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Biology
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Date: _____________ Period: _______
Evolution Review
History of Evolutionary Thought
1735- Carl Linnaeus
Published the first edition of his classification of living things, the Systema
Naturae
1785- James Hutton
Hutton proposes that Earth is shaped by geological forces that took place over
extremely long periods of time. He cited volcanic eruptions, earthquakes, and
erosion impacting geology now just as it had in the past.
He estimates the Earth to be millions- not thousands- of years old.
1798- Thomas Malthus
In his Essay on the Principle of Population, Malthus predicts that the human
population will grow faster than the space and food supplies needed to sustain
it.
Malthus reasoned that if the human population continued to grow unchecked,
sooner or later there would be insufficient living space and food for everyone.
He proposed that war, famine, and disease limited the growth of human
populations.
1809- Jean-Baptiste Lamarck
Lamarck publishes his theory of the inheritance of acquired traits.
The theory is flawed, but he is one of the first to propose a mechanism
explaining how organisms change over time.
Lamarck believed that organs could be altered in shape or size based on use or
disuse. He believed that these acquired traits could then be inherited.
1831- Charles Darwin
Darwin sets sail on the HMS Beagle, a voyage that would provide him with
vast amounts of evidence that lead to his theory of evolution
Darwin realized that both living organisms and fossils were the key to
understanding the natural world.
The Galapagos islands were some of the most influential to Darwin and his
theories. Darwin observed that the characteristics of many animals (tortoises
and finches) and plants varied noticeably among the different islands of the
Galapagos.
1833- Charles Lyell
In the second and final volume of Principles of Geology, Lyell explained that
processes occurring now have shaped Earth’s geological features over long
periods of time
1858- Alfred Wallace
Wallace writes to Darwin, speculating on evolution by natural selection, based
on his studies of the distribution of plants and animals
Darwin presents Wallace’s essay to the Linnaean Society
1859- Charles Darwin
Publishes On the Origin of Species
After years of compiling data and ideas, it was a colleague’s paper on
evolution (Alfred Russel Wallace) that pushed Darwin to complete and
publish his own work.
Darwin rejected the idea of species being perfect and unchanging in favor of
natural variation.
Darwin’s greatest insight was to compare processes in nature with artificial
selection.
There are three key aspects of Darwin’s Theory of Natural Selection:
The Struggle for Existence - members of each species compete
regularly to obtain food, living space, and other necessities of life.
A key factor in the struggle for existence was an animal’s
fitness.
Fitness – the ability of an individual to survive and reproduce
in its specific environment.
Darwin proposed that fitness is the result of adaptations.
Adaptation – inherited characteristic that increases an
organisms chance of survival
Adaptations can be physical (i.e. shells, quills) or behavioral
(i.e. group hunting)
Survival of the Fittest
Because each individual differs from other members of its
species, each has unique advantages and disadvantages.
Individuals with characteristics not well suited to their
environment either die or leave few offspring.
Individuals that are better suited to their environment survive
and reproduce successfully.
Descent With Modification
Over time, natural selection results in changes in the inherited
characteristics of a population.
These changes increase a species’ fitness in its environment.
Natural selection then produces organisms that have different
structures, establish different niches, or occupy different
habitats thus looking different from their ancestors.
Thus each living species has descended, with changes, from
other species over time – a process Darwin called descent with
modification.
Thus if we look back far enough we could find a common
ancestor for all living things; an idea know as common descent.
Evidence for evolution
Evidence for this process could be found in
the fossil record,
the geographical distribution of living species,
Beaver
Beaver
Muskrat
NORTH
AMERICA
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH AMERICA
Coypu and
Capybara
Coypu
homologous structure of living organisms, and
similarities in early development.
Population Evolution
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Evolution is a branching or splitting process in which populations split off from
one another and gradually become different.
It was not until around 1910 that biologists began to realize that genes were the
key source of evolutionary change.
There are two main sources of genetic variation:
o Mutations
o Gene Shuffling (the result of sexual reproduction)
A gene pool is the combined genetic information of all the members of a
particular population.
The relative frequency of an allele is the number of times that allele occurs in a
gene pool compared with the number of times other alleles occur (usually
expressed as a percent).
Keep in mind, natural selection acts on the phenotype of an organism (not its
genotype).
In small populations, individuals that carry a particular allele may leave more
descendants than other individuals, just by chance. Over time, a series of chance
occurrences of this type can cause an allele to become common in a population –
this is known as genetic drift.
Natural selection can affect the distributions of phenotypes in any of three ways:
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o Directional selection occurs when the environment of a population is
changing in some definitive way (pepper moths).
o Stabilizing selection is when individuals in the center of the population
have higher fitness than either extreme. Stabilizing selection is the one
mode that does not result in adaptive change and/or evolution.
o Disruptive selection is when individuals at both extremes have higher
fitness than individuals near the middle.
Genetic equilibrium is the situation in which allele frequencies remain constant is
called genetic equilibrium. If allele frequencies do not change, the population
will not evolve.
Five conditions are required to maintain genetic equilibrium from generation to
generation:
o There must be random mating
o The population must be very large
o There can be no movement into or out of the population
o There can be no mutations
o There can be no natural selection
In addition to disruptive selection, new species can be created when segments of a
population are separated. This separation creates isolated populations. There are
various types of isolation:
o Behavioral isolation - occurs when two populations are capable of
interbreeding, but have differences in courtship rituals or other types of
behavior.
o By preventing the mating between formerly interbreeding groups or the
inability of these groups to produce fertile offspring leads to reproductive
isolation.
o Geographic isolation is when a physical barrier is present which divides a
population.
o Temporal isolation is when two or more species reproduce at different
times, this is called temporal isolation.
Disruptive selection can lead to adaptive radiation – where one species evolves
into several.
Speciation is the formation of new species
Convergent evolution is a process by which unrelated organisms independently
evolve similarities when adapting to similar environments.
Coevolution is a process by which two species evolve in response to changes in
each other. Many symbiotic
relationships co-evolve over the
course of their existence.
In gradualism, organisms change
slowly over time at a steady rate.
In punctuated equilibrium, there are
long periods of time with no change,
followed by short periods of rapid
evolution.
The Fossil Record
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The remains of ancient life are called fossils.
Fossils occur in a particular order. Certain fossils in certain rocks.
Over billions of years, ancient unicellular organisms have given rise to currently
existing life on Earth.
More than 99% of all species that ever lived on Earth are now extinct.
Fossils include preserved forms of the following:
• Complete animals
• Animal fragments
• Eggs
• Footprints
• Animal droppings
• Plants or plant parts
How We Use The Fossil Record (know table comparing!)
• Radioactive dating relies on half-life decay of radioactive elements to
allow scientists to date rocks and materials directly.
• Relative dating provides a sequence of events from which relative dates
can be extrapolated.
• Molecular clocks allow scientists to use the amount of genetic divergence
between organisms to extrapolate backwards to estimate dates.
Radioactive dating is the use of half-lives to determine the age of a sample.
• In radioactive dating, scientists calculate the age of a sample based on the
amount of remaining radioactive isotopes it contains.
In relative dating, the age of a fossil is determined by comparing its placement
with that of fossils in other layers of rock.
• The rock layers form in order by age – the oldest layers on the bottom,
with more recent layers on top, closer to Earth’s surface.
• To perform relative dating, scientists use index fossils to compare the
relative ages of fossils.
• An index fossil is a species that is easily recognized and must have existed
for a short period but in only a few layers of rock.
In the absence of index fossils, scientists may use bracketing to date a particular
layer of fossils.
• Fossils are generally found in sedimentary rock—not igneous rock.
Sedimentary rocks can be dated using radioactive carbon, but because
carbon decays relatively quickly, this only works for rocks younger than
about 60 thousand years.
• In order to date most older fossils, scientists look for layers of igneous
rock or volcanic ash above and below the fossil. Scientists date igneous
rock using elements that are slow to decay (uranium and potassium).
• By dating these surrounding layers, they can figure out the youngest and
oldest that the fossil might be.
Geologic Time
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Earth’s early atmosphere probably contained hydrogen cyanide, carbon dioxide,
carbon monoxide, nitrogen, hydrogen sulfide, and water.
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Scientists Miller and Urey’s experiments suggested how mixtures of the organic
compounds necessary for life could have arisen from simpler compounds present
on a primitive Earth.
• From these organic molecules arose RNA and DNA. Molecular biologists
have discovered that RNA is very versatile and can actually under certain
circumstances duplicate
themselves.
The endosymbiotic theory proposes that
eukaryotic cells arose from living
communities formed by prokaryotic
organisms.
Paleontologists use divisions of the
geologic time scale to represent
evolutionary time.
This time scale was originally developed
as geologists studied rock layers and
index fossils. Changes in the fossil
record were used to mark where one
segment ends and another begins – long
before these segments were assigned dates.
Later radioactive dating was used to determine time frames for these shifts.
Precambrian Time - Anaerobic, then photosynthetic prokaryotes; eukaryotes,
then multicellular life
Paleozoic Era – “Age of Fishes”
• Cambrian – Marine invertebrates diversified; most animal phyla evolved
• Ordovician – Aquatic arthropods; mollusks; vertebrates (jawless fishes)
• Silurian – First land plants; first land animals (arthropods)
• Devonian – Fishes diversified; land vertebrates colonize and begin to
diversify (primitive amphibians)
• Carboniferous – First reptiles; winged insects diversified; coal swamps
• Permian – Reptiles diversified; seed plants; mass extinction
Mesozoic Era – “Age of Reptiles”
• Triassic – First dinosaurs; small mammals; cone-bearing plants
• Jurassic – Dinosaurs diversified; birds
• Cretaceous – Aquatic reptiles diversified; flowering plants; mass
extinction
Cenozoic Era – “Age of Mammals”
• Tertiary – Mammals diversified; grasses
• Quaternary – Glaciations; mammals increased; humans
Extinctions occur all the time. More than 99% of all species that ever lived are
now extinct. Mass extinction is an episode in which many species suddenly
become extinct
Classification
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Linnaeus was a Swedish botanist who developed a classification system for the
living world that included seven different levels of order. These are:
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1. Kingdom
2. Phylum
3. Class
4. Order
5. Family
6. Genus
7. Species
These groups or levels of organization are called taxons. Thus the term taxonomy
for the discipline of classification and naming of organisms.
Linnaeus also gave us a two-part naming system called binomial nomenclature.
This system provides a scientific name that described the organism using its genus
and species.
Traditional classification groups organisms based on their physical traits.
Cladograms group organisms based on their evolutionary history (physical traits
& DNA similarity)
Appendages
Crab
Conical Shells
Barnacle
Limpet
Crustaceans
Crab
Gastropod
Barnacle
Limpet
Molted
exoskeleton
Segmentation
Tiny free-swimming
larva
TRADITIONAL
CLASSIFICATION
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CLADOGRAM
Characteristics found in recent lineages but not older members are called derived
characters.
Vestigial traits are largely or entirely functionless (a hold over from earlier
evolutionary forms). A vestigial structure may retain lesser functions or develop
minor new ones.
A model known as a molecular clock uses DNA comparisons to estimate the
length of time that two species have been evolving independently
Currently there are three domains that scientists identify relating life on earth.
• Bacteria
• Archaea
• Eukarya
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Scientists currently recognize six different kingdoms.
• Eubacteria (Bacteria)
• Archaebacteria (Archaea)
• Protista (Eukarya)
• Fungi (Eukarya)
• Plantae (Eukarya)
• Animalia (Eukarya)