Transcript What is Evolution?

Evolution and the
Diversity of Life
Classification of Life
What is Evolution?
In the simplest biological terms
evolution is defined as change
over time. However, it is much
more than that.
Who was Charles Darwin
• Charles Darwin first published an
explanation of how species changed
over time, or evolved.
• Darwin argued that contemporary
species arose from ancestors
• Through a process of “descent with
modification,” with natural selection
as the mechanism.
How did he explain evolution?
• Natural Selection: Occurs in natural
populations when organisms with
certain traits pass those traits on to
the next generation.
• The following are required for natural
selection to take place.
1. Organisms can change over generations.
2. Individuals with certain heritable traits
produce more surviving offspring than
others.
3. The result of natural selection is
evolutionary adaptation.
Seahorse Camouflage
Natural Selection
• Natural selection is the
mechanism for evolution.
• It only acts on populations.
• It changes the frequency of
genes in a population –
not in an individual.
What traits are usually
selected?
• Traits that allow the organism to
survive and reproduce.
http://evolution.berkeley.edu/evolibrary/article//bergstrom_02
Peppered
Moth Example
• Originally White
• Now more black than white
• Causes
– Industrial Pollution
• Soot covered trees
– Industrial Melanism
http://www.amphi.com/~crobson/pepperMoths.swf
How does natural
selection happen?
Evolution only occurs when there is
a change in gene frequency within
a population over time.
Change Over Time
Evidence for evolution
The Evidence
Evidence of evolution comes from
wide range of areas.
1. Fossils
• In biological terms a fossil can be defined as
evidence of an organism that lived some
time in the past.
• Are often found in sedimentary rocks.
Fossils
The fossil record
• Is the ordered sequence
of fossils as they appear
in rock layers.
• Reveals the appearance
of organisms in a
historical sequence.
• Fits with other evidence
of evolution.
• Paleontologists study
fossils
Fossils
Fossils show a succession from
very simple forms early in the
fossil record to much more
complex forms that appear much
later in the fossil record.
Fossils
Fossils show
multiple
examples of
transitional
forms.
Fossils
Fossils and Geological Time
• Scientists will date the rocks in an
attempt to determine the age of the
fossil. Two ways to do this:
• Relative dating: When you compare
the depth of the layer of rock the fossil
was formed in relative to other layers
of rock.
• Radiometric dating: Uses
isotopes.
Fossils
Relative Dating
aka Law of Superposition
• Relative dating uses layers to determine
age by order of appearance.
• Relative dating will not give you a
specific age in years, just relative to the
layers above and below the fossil.
• Compare rock layers to layers of
clothing in your laundry hamper…Oldest
on the bottom (unless disturbed).
Fossils
Radiometric Dating
• Technique involves using radioactive
isotopes, which are atoms with unstable
nuclei that break down (decay) over
time, giving off radiation.
• Most fossils cannot be directly
radiometrically dated.
• Most dates are for volcanic or
igneous rocks, or metamorphic
rocks that are closely associated
with sedimentary rocks.
2. Biogeography
• Is the study of the geographic distribution of
species.
• First suggested to Darwin that today’s
organisms evolved from ancestral forms.
• Many examples from biogeography support
evolutionary theory.
Island Biogeography
• Theory of Island Biogeography
– Islands have fewer species than continents
– The smaller the island, the fewer the species
• Adaptive Radiation:
– The process that occurs when a species enters a new
habitat that has unoccupied niches and evolves into
a group of new species, each adapted to one of these
niches.
• Ecological Island:
– An area that is biologically isolated so that
a species occurring within the area rarely
mixes with any other population of the
same species.
Convergent and Divergent
Evolution
• Divergent
– Organisms with the same ancestral genetic heritage
migrate to different habitats and evolve into species
with different external forms and structures, but
continue to use the same type of habitats
• Ex) Ostrich
• Convergent
– The process by which species evolve in different
places of times and, although they have
different genetic heritages, develop similar
external forms and structures as a result of
adaptation to similar environments
• Ex) shapes of sharks
3. Comparative Anatomy
A. Homologous Structures –
structural features with a
common evolutionary origin –
shared by related species.
Although used for such different functions as throwing,
swimming, and flying, the same basic structural plan is evident in
them all. In each case, the bone shown in color is the radius.
Comparative Anatomy
B. Analogous Structures –
Structural features which serve the
same function in different
species, but they evolved
independently.
Example:
Butterfly wings, Bat wings
Bird wings
Comparative Anatomy
C. Vestigial Structures – Humans
have a vestigial tailbone. Vestigial toes
in the horse. Vestigial limbs in whales
and snakes.
3b. Structural Adaptations
A. Mimicry: A structural adaptation
that protects an organism by copying
the appearance of another species.
–
Example: Gopher snake
B. Camouflage – A structural
adaptation that allows an organism
to blend in with its environment.
–
Example: Snowshoe hare
Gopher Snakes?
The one on the left is a rattlesnake,
the one on the left is a gopher snake.
Showshoe Hare
Summer
Winter
4. Comparative Embryology
Embryology – Early embryos of
very different organisms closely
resemble each other.
5. Molecular biology
Biochemistry - The biochemistry
of a bat is much closer to that of a
whale, rather than a bird. Not
expected unless bat and whale
have a more recent common
ancestor than bat and bird, but
evolution predicts this.
5. Biochemistry
Vocabulary
The total number of genes present
in a population is called the gene
pool of that population.
Vocabulary
The frequency of an allele for a
specific trait is called the allelic
frequency.
Vocabulary
The genetic equilibrium of any
population is when the allelic
frequency if alleles remains the
same over time.
Microevolution as Change
in a Gene Pool
– Microevolution is defined as
• A generation-to-generation change in a
population’s frequencies of alleles.
– Hardy-Weinberg equilibrium
• Describes a non-evolving population that is
in genetic equilibrium.
• We will discuss this equilibrium in
more detail later.
Mechanisms of
Microevolution
The main causes of microevolution are
• Mutations.
• Genetic drift.
• Gene flow.
• Natural selection.
Ways to Change Genetic
Equilibrium
1. Mutation – Can be caused be
different factors, environmental
or random chance.
Ways to Change Genetic Equilibrium
2. Genetic Drift – Changes in allelic
frequencies due to chance events.
Ex: The founder effect
• Explains the relatively high frequency of
certain inherited disorders among some
populations.
Ex:The bottleneck effect
• Results from a drastic
reduction in population size.
• Usually results in a reduction in variation
Ways to Change Genetic
Equilibrium
3. Movement – Can be into or
out of the population. Also
referred to as gene flow.
Darwinian Fitness
• Is the contribution an individual makes to
the gene pool of the next generation relative
to the contributions of other individuals.
Natural Selection
• What about natural selection?
• There are 3 types
1. Stabilizing – Where the average
trait is selected for. This is often
mistaken for "no selection". A real-life
example is that of birth weight of
human babies.
Natural Selection
• Directional - one extreme trait of the
frequency distribution is favored, so the
distribution in the subsequent
generation is shifted from where it was
in the parental generation, towards that
of the favored trait. This is what is
usually thought of as natural selection.
A real-life example would be the
evolution of long bills in
woodpeckers.
Natural Selection
• Disruptive - both extreme traits are
favored at the expense of intermediate
varieties. For example very dark and
very light moths are selected over
medium shaded moths.
http://www.ibri.org/Books/Pun_Evolution/Chapter1/1.4.htm
Hardy Weinberg
Table 1. Frequencies of Alleles, Genotypes and
Appearances for Students in Class
Appearance & Genotype 
Frequencies (decimal)
W
w
W2
2Ww
w2
Table 2. Frequencies of Alleles/Genotypes
and Appearances for 4 Class Groups
Appearance & Genotype 
Group 1 Frequencies
Group 2 Frequencies
Group 3 Frequencies
Group 4 Frequencies
W
w
W2
2Ww
w2
The Hardy Weinberg
Formula
• Is a mathematical representation of a gene
pool.
• Adds up all of the genotypes in a population.
Alleles in a gene pool
• Occur in certain frequencies.
• Can be symbolized by p for the relative
frequency of the dominant allele in the
population and q for the frequency
of the recessive allele in the population.
Population Genetics and
Health Science
– The Hardy-Weinberg formula can be used
to calculate the percentage of a human
population that carries the allele for a
particular inherited disease.
Macroevolution and the
Diversity of Life
• Macroevolution encompasses the major
biological changes evident in the fossil record.
• Includes the formation of new species.
– How does this relate to microevolution?
Speciation
• The evolution of new species
is called speciation.
• Is the focal point of macroevolution.
• May occur based on two contrasting
patterns.
1. In nonbranching evolution, a population
transforms but does not create a new species.
2. In branching evolution, one or more new
species branch from a parent species that may
continue to exist.
What is a species???
What Is a Species?
– The biological species concept defines a
species as
• A population or group of populations whose
members have the potential to interbreed and
produce fertile offspring.
Galápagos Sea Lion
Galápagos Tortoise
How does speciation occur?
• Speciation occurs only when there are
reproductive barriers between the
isolated population and its parent
population.
1. Reproductive isolation
– When groups of individuals can
no longer mate and produce
fertile offspring.
2. Geographic isolation
– when a physical barrier divides a
population.
Mechanisms of Speciation
– A key event in the potential origin of a
species occurs when a population is
somehow severed from other populations
of the parent species.
– The two modes of speciation are
• Allopatric speciation.
• Sympatric speciation.
Allopatric Speciation
– Geologic processes
• Can fragment a population into two or more
isolated populations.
• Can contribute to allopatric speciation.
Grand Canyon
Galápagos Islands Overview
Galápagos Marine Iguana
Sympatric Speciation
– Sympatric speciation occurs if a genetic
change produces a reproductive
barrier between mutants and the parent
population.
• Polyploidy, a mechanism of sympatric
speciation, was first observed by Hugo de
Vries.
Punctuated Equilibrium
Is a contrasting model of evolution.
• States that species most often diverge in
spurts of relatively sudden change.
• Accounts for the relative rarity of transitional
fossils.
Where do living
things come from?
• One theory held in the past is referred
to as Spontaneous generation. This
theory held that nonliving material can
produce life.
• Fancesco Redi disproved this theory
with an experiment now known as the
Redi Experiment. This experiment
helped to disprove the spontaneous
generation of large organisms,
but not microorganisms.
Redi’s (1626-1697) Experiments
Evidence against spontaneous generation:
1. Unsealed – maggots on meat
2. Sealed – no maggots on meat
3. Gauze – few maggots on gauze, none on meat
The Origin of Life
• Likewise, Louis Pasteur designed
an experiment to disprove the
spontaneous generation of
microorganisms.
Louis Pasteur (1822-1895)
Pasteur's Problem
• Hypothesis: Microbes come from cells
of organisms on dust particles in the
air; not the air itself.
• Pasteur put broth into several special
S-shaped flasks
• Each flask was boiled and
placed at various locations
Pasteur's Experiment Step 1
• S-shaped Flask
• Filled with broth
• The special shaped was
intended to trap any
dust particles
containing bacteria
Pasteur's Experiment Step 2
• Flasks boiled
• Microbes Killed
Pasteur's Experiment Step 3
• Flask left at various
locations
• Did not turn cloudy
• Microbes not found
• Notice the dust that
collected in the neck of the
flask
Pasteur's Experimental Results
Question:
So what do Pasteur's experimental results
mean?
So what now?
The Theory of Biogenesis
• Pasteur’s S-shaped flask kept microbes
out but let air in.
• Proved microbes only come from other
microbes (life from life) - biogenesis
Figure 1.3
The Origin of Life
• Biogenesis – All living organisms
must come from other living
organisms.
• Simple Prokaryotic cells were
probably the first cells and over
time the would have evolved
into Eukaryotic cells.
Evidence for this is seen in
mitochondrial DNA.
Table 14.1
Mass Extinctions and
Explosive
Diversifications of Life
– The fossil record reveals an episodic
history,
• With long, relatively stable periods
punctuated by briefer intervals when the
turnover in species composition was much
more extensive.
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
– Extinction is inevitable in a changing world
and occurs all the time.
• However, extinction rates have not been
steady.
– Extinctions typically eliminate various
species of organisms
• And are followed by explosive
diversifications of organisms.
How many extinctions have happened?
Are we in an extinction now?
Classifying the Diversity
of Life
– Systematics
• Is the study of the diversity and
relationships of organisms, both past and
present.
– Taxonomy
• Is the identification, naming, and
classification of species.
Systems of Classification
• Classifying is a way of organizing information
• Classify = to put objects or ideas into groups on
the basis of similarity
• Taxonomist – scientists who
study classification
• Phylogony – evolutionary
history of an organism.
• Why have a system of naming?
– Local or common names of
species can be different
– Different languages name
species differently
Aristotle
first system of classification
• Two groups: All
organisms as plants or
animals
• Each animal according to
where it lived
– Land
– Water
– Air
• Each plant according to
– Size
– Structure
Carolus von Linneaus
mid-1700’s
• Determined levels
of classification
– He used similarities in structure to
determine relationships among
organisms.
• Binomial Nomenclature
• Two-word naming system
LATIN!
– Genus
• Noun, Capitalized,
Underlined
– species
• Descriptive, Lower Case,
Underlined
Hierarchical Classification
– The taxonomic hierarchy:
– Write them down from
largest (Domain) to
smallest
– Can you think of a
mnemonic device?
Write it down 
Classification and
Phylogeny
– The goal of classification is to reflect
phylogeny, the evolutionary history of
a species.
Sorting Homology from
Analogy
– Homologous structures
• What are they?
• Are one of the best sources of information
about phylogenetic relationships.
– Convergent evolution
• Involves superficially similar structures in
unrelated organisms based on natural
selection.
– Analogy
• Is similarity due to convergence.
Molecular Biology as a
Tool in Systematics
– Molecular systematics
• Compares DNA and amino acid sequences
between organisms.
• Can reveal evolutionary relationships.
The Cladistic Revolution
– Cladistics
• Is the scientific search for clades,
• Clades are distinctive branches in the
history of life.
– Cladistics
• Has ______________ traditional
classification of some organisms.
Arranging Life into
Kingdoms:
A Work in Progress
– Linnaeus designed a two-kingdom system
of classification,
• Which was replaced by a five-kingdom system
in the mid-20th century.
• Now we use a six-kingdom system,
which may change again!
Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings
– In the late 20th century,
• Molecular studies and cladistics led to the
development of a three-domain system.
Classification Schemes
Tools!
• Dichotomous Key: Allows people
to identify organisms in the real
world based on a series of two
choices at each step.
Identify This Tree
http://www.uwsp.edu/cnr/leaf/Treekey/tkframe.htm
Dichotomous Key Activity!
• Are you ready to try this in more
detail?