Transcript Bio stuff part 1

EVOLUTION
UNIT 7A
Part 1 of 2
DARWIN, NATURAL
SELECTION, HARDYWEINBERG
Ch. 1 (p. 8-13) and Ch. 13 (all)
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All life is connected.
The basis for this kinship is
evolution
Evolution has transformed
life on Earth from its earliest
beginnings to its extensive
diversity today
Evolutionary view came into
focus in 1859 with Darwin’s
book
Photo on left is Charles
Darwin (1809-1882)(British
biologist) with son William
in 1842.
One of Britain’s most
renowned biologists
Published The Origin of
Species 17 years later.
Was the the most influential
scientist in the development
of modern biology.
Buried next to Isaac
Newton in London’s
Westminster Abbey.
• 2 main points in book:
• 1) species living today
descended from ancestral
species = “descent with
modification” = evolution
• Ex: the diversity of bears is
based on different
modifications of a common
ancestor from which all
bears descended.
• 2) the mechanism for
evolution is “natural
selection” (see next slides)
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Darwin loved nature. Disliked medical school. Became a minister. Became a
naturalist for a voyage around the world when he was 22 years old.
Darwin’s “Voyage of the HMS Beagle” is shown above.
Observed and collected thousands of specimens. Observed adaptations of
organisms. Most of animals of Galapagos Islands live nowhere else in world,
but they resemble species living on the South American mainland. It was as
though the animals strayed from mainland, then diversified as they adapted
to environments on the different islands.
• Darwin saw large diversity of animals on
Galapagos Islands, off coast of South America
• If an ocean separated islands, it isolated 2
populations of a single species. The populations
could diverge more and more in appearance as
each adapted to local environmental conditions.
• After many generations, 2 populations could
become dissimilar enough to be separate species
- 14 species in the case of the birds called
Galapagos finches. (This is now called
divergent evolution)
• They have beak shapes and colorations that are
adapted to their environments
• The beaks are adapted to certain food sources
on the different islands; the colors protect them
from predators
• See next page for the finches!
Darwin’s Finches
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Q:How did Darwin explain these
adaptations, or different beaks?
A:Natural selection! 3 main points:
1. Far more offspring are produced than the
environment can hold. Overproduction leads
to a struggle for existence among the
individuals of a population.
2) Individuals in a population vary in many
traits - no two individuals are alike.
3) Those individuals with traits best suited to
the local environment will have the greatest
reproductive success. They will leave the
greatest number of surviving, fertile offspring.
They will reproduce more of the same. This
unequal reproductive success = natural
selection.
Nature decides what traits are most fit.
Adaptation is the accumulation of favorable
variations in a population over time.
Ex: beaks well equipped for available food
sources, and markings that reduce predation
= finches survive to produce more. (Survival of the
Fittest)
•Darwin also looked at “Artificial Selection” going on with farming.
•Humans have been modifying other species for centuries by selecting
breeding stock with certain traits.
•These vegetables and flowers no longer look like their ancestors.
Artificial Selection in pets - have been bred for human fancy.
Dog breeds - all are descendants from one ancestral population
of wolves
“Humans” screened the heritable traits of populations instead of
“nature’” or the natural environment.
• Natural selection
in action today:
Antibioticresistant forms of
tuberculosiscausing bacteria
have made the
disease a threat
again in the U.S.
The lung
infection of this
patient is shown
in red.
• Example of human
diversity.
• However, all humans
are connected by
descent from African
ancestors.
• Example of natural
selection - abuse of
antibiotics has sped
up the evolution of
antibiotic-resistant
bacteria.
• Evolution of
pesticide
resistant insects:
by spraying
crops with
poisons to kill
insect pests,
humans have
favored the
reproductive
success of
insects with
inherent
resistance to the
poisons
A flower mantid in Malaysia
A leaf mantid in Costa Rica
• Related species of
insects called mantids
have diverse shapes
and colors that evolved
in different
environments.
• Camouflage is an
example of evolutionary
adaptation.
• Evolution -2 modern
definitions:
• A. the genetic compostion
of a population changes
over time
• B. all life descended from
a common ancestor, from
the earliest microbes to
modern day organisms
• Darwin is ranked as the
4th most influential person
of the past 1000 years.
But who influenced him?
Darwin, 1859
Darwin, 1874
• Most scientists in Darwin’s day
thought:
• Earth was young (6000 years old)
• Earth was populated by millions of
unrelated species
• Darwin’s book challenged that,
and was radical for its time
• Anazimander (Greek philosopher)
had idea that life arose in water,
and simpler forms of life preceded
more complex ones.
• Aristotle (Greek philosopher)held
that species are fixed or
permanent, and do not evolve
(are static).
• A cartoon of Charles
Darwin - his book and
beliefs were radical
for its time
Lamarck
• Buffon (1700’s) (French naturalist) studied
fossils - said Earth may be much older
than 6000 years. Proposed that a species
in a fossil could be an ancient version of a
living species
• Lamarck (1800’s) (French naturalist) said
that life evolves through adaptation; ex: a
powerful bird’s beak.
• However, he had an erroneous views of
how adaptations evolve:
• He said “Inheritance of Acquired
Characteristics” - by using or not using
body parts, one can develop certain
characteristics, which can pass on to
offspring.
• Ex: if you exercise beaks and get stronger
you can pass that trait down to offspring.
(Use & Disuse Theory) Incompatible with
modern genetics.
Lyell
Wallace
• Lyell (Scottish geologist) - said ancient
Earth was sculpted by gradual geologic
processes that continue today.
(Mountains, earthquakes, erosion.)
Earth was very old. Gradualism
principle.
• Wallace (British naturalist) (1850’s)
developed a concept of natural
selection identical to Darwin - both were
presented to the scientific community.
• Darwin’s book evidenced 2 major
points:
• Organisms on Earth today descended
from ancestral species, accumulating
different modifications or adaptations “descent with modification.” History of
life is analogous to a tree.
• Natural selection is the mechanism for
Elephant family: Example of “descent with
modification”
What is some evidence in
support of evolution? (5
examples)
• 1. The Fossil Record
• Fossils - preserved remnants or
impressions left by organisms that lived
in the past
• Most found in sedimentary rocks
• Younger strata are on top of older ones;
positions of fossils in the strata reveal
their relative age
• Fossil record - chronology of fossil
appearances in rock layers, marking
passing of geologic time
• Oldest fossils date from 3.5 billion years
ago, are prokaryotes.
• Fishlike fossils are oldest vertebrates,
then amphibians, reptiles, then mammals
and birds.
• Paleontologists - scientists who study
fossils - found fossilized whales that
connect them to their land-dwelling
ancestors
• 2. Biogeography- the geographic distribution of species
• Ex: Tropical animals in South America are more closely related to
species in South American deserts than to species in African tropics.
• Ex: Australia has a diversity of pouched mammals (marsupials) but few
placental mammals. They are hospitable to placental mammals.
Unique Australian wildlife evolved on island continent in isolation
from regions where early placental mammals diversified.
• Biogeography makes little sense if species were individually placed in
suitable environments. Instead, species are where they are because they
evolved from ancestors that inhabited those regions.
• Top photo shows the
isolated Australian
continent.
• Bottom photo shows
pouched (marsupial)
mammal; many
marsupials are
common to Australia.
• 3. Comparative Anatomy the same skeletal elements
make up the forelimbs of
humans, cats, whales, and
bats - all are mammals.
• The functions differ, but
structural similarity indicate
they descended from a
common ancestor -homology.
• Ex: forelimbs of diverse
mammals, all have same
bones (photo on left)
• Ex: human spine and knee
joints derived from 4-legged
mammals - are subject to
sprains, spasms, common
injuries because of our
bipedal posture.
• Darwin Review:
• 1. Overproduction of
offspring; competition for
limited resources and
struggle for existence
• 2. Individual variation
1.Overproduction of spores
• 3. Differential reproductive
success (natural
selection). Environment
(nature) determines who is
fit. Those most fit survive &
reproduce. Favored traits
2.Variation in beetles
accumulate in population
over generations =
adaptive evolution.
Ex: Vestigial Structures
• These are some of the
most interesting
homologous structures
which have marginal, if
any, use or importance
to the organism. They
are historical remnants
of structures which had
important functions in
ancestors.
• Ex: the whales of today
lack hind limbs, but have
vestiges of pelvic and
leg bones of their fourfooted terrestrial
ancestors.
• Vestigial organs are
evidence of evolution shows linkage to a past
• 4. Comparative
Embryology - comparison
of structures that appear
during development of
different organisms
• A sign that vertebrates
evolved from a common
ancestor: all of them have
have an embryonic stage
in which gill pouches
appear on sides of throat
• At this stage, embryos of
fish, frogs, snakes, birds &
apes look more alike than
different.
• As development
progresses, the vertebrates
take on more distinctive
features.
• 5. Molecular Biology- there is a common genetic code shared by all
species. This genetic language has been passed along through all
branches of evolution since an early form of life.
• Ex: DNA bases same, RNA, amino acids, use ATP for energy.
• Ex: In above chart- chimps & humans are less than 2% different in DNA
sequences
Large ground finch
Woodpecker finch
Small tree finch
Natural Selection in Action
• Ex: Evolution of finches on Galapagos Islands: the islands were
colonized by finches that strayed from the South American mainland,
then diversified on the different islands.Adaptive evolution/radiation.
• Ex: Pesticides - do not create resistant individuals, but selects for
resistant insects that were already present in the population
• Ex: 2 populations of
trees are separated
by a river. (Partially
isolated from each
other)
• Trees are more likely
to breed with
members of the
same population on
same side of river.
• Could each side of
trees evolve different
traits?
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Variations (polymorphism) in garter
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snakes
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MODERN SYNTHESIS - the fusion of genetics
with biology
Study of variations in populations caused by
mutations and sexual recombination
Population-group of same species living in same
area at same time.
Looks at gene pools - all of the alleles in all the
individuals making up a population
Ex: Wildflower with only two varietiesRed flowers = R & white flowers = r.
Suppose 80% or .8 of all flowers in the gene pool
have the R allele.
p = relative frequency of the dominant allele, so p
= .8
r must be present at the other 20%, or .2
q = frequency of the recessive allele, so q = .2
Since there are only 2 alleles for flower color, then
p+q=1
If you know p, how can you find q? ________
If you know q, how can you find p? ________
Hardy
• We have just found the
frequencies of alleles. (p + q =
1)
• NEXT, we can find the
frequencies of the different
genotypes in the population if
the gene pool is completely
stable (non-evolving).
• This is called Hardy-Weinberg
equilibrium.
• G.H. Hardy, an English
mathematician in 1908, and G.
Weinberg, a German physician,
asked “How can both dominant
and recessive alleles remain in
populations? Why don’t
dominants simply drive out
recessives? Ex:
Brachydactylism is caused by a
dominant allele, so why don’t
• They found that genetic recombination does not by
itself change the overall composition of the gene
pool. To demonstrate this, they examined the
behavior of alleles in an idealized population in which
five conditions hold:
• 1. No mutations occur
• 2. No net movement of individuals in or out of the
population
• 3. Population is large enough
• 4. Mating is random
• 5. All alleles are equally viable (no natural selection)
• (These are seldom likely to be met in a natural
population, but it provides a standard against which
to measure.)
• This is Hardy-Weinberg equilibrium, or steady state.
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Back to the wildflower problem...
p+q=1
.8 + .2 = 1
Q: In the wildflower population, what is the
probability of producing an RR individual by
“drawing” two R alleles from the pool of
gametes?
R sperm x R egg, or p x p
.8 x .8 = .64, or 64% of the plants in the
population will have the RR genotype.
Q: What is the frequency of rr individuals in the
population?
r x r, or q x q
.2 x .2 = .04, or 4% of the plants in the
population will have the rr genotype.
Q: What is the frequency of Rr in the
population?
Rr + rR , or 2pq
2 (.8 x .2) = .32, or 32% are Rr with Red
flowers.
General formula = p2 + 2pq + q2 = 1
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Do the Punnett Square here: •
p
q
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p
q
.0001
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How can we apply this to real life?
Use the Hardy-Weinberg formula to calculate the
percentage of a human population that carries the
allele for a particular inherited disease: Ex: PKU.
PKU occurs in about 1/10,000 babies born in U.S.
If untreated, causes severe mental retardation; need a
strict diet. It is a recessive genetic disease.
Newborn babies are now routinely tested for PKU.
A PKU baby is q2 = 1/10,000 = .0001.
q = square root of .0001 or .01.
p = 1 - q, or 1 - .01 = 0.99
Carriers are 2pq or 2 x 0.99 x 0.01, or .0198.
Thus,1.98% (around 2%) of the U.S. population
carries the PKU allele. This is essential information
for any public health program dealing with genetic
diseases. (Note: Also do Punnett Square method on
left.)
Now-You try some problems in your UP. Remember:
If they ask for frequency of an allele, that is p or q. If
they ask for the % of individuals, that is pp or qq or
2pq. (The “individuals” are in the box.)
• We just discussed a “non-evolving” population.
• How can we tell if a population is evolving?
• Ex: What if an insect is attracted to the white flowers
instead of the red, and the white get pollinated more?
This could cause the population to change over the
generations.
• This is called microevolution, evolution on a small
scale.
• 4 examples of microevolution:
• 1. Genetic Drift:
• 1. Genetic Drift - chance causes the frequencies of the alleles to
change over the generations in a small gene pool, not natural
selection. (The smaller the sample, the greater the chance of deviation
from an idealized result.) See example above.
• 2 examples of Genetic Drift:
• A. Bottleneck Effect - disasters
(earthquakes, floods, droughts,
fires) may drastically reduce the
size of a population.
• Small surviving population may
not be representative of the
original population’s gene pool.
• Some alleles may be lost from the
gene pool - reducing the overall
genetic variability in a
population.
• Ex: Cheetahs have been
overhunted. Only 3 small
populations are left in wild; have
low genetic variability. May be
less adaptable to diseases, or
environmental changes.
Tristan da Cunha. 1900’s
• B. The Founder Effect- a few
individuals colonize an isolated
island, lake, or other new habitat
• The smaller the colony, the less its
genetic makeup represents the
gene pool of the original
population from which they
emigrated.
• Ex: In 1814, 15 people founded a
British colony on small islands in
Atlantic Ocean.
• One colonist carried a recessive
allele for retinitis pigmentosa;
causes blindness.
• In 1960’s, 4/120 descendants had it
and 9 were carriers - much higher
frequency than in Great Britain.
A blend of several races:
computer image. Are races
blending together due to
travel and gene flow?
• Microevolution con’t.:
• 2. Gene Flow- a
population may gain or
lose alleles by genetic
exchange with another
population
• Ex: a windstorm blows
pollen to our wildflowers
from the neighboring
white population increases frequency of the
white flower allele
• Tends to reduce genetic
differences between
population
• 3. Mutations -change in organisms DNA.
• Ex: a mutation causes white flowers to
produce red flowers.
• Mutations at a particular gene locus are rare,
but the cumulative impact of all mutations at
all loci can be significant.
• Over the long term, mutation is important to
evolution - it serves as the raw material for
natural selection.
• 4. Natural Selection - a blend
of chance and sorting.
• Those that work best in the
environment leave the most
offspring, and have a
disproportionate impact on the
gene pool.
• Darwinian fitness - the
contribution an individual
makes to the gene pool of the
next generation relative to the
contribution of other
individuals
• Ex: (left) Flowers which
attract the most pollinators are
most fit
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3 outcomes of natural selection:
1) Directional selection - selects in favor of some extreme phenotype, when
environment changes. Ex: pesticide resistant individuals
2) Diversifying selection - leads to a balance between 2 or more contrasting morphs.
Ex: a patchy environment with snakes
3) Stabilizing selection - maintains variation for a trait within a narrow range.. Ex:
majority of human birth weights 6.5-9 pounds. Occurs in a relatively stable
environment, populations are already well adapted.
End Thought: Population Genetics of Sickle-Cell
Allele
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Why is the sickle-cell allele so much
more common in African Americans
than in the general U.S. population?
In some African populations, sicklecell allele has a frequency of 0.2, or
20%.
This is q.
Q: Find the number of individuals that
benefit from having a sickle cell
allele, (resistant to malaria) vs. how
many get the disease from it. (Do a
punnett square.)
A: 32% benefit, 4% get the disease
This explains the high frequency of
the sickle cell allele compared to other
disease alleles.
This is “Darwinian medicine” Biology is the foundation of all
medicine.
HONORS BIOLOGY
UNIT 7B:
EVOLUTION & HUMAN
ANCESTRY
Ch. 15, 14, and 17
How did life on ancient Earth evolve? (Ch. 15)
• Examine the
chart on the
left.
• What are some
major episodes
in the history
of life?
• Q: What is this
chart based
on?
• A: Fossil
evidence and
molecular
analysis.
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Conditions on Early Earth:
1. Q: When was Planet Earth born?
A: About 4.5 billion years ago.
How? A current belief is
“The Big Bang” theory:
10-20 billion years ago the universe was
a dense compaction that exploded,
hurling dust, debris, & gases into space.
Material has been hurling outward ever
since; universe is still expanding.
Materials cooled, atoms like H and He
formed. Cooling and compression
formed stars & planets. Our sun formed
5-10 billion years ago. Material ejected
from sun formed planets.
Earth was originally cold, but heat built
up with gravitational compaction,
radioactive decay, gases and heat from
hot springs and volcanoes, or a collision
with other objects.
• 2. What was the early atmosphere like
on earth?
• CO2, H2O, CO, H2, N2, H N3
(ammonia), H2S and CH4 (methane).
• No free O2 present.
• Earth slowly cooled, water vapor
condensed, rains fell forming oceans.
Erosion from earth’s surface added
minerals, making them “salty.”
• 4 conditions were necessary for chemical
evolution to occur:
• 1. Absence of free O2 (it would have
broken down organic molecules)
• 2. Energy (violent storms, volcanoes,
UV radiation)
• 3. Chemicals
• 4. Time
• Geologic evidence shows appearance of
simple life forms 3.5 billion years ago.
Stanley Miller
• 3. How did Organic Molecules
form?
• Oparin hypothesis, later tested
by Urey and Miller, 1950’s
• Designed an apparatus that
simulated conditions on early
earth.
• Started with H2, CH4, H2O, and
NH3.
• Exposed it to an electric
discharge, simulated lightning.
• Produced amino acids and other
building blocks!
• Similar experiments involving
different combinations of gases
have produced produced a
variety of organic molecules
including RNA and DNA bases.
• 4. How did life form?
• The ancient Greeks believed in
“spontaneous generation,” life
from non-living things.
• In 1862, Louis Pasteur, using
bacteria, proved “life-fromlife,” or biogenesis.
• How did first life on Earth
form?
• Hypothesis is: Earth’s
primordial environment
(organic soup) could
eventually have produced very
simple cells through a
sequence of stages.
• See next slide for stages:
Louis Pasteur
Earth 3 billion years ago.(drawing).
Pads are colonies of prokaryotes
• 4-Stage Hypothesis for the Origin of Life:
• Stage 1: Synthesis of small organic molecules from abiotic chemicals.
(Stanley Miller experiment. Others have produced all 20 A.A., sugars,
lipids, ATP, and monomers of DNA & RNA). OR - organic compounds
could have reached the Earth from space.
• Stage 2: Link above organic monomers together to form polymers.
(Have formed polypeptides by dripping monomers onto hot sand, clay or
rock.)
• Stage 3: Origin of Self-Replicating Molecules, like RNA, for
inheritance.(Short strands of RNA can assemble spontaneously from
nucleotide monomers.) (See above picture.)
The pre-cell
• Stage 4: Formation of Pre-Cells molecular packages with some of the
properties of life (see left)
(Laboratory experiments demonstrate
this.)
• With natural selection and evolution
these pre-cells could become more
cell-like.
• Prokaryotes flourished at least 3.5
billion years ago; Bacteria was
unicellular, anaerobic, asexual,
heterotrophic.
• With chlorophyll, bacteria became
photosynthetic/autotrophic, O2 was
introduced into atmosphere, ozone
layer formed.
• With time; aerobic organisms,
eukaryotic cells, sexual reproduction,
multicellular organisms.
• END OF CH. 15 NOTES
How Do Species on Earth Evolve?
(Ch. 14)
• The history of life on Earth
includes stories of species dying
out while other multiply and
diversify.
• How are new species made?
• How do species die off?
• Ex: All dinosaurs, and 1/2 of
other species at the time,
became extinct in less than 10
million years. Why?
Huge impact crater when a
meteorite or asteroid slammed • Fossil record shows that climate
into Earth, in Caribbean Sea.
cooled, shallow seas receded,
& a large meteorite or asteroid
hit Earth which blocked light,
disturbed climate, killed off many
• Q: How does macroevolution
occur? Macroevolution =
multiplication of species,
biological diversity, evolutionary
novelty (wings, feathers, big
brains)
• A: The beginning of new forms of
life can occur through speciation the origin of new/different
species.
• Ex: See Left
• Nonbranching - a population
changes through adaptation to a
changing environment. Becomes a
new species.
• Branching - one or more new
species branch from a parent
species that may continue to exist.
• Species - a population(s) whose
members have the potential to
interbreed with one another in
nature to produce fertile offspring,
and cannot with members of other
species.
• Ex: (Left) These birds look
similar, but cannot interbreed with
one another. Q: Are they two
different species?
• Yes.
• Ex: Breeds of dogs look different
from one another, but all can
interbreed. Q: Are they all
different species?
• No. They are all the same species.
• Ex: These humans may live
in different geographical
areas, and may never get
together. But if they did,
could they interbreed? Are
they the same species?
• Yes, all humans belong to
the same species.
• Q: Are humans and
chimpanzees the same
species?
• A: No
• Q: What about dogs and
wolves?
Q: What prevents two species from reproducing with each other?
A: Reproductive Barriers!
Courtship rituals of Blue-footed
boobies in Galapagos Islands.
Male does “high-step,”showing
bright blue feet.
• 2 types of Reproductive Barriers:
• I. Pre-zygotic barriers - impedes
mating or hinders fertilization of eggs.
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A. Temporal isolation - time based.
Ex: Western spotted skunks breed in the
fall, but eastern species breed in late
winter.
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B. Habitat isolation - spatially
segregated. Ex: one species of garter
snake lives in water, and a closely
related species lives on land.
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C. Behavioral isolation - courtship
rituals. Ex: in bird species, courtship is
so elaborate that individuals are unlikely
to mistake a bird of a different species as
one of their kind.
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D. Mechanical isolation male and female sex organs
of different species are
anatomically incompatible.
Ex: 2 insects’ copulatory
organs may not fit together
correctly; no sperm is
transferred.
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E. Gametic isolation individuals may copulate,
but their gametes are
incompatible and
fertilization does not occur.
Ex: mammal sperm may not
survive in female of a
different species.
II. Post-zygotic barriers - if mating actually occurs between different species
and a zygote is formed, these mechanisms affect the hybrid offspring. (baby)
A. Hybrid inviability - the hybrid offspring die before reaching reproductive
maturity. Ex: certain frogs
B. Hybrid sterility - the hybrid offspring may become vigorous adults,
but are infertile. Ex: see below
Horse
+
Donkey
=
Mule
(but is sterile)
Some confusing hybrids…
By far the largest and most unusual cat at the Shambala Preserve, Patrick is a liger:
the hybrid offspring of a lion father and a tiger mother. Weighing in at an estimated
800 pounds, his ruddy coat shows faint stripes and he also has a modest mane.
He "fuffs" like a tiger and roars like a lion, although without adding the deep grunts
at the end that most lions do. www.shambala.org
Patrick,a liger
Noelle, on right is a tigon (tiger father
and lioness mother, born in 1978)
She was thought to be sterile, but after
mating with a male Siberian tiger, she
gave birth to Nathaniel on left in1983,
a ti-tigon. Both have since died.
A wolf hybrid
• Mechanisms of Speciation:
• When the gene pool of a population is separated
from other parent species populations, then the
new population can follow its own evolutionary
course. 2 Types:
• 1. Allopatric speciation - (“other country”) - a
physical barrier physically isolates the new
population. (see left)
• Ex: mountain range, glaciers, bridges, lakes,
islands, canyons
• More likely when a population is small &
isolated
• 2. Sympatric speciation - (“together country”) the new population becomes reproductively
isolated right in the midst of the parent
population. (see left)
• Ex: 25% of all plants, incld. wheat
• Plants have accidents during cell division,
become polyploid cells - each cell has more than
2 complete sets of chromosomes. Can no longer
mate w. parent population.
• All squirrels used to be the same in the Grand Canyon.
Over time, one population migrated to the south rim (left),
the other to the north rim (right). Due to the large distance,
the 2 populations seldom got back together. Each
population adapted differently to their surroundings, had
different mutations. Now they cannot mate and produce
fertile offspring.
• Q: Are they the same or different species?
• Q: What is this an example of?
• A: Different species; Allopatric speciation
Explain this diagram:
•
• How fast can speciation occur?
• Gradualist model - traditional
evolutionary trees show
branches diverge gradually
• Punctuated equilibrium model more recent - species diverge in
spurts of relatively rapid
changes, instead of slowly and
gradually.
• Ex: polyploidy is sudden
speciation
• Ex: a species has a spurt of
evolution its first 50,000 years,
then has little or no change for 4
million years, then becomes
extinct.
The Evolution of Biological Novelty
• How can we account for flight
in birds?
• Birds are derived from
earthbound reptiles.
• Birds have lightweight
skeletons w. honeycombed
bones, homologous to reptilian
ancestors.
• These bones/winglike forelimbs
must have had some function on
the ground.
• The first flights may have only
been glides/hops.
• Natural selection - those who
were able to fly better, survived.
The Fossil Record
• The fossil record is an archive of
macroevolution.
• A 40 million year old leaf in
sedimentary rock. (top left)
• A fossilized dinosaur bone in
sandstone in Dinosaur National
Park in Utah and Colorado. (top
right)
• Petrified stone trees in Petrified
National Forest in Arizona are
about 190 million years old.
• A 30 million year old scorpion
embedded in amber. (hardened
resin from a tree).
Fossils Continued
• The skull of Homo erectus, an
ancestor of humans that lived
about 1.5 million years ago. (top
left)
• These casts form when the shells
of decayed marine organisms
called ammonites are filled by
minerals dissolved in water. (top
right)
• Trace fossils are foot prints,
burrows, and other remnants of
ancient organism’s
behavior.(bottom left)
• These tusks belong to a whole
23,000 year old mammoth, which
scientists discovered in Siberian
ice in 1999. (bottom right)
How can we tell geologic time using fossils?
Dinosaur bone
• Fossil record shows macroevolution.
• Sedimentary rocks are richest sources of
fossils
• Provide a record of life on Earth in their
layers
• Dead organisms get trapped in sediments,
freezing fossils in time
• Younger sediments are superimposed on
older ones; layers of sediment tell the
relative ages of fossils.
• A Geologic time scale can be made,
studying many different sites
• Geologists divided time into 4 eras:
Precambrian, Paleozoic, Mesozoic, &
Cenozoic (see packet charts & text p. 283)
• Can tell relative ages of fossils - older
fossils are in the lowest layers.
• For absolute dating, scientists use radiometric dating to determine the ages of
fossils in years.
• Scientists measure the radiation that fossils emit as they decompose. This clocklike decay can be used to date fossils.
• Ex: Carbon-14 is found in organisms and is radioactive. It takes 5600 years for
half of the C14 to decay after an organism dies; that is its half-life.
• The age of a fossil is determined by measuring the ratio of C14 relative to the more
common C12. (The less C14, the older the fossil.)
• Ex: If ratio of C14 to C12 is
25% that of a living organism,
that means it went through 2
half-lives. 5600 x 2 = 11,200
years old. (see chart)
• Because the half-life of
carbon-14 is relatively short,
the isotope is only useful for
dating fossils less than about
50,000 years old. To date
older fossils, paleontologists
use radioactive isotopes with
longer half-lives.
Evolution and Geology:
• Plate boundaries
• San Andreas Fault in
California - many
earthquakes occur at plate
boundaries. This fault is at
the border where 2 plates
slide past each other.
• The history life has included
many extinctions.
• Extinction of a species may
occur because its habitat has
been destroyed, or unfavorable
climatic changes.
• 6 distinct periods of mass
extinction over the last 600
million years.
• The rate of species loss worldwide may be 50 times higher
now than at any time in the past
100,000 years. Why?
• See video “Extinction”
• END OF CH. 14 NOTES
The extinct Dodo bird
• Continental Drift:
• Continents used to be locked
up-Pangaea
• Later drifted apart,and began
to break up
• Reshaped biological diversitycaused extinctions, and new
opportunities for survivors.
• One result: Isolated continent
of Australia - fauna and flora
contrast sharply with rest of
the world.
• Humans emerged on
one very young twig
on the vertebrate
branch.
• Humans and chimps
diverged from a
common ancestor 57 million years ago.
• Q: Are our ancestors
chimps or modern
apes?
• A: No. We represent
2 divergent branches
of the anthropoid
tree that evolved
from a common
ancestor.
• Chimps are more
like our cousins or
siblings, but not our
parent species.