Download Evidence of Evolution

Evidence of Evolution
Day 3
Evolution
1.
Theory - an accepted hypothesis that has been tested over and
over again without yet being disproved
2.
Definition - Evolution is the change in the overall genetic makeup
(allele frequency) of a population over time
3.
Three Basic Components
a. Individuals cannot evolve. Populations evolve.
b. Natural selection is the mechanism of ADAPTIVE evolution.
c. Evolution occurs by chance (NOT GOAL ORIENTED).
Interpreting the Evidence Supporting the
Theory of Evolution
 Homologies
• Anatomical
• Vestigial Organs
 Speciation
• Biogeography – Distribution of Living Species
 Fossil Record Evidence
 Comparative Embryology
• Ontogeny
• Phylogeny
 Molecular, Genetic and DNA Similarities
Homologies


Homologous structures are
similar structures occurring in
different species that are
believed to be derived from a
common ancestor.
Analogous structures are
similar structures occurring in
different species that are
believed to be the result of
convergent evolution.
Homologies

The forelimbs of all mammals, including humans,
cats, whales, and bats, show the same arrangement
of bones from the shoulder to the tips of the digits,
even though these appendages can have very
different functions – lifting, walking, swimming, and
flying.
Vestigial Organs
 A structure of
marginal, if any,
importance to an
organism.
• Vestigial organs are
historical remnants of
structures that had
important functions in
ancestors.
Geographic Distribution of
Living Species (Biogeography)

Because some animals on
different continents live
under similar ecological
conditions, they are
exposed to similar
pressures of natural
selection  thus evolve
similarly
•
Because of these similar
pressures, different animals
ended up evolving striking
features in common
Fossil Record Evidence
 The succession of forms observed in the fossil record is
consistent with other inferences about the major branches
of descent in the tree of life.
• Comparative data from biochemistry, molecular biology,
and cell biology suggest that prokaryotes are the
ancestors of all life and predict that prokaryotes should
precede all eukaryotic life in the fossil record.
• The oldest known fossils are prokaryotes…but why are there “missing
links” in the fossil record?
Similarities in Early Development:
Comparative Embryology
 Ontogeny:
embryonic
development process
of a certain species
 Phylogeny: A
species evolutionary
history
• The biogenetic law
states that ontogeny
in abbreviated form
reflects phylogeny.
Molecular
Homologies
The data show the same pattern of
evolutionary relationships that
researchers find when they
compare other proteins or assess
relationships based on nonmolecular methods, such as
skeletal anatomy.
Homologies mirror the taxonomic
hierarchy of the tree of life – the
Darwinian view of life predicts that
different kinds of homologies in a
group of organisms will all tend to
show the same branching pattern
through their evolutionary history.
Genetics & DNA Similarities

Systematists compare long
stretches of DNA and even
entire genomes to assess
relationships between
species.

If genes in two organisms
share many portions of
their nucleotide sequences,
it is highly likely that the
genes are homologous.
Summary of Darwin’s Theory
1.
2.
3.
4.
5.
6.
7.
Individual organisms in nature differ from one another and
some of this variation is inherited
Organisms in nature produce more offspring than can
survive – and many that survive do not reproduce
Members of each species must compete for resources
Individuals best suited to their environment survive and
reproduce most successfully – they pass their traits
onto their offspring
Species change over time – this is caused by natural
selection – new species arise and other species disappear
Species alive today have descended with modifications
from species that lived in the past
All organisms on Earth are united into a single tree of life
by common descent
Natural Selection
Day 4
Natural selection
is differential success
in reproduction
–That results from
the interaction
between individuals
that vary in heritable
traits and their
environment
Evolution & Genetics



Darwin had a disadvantage when he developed
his theory of evolution…he did not understand
the mechanisms of heredity.
Today, we understand how genes, heredity, and
evolution all tie together.
Single-Gene Traits vs. Polygenic Traits
Both lead to evolution, but polygenic traits (wide
variety of phenotypes possible) lead to a more
complex process of natural selection.
Three effects of selection on a
characteristic:



1. Directional Selection
2. Stabilizing Selection
3. Disruptive Selection
Directional Selection



When individuals at one end of the
population curve have higher fitness than
individuals in the middle or at either end of
the population curve.
Causes entire curve to move as character trait
changes
Ex:
beak size of Galapagos finches
peppered moths
 antibiotic
resistance
Section 16-2
Directional
Selection
Key
Directional Selection
Low mortality,
high fitness
Food becomes scarce.
High mortality,
low fitness
Stabilizing Selection



When individuals near the center of the curve
have higher fitness than individuals at either
end of the curve
Intermediate forms of a trait are favored and
alleles that specify extreme forms are
eliminated from a pop.
Counteracts the effects of mutation, gene flow,
and genetic drift – preserves the most common
phenotypes.
Ex. Weight of human babies at birth
Section 16-2
Stabilizing Selection
Stabilizing Selection
Key
Low mortality,
high fitness
High mortality,
low fitness
Birth Weight
Selection
against both
extremes keep
curve narrow
and in same
place.
Disruptive Selection

When individuals at the upper and lower ends
of the curve have higher fitness than
individuals near the middle.

Forms at both ends of the range of variation are
favored and intermediate forms are selected
against
– selection creates two, distinct phenotypes
Ex: Bird beak size – no middle sized seeds,
only large seeds and small seeds; thus, small
and large beaks are favored
Section 16-2
Disruptive Selection
Disruptive Selection
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two subgroups
specializing in
different seeds.
Beak Size
Number of Birds
in Population
Key
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size