Ch. 5
Evolution
APES
I. Origins of Life
• How do we know?
• Chemical analysis: chemists have
conducted lab experiments to show how
simple organic compounds could have
been created.
• Radioactive dating: radiocarbon,
radiometric dating with radioactive rocks
and fossils
H2O
CH4
Water vapor
CO2
N2
NH3
Electrode
H2
Electrical sparks
simulating lighting
provide energy to
synthesize organic
compounds
Condenser
Cold water
Cooled water
containing organic
compounds
H2O
Sample for
chemical
analysis
Fig. 5.3, p. 104
Life evolved in two phases over the
course of 4.7-4.8 billion years
• Chemical evolution of organic
molecules and polymers
• Biological evolution from single celled
prokaryotic bacteria to multi-cellular
eukaryotic organisms
Chemical Evolution
• Formation of the Earth’s Crust: 4.6 to 4.7
billion years ago a cloud of cosmic dust
condensed into planet earth which
soon turned molten due to radioactive
decay and meteorite impacts. As
cooling took place a thin crust
developed.
• Formation of the earth’s seas: volcanic
eruptions and comet impacts brought
water vapor that rained down on earth
to create the sea
Chemical Evolution (cont.)
• Small organic molecules form in the seas:
from eroded minerals from rocks
• 4.4 billion years ago the first atmosphere
was formed. The main components were
believed to be: CO2, N2,H2O , CH4, NH3,
H2S, HCL, no oxygen
• This mixture is often to as: The
primordial stew or soup theory.
Chemical Evolution (cont.)
• Large organic molecules form in the seas:
energy from lightening, heat from
volcanoes, and UV light and the
chemicals in the atmosphere combined
to form the first large organic molecules
such as amino acids and carbs.
• Another theory is that these large
molecules formed in hydrothermal vents.
• First protocells form in the seas: these new
compounds washed into the seas and
sat for millions of years to form the first
DNA and protocells
Chemical Evolution
(1 billion years)
Formation
of the
earth’s
early
crust and
atmosphere
Small
organic
molecules
form in
the seas
Large
organic
molecules
(biopolymers)
form in
the seas
First
protocells
form in
the seas
Biological Evolution
(3.7 billion years)
Single-cell
prokaryotes
form in
the seas
Single-cell
eukaryotes
form in
the seas
Variety of
multicellular
organisms
form, first
in the seas
and later
on land
Fig. 5.2, p. 103
Biological Evolution
• 3.5 to 3.8 billion years ago, well below the surface of the sea
away from harmful UV radiation the first prokaryotic cells
formed: PROKARYOTIC
• 2.3 to 2.5 billion years ago the first cyanobacteria appear and
they: photosynthesize
• 2.0-2.1 billion years ago oxygen: formed from cyanobacteria
• 1.2 billion years ago we see the first eukaryotic cells arrive,
which could reproduce sexually and produce a wide variety
of organisms
• 400-500 million years ago we see: the first land plants and
animals
• How do we know what organisms were around:
– Fossil record
– Radiometric dating of rocks near the fossils
Modern humans (Homo sapiens) appear
about 2 seconds before midnight
Age of
reptiles
Insects and
amphibians
invade the land
Age of
mammals
Recorded human history begins 1/4
second before midnight
Origin of life (3.6–3.8 billion years ago)
Plants
invade the
land
Fossils
become
abundant
Fossils
present
but rare
Evolution and
expansion of life
Fig. 5.4, p. 105
Evolution
•
•
•
Heritable changes in a population’s
genetic make-up through successive
generations
An overwhelming majority of biologists
believe that this is the best
explanation for the changes that
have occurred over the last 3.7 billion
years and also for why life on earth
today is so diverse.
The theory of evolution is based on the
idea that all species descended from
other species http://www.hippocam
pus.org/Biology
1st generation
2nd Generation
GG, Gg = green beetle
gg = brown beetle
Evolution= shift in gene frequency in a population
Macroevolution
•
long term, large
scale
evolutionary
changes
among a group
or species. One
species leads to
the
appearance of
many other
species.
Genetic persistence:
• The inheritance of DNA molecules
from the origin of the first cells
through all subsequent lines of
descent which is the basis of the
unity of life
Genetic divergence
• Long term changes in lineage’s of
species, which are the basis of the
diversity of life
Genetic losses
• The steady background extinction
or relatively abrupt catastrophic
loss of lineage
• Microevolution: the small genetic
changes that a population
experiences
• How does microevolution work?
• It is the development of genetic
variability in a population
• A population’s gene pool is the
sum total of all genes possessed
by the individuals of the
population’s species
• Microevolution
is a change in
the species
gene pool over
time
•
Members of a
population have
different molecular
forms of the same
gene called alleles.
Sexual reproduction
leads to a shuffling
of alleles. As a result
each individual has
a different
combination of
alleles. This is called
genetic variability
• Microevolution works through a
combination of four processes:
every
• Mutation, natural selection, gene
flow, genetic drift
Mutation:
• The source for all new alleles (genes) is
mutations, which are random changes in the
structure of DNA molecules in a cell.
• Adaptation: any genetically controlled trait that
helps an organism survive and reproduce under
a given set of environmental conditions
• Every so often a mutation is beneficial and the
result is a new genetic trait that will ensure the
survival of offspring better
• Mutations are rare
Natural Selection
• Differential reproduction: because of
random shuffling or recombination of genes,
certain individuals may by chance have one
or more beneficial adaptations that allow
them to survive under various environmental
conditions. As a result they are more likely to
reproduce than individuals that do not have
such adaptations.
• Natural selection does not create
favorable genes; instead it favors some
individuals over others by acting on
genes already in the gene pool.
• Natural selection occurs when the
combined effects of adaptation and
differential reproduction result in a
particular beneficial gene becoming
more common in succeeding
generations
Three types of Natural Selection:
• Directional: it pays to be different:
changing environmental
conditions cause gene frequencies
to shift so that individuals with traits
at one end of the normal range
become more common than
midrange species
Snail coloration
best adapted
to conditions
Average
Natural
selection
Number of individuals
Number of individuals
Directional Natural Selection
New average
Coloration of snails
Previous
average
Average shifts
Coloration of snails
Proportion of light-colored
snails in population increases
Fig. 5.6a, p. 110
• Stabilizing: it pays to be average:
in a stable environment species
that have abnormal genes have
no advantage and tend to be
eliminated.
Light snails
eliminated
Dark snails
eliminated
Natural
selection
Number of individuals
Number of individuals
Stabilizing Natural Selection
Snails with
extreme
coloration are
eliminated
Coloration of snails
Coloration of snails
Average remains the same,
but the number of individuals with
intermediate coloration increases
Fig. 5.6b, p. 110
• Diversifying: it doesn’t pay to be
normal: when environmental
conditions favor individuals at both
extremes of the genetic spectrum
and sharply reduce the number of
mid-range individuals.
Intermediate-colored snails
are selected against
Light
coloration
is favored
Dark
coloration
is favored
Natural
selection
Number of individuals
Number of individuals
Diversifying Natural Selection
Snails with light and dark
colors dominate
Coloration of snails
Coloration of snails
Number of individuals
with light and dark coloration
increases, and the number with
intermediate coloration decreases
Fig. 5.6c, p. 110
Gene Flow:
Movement of
genes between
populations
Genetic drift:
•
involves change
in a genetic
composition of
a population by
chance and is
important in
small
populations
Co evolution
• When populations of two
different species interact over a
long time, changes in the gene
pool of one species can lead to
changes in the gene pool of the
other species. For example:
An Example of evolution by
natural selection:
The peppered moths of England
During the industrial revolution.
http://www.echalk.co.uk/Science/Bi
ology/PepperedMoth/Peppered_
MothWEB.swf
Coevolution
Coevolution can occur
between animals that have a
symbiotic relationship as well
those who have a predator
prey relationship
Coevolution
gone awry
Ecological Niches and
Adaptation
Ecological niche: the species way of life
or the functional role of the species in
an ecosystem. For example:
• a. types of resources used
• b. range of tolerance
• c. how it interacts with components of
the ecosystem
• d. its role in flow of energy and matter
cycling
Fundamental vs realized niche
• Fundamental niche vs. realize
niche: Your fundamental niche is
all the possible conditions that
you can live under. Your realized
niche is how you are actually
living. For example: you may be
capable being a star, but
competition keeps you from
getting the job
Number of individuals
Niche
separation
Generalist species
with a narrow niche
Niche
breadth
Generalist species
with a broad niche
Region of
niche overlap
Resource use
Fig. 5.7, p. 111
Generalist species vs. Specialist
species
Generalist: have very broad niches and
eat a variety of foods and can live in
a variety of places under differing
conditions. For example cockroach
Specialist: narrow niche, may only be
able to live in one type of habitat or
eat only one type of food. For
example: panda bear
–
Is it better to be a generalist or a
specialist?
Speciation
• Two species arise from one species in
response to changes in environmental
conditions.
• The mechanism for speciation occurs in two
phases
– Geographic isolation: occurs when two
populations of a species becomes
physically separated for long periods
– Reproductive isolation: occurs as mutation
and natural selection occur independently
in two separated populations of the same
species. Eventually, the changes are so
great that two groups will no longer
interbreed.
Northern
population
Arctic Fox
Early fox
population
Spreads
northward
and
southward
and
separates
Adapted to cold
through heavier
fur, short ears,
short legs, short
nose. White fur
matches snow
for camouflage.
Different environmental
conditions lead to different
selective pressures and evolution
into two different species.
Southern
population
Gray Fox
Adapted to heat
through lightweight
fur and long ears,
legs, and nose, which
give off more heat.
Fig. 5.8, p. 113
Convergent evolution:
• Two separate species
will evolve separately to
create animals with
similar characteristics.
Species that have
similar niches tend to
evolve similar sets of
traits in response similar
environmental
conditions. For example:
Divergent evolution: speciation
creates separate species
Extinction
•
•
•
•
•
•
When environmental changes occur species either
evolve or cease to exist and their genetic material is
permanently lost.
Extinction patterns have been caused by large-scale
movements of the continents and gradual climate
changes like those from meteors and volcanoes.
All species inevitably disappear
Background extinction is the low rate that species
constantly disappear. It is the normal level. Approx.
3 species per year
Mass extinction: an abrupt rise in extinction rates above
the background rate. It is catastrophic, global and often
results in 25% to 70% loss of species
There are have been five previous mass extinctions and
we are currently in the six mass extinction, which is
being caused by humans.
– Speciation minus extinction equals biodiversity
– Although extinction is a natural process,
humans have sped up the process and we
have lost a lot of genetic material
– This mass extinction is different from previous
extinctions in the following ways:
– 1. First time it has ever been caused by one
species
– 2. This is the fastest it has every happened
– 3. Adaptive Radiation will be slow after
because we are destroying habitats
Cenozoic
Era
Period
Millions of
years ago
Quaternary
Today
Bar width represents relative
number of living species
Extinction
Tertiary
65
Extinction
Mesozoic
Cretaceous
Current extinction crisis caused
by human activities. Many species
are expected to become extinct
within the next 50–100 years.
Cretaceous: up to 80% of ruling
reptiles (dinosaurs); many marine
species including many
foraminiferans and mollusks.
Jurassic
180
Extinction
Triassic: 35% of animal families, including
many reptiles and marine mollusks.
Triassic
250
Extinction
Permian
Carboniferous
Paleozoic
Species and families experiencing
mass extinction
345
Permian: 90% of animal families, including
over 95% of marine species; many trees,
amphibians, most bryozoans and
brachiopods, all trilobites.
Extinction
Devonian: 30% of animal families,
including agnathan and placoderm
fishes and many trilobites.
Extinction
Ordovician: 50% of
animal families,
including many
trilobites
Devonian
Silurian
Ordovician
500
Cambrian
Fig. 5.10, p. 115
Adaptive Radiation
• Adaptive radiation: an extinction of one
species is an opportunity for another
species and after a mass extinction there
is a period in which numerous new
species can evolve
• Speciation and extinction affects
biodiversity:
Mesozoic
Cenozoic
Marsupials
(kangaroos, etc.)
Rabbits
Rodents
Primates
Bats
Insectivores
Carnivores
Whales
Even-toed
hoofed mammals
Odd-toed
hoofed mammals
Elephants
Monotremes
(platypus, etc.)
Fig. 5.11, p. 116
How does Macroevolution
occur?
A. Macroevolution is concerned with how evolution takes
place above the level of species and over long
periods of time and shows how small changes can
lead to the eventual creation of many different
species, genera and families.
B. Gradualist model: theory that says macro evolutionary
change occurs over many millions of years
C. Punctuated Equilibrium: opposing theory that says
there are long periods of relatively punctuated with
brief periods of very rapid changes.
•
D. In reality it is probably a combination of
both
Common Misconceptions about
Evolution
• “Survival of the fittest” is often misinterpreted
as “survival of the strongest”. In biological
terms fitness is a measure of reproductive
success and the ones with the most
descendants are the fittest. Natural selection
is not "tooth and claw” competition.
• “Humans evolved from apes”, this is not true.
Apes and humans have a common ancestor
from which both are descended.
• Nature has a grand plan in which species
become progressively more perfect, natural
selection is random and there is no goal of
perfection.
• 1) Before 5 mya: In Africa, our ancestral lineage and the chimpanzee
lineage split.
• 2) Before 4 mya: The hominid Australopithecus anamensis walked
around what is now Kenya on its hind legs.
• 3) >3 mya: Australopithecus afarensis (“Lucy”) lived in Africa.
• 4) 2.5 mya: Some hominids made tools by chipping stones to form a
cutting edge. There were perhaps four or more species of hominid
living in Africa.
• 5) 2 mya: The first members of the Homo clade, with their relatively
large brains, lived in Africa
• 6) 1.5 mya: Hand axes were used. Also, hominids had spread out of
Africa and into much of Asia and Europe. These hominids included
the ancestors of Neanderthals (Homo neanderthalensis) in Europe
and Homo erectus in Asia.
• 7) 100,000 years ago: Human brains reached more or less the current
range of sizes. Early Homo sapiens lived in Africa. At the same time,
Homo neanderthalensis and Homo erectus lived in other parts of the
Old World.
• 8) 50,000 years ago: Human cultures produced cave paintings and
body adornment, and constructed elaborate burials. Also, some
groups of modern humans extended their range beyond Africa.
• 9) 25,000 years ago: Other Homo species had gone extinct, leaving
only modern humans, Homo sapiens, spread throughout the Old