Download File - Mr. Shanks` Class

Lesson # 4: Evolution
(On the Origins of Species +
Modern Theory of Evolution)
Review
Questions
What structure does this
picture represent?
Answer: Homologous Traits
What is an adaptation?
A) A test for natural selection
B) A physical or behavioral characteristic that has developed
to allow an organism to better survive in its environment
C) A by – product
D) A characteristics that has developed to limit the chances
of an organisms survival
Answer: B
Which theorist proposed the theory
of geological gradualism?
A)James Hutton
B)Georges Cuvier
C)Jean Baptist Lamarck
D)Charles Darwin
Answer: A
What represents a trait that once
served a purpose but is now
useless?
A)Homologous Trait
B)Analogous Trait
C)Duplication Mutation
D)Vestigial Trait
Answer: D
On the Origin of Species
(Theory of Evolution by Natural Selection)
Natural Selection
- The way in which nature favours the reproductive success of
some individuals within a population over others
- Some individuals would have a better chance of success than
others
- Ex. faster cheetahs would be more likely to catch prey,
stronger male lion would be more likely to defend and mate
with females
- If this were true and these differences were inherited, then
traits of favoured individuals would become more common in
the next generation and these individuals would produce
more offspring
- Key is to favour REPRODUCTIVE success
Herbert Spencer vs. Darwin
Survival of the Fittest
- A phrase that has been used to describe the process of natural selection
- This phrase can be misleading
- An individual that lives a long life or has a strong physical appearance may
be seen as physically “fit,”
- But if the individual is unable to reproduce and pass on genes to the next
generation according to Darwin’s theory such individual would not be “fit”
- As previously mentioned, natural selection lies in its ability to favour
reproductive success
Adaptation
- A characteristic or feature of a species that makes it well suited for survival
or reproduce success in its environment
- Theory of evolution by natural selection can be extended to virtually every
biological characteristic or adaptation
* Darwin understood that with a diversity of environments, the process of
natural selection acting over thousands of generations could produce an
unlimited variety of species *
Darwin’s Theories of Evolution
Prediction
- Theory of natural selection enables scientists to make
predictions about how species may change over time, for
example that species will evolve in response to climate
change because different environmental conditions will
favour different traits
Testing and Falsification
- To be a scientific theory it must have the potential to be
falsified and testable to have the possibility of being
proven wrong
Reconsidering the Galapagos
Islands
Summary
 Darwin’s theory of evolution by means of natural selection
explains how the environment acts to favour the reproductive
success of individuals with certain heritable traits over others
 Darwin’s theory of evolution by means of natural selection is
able to explain how an adaptation can arise
 Darwin’s theory of evolution by means of natural selection can
be used to make predictions about the future evolution of
species
 Darwin’s theory of evolution by means of natural selection is a
testable scientific theory
The Modern Theory of Evolution
The Age of Earth
- Until the twentieth C many believed Earth was less than 10,000 years old
and that species never changed they just had always been present
- Emerging sciences of paleontology and geology started to cast serious
doubt on the belief in a young earth
Paleontology
- The scientific investigation of prehistoric life through the study of fossils
Geology
- The science that deals with the earth’s physical structure and substance,
its history and the processes that act on it
Today’s evidence
- Scientific consensus that Earth is more than 4.5 billion years old and that
the universe is approximately 13 billion years old
- This evidence is largely a product of recent advances in technology and
understanding
Radiometric Dating
Radioisotopes
- Atoms that undergo radioactive decay - An atom with an
unstable nucleus that is capable of undergoing radioactive decay
- Paleontologists are able to use radioisotopes to obtain precise
estimates of the ages of rocks
- The nuclei of these atoms are unstable and release subatomic
particles changing from one form, the parent isotope into another,
the daughter isotope
Radiometric Dating
- Based on the ratio of parent isotopes in rock formations
- Radioisotopes undergo decay in a very precise way (half – life)
Half Life
- The length of time required for half the quantity of radioactive
substance to undergo decay… the half life is a constant for any
given isotope
- The time it takes for exactly 50 % of a parent isotope to decay
into a daughter isotope
The Modern Synthesis
 The knowledge and understanding of genetics and
other fields of biology have been combined with
Darwin’s theory of natural selection to form the
modern evolutionary synthesis
 Biologists define evolution as changes in the gene
pool of a species over time
Gene Pool
- The complete set of all alleles contained within a
species or population
- Individuals vary in their traits because they inherit
different combinations of alleles
- Natural selection acts to favour some genetic
combinations over others
Mutations: The Source of Variation
 Different individuals have different combinations of the many
alleles that are already present in the population
 Sexual reproduction recombines these alleles and produces an
almost unlimited number of combinations
 New or altered traits arise when new alleles and genes are
produced by mutation and acted upon by natural selection
Genetic Mutation
- Change in DNA
- The bases that make up DNA may be switched or lost, and / or
new bases may be inserted
 Mutation event can also result in an individual having duplicate
copies of genes
 Duplication events are usually the result of mismatches during
crossover in meiosis
Crossing Over
Crossing Over
- The exchange of chromosome segments
between homologous pairs during synapsis
- A misalignment of the chromosomes
during crossover causes an unequal
exchange – transferring a portion of one
chromosome to another and that
transferred portion is likely to contain
many genes
- Gametes that receive a chromosome that is
missing a section will have a low chance
of survival, while gametes that receive a
chromosome with duplicated genes are
often viable
Gene Duplication
 Gene duplication is an important type of mutation because it is
a source of a new genes
 The extra copy of the gene is free to mutate and may gain a new
function
 If a mutation in a gene results in a new protein that can no
longer perform a vital function, the organism may die (even if it
is beneficial in some other way)
 But might result in the creation of a new and potentially
beneficial protein
 The duplication and mutation of gene copies can result in entire
“families” of closely related genes
The Effects of Mutations
 Most mutations are neutral because they occur in non – coding portions of
DNA and therefore produce no visible change in an individual
Neutral Mutation
- A mutation that does not result in any selective advantage or disadvantage
- The environment does not favour or select against individuals with neutral
mutations
Beneficial Mutation
- Any mutation that increases that reproductive success of an organism
- Relatively rare but are favoured by natural selection and accumulate in
populations over time
Harmful Mutation
- Any mutation that reduces the reproductive success of an individual and is
therefore selected against
- May make an organism less able to resist disease or avoid predators, or
less efficient at obtaining food
- Less successful at reproductive success and tend to disappear
Mutation Rates
 Individual mutation rates are very difficult to estimate, but
recent studies suggest that species with large genomes are
likely to have mutations averaging more than one per
individual
 Humans may average 20 or more mutations per individual
(almost always neutral)
 Human population carries over 100 billion genetic mutations
 Relatively low for individuals but can be numerous in
population overall
Duplication Mutations
- Often neutral and so do not immediately benefit the
individual, but provide a source of new genetic material with
the potential to evolve into new genes
Homologous Genes and Pseudogenes
 Closely related species inherit homologous genes
 These genes inherited from a common ancestor mutate and
evolve over time
 Similarity between genes provides good evidence for the
degree of related species
 More closely related two species are, the more similar we
would expect their homologous genes to be
Pseudogenes
- A vestigial gene that no longer codes for a functioning protein
- Genes that have undergone mutations and no longer serve a
useful purpose
- Are found in virtually all species
- Ex. human dysfunctional copy of the GULO gene (necessary
for production of vitamin C, but we don’t need it because we
normally produce adequate amounts of this in our diet)
Modern Paleontology
 Distribution of fossils provided Darwin with important
evidence for his theory of evolution
Today’s evidence
- Human ancestors and primitive whales in Pakistan
- Feathered dinosaurs in China
- Fossils of dinosaurs in Canada
 Until the 1960s, the locations of some fossils were quite
puzzling, specifically when the discovery of fossils of the same
species in Africa, India and Antarctica (but nowhere else)
 Today the study of biogeography has been complemented by
great advances in the study of plate tectonics and continental
drift
Plate Tectonics
- The scientific theory that describes the large scale movements
and features of earth’s crust (accounts for many large surface
features i.e. mountains, volcanoes)
THE END!!