my
least favorite insects. My
father noticed that it was very quiet – very peaceful and a great

place to read – I think he
was telling me I should get away to this island and quit
bothering him with my studies.
We hiked up its small hills and took leaves and plants for study.
We noticed that
there were very few insects buzzing around us. “How great,” I
thought, “no bugs around
to bother us.” I had always disliked the arthropods, all of the
insect classes, in fact.
I recalled times when deer flies bit through a shirt into my neck
when I was gardening.
“They are good for nothing,” I reminded myself, happy to be
relieved of them for at least
this walk. There were only small farms on the island, which
consisted of quiet country-
side cottages. Oddly though, on our walk there were neither
birds nor insects to make
noise–well, peace at last.
The island had developed a great deal of farming, and the crops
looked very healthy.
My father commented, “This is what England needs,
productivity. Big farms like this
one will make Britain strong again!” I had read in a journal
article that two-thirds of Brit-
ain’s 337 large moth species are in significant decline. It was
evening, and I again appre-
ciated that there were no moths buzzing around our heads by the
lamplights on the road.
“A nice quiet night but where were the moths that I once
watched in the lamps along
the road?,” I envisioned, recalling their bulbous bodies. As a
biology student, I knew that
moths were an insect class, Lepidoptera, with 150,000 known

species. Moths were not
beautiful like butterflies and were pretty gangly, throwing
themselves at lights. I would
never be an entomologist, who studies arthropods for a living.
My teacher made us read an article reporting that there had been
a 99% decline
in common garden moths, Marcaria wauaria, in the past few
decades. The total num-
ber of large moths was down by almost 50% in southern
England. Three species of
CheCk in
From reading this chapter, students will be able to:
• Explain the relationship between evolution,
biodiversity, and society’s role.
• Use moth population changes as an example of
evolution and species changes over time.
• Discuss the history of how life’s origins
were discovered, using ideason spontaneous
generation.
• Describe how natural selection leadsto species
changes.
• Define the types of natural selection.
• Examine the role of speciation as a cause of
biodiversity.
• Describe extinction and its role in biodiversity
changes throughout Earth’s history.
• Discuss and evaluate the evidence for evolution.
• Use sexual selection to explain the development
of organisms over time.
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Chapter 7: Evolution Gives our Biodiversity 237
moths had disappeared from southern England in the past
decade: Orange upperwing,
Jodiacroceago; Bordered gothic, Heliophobus reticulate; and
Brighton wainscot, Oria
musculosa. “Good riddance, life goes on without them; but I
wonder why so many were
gone?” I pondered.
When we started back to the coast, I realized the wind was
against us. I didn’t really

know what to do when the wind did not have our sail. My father
and I struggled to keep
the sail straight and steered helplessly through the waves that
had developed while we
were on the island. It had become a nightmare. I frantically
tried to steer and pull as the
boat went out of control. The boom hit my father’s head in the
confusion. He yelled,
“You idiot, you’ll kill us yet! Why didn’t you tell me you had
never sailed?” He was
bleeding and I felt terrible. How was I supposed to know that
sailing could get so out of
control? It seemed easy when the conditions were just right. It
dawned on me that the
slight shift in wind direction, much like one fluctuation in moth
populations, could usher
in significant change leading to disastrous effects.
Moths are an indicator species, meaning that the state of the
environment is first
indicated by moth population health. Fewer moths mean less
food for birds and bats,
which eat moths. Those organisms eating birds and bats also are
affected. One change in
the environment can have profound impacts on the whole
ecosystem.
The island was quiet like the sea when we arrived. There were
few insects and few
birds to make sounds, but the quiet island had spoken – and it
was quiet no more.
CheCk Up SeCtiOn
In the story, our character is at first happy
about the loss of biodiversity on the island.

By the end of
the story, it dawns on him or her that there
may be more to the quietisland. Changing
environmental
factors, much like sailing conditions, can be
unpredictable and get out of control. Moths in
England
declined in numbers in part due to habitat loss:
large-scale farming destroyed hedges lining
smaller
farms, an area where moths thrive; pesticides
also were shown to kill off many moths.
Study the life history of the Marcaria wauaria,
noting its prevalence, habitat use, and the pur-
ported reasons for its decline in southern
England. Some species of moths saw
population increases
in southern England. The least carpet moth
increased by 75,000%. Research why this occurred:
How
might changes in moth prevalence impact on
our society? Do you thinkthe narrator in the
storyhad a
change of heartabout moths, about the
environment?
What Are the Origins of Life?
Life originated about 3.5–4.1 billion years ago, giving rise to
the great diversity of organ-
isms we see today. The origins of our biodiversity emanate from
a small set of species
of prokaryotes. Stacks of sediment made by colonies of
bacteria, called stromatolites,
are evidence of our primitive ancestors. Found in Africa,
Australia, and the Bahamas,

stromatolite layers contain carbon from bacteria dating back to
early Earth. Since Earth
was formed 4.6 billion years ago, life began relatively early in
Earth’s history.
How did life originate from our molten ball of Earth chemicals?
Early scientific
thinkers believed that life originated from nonliving matter. The
idea that life appeared
from nowhere, called spontaneous generation, was held firmly
by scientists for many
centuries.
Spontaneous
generation
The idea that states
that life appeared from
nowhere.
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The 17th-century scientists hypothesized that organic matter in
food automatically
generated maggots and all associated life when coming into
contact with air. (You can
make the same observation if you leave food at room
temperature for a long-enough
period of time; you will likely see mold and flies at the least.)
Then, Francesco Redi
(1636–1697), an Italian naturalist, became the first to disprove
spontaneous generation.
Redi devised an experiment that involved placing a piece of
meat into a glass jar.
The jar was covered with gauze, which allowed air flow to the
meat but no other agents
larger than the holes in the gauze. A second control jar was left
uncovered to allow con-
tact with any external agent. Redi’s experiment is shown in
Figure 7.1.
Redi’s results showed that the gauze-covered jar did not have
maggots, but that the
uncovered jar did. Realizing that some other agent had caused
maggots and not the meat

itself, Redi’s experiment was the first to disprove the idea of
spontaneous generation.
We now understand that flies were the cause of new life on
decaying meat, with maggots
growing from eggs laid on the organic material.
There were no microscopes in the 1600s to view the developing
fly eggs on meat.
The mechanism for new species growth on food was therefore
unknown. However, Redi
was criticized because new growth spoiled foods in both his
control and his experi-
mental jars – we now know the bacteria of decay cause the food
to spoil. Thus, debate
continued on whether life could arise spontaneously. Scientists
also sparred over what
caused milk and beer to sour. French biologist, Felix Pouchet
(1800–1873) believed that
microorganisms spontaneously arose in some foods, such as
milk and beer, which had
the right combinations to create life.
Pouchet heated flasks of hay brews to 100° C. He sealed the
flasks, but even though
they were sterilized, bacteria formed. Pouchet thus concluded
that organisms could arise
from a good mixture of materials, as found in beer and other
fermentation environments.
He tried many times to sterilize the flasks, but in every case
within a short period of
time, he observed a sea of bacteria. Pouchet thus reopened the
defense of spontaneous
generation.
Louis Pasteur (1833–1895) proposed an alternate hypothesis,
arguing that bacte-

ria were everywhere. He claimed that Pouchet’s experiment was
contaminated when he
JAR 1 JAR 2
Figure 7.1 Redi’s experiment. After covering jars,
Redi determined that a covered
jar does not lead to maggot formation on
meat. It was a first attempt to disprove
the spontaneous generation of life.
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placed lids onto the flasks. Pasteur designed special long-
necked flasks to keep broth
placed inside free from bacterial growth as he sterilized its
contents. Air was still able
to get through to the broth; this eliminated the criticism that life
might not have air to
breathe, as in Redi’s sealed jars. The lower part of the neck of
the flask trapped the
heavier dust particles and microbes. His flask design is shown
in Figure 7.2.
With no external agent, Pasteur reasoned correctly that the
“trap” in the neck kept
out microbes, and no new life formed in his flasks. When
Pasteur tipped a flask to allow
broth to touch the trap, bacteria appeared in the broth in a few
days. His rejection of
Pouchet’s results brought Pasteur membership in and an award
from the French Acad-
emy of Science. Pasteur’s experiment showed how his critical
thinking led to a solid
disproof of spontaneous generation – and led to the birth of
microbiology as a discipline.
Personally, Pasteur was a devout Roman Catholic. He performed
the experiment to
emphasize the sanctity of life. He reasoned that if spontaneous
generation were true,
then there would be no need for a creator God to exist. His
disproof of spontaneous
generation was actually a movement against atheism. It worked

toward a resurgence of
religious faith in the 1800s. While Pasteur promoted his work as
an example of pure
science, it may show how one’s personal beliefs, even as a
scientist, influences thinking
about scientific research.
The Pasteur–Pouchet debate illustrates how scientific arguments
continue through
the centuries. The germ theory of biology, which places a focus
on sterile techniques to
prevent microbial disease spread, led to important
improvements in medicine. The wide-
spread use of sterile techniques decreased deaths, especially
during childbirth.
The origin of life is of continual interest to scientists. In 1953,
physical chemists
Stanley Miller (1930–2007) and Harold Urey (1893–1981)
devised an experiment
demonstrating that precursors to life could have formed from
the right mixture of chem-
icals. Conditions on early Earth were simulated in a glass tube
containing methane,
hydrogen sulfide, hydrogen gas, and water vapor. The
experiment in Figure 7.3 shows
the design of Miller and Urey’s experiment.
An electrode was placed in the glass tube which simulated X-
rays, ultraviolet light,
and lightning of the early Earth. The environment in Miller and
Urey’s glass tube was an
oxygen-free system, just like on early Earth. When an electric
charge was applied to this
primordial mixture of chemicals, organic molecules formed.
Fats, sugars, proteins, and

genetic material were produced from the simulation.
Organic molecules make up life, and as discussed in Chapter 2,
are able to self-
assemble based on their chemistry. It is hypothesized that
droplets of organic material
Germ theory
The theory that
places a focus on
sterile techniques
to prevent microbial
disease spread,
led to important
improvements in
medicine.
Figure 7.2 Pasteur’s experiment.
Nutrient broth
is sterilized
No microorganisms
grow
Dust particles,
bacteria, and
other airborne
materials trapped
Microorganisms
thrive
Airborne bacteria

can now reach
the broth
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formed from the newly made organic products. As shown in
Figure 7.4, the droplets

formed a sphere that was separate from its environment. This
sphere of organic material
is called a prebiont and was the first form of new life. It was
capable of replicating,
absorbing genetic material, and forming new prebionts. These
new “cells” further devel-
oped into prokaryotes found as fossils within stromatolites. But
how did so much life
originate from such a simple prebiont?
natural Selection and Biodiversity
Take a moment to ponder the fact that living organisms, in all
their magnificent diver-
sity, emerged from a simple assortment of chemicals on early
Earth. Chapter 1 discussed
Darwin’s principles of evolution; we will expand on some of
those principles here.
When populations have more individuals than an environment
can support there
is inevitably a struggle for survival. Individuals have varied
characteristics, with some
better able to survive than others. These more successful
organisms reproduce more and
thus have better reproductive success (RS), defined as the
number of viable offspring
Prebiont
A sphere of organic
material that led to
first living cells.
Reproductive
success

Is the number of viable
offspring an individual
produces.
Figure 7.3 Miller and Urey apparatus. Gases in
the glass tubes reacted to form
organic molecules, precursors to life.
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Figure 7.4 Prebionts. These tiny spheres share

somecharacteristics of life, including
a separate membraneto keep it distinct from its
environment.
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an individual produces. The frequency with which genes appear
in a population change
based upon these different RS rates. Organisms with a
successful RS increase their
relative proportions of genes in a population.
The change in gene frequencies in a population, over time, is
defined as evolution.
However, evolution acts only upon phenotypes, or the physical
characteristics of one’s
genes. Those organisms with traits better adapted for a
particular environment will
increase in numbers. The driving force behind evolution is thus

natural selection, or nature
selecting for or against certain attributes. It results from an
interaction between organisms
and their environments. Consider the polar bear, Ursus
maritimus, which has white fur.
Over time, those bears with a light color as camouflage were
better able to blend in with
their snowy surroundings. Contrast the darker colors of the
brown bear, Ursus ameri-
canus, which blends better within darker forests of North
America (Figure 7.5).
Their respective environments influence the phenotypic traits
that are selected for
and against. To illustrate, the dark color of a brown bear
roaming the polar ice caps
would stand out like a sore thumb, making it easy prey for its
enemies and obvious pred-
ators to its prey. Thus, different environmental conditions favor
different phenotypes
at different times. If the ice caps were to melt, becoming
forests, polar bears would no
longer have an advantage with respect to fur coloration. In our
story, the characters wit-
ness changes in moth populations on the island. Moth species
thus experience a change
in gene frequencies within their populations, with some
decreasing and some thriving.
With declines in the V-moth, Marcaria wauaria and extinctions
of three moth species in
England, Orange upperwing, Jodia croceago; Bordered gothic,
Heliophobus reticulate;
and Brighton wainscot, Oria musculosa, natural selection is at
work. Changed environ-
mental conditions, such as loss of habitats and harmful
pesticides in farming, contrib-

uted to moth species changes (Figure 7.6).
Why the changes in moth populations in England? Consider that
currants and
gooseberries, once very popular and found in many gardens, lost
favor across house-
holds. Currants and gooseberries are a big part of V-moth diets.
Without easy access to
these foods, V-moth populations declined substantially. On the
other hand, some con-
ditions favored certain species of moths. In fact, one-third of
moth species experienced
increased numbers in the region discussed in our story. The
reason was the improve-
ments in air pollution and acid rain led to a rise in lichens,
which are fungi–algae colo-
nies. Moth species that increased in numbers had one common
feature – they all fed on
lichens. This is an example of natural selection occurring before
our eyes – changes in
moth species in our opening island story due to a response from
environmental factors.
Evolution
The change in gene
frequencies in a
population, over time.
Natural selection
The natural selection
for or against certain
attributes.
Figure 7.5 a. Brown bear. b. Polar bear.

(a) (b)
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In order for natural selection to occur on a particular trait, three
conditions must
exist: 1) there needs to be genetic variation in a population; 2)
variation in traits must be

heritable, that is, able to be inherited from one generation to the
next; and 3) individuals
with one trait must have better RS than individuals with another
trait. In the case of the
British moths in the story, their characteristics must be different
from those of other spe-
cies in some ways, and these differences must be inherited for
natural selection to work.
In addition to losing important food sources, the declining
species differ in their
appearance and in their habitat requirements from other moths.
Large farms recently
emerged, reducing their shrubby habitats. Without places to
deposit eggs and food for
their offspring, their numbers dwindled. In contrast, it is widely
believed that climate
change and increased temperatures allowed many of their
competitor moths to colonize
the island, thus forcing them out. The three moth species
experienced low RS, given the
changed environmental conditions, resulting in their extinction
from England. Changes
in the environment may be temporary, but if the gene
frequencies within a population
also change, sometimes evolution has irreversible results.
types of natural Selection
If a person has a harmful trait such as porphyria seen in the
story in chapter 6, it affects
that person’s survival. If another person is a carrier for
porphyria, then his or her phe-
notype is normal, and natural selection does not affect survival.
Natural selection acts
only on phenotypes because the environment only works on
those traits expressed by an

organism. While nature acts on one’s phenotype, phenotype
emerges from one’s genes.
The genes within an organism give rise to its physical
appearance. Thus, gene frequen-
cies change when a population is evolving due to natural
selection.
There are three types of effects by natural selection: directional
selection, stabiliz-
ing selection, and disruptive selection (Figure 7.7). Directional
selection occurs when
individuals at one extreme of the range of variation in a
population have a higher degree
of fitness. If a group of dogs is bred, allowing only those with
an aggressive disposition
to mate, the offspring are likely to exhibit more aggression.
Vicious dog breeds are
commonly used as attack dogs by owners. The idea that
behavior can be modified by
selecting for certain characteristics is a theme of behavioral
genetics.
Directional
selection
The process that
occurs when
individuals at one
extreme of the
range of variation
in a population have
a higher degree of
fitness.
Figure 7.6 There are light and dark moths on both
the light and dark trees. Which

moths do you thinkare more likely to be spotted
and eaten by predatory birds? Why?
From BSCS Biology: An Ecological Approach, 9th Edition
by BSCS.
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EvolutioN DoES Not CauSE thE BESt oRGaNiSmS to
SuRvivE
Evolution is not the survival of the best organisms,
only those best adapted
to their particular surroundings at any one
time. Evolution is a product of
the pressure by nature to select out the weak
and keep those organisms best
adapted for a particular environment. The
strongest do not always survive.
Consider dinosaurs,which were very strong, according to
fossil prototypes,
but were selected out; they were not the best adapted at

somepointin the
past. Dinosaurs are believed to have died as a result
of a giantmeteor impact
that added dust and debris to the atmosphere,
causing a cool down.
The extinction of dinosaurs is a hotlyexamined topic.
There is a debate
between geologists and biologists as to the cause of
their extinction. It has
long been held that an asteroid hit the Earth
about 65.5 million years ago,
causing a major shift in climate. Dust
from the impact led to less sunlight,
fewer plants, and thus less food for dinosaurs and
otherspecies. Fossil evi-
dence dating back to that period shows higher
than normal amounts of certain
materials, including iridium, indicating meteor-like hits.
The layerof soil con-
taining theseparticles is known as the K–T
boundary (Cretaceous–Paleocene
boundary) and correlates with a high extinction rate for
many species types.
The largecrater on the Yucatan peninsula is thought
to be evidence for this
meteor impact.
There is an alternate hypothesis that microbial
infections spread through-
out dinosaur populations leading to their extinction.
Emerging theories of dis-
ease or infection as the cause implicate a viral or
otherparasitic infection as
the reason for the dinosaur extinction. The hyper-
disease theory of dinosaur

extinction states that a microbe evolved rapidly to
kill off otherliving creatures
during the time period. While weather-related or
biological causes led to their
destruction, dinosaurs disappeared from the Earth
due to the forces of natural
selection, despite their impressive physical strength.
Death from global infectious diseases has
had major impacts on society
more recently in human history. For example, over
70% of Native American
Indians died due to diseases brought by Europeans
and not through battles.
They lacked a natural immunity to those
infectious pathogens such as influenza,
small pox, and bubonic plague. The power of
epidemics to destroy human cul-
tures and otherspecies has historical grounding.
hyper-disease
theory
The theory that states
that a microbe evolved
rapidly to kill off other
living creatures during
the time period.
Stabilizing selection occurs when individuals at the mean or
average range of varia-
tion in a population have a higher fitness. In human birth
weight, for example, the aver-
age newborn is 7.1 pounds or 3.3 kg. This is also the weight
associated with the lowest
infant mortality and is thus selected for in nature. At other ends

of the spectrum, infants
with a low birth rate suffer more health complications without
the required body fat; and
at the higher end, birthing is difficult due to the large size of
the baby. Modern medical
treatments are allowing greater variation in birth-weight
survival.
In disruptive selection, individuals at extremes of the variation
spectrum experi-
ence higher fitness than at the middle. In fish, larger males are
stronger and able to
Stabilizing selection
Occurs when
individuals at mean
or average range
of variation in a
population have higher
fitness.
Disruptive selection
The process in which
individuals at extremes
of the variation
spectrum experience
higher fitness than at
the middle.
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obtain females more readily. Oddly, smaller males, known as
sneaker males, also have
better chances of survival than those of intermediate size.
Sneaker males are able to
“sneak” into a nest and impregnate a female without the larger
male detecting him.
It is a peculiar strategy for survival and works to help smaller
sized fish persist in
populations.
In our story, certain phenotypes result from a winning
combination of genes. To
illustrate, a set of genes determines the odd pattern on the eyed

hawk-moth, Smerin-
thus ocellatus. Its coloration allows it to remain camouflaged
along bark when it is
at rest, and when disturbed, it displays a set of “eyes” that
startle its predators, allow-
ing it time to escape. As shown in Figure 7.8, a phenotype
enabling greater survival
chances for an organism such as the eyed hawk-moth increases
those gene frequen-
cies, causing the species to evolve that trait. Natural selection
pushes changes in gene
frequencies in certain directions based on their efficacy in an
environment, allowing
organisms to adapt.
Figure 7.7 Graphs showing threetypes of natural
selection.
A. Stabilizing selection
Normal distribution with both
extremes removed
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B. Directional selection

Normal distribution with one
extreme removed
C. Disruptive selection
Bimodal distribution with
average size removed ©
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Speciation increases Biodiversity
In Chapter 1, a species was defined as a population of
organisms that are able to inter-
breed and produce live, fertile offspring. Speciation is defined
as the process by which
natural selection drives one species to split into two or more
species. It occurs when the
new groups of species cannot interbreed with each other. Their
inability to mate is called
reproductive isolation. Several conditions may lead to
reproductive isolation: mating
songs may be so different that organisms don’t mate; changes in
the genetic composition
of two groups of organisms may make their offspring unviable,
as in the case of the ster-
ile mule, which is the offspring of a female horse and a male
donkey; and divergence of
groups into new geographic areas may prevent members of the
new group from mating.
It is likely that the eyed hawk-moth evolved from an ancestor
that lacked “eyes.”
This beneficial moth phenotype, its “eyes,” enabled greater
survival. Those organisms
with the trait …

235evolution Gives our Biodiversity7© Kendall Hu.docx

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