CHAPTER 22


Carl Linnaeus (1707-1778) –
founder of taxonomy (scientific
name) grouped similar species into
same genus
Georges Cuvier (1769-1832) –
catastrophism – different species
in layered rock due to catastrophic
events like floods



James Hutton (1726-1797) –
gradualism – profound change is a
cumulative product of slow but
continuous process; ex. Rivers
making canyons
Charles Lyell (1797-1875) –
uniformitarianism – geological
process have not changed
throughout Earth’s history
Jean Baptiste Lamarck (17441829)- thought acquired
characteristics can be passes on
to offspring



Worked on the HMS Beagle in 1830’s
Observed and collected thousands of
different species
Galapagos Islands (west of S.
America) most interesting
“The Galápagos tortoise (or Galápagos giant tortoise), is the
largest living tortoise, endemic to nine islands of the Galápagos
archipelago. Adults of large subspecies can weigh over 300
kilograms (660lb) and measure 1.2 meters (4 ft) long. Although the
maximum life expectancy of a wild tortoise is unknown, the average
life expectancy is estimated to be 150-200 years.”
Source: en.wikipedia.org/wiki/Gal%C3%A1pagos_tortoise



Darwin read Lyell’s Principles of
Geology and felt age of earth was
much older than previously thought
1844 Darwin wrote essay on the origin
of species
1858 – Alfred Wallace sends
manuscript to Darwin about Natural
Selection


Lyell presented Wallace’s paper as
well as Darwin’s 1844 essay to
scientists
1859 The Origin of Species published
by Darwin
 Descent with modification
 Natural selection (the mechanism)




Individuals vary within a population
Traits inherited
All species are capable of
overproduction
Many offspring do not survive


Individuals with inherited traits
that give them a better chance of
surviving and reproducing tend to
leave more offspring than those
without those traits
Unequal ability of individuals to
survive will lead to favorable traits
in populations over generations.



A population evolves, not an
individual!
Acquired characteristics may be
adaptable but are not inherited!**
The environment does not create
a best fit characteristic, but
selects for it!
Goldendoodle and a
liger
AP:April. 29, 2005
ST. THOMAS, Barbados - It's male. But what is
it? A zonkey? A deebra? That's the debate in
Barbados since a zebra gave birth to a foal sired by a
donkey.



Biogeography – geographical
distribution of species
 Ex. Islands with similar species to
mainland
Fossil record – transitional forms
Comparative Anatomy – homologous
structures among different organisms
Vestigial organs –marginal, if any
importance, remnants of
structures that once served a
function
 Whale pelvis and leg bones and
human appendix
Comparative Embryology – most
vertebrates share common early
development (gill slits)
Molecular Biology – similar overall
DNA, similar proteins (ex.
Cytochrome c)



Chapter 23

Genetic variation that makes evolution
possible
 Mutations
 Change in DNA sequences
 Average 1 in 100,000 genes per
generation
 Sexual reproduction
 Crossing over
 Independent assortment
 Fertilization





Population – localized group of individuals
belonging to the same species
Species – organisms that can interbreed and
produce fertile offspring
Gene pool – total genes in a population
If all members of a population are
homozygous for the same allele, that allele is
fixed.
Gene frequency - two or more alleles for a
gene, each having a relative frequency
(proportion) in the gene pool


Example:
 A = pink
 a = white
 1000 plants = 200 white + 800 pink
 800 pink = 340(AA) + 460(Aa)
Find A’s frequency
 From AA: 340 x 2 = 680
 From Aa: 460 x 1 = 460
 680 + 460 = 1140
 1140/2000 = .57 = .6
 The 2000 is total number of alleles for
1000 plants


Find a’s frequency
 From aa: 200 x 2 = 400
 From Aa: 460 x 1 = 460
 400 + 460 = 860
 860/2000 = .43 = .4
Find A’s frequency
 1- .4 = .6

Frequencies of alleles and
genotypes in a population’s gene pool
remain constant over the
generations unless acted upon by
agents other than random sexual
recombination
 Hardy-Weinberg
tells us
what to expect if a
population is NOT
evolving!!
Random Gamete production



Probability of picking 2 A from
example
 .6 x .6 = .36
Probability of picking 2 a from
example
 .4 x .4 = .16
Probability of picking Aa from
example (aA or Aa)
 (.4 x .6) + (.6 x .4 ) = .48



The sexual process of meiosis and random
fertilization maintain the same allele and
genotype frequencies over generations.
In the example:
 p = .6 = A
 q = .4 = a
p+q=1
 p = 1 - q and q = 1 - p
p2 + 2pq + q2 =
(AA)+ (2Aa) + (aa) =
1
1
1. Very large population size
2. No gene flow (genes entering or
leaving a population)
3. No net mutations
4. Random mating
5. No natural selection
These mean NO EVOLUTION!

Microevolution – generational change in
a population’s frequencies of alleles or
genotypes
1. Genetic Drift – rapid changes in a gene
pool of a small, isolated population due
to chance
 Flip coin 10 times: may get 7 heads
and 3 tails
 Flip coin 1000 times: unlikely to get
700 head and 300 tails
a. Bottleneck Effect – genetic makeup of
a small surviving population is unlikely
to be representative of original
population
 Northern elephant seals nearly
extinct due to hunting in late 1890’s
which caused little genetic variation
at 24 different loci
b.The Founder Effect – occurs when a
few individuals colonize a new habitat;
the smaller the sample size, the less
the genetic makeup of the colonists
will represent the gene pool of the
large population they left
2. Gene Flow – a population may gain or
lose alleles through genetic exchange
due to immigration and/or emigration
 Example: wind blowing pollen
3. Mutations- change in an organism’s
DNA
 For any one gene locus, mutation
does not have much effect on
population unless mutation is a
benefit and allows for more
offspring
 Example: bacteria resistant to
antibiotics

Mutations – can only be passed on to
offspring when they occur in cells that
produce gametes
 On rare occasions, a mutant allele may
be beneficial
 Ex. Houseflies resistant to DDT
 A single bacterium can make a billion
cells in 10 hours so mutations can
change whole populations quickly.
4. Nonrandom mating – individuals
choosing mates
 Inbreeding – mating between
closely related partners (extreme
example is self-fertilization)
 Increases homozygous offspring,
decreases heterozygous
offspring
 Assortive mating – individuals
select partners like themselves
5. Natural Selection – populations consist
of varied individuals and some of these
variants leave more offspring then others
 White flowers easily seen by
herbivorous insects so more pink
survive to make more pink plants
 Of all the agents of microevolution
that change gene pools, only natural
selection is likely to adapt a
population to its environment.

Neutral Variation – variation that
appears to have no selective advantage
 Example: fingerprints



Natural selection is the mechanism for adaptive
evolution.
Darwinian fitness – the relative contribution that
an individual makes to the gene pool of the next
generation
Relative fitness – the contribution of a genotype
to the next generation compared to other
alternative genotypes for same locus
 The highest relative fitness a genotype can have
is 1
 If plants with white flowers average 80% as
many offspring as pink flowered plants, their
relative fitness is 0.8

Stabilizing selection– acts against
both of the extreme phenotypes and
favors intermediates
 Examples:
 human birth weight in 3-4Kg
range
 horseshoe crab

Directional selection– shifts towards
one extreme phenotype (often during
periods of environmental change)
 Examples:
 bacteria resistant to antibiotics
 light vs. dark moths in England

Diversifying (disruptive) selection – when
environmental conditions favors both
extremes of a phenotypic range
 Examples:
 finch population with 2 bill sizes
 butterfly with 2 distinct morphs


Sexual dimorphism – distinction
between the secondary
characteristics of male and females
Sexual selection – selection process
leading to sexual dimorphism


Recessive alleles persist in environment
due to heterozygotes
The rarer a recessive allele, the greater
degree of protection a hybrid offers
(especially if recessive allele is harmful)


Heterozygote advantage – when a
heterozygote has greater survivorship
and reproductive success than any
homozygote
 Example: those who are carriers for
sickle cell anemia are resistant to
malaria
Inbreeding can cause excessive
homozygous conditions

Frequency-dependent selection – the
reproductive success of any one morph
declines if that phenotypic form
becomes too common
 Female African swallowtail
butterflies mimic several noxious
species
 This would be less effective if only
one species was imitated.
 Right and left mouthed fish (cichlids)
have different shaped mouths for
approaching prey and eating scales
Chapter 24
Macroevolution – the origin of
new taxonomic groups
 Speciation – the origin of new
species
 How does one species split into
two?????


Species - population(s) whose
members interbreed in nature
and produce fertile offspring
The biological species concept is based on interfertility rather than physical similarity
Barriers that prevent different
species from interbreeding:

Reproductive isolation – barriers
that prevent two species from
producing viable, fertile offspring
1. Prezygotic – impede mating
between species by hindering the
fertilization of ova
2. Postzygotic – impede mating
between species by preventing the
zygote from developing into a
viable, fertile adult
a.
b.
Habitat Isolation – living in
different habitats within same
area
• Example: snakes in water vs. land
Behavioral Isolation – special
signals to attract mates (probably
most important barrier)
• Example: fireflies using
different blinking signals
c.
Temporal Isolation – breeding during different
seasons or years
•
d.
Example: skunks mating in summer vs. late
winter
Mechanical Isolation – cannot mate due to
anatomical differences
•
Example: flowers with different
structures for different pollinators
Gametic Isolation – gametes unable to fuse
together to make zygote
e.
•
Example: sperm not surviving vaginal
environment
a.
Reduced Hybrid Viability – zygotes/embryos
aborted (miscarriage)
•
b.
•
Example: frogs (Ranus)
Reduced Hybrid Fertility – offspring end up
being mostly sterile
Example: horses mating with donkeys to
make sterile mules
Hybrid Breakdown – offspring are fertile, but
next generation is sterile
c.
•
Example: cotton
Extinct organisms
 Asexual organisms
 Too rigid: dogs and coyotes
 Gene flow through subspecies

Morphological – physical features
 Recognition – mating adaptations
 Cohesion –phenotype (genes and
adaptations)
 Ecological – live and do (niches)
 Evolutionary – sequence of
ancestral and descendant
populations

1.
2.
Allopatric – a geographic
barrier isolates populations
blocking gene flow
Sympatric – intrinsic factors
alter gene flow (like nonrandom
mating)

Geographical barriers – mountains
forming, canyons forming, climate
changing land
Example: pupfishes (Cyprinodon)
in springs of Death Valley CA and
OR (drying caused separated
“pools” in which speciation
occurred)
Peripheral isolate already
different from original
population (ex. phenotypic
extremes)
 Genetic drift at work
because smaller population
size
 Different natural selection in
new environment


Mate choice in two species of Lake Victoria cichlids: females
chose mates that have same color as themselves. Under
monochromatic light, females chose both colors equally
because they look the same. (Nonrandom mating causes
sympatric speciation)

Adaptive divergence – when
2 populations adapt to
different environments, they
accumulate differences in
their gene pools
 Reproductive barriers may
evolve coincidentally causing
the populations to
differentiate into 2 species
Two populations get back together
and interbreed = no new species
 Two populations get back together
and do not interbreed = 2 new
species
 Hybrid Zone = where 2 populations
get back together and interbreed to
make hybrids only around the region
where they overlap

Alleles specific to yellow-bellied toads decrease from
100% in areas where only they are found, to 50% in
hybrid area, to almost 0% in fire-bellied area.


Speciation can occur rapidly or slowly and
can result from changes in few or many
genes
Punctuated equilibrium – describes periods
of apparent stasis “punctuated” by sudden
change
CHAPTER 25


Life originated between 3.5 and 4
billion years ago
 Stromatolites – fossilized mats
that contain banded domes of
sedimentary rock (3.5 bya) and
contain prokaryotes
Oldest rocks are 3.9 billion
(Greenland)

To produce simple cells via chemical/physical
processes and natural selection:
1. Abiotic synthesis of small organic
molecules (ex. amino acids)
2. Joining of smaller molecules into
macromolecules (ex. proteins)
3. Packaging macromolecules into protobionts
where internal and external environments
are different
4. Origin of self-replicating molecules that
lead to inheritance





A.I. Oparin and J.B.S. Haldane (1920’s) –
early atmosphere of earth favored chemical
reactions that could produce organic
compounds
Low oxygen = a reducing (electron adding)
atmosphere
Energy from lightning and higher UV radiation
needed to make bonds
Stanley Miller and Harold Urey (1953) –
made amino acids from H20, CH4, NH3, H2 and
electricity
Now we wonder where this occurred –
atmosphere or deep sea vents?

Proteinoids – proteins formed from
abiotic means (no enzymes)
 Need a substratum like hot sand,
clay, or rock
 Vaporization would concentrate
monomers on substratum
 Metals in substratum act as
catalysts to bind monomers
together


Aggregates of abiotically produced
molecules
Not capable of precise
reproduction, but maintain different
internal conditions than external
environment
 Liposomes – found to form
spontaneously and are made of
lipids
 Can have membrane potential and
undergo osmotic pressure


When a RNA strand is added to a solution
of RNA nucleotides, small sequences can be
made using strand as template and base
pairing
Thomas Cech (1980s) found ribozyme
(enzyme that is not a protein) which
catalyzes RNA synthesis




RNA can make a variety of shapes
due to different sequences
This could lead to natural selection
of certain shapes (sequences)
Weak binding of amino acids to
strand of RNA allows protein to be
made (this happens today in
rRNA/protein interactions)
Packaging of RNA genes and their
products within a membrane a great
milestone!




Laboratory experiments prove that life
could have evolved in the “primordial
soup”, but cannot prove that it did.
First bacteria able to survive extreme
heat so life could have evolved near
deep sea vents and volcanoes
Extraterrestrial source?
Line between protobionts and live cells
blurry

Radiometric dating – absolute dating
 Half-life – the amount of time that it
takes for 50% of the original sample to
decay
 Carbon-14 has a half life of 5,730 years
so its used for younger fossils
 Uranium-238 has a half-life is 4.5 billion
years so its used for older fossils
 Not temperature sensitive


Earth is approximately 4,600,000,000
years old
Precambrian – (4.6 bya to 542 mya)
 Only bacteria for a billion years
 Towards end of era there were some
eukaryotes which included algae and softbodied invertebrates (some multicellular)
 Gradual increase of oxygen caused by
photosynthetic bacteria (2.7 – 2.2 bya)
 Oxygen revolution followed with great
increase in O2. Why? Maybe
chloroplasts???


Larger prokaryotes engulfed smaller
prokaryotes (ancestor of mitochondria and
chloroplasts) for origin of eukaryotes
Evidence for endosymbiosis
 Inner membranes of both organelles have
ETC like prokaryotes
 Both organelles replicate like binary fission,
have ribosomes, and circular DNA like
prokaryotes
 Many genes move to nucleus (transposons)
 Eukaryote genome “chimera” like – mixture of
prokaryotic genes and cell parts

Paleozoic – (542 – 245 mya)
 Cambrian explosion of animals
 Mostly marine life
 Colonization of land by plants and
later animals
 First amphibians, reptiles and
insects
 Shallow seas
 Extinction of marine life at end
 Pangaea formed at end


Mesozoic – (245 – 65 mya)
 Flowering plants appear
 Pangaea breaks up
 Small mammals appear
 Extinction of dinosaurs as well as
many other organisms (65mya)
Cenozoic – (65 mya – present)
 Major radiation of mammals
 Humans appear 500,000 years ago

Long periods of slow change
punctuated by briefer intervals when
turnover of species was extensive
 Mass extinctions
 Explosive adaptive radiation
 Survivors became adapted to vacant
niches left by extinctions


Examples: dozen or more in fossil
record
Two most studied
 Permian Extinctions (end of
Paleozoic)
 Cretaceous Extinctions (end of
Mesozoic)



Claimed 90% of marine life
Occurred in less than 5 million years
Possible causes:
 Pangaea forming, Siberian volcanoes
caused global warming, reduced
temperature differences causing low
O2 in oceans


Claimed half of marine species and
most dinosaurs
Possible causes:
 Continental drift (volcanoes etc.)
 Asteroid hitting earth on the
Yucatan coast of Mexico
 Chicxulub crater approximately
180 km in diameter

Evidence supporting Chicxulub:
 Thin layer of iridium in rock layers
(from ET debris)
 Dust cloud blocks sun and makes
acid rain
 Extinction rates in N. America
more severe and occurred faster
 Extinction rates not uniform
across the globe
Adaptive Radiation







4.6 bya – Origin of earth
4 bya – first prokaryotes
Oxygen increases due to
photosynthesis by cyanobacteria
(2.7 billion)
2.1 bya - first eukaryotes
1.2 bya – first multicellular
organisms
Snowball earth – possible severe ice
age that ended ~570 mya which
allowed explosion of life
570 mya – oldest animal fossils






500 mya – plants and symbiotic fungi
colonize land
66 mya – dinosaurs extinct
5 mya – apelike humans
500,000 years ago – first “humans”
Animals more like fungi than plants
Most of life on earth has been
aquatic


Evolution is NOT goal oriented!
Evolution is like tinkering—it is a process
in which new forms arise by the slight
modification of existing forms
Fig. 25-25
Recent
(11,500 ya)
Equus
Pleistocene
(1.8 mya)
Hippidion and other genera
Nannippus
Pliohippus
Pliocene
(5.3 mya)
Hipparion Neohipparion
Sinohippus
Megahippus
Callippus
Archaeohippus
Miocene
(23 mya)
Merychippus
Hypohippus
Anchitherium
Parahippus
Miohippus
Oligocene
(33.9 mya)
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Eocene
(55.8 mya)
Pachynolophus
Orohippus
Key
Hyracotherium
Grazers
Browsers
CHAPTER 26

Phylogeny – evolutionary
history of a species or related
species
Incomplete record
 Minerals replace organic
material
 Hard parts leave fossils
 Some tissues preserved
 Molds made
 Relative dating (older fossils in
bottom layers of rock)

Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species

Scientific Name = Genus species
 Homo sapiens
 Any
level is a taxon (pl. taxa)
 Example:
phyla and order etc.



Monophyletic – when a single
common ancestor gave rise to all
species within that taxon (ideal)
Polyphyletic – members of a taxa
are derived from 2 or more
common ancestors
Paraphyletic – when a taxon
excludes species that share a
common ancestor



Homology – shared likeness due
to common ancestry
Analogy – shared likeness due to
convergent evolution
Convergent evolution – species
from different evolutionary
branches may come to resemble
each other due to similar
ecological roles and natural
selection
The ocotillo of southwestern N. America (left) looks like Alluaudia
of Madagascar (right).
Species diverge only when
changes occur in nucleotide
sequences
 Species that are phylogenetically
closely related have more
similar nucleotide sequences



The number of differences in nucleotide
bases between homologous sequences is
a measure of evolutionary distance
Clocks calibrated by graphing differences
in sequences against known events in
fossil record
 Assumes constant mutation rates
 Natural selection would alter mutation
rates
•Most widespread
strain of HIV
•Estimated to jump
to humans in
1930’s
•Based on DNA
sequences from
1980 – 1990’s
Use PCR
 DNA may be contaminated
with bacterial DNA or other
DNA
 Even with DNA cloned, cannot
make dinosaurs until we
understand the developmental
steps involved



Phenetics – based on measurable
similarities and makes no phylogenetic
assumptions
Cladistics – classifies according to the order
in time that branches arose along a
dichotomous tree
Clade – an evolutionary branch
 Outgroup – a species that is
relatively closely related to the group
of species being studied, but is
clearly not as closely related as any
study group members are to each
other

 Synapomorphies
– shared
derived characteristics
 Characteristics that are
homologous and evolved in an
ancestor that is common to all
species on one branch of a fork,
but not common to other branch
 Parsimony
– find the simplest
explanation



Cladistics accepts only monophyletic taxa
Example: birds are more closely related to
crocodiles than snakes and lizard are to
crocodiles (birds and crocodiles have
synapomorphies not present in snakes and
lizards)
 Class Aves and Class Reptilia wrong
cladistically because birds should be in same
group as crocodiles
On other hand both mammals and birds have 4chambered hearts and yet birds are more closely
related to reptiles (not mammals)
 Four chambered heart evolved more than once