Mr. Ramos
Evolution Study Guide
Students, here is a study guide for the Evolution Test. Read it and study it carefully in conjunction with
your class & book notes. Remember the Evolution test is 50 Multiple Choice questions worth 50% of
your total class grade. The test is curved. Study hard! Evolution is perhaps the most difficult biology test
you will take all year. Also, take advantage of this generous study guide. I will NOT always do these nice
things for you all.
*Note: When you have a doubt, choose natural selection or common ancestor as the answer.
Introduction to Evolution
Charles Darwin and Alfred Russell Wallace are the fathers of evolution (but mainly Darwin).
Biological evolution is a change in the population over time. Populations evolve, not individuals.
Darwin used the term descent with modification to describe evolution. We (the descendents) are
modified versions of our ancestors.
Charles Darwin was a naturalist (someone who studies nature). He went on a 5 year voyage on a big
British ship called the H.M.S. Beagle. On his journey around the world, he noticed that species vary
globally, locally, and over time.
Darwin’s greatest work came from studying the animals in the Galapagos Islands off the coast of
Ecuador. Darwin realized that tortoises on one island had short necks while tortoises on the other island
had long necks.
Darwin realized that these differences in tortoise necks were not coincidences. The tortoises were built
to live and dwell in the environment that they were in. For example, the tortoises with short necks were
on an island with plenty of vegetation on the ground. Meanwhile, the tortoises with long necks were on
an island where there was no vegetation on the ground. These tortoises needed long necks to reach for
food up high.
Species vary locally
Darwin noticed three different types of birds as he travelled the world: the Rhea (found in S. America),
the Ostrich (found in Africa) and the Emu (found in Australia). These birds look almost the same, but if
you look carefully, they are all different.
Species vary globally
Darwin also noticed that species change over time. This concept was not acceptable back in the day, for
it was thought that all species were created perfect and could not change. Darwin saw these changes in
the fossil record. Take a look the picture of the armadillo shown below and its extinct ancestor the
glyptodont.
Species vary over time
Ideas that Shaped Darwin’s Thinking
Back in the old days people thought the Earth was 5,000 years old. This idea of Earth’s age was
calculated by Archbishop James Usher.
Now, thanks to carbon dating, fossils, and geology we know that the Earth is approximately 4.54 billion
years old.
Darwin did not believe the Earth was only 5,000 years old. He was highly influenced by the works of
Hutton and Lyell, who concluded that the Earth is extremely old, and the processes that changed Earth
in the past are the same processes that operate in the present. Since the Earth may be a lot older, then
Darwin’s theory would make more sense, since it takes a really long time for new organisms to arise.
Jean-Baptiste Lamarck was a French naturalist who highly influenced Charles Darwin. Lamarck was one
of the first persons to say that species change. Lamarck’s ideas, however, were incorrect and thus
ridiculed. His theory was called Inheritance of Acquired Characteristics. This theory involved a concept
called use and disuses. Organism, such as giraffes, that use their necks to reach the leaves of trees will
pass those characteristics to their offspring. The more you use something, the better it becomes, and it
is passed on to the offspring. (Remember: Lamarck was wrong! Individuals do not evolve. Populations
evolve).
Lamarck thought that evolution led to perfection. However, we know that the process of evolution does
NOT make you better or perfect.
Another man who influenced Darwin was the economist, Thomas Malthus. Malthus said that war,
famine, and disease, would force the human population to reach a carrying capacity during his time.
Malthus, however, was wrong. We are in 2014 and there are about 7.2 billion people on Earth.
Darwin realized that although Malthus’s work did not apply to humans (because of technological
advancements); his work applied more to animals. Populations tend to stabilize and only those fit to
their specific environments will survive. Nature is a dangerous place.
Philosophical Dilemma with Evolution
Back then, philosophers and scientists did not believe in “evolution” because of the following:
‘you cannot get order and complexity from random chaos alone’
Keep in mind that evolution was thought to occur because of random mutations. So how could these
random mutations lead to such beautiful organisms on Earth with their complex structures?
Charles Darwin realized that such order can occur in nature as a result of a process called natural
selection. Natural selection states that nature will select those individuals that are better suited to their
environments. These individuals will survive, reproduce, and pass on their genetic information to their
offspring.
In better terms: natural selection is the process by which random evolutionary changes are selected for
by nature in a consistent, orderly, non-random way.
But how does this work exactly? Notice the picture below with the light and dark moths. Think for a
second, which moth is better? The answer is none because they are both moths. The only difference is
that one is light and the other dark. Natural selection does not select the best organisms. Natural
selection selects those organisms that are better suited to their environments to survive and reproduce.
In the first example with the light tree, natural selection chooses the light moth to live and reproduce in
that environment because of its ability to camouflage. In the second example with the dark tree, natural
selection chooses the dark moth to live and reproduce in that environment because of its ability to
camouflage.
So you see, nature does not have a thinking mind, but it somehow selects the organisms best suited to
their environments to survive and reproduce based on the organisms’ adaptations.
*Natural selection goes side by side with adaptation and survival of the fittest.
Nature selects those variations that are best adapted to the environments in which they are in, leading
to the reproduction of the organisms, which is termed fitness.
Evolution is like a “car,” and natural selection is like the “engine.” Natural selection drives evolution.
Darwin’s Idea of Natural Selection came from Artificial Selection
Darwin was curious as to what caused these changes in nature, so Darwin studied changes based on
Artificial Selection. In artificial selection, nature provides the variations, and humans select those they
find useful.
Artificial selection is used to create different breeds of dogs, such as the Boxer, Rottweiler, and German
shepherd. Humans choose the traits they like and thus create different breeds for different purposes.
Artificial selection is also used to grow crops. Broccoli, Cauliflower, Kale, Brussle sprouts, and Cabbage
are all just different breeds of a weed found in the English Channel.
More on Natural Selection
Natural selection is based on the idea that
- nature selects who lives or dies
- organisms struggle to exist
- organisms have variations that allow adaptation
- Fitness (survival of the fittest): those organisms that survive will reproduce & pass their adaptations to
the next generation.
Natural selection only acts on inherited traits because these are the only characteristics that parents can
pass on to their offspring.
Natural selection does NOT make organisms “better.”
Evidence for Evolution
The fossil record provides strong evidence to the theory of evolution. We have found the skulls of
human-like ancestors that may show the gradual change in the human species.
Fossil Record
Embryology, or the study of embryos, provides clues as to how all organisms begin life in a very similar
fashion.
4 different Embryos
Comparative anatomy involves comparing the structures of various organisms to determine their
similarities and differences. Notice on the picture below that man, cow, horse, whale, and bird all have
similar structures but different functions. This must mean that they share a common ancestor.
Homologous Structures: similar structures but different
functions (they share a common ancestor). Ask yourselves
“why do whales and birds have bones similar to the hands
of man?” Could it be that whales, birds, and man all
descended from a common ancestor with hand-like
structures?
Vestigial structures are homologous structures that serve no major function or have lost their function
over time. Examples include the human tail-bone, the wisdom teeth, and the appendix. Ask yourselves
“why do we have wisdom teeth if they serve no function and usually don’t fit in our mouth?” Could it be
that our ancestors, the Neanderthals, had bigger mouths as a result of a different diet? Ask yourselves
“why do we have an appendix if it serves no function?” Could it be that the appendix helped us digest
plants in the past?
Biogeography serves as evidence for evolution because we ask ourselves how is it possible for finches
that live so close to each other in neighboring islands in the Galapagos to all be different species of
finch. This may be due to the kinds of food present on each island of the Galapagos. In some islands
there are plenty of hard seeds, so the finches in this island have grown large beaks to break the seed. In
other islands the only food available is nectar found inside of flowers, so these finches need a long
pointy beak to survive.
Molecular Biology
Ultimately, molecular evidence suggests that mutations, or changes in the DNA as a result of error, lead
to variations among species that would add up over generations and result in all the diversity there is on
Earth today. We see molecular evidence for evolution by comparing DNA from different organisms.
Chimpanzees and humans for example have almost the same DNA.
Notice how the chimpanzee has 0 differences in amino acids when
compared to humans. Thus, the chimp is our closest relative, at least
when it comes to cytochrome c.
Analogous structures are structures that have a similar function but a different structure.
*Note: Analogous structures do not indicate a recent common ancestor.
Evolution in Genetics Terms
In genetics terms, evolution is the change in allele frequency in a population over time.
An allele is a variation of a gene, and a gene is a piece of a chromosome that codes for information.
There are many genes (eye color gene, rolling tongue gene, widow’s peak gene, etc). The eye color gene
may have variations, such as green eyes, brown eyes, blue eyes, etc. These variations in a gene are
called alleles.
If the population is 80% white and 20% black (allele frequency), and in a few years the alleles become
different (let’s say 40 % white and 60% black), then the population has evolved. The allele frequencies
have changed in the population over time.
All the genes in a population make up the population’s gene pool.
What causes genetic variations for natural selection to act on individuals?
1. Mutations, which are changes in the DNA as a result of a mistake, introduce new
variations.
2. Genetic recombination during sexual reproduction occurs when the DNA from
mommy and daddy combine and shuffle to produce many variations that result in
differences between you and your siblings. This recombination of genes occurs during
sexual reproduction (when mom and dad decide to make a baby).
3. Lateral gene transfer introduces new genes into the new population. This
occurs when on organism, such as a bacterium, transfers its special DNA into
another bacterium. When bacteria have “sex” and transfer information from
one bacterium to the other, this is called conjugation.
Natural selection acts upon phenotypes, not genotypes. A genotype is the genetic information of an
organism (BB, Bb, bb). The phenotype is the physical expression of a genotype (BB = brown eyes, Bb =
brown eyes, bb = blue eyes).
Some traits, such as the widow’s peak or butt chin are single-gene traits. This means that the trait is
controlled by one gene. Therefore, you either have the trait or not.
Polygenic traits are controlled by more than one gene. Therefore, polygenic traits will have a range of
variations. Skin color, weight, and height are examples of polygenic traits. Evolution may drive polygenic
traits into various modes: stabilizing selection, directional selection, or disruptive selection.
In stabilizing selection, the majority of the population
will exhibit the trait that is in the middle of the bell
curve distribution.
In directional selection, the majority of the population
will shift to the right or left to exhibit one of the two
extreme forms of the trait in the bell curve
distribution.
In disruptive selection, the majority of the population
will sway away from the center of the bell curve and
exhibit traits in either extreme of the bell curve
distribution.
Genetic drift may cause populations to evolve by accident. Genetic drift affects small populations.
Notice the picture below – the man did not intentionally mean to step on the beetles, but he
“accidentally” stepped on a portion of the population of beetles that were green. The population drifted
towards brown.
The bottleneck effect is a type of genetic drift that occurs in a population
when there is a natural disaster and only a few members of the population
survive.
The founder effect is another example of genetic drift. The founder effect
occurs when small populations of individuals settle in a place, such as an island
or country that is rather uninhabited. This small population of founders may
carry bad genes that can spread to future generations, harming the population.
Hardy and Weinberg indirectly proved that allele frequency in populations change, thus evolution takes
place. They stated that 5 factors need to occur in order for a population not to evolve. When these 5
factors are present, the population does not evolve and is said to be in Hardy-Weinberg Equilibrium.
A population will NOT evolve if the following 5 principles are met:
1. Random mating
2. Extremely large population
3. No mutations
4. No natural selection
5. No gene flow (no immigration or emigration)
However, we do not mate randomly, our population is not infinitely large, there are mutations, natural
selection does take place, and gene flow is seen when individuals leave and enter countries. Therefore,
because these 5 principles are NOT met, then the population is NOT in Hardy-Weinberg Equilibrium and
is therefore evolving.
The Hardy-Weinberg Principle was expressed mathematically as p + q = 1 and p2 +2pq +q2 =1
(You don’t need to solve any math for the EOC exam)
Speciation
How do you know that a dog and a cat are different species? We use the definition below for biological
species concept to address this question.
Biological species concept:
1. The two species must be able to produce an offspring
2. If an offspring is produced, the offspring must be fertile (this means that it must be able to reproduce)
The horse and the donkey are different species, but they can produce a mule! (Don’t worry guys; use the
second part of the definition. Ask yourself, “Can the mule reproduce?” The mule is sterile and cannot
reproduce; therefore, the horse and donkey are different species.)
Brand new species may form through a process called speciation.
Reproductive isolation leads to speciation. There are three forms of reproductive isolations: behavioral
isolation, geographic isolation, and temporal isolation
Isolation means to be left alone (If you behave bad in class, I will isolate you from your friends,
muahaha). Anyway, some species of meadowlarks have developed as a result of behavioral isolation.
They perform different behaviors, such as mating songs. Even though the meadowlarks’ habitats
overlap, they will not mate with the other species of bird. Geographic isolation can be seen in two
species of squirrels that were separated geographically by mountains and rivers (this is in your book).
Temporal isolation happens when two or more species reproduce at different times. Your book uses the
example of different species of orchids that produce leaves at different times and must be pollinated
that same day.
HIV Evolution
HIV is a virus that destroys a person’s immune system.
Viruses may contain a DNA or RNA genome, but not both at the same time. HIV is an RNA virus.
Viruses are considered nonliving obligate intracellular parasite. They must get inside of a cell to
reproduce.
HIV is a perfect example of microevolution. The virus is error-prone. It makes a lot of mistakes when
copies of the virus are being made. These mistakes, or mutations, cause new HIV to form. These
mutations allow HIV to always be one step ahead of medications.
Viruses contain a protein coat to protect their genome.
HIV infects all cells that contain CD-4 Receptors. The majority of cells that contain CD-4 receptors are the
Helper T-cells (aka Helper T-lymphocytes)
The Fossil Record
Relative dating allows paleontologists (scientists that study
fossils) to determine whether a fossil is older or younger than
other fossils. Notice that relative dating does not tell us the
absolute age of the fossil. Relative dating can only compare
fossils. The fossils found deeper in the ground are older than the
fossils at the top.
Index fossils are distinctive fossils used to establish and compare the relative
ages of rock layers & the fossils they contain. In other words, we use index fossils
to determine if another fossil is older or younger. On the side is a picture of a
trilobite fossil. These fossils were present in the Paleozoic era. We can use this
fossil as an index fossil to compare other fossil’s ages.
Radiometric dating relies on radioactive isotopes, which decay, or break down, into stable isotopes at a
steady rate. Carbon dating is an example of radiometric dating that uses the radioactive isotope called
carbon-14 to determine the age of a fossil.
Carbon-14 will decay by half every 5,730 years. In other words, if you start with a 100% sample of
carbon-14 and wait 5,730 years, you will be left with 50% of carbon-14. If you wait another 5,730 years,
then you will have 25% of carbon-14….and so on. This life expectancy of carbon-14, which is reduced by
half every 5,730 years is called the half-life of carbon-14.
A half-life is the time required for HALF of the radioactive atoms to decay.
*Elements with long half-lives are used for dating older fossils.
Potassium-40 has a half-life of 1.26 billion years
Uranium-238 has a half-life of 4.5 billion years
The Origin of Life
All living things have cells. Cells are categorized as two types: prokaryotic cells and eukaryotic cells
The prokaryotes are believed to be the first types of cells, which eventually evolved to the eukaryotes.
Prokaryotes do not have a nucleus (pro – before; karyon – nucleus). Eukaryotes on the other hand do
have a nucleus (Eu – true; karyon – nucleus).
Bacteria and Archaea are prokaryotes (cells without a nucleus).
Animals, plants, fungi, and protists are eukaryotes (cells with a nucleus).
Eukaryotic cells contain organelles and are much larger cells than prokaryotes. However, some
organelles appear to be independent cells. The mitochondria and the chloroplasts are two organelles
different from all others.
The mitochondria and chloroplast contain their own DNA
and are very similar to bacteria cells. As a result, it is
hypothesized that mitochondria and chloroplast were
independent cells in the past, and it is believed that the
mitochondria and chloroplast were swallowed by a larger
cell. This resulted in a mutualistic relationship between
these present-day organelles and eukaryotic cells. This is
known as the endosymbiotic theory.
Stanley Miller and Harold Urey were two scientists trying to
replicate the conditions of early Earth. How could organic
compounds (the key ingredients to life) be formed from
inorganic compounds? They performed the experiment with
inorganic gases that are believed to have been in Earth’s early
atmosphere, such as water vapor, hydrogen gas, methane,
carbon monoxide, and ammonia. Adding electricity to the
experiment resulted in the formation of organic compounds.
Taxonomy
Taxonomy is the study of classification, and the father of taxonomy is Carolus Linnaeus.
People all over the world speak many different languages, and scientists use one language, Latin, to
communicate. Scientists classify organisms using two Latin names. The first name is called the genus
name and the second name is the species name.
Canis latrans (cayote)
Canis lupus (wolf)
Canis familiaris (dog)
Notice that the first name is capitalized; it is called the genus name (Canis); and it is the same for the
cayote, wolf, and dog. This indicates a relationship of common descent between the cayote, wolf, and
dog.
The species name (latrans, lupus, and familiaris) is lower-cased and is unique to each species.
The classification system used in taxonomy is the following:
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
(Genus and Species name are in RED color so you remember those are the names used to name
organisms)
Human and Chimp common ancestor
Phylogeny
Phylogeny or phylogenetics a branch in biology concerned with
evolutionary relationships between species.
Scientists build Darwinian trees (aka phylogenetic trees or
cladograms) based on DNA similarities common to each species.
Look at the phylogenetic tree on the right and notice the human
and the chimpanzee. Notice that evolution does not say that
chimps turned into humans. Evolution says that humans and
chimps share a common ancestor.
A clade is a group of species that includes a single common
ancestor and all descendents of that ancestor. Do you see the
blue arrow pointing to the common ancestor for the human and
the chimp? Well, that point, or node, forms a clade. Every point on the tree above that separates into
many species represents a clade. There are many clades in the phylogenetic tree.
This point, or node, represents a
common ancestor that evolved over
time into various groups that became
its descendents: lizards, turtles,
crocodiles, and birds. This point is
one clade. Every point represents a
clade, or a monophyletic group.
From the picture above notice that birds and crocodiles are more closely related than birds and turtles
because birds and crocodiles share a closer common ancestor.
Who is closer related, mammals and lizards or birds and lizards? To answer this question you need to
find the common ancestor point, or node. The birds and lizards are closer related because they share a
closer common ancestor than mammals and lizards.