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Biology Content Standards
5. Evolution and Biodiversity
Broad Concept: Genes allow for the storage and transmission of genetic
information. They are a set of instructions encoded in the nucleotide sequence
of each organism. Genes code for the specific sequences of amino acids that
comprise the proteins that are characteristic of that organism.
5.1 Explain how evolution is demonstrated by evidence from the fossil record,
comparative anatomy, genetics, molecular biology, and examples of natural
selection.
5.2 Describe species as reproductively distinct groups of organisms. Recognize
that species are further classified into a hierarchical taxonomic system
(kingdom, phylum, class, order, family, genus, species) based on morphological,
behavioral, and molecular similarities. Describe the role that geographic
isolation can play in speciation.
5.3 Explain how evolution through natural selection can result in changes in
biodiversity through the increase or decrease of genetic diversity from a
population.
What is Evolution ?
• The processes that have
transformed life on earth
from its earliest forms to
the vast diversity that
characterizes it today.
• A change in the genes!
• Charles Darwin – “Father of Evolution”
Evolution
Evolution is the cause of something as insignificant as an
increase in the frequency of the gene for dark wings in
beetles from one generation to the next, to something as
grand as the evolution of the dinosaur lineage.
These two extremes represent classic examples of
microevolution and macroevolution.
Microevolution: small scale (w/in a population)
Macroevolution: transcends the boundaries of
a single species.
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Old Theories of Evolution
Jean Baptiste Lamarck
Ideas that shaped Darwin
•
over time.
(1744-1829)
He was among the 1st scientists to recognize that living
things changed over time. He also, long before Darwin,
realized that organisms were somehow adapted to their
environments. In explaining how adaptation occurred,
however, he relied on 3 assumptions we now know to be
incorrect …
• Desire to change
• Use and Disuse
• Inheritance of Acquired
Geology – Earth is very old and changes
Characteristics
Ideas that shaped Darwin
• Charles Lyell – Principles of Geology
•
Farmers – Farmers altered and improved
their crops and livestock through breeding
programs. Artificial selection allowed only the
individuals who suited the farmers’ needs to
produce offspring. But, in nature there is no
human intervention … Darwin wondered,
“how could such a process therefore operate?”
”
Charles Robert Darwin
Malthus & Population Controls – Thomas
Malthus was an economist. If the human population
continues to increase, there will not be enough living
space and food. The Malthusian Doctrine states,
“The only conditions that will prevent the endless
growth of human populations are famine, disease,
and war.”
” Darwin realized that the Malthusian
Doctrine applied more to animals and plants than
humans, for most other species produce far more
offspring than we do. What determines which
individuals survive and reproduce?
British ;aturalist
1809 -1882
From 1831 to 1836 Darwin
served as a naturalist aboard
the H.M.S. Beagle on a British
science expedition around the
world.
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Charles Robert Darwin
The H.M.S. Beagle was chartered for a 5-year
mapping and collecting expedition to South
America and the South Pacific. Darwin’s post as a
naturalist required that he collect specimens and
keep careful records of his observations. During
the Beagle’s 5 year trip, Darwin often left the ship
at one port and was picked up months later at
another port. During his time on land, Darwin
trekked 100’s of kilometers through unmapped
regions. He collected many different types of
fossils and observed 1000’s of species of organisms!
Charles Robert Darwin
Two main points:
1. Species were not created in their present
form, but evolved from ancestral species...
Common Descent
2. Proposed a mechanism for evolution:
1ATURAL SELECTIO1
Charles Robert Darwin
On the Galapagos
Islands,, Darwin
Islands
observed species
that lived no
where else in the
world.
These observations
led Darwin to write
a book. 1859
Galapagos tortoise
On the Origin of
Species by
Means of 1atural
Selection.
Theory of Natural Selection
1. Variation
2. Overproduction of offspring
Far more organisms are born than ever grow to adulthood!
3. Struggle for existence
Organisms compete with each other (limited
resources).
4. Differential survival and reproduction
Organisms will evolve or change over very long periods of time. Generation after
generation of this kind of selection causes organisms to become better and better
adapted to their environment.
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Adaptation
Feature common in a population because it provides
some improved function.
Many forms:
• Behavior: better evasion of predators.
• Protein: functions better at body temperature
• Anatomical feature: allows the organism to
access a valuable new resource.
Many of the things that impress us most in nature
are thought to be adaptations!
The creosote bush is a desert-dwelling plant that
produces toxins. These toxins are an adaptation
that prevent other plants from growing nearby,
thus reducing competition for nutrients and
water.
Mimicry of leaves by insects is an
adaptation for evading predators. This
example is a katydid from Costa Rica.
Echolocation
in bats is an
adaptation
for catching
insects.
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Evidence of Evolution
FOSSILS - trace of a long-dead organism
Scientists who study fossils are called PALEO;TOLOGISTS.
• The Earth is very old:
more than 4 billion
years old
Sedimentary fossils usually
develop from the hard body
parts of an organism, such as
the shell, bones, teeth, or, in
the case of plants, the woody
stem.
• Earth’
’s land is
constantly
moving and shifting.
• Life on Earth has also
changed over time.
Fossils are often found in
layers of sedimentary rock,
which is formed when
sediment, such as dust, sand,
or mud, is deposited by wind
or water.
Nebraska's Ashfall Fossil Beds
Over long periods of time,
hard minerals replace the
tissue of the organism,
leaving rocklike structures.
Relative Dating
One of the few animals for which we have a fairly complete evolutionary
record is the horse. All the main stages of horse evolution have been
preserved in fossil form. Over 60 million years the horse evolved from a dogsized rainforest-dwelling creature, into an animal adapted to plains-dwelling
and standing up to 2 meters high. In the process it traded-in its multi-toed
feet, adapted for walking across the forest floor, for single-toed hooves, suited
for running over open country.
Technique used to
determine the age
of fossils relative
to other fossils in
different layers
of rock.
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Radioactive Dating – method of measuring
rates of decay of radioactive materials to determine how long
ago an event occurred or an organism lived.
Fossils and DNA
- The greater the
differences between genes of related species the longer
the time since those species shared a common ancestor.
• Half-life – length of time required for ½ of
the radioactive atoms in a sample to decay.
(Ex) ½ life of C-14 is 5770 years. During that
period, ½ the C-14 decays to ;-14.
• C-14 is particularly useful because it can be used
to date material that was once alive such as bones,
or to date objects that contain once-living material.
Because it has a relatively short ½ life, C14 is not
really useful in dating samples that are more than
60,000 years old.
Evidence of Evolution
EMBRYOLOGY
Living fossils
are those relatively rare species that remain
unchanged for long periods of time. One example is the
horseshoe crab, Limulus, whose living members are almost
identical to ancestors that lived hundreds of millions of years
ago. They are exceptionally well adapted. Also, no new species
entered into competition.
Each of these species inherited the same genes
for early embryonic development. ;ature takes
the development plan and modifies it at
different stages to produce different adults.
The similarity of early
embryonic development
demonstrates that all the
vertebrates share a
common ancestor.
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Evidence of Evolution
Evidence of Evolution
HOMOLOGOUS STRUCTURES
A;ALOGOUS STRUCTURES
Parts of different organisms with similar structure, but different
functions – suggest common ancestry - Divergent
Evolution.
Parts of different organisms with similar function, but
different structures. – Convergent
Evolution.
Evidence of Evolution
Evidence of Evolution
VESTIGIAL ORGA;S
SIMILARITIES in MACROMOLECULES
They are usually degenerated or underdeveloped. These organs
are thought to have been functional in the ancestral species but
have now become unnecessary and non-functional.
Wings of flightless birds
Protein
Pelvic bones of whales
D;A
Hemoglobin
Cytochrome c
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Evolution of Populations
Microevolution
Population
A localized group of individuals
belonging to the same species.
Some scientists view evolution
as a process of change where
minor genetic changes occur
in populations through
random mutations which can
lead to a change in gene
frequency.
A population is the smallest
unit of living organisms that
can undergo evolution!
changes in allele
frequencies within a species.
A group of populations whose individuals have the
Refers to
Gene Pool
The total collection of genes in a population at any one time.
Within a gene pool, every
allele has a particular
ratio or frequency.
Species
potential to interbreed and produce viable offspring.
Five Mechanisms of Microevolution
1. Mutation
2. Migration (Gene Flow)
3. ;on-random mating
The frequency of an allele
is the number of
occurrences of that allele
in that population
4. Genetic Drift
5. ;atural selection
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Mutation
Migration (Gene Flow)
The gain or loss of alleles from a population by the movement of
individuals or gametes (pollen). Immigration or Emigration.
Genes from crops rapidly can take over
those in related wild plants. The end result
could be major changes in the genetic
make-up of wild plants, decreases in their
population size, and the permanent loss of
natural traits that could improve crop
health.
“The fact is that most genes for crop
It is probable that melanism is a favorable evolutionary mutation with a
selective advantage under certain conditions for its possessor, since it is more
commonly found in regions of dense forest, where light levels are lower.
NonNon-Random Mating
Artificial Selection
improvement have come from wild relatives
of those same crops. Gene flow from crops to
wild relatives is one of a host of
environmental issues that humans must deal
with.”
Genetic Drift
Change in the gene pool of a small
population due to chance.
The selective breeding of domesticated plants and animals by man.
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Genetic Drift
Bottleneck Effect
Two examples:
1.
Bottleneck effect
Resulting from a disaster that
drastically reduces population
size. (Earthquakes & Volcanoes)
2.
Founder effect
Resulting from the colonization of a new location
by a small number of individuals.
;atural Selection
Founder
Effect
The pressures of natural selection can affect the
distribution of phenotypes in a population in
several ways …
• Directional Selection
• Stabilizing Selection
• Disruptive Selection
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Directional Selection
A population may find
itself in circumstances
where individuals
occupying one extreme
in the range of
phenotypes are favored
over the others.
Over long periods of time, in the constant presence of hungry
peccaries, the population of cacti will gradually shift in the
direction of the more heavily spined cactus varieties.
Disruptive Selection
Individuals at both extremes of a range of
phenotypes are favored over those in the middle.
Stabilizing Selection
Individuals at both
extremes of a range of
phenotypes are being
“weeded out”, resulting
in the reproductive
success of those near the
mean. Stabilizing selection is common. In
humans, for example, the incidence of infant
mortality is higher for very heavy as well as
for very light babies.
Speciation
How new species evolve from old ones.
SPECIES
group of organisms
with similar
characteristics
that can interbreed
with one another
to produce fertile
offspring.
Individuals in the
same species share a
common gene pool.
Canis familiaris
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The Competitive Exclusion Principle
(Gause’s Principle):
;O two species can occupy the same ;ICHE in
the same location for a long period of time!
;ICHE
Combination of an
organism’s habitat
and its role in that
habitat.
Speciation begins with …
REPRODUCTIVE ISOLATIO;!
Results from barriers to successful breeding between
population groups in the same area. ;ew species arise
when genetic differences accumulate to the point when
the two groups can no longer successfully mate and
reproduce (if and when they come back into contact).
Allopatric Speciation = populations are physically separated
Sympatric Speciation = populations are ;OT physically
separated
Allopatric Speciation
Isolation might occur because of great distance or a physical
barrier, such as a desert or river, as shown below. In order for a
speciation even to be considered “allopatric,”
” gene flow between
the soon-to-be species must be greatly reduced — but it doesn’’t
have to be reduced completely to zero.
Sympatric Speciation
Gene flow has been reduced between flies that feed on different food
varieties, even though they both live in the same geographic area.
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200 years ago, the ancestors of Apple maggot
flies laid their eggs only on hawthorns—but
today, these flies lay eggs on hawthorns (which
are native to America) and domestic apples
(which were introduced to America by
Apple maggot flies
immigrants and bred). Females generally choose
to lay their eggs on the type of fruit they grew up
in, and males tend to look for mates on the type
of fruit they grew up in. So hawthorn flies
generally end up mating with other hawthorn
flies and apple flies generally end up mating
Apples
with other apple flies. This means that gene
flow between parts of the population that mate
on different types of fruit is reduced. This host
shift from hawthorns to apples may be the first
step toward sympatric speciation — in fewer
than 200 years, some genetic differences
Hawthorns
between these two groups of flies have evolved.
Reproductive Barriers
Behavioral Isolation
Little or no sexual attraction between populations.
• Pre-zygotic barriers
• Post-zygotic barriers
12 different species of fiddler crabs on the same beach in Panama
could be distinguished by the display of waving their large
cheliped, elevating the body, and moving around in their burrow
courtship display ritual!
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Geographic Isolation
Physical separation of members of a population
• Islands of land in a sea of water
• Islands of water in a sea of land
• Islands of trees in a sea of grass
• Mountains as barriers
• Rivers and canyons as barriers
Galapagos Finches
• Darwin studied 13 similar but separate species of Galapagos finches.
• Each finch species had a distinctive bill that is specialized for a
particular food source. Despite the bill differences, the overwhelming
similarities of the Galapagos finches implied that the finches shared a
recent common ancestor, meaning they descended from a single species.
• Darwin thought that perhaps all of the islands’
’ finches had descended
from a few birds or even a single female that had blown off course from
South America.
• Because the Galapagos are geologically young islands, @ 5 million
years old, Darwin assumed that the offspring of the original finches
had been adapting to different environments and food sources for a
relatively short time . Darwin reasoned, therefore, that over many
millions of years, many large differences could accumulate between
species.
Temporal Isolation
Breeding occurs at different times for different species.
Rana aurora - breeds January - March
Rana boylii - breeds late March - May
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Patterns of Evolution
Macroevolution = large-scale evolutionary
changes that take place over long periods of time. It
refers to changes in populations of plants and animals
so that new species develop from old ones.
There are 6 important patterns:
•
•
•
•
•
•
Mass Extinctions
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium
Changes in Developmental Genes
Adaptive
Radiation
Many related species
evolve from a single
ancestral species.
The Galapagos finches
diverged in response to
the availability of
different types of food
in their different
habitats.
Mass Extinctions
Huge numbers of species disappear!
The Permian Extinction was the greatest mass extinction
ever, but it’
’s not the only big one.
Five times in Earth’
’s history—at the end of the
Ordovician (440 million years ago), the Devonian (370 m.y.a.),
the Permian (250 m.y.a.), the Triassic (210 m.y.a.), and the
Cretaceous (65 m.y.a.) periods— mysterious events wiped
out more than half the species alive. Some researchers
think that humans have put so much stress on the
environment that we’
’re causing another mass extinction
(see “The Sixth Extinction,”
” 1ational Geographic
Magazine, February 1999). www.nationalgeographic.com
Convergent Evolution
Unrelated species become more similar as they adapt
to the same kind of environment.
EXAMPLE: Shark and porpoise have analogous
structures. Sharks are fishes. Porpoises are mammals.
They have analogous structures – similar fins. They
have large, streamlined bodies.
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Coevolution
The mutual evolution of 2 different
species interacting with one another.
EXAMPLE: Plants and the animals that pollinate them.
Gradualism
This is the classical,
traditional view stating
that large changes
(reproductive isolation
and morphological
differentiation) occur
due to the gradual accumulation of many genetic
changes. The classic example put forth in many
natural history museums in the form of a nice
display is that of the evolution of the modern
horse.
Punctuated Equilibrium
This newer hypothesis was put forth in 1972 by Eldredge and Gould.
They suggested that major changes occur relatively suddenly, and are
"punctuated" by periods of relatively little change. Evidence for this
theory is supplied by the fossil record. By studying the fossil record
scientists have found what appears to be long periods of time with
relatively little change in species followed by sudden periods of intense
change
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
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