Evolution
Changes in types of organisms
over a period of time
Fossils
• A fossil is some remnant of an organism
that proves its existence
– Imprints of bacteria, leaves or footprints
– Insects, pollen, or flower parts in amber
– Tools or pottery shards
– Bones of organisms in sedimentary rock
– Cave drawings
Determining fossil age
• Relative dating
• Oldest fossils are in
the deepest
sedimentary rock
layers
• Younger layers hold
newer, more complex
fossils
• Absolute dating
• Can be used to determine a precise age in
years
• Use the decay rate of radio-isotopes like
carbon 14
• The oldest known fossils are
approximately 3 billion years old
Comparative studies
• Researchers use comparative studies to
establish evolutionary relationships
between organisms
Comparative anatomy
• Comparing specific
body structures
• Analogous structures
have a similar
function but the
structure is different
– Ex the wing of an
insect and the wing of
a bird
• Homologous
structures are similar
in structure but may
have different
functions
– Ex) human hand, cat
paw, whale flipper, bat
wing
• Vestigial structures
are reduced in size
and have no known
function
• They resemble
structures in other
organisms
– Ex) the human
appendix or the pelvis
bone in a whale
Comparative embryology
• The comparison of
embryonic
development
• Early development is
similar in many
species
• The closer the
relationship between
species the more
similar is
development
Comparative cytology
• Observing
similarities in cell
structures
• All cells have some
common organelles
that perform identical
functions
– Plasma membrane,
cytoplasm, and
ribosomes
Comparative Biochemistry
• Similarities involving proteins, enzymes
and nucleic acids
– All organisms share genetic codes
• Transcription and translation
– All organisms carry on cell respiration in the
same way
– All autotrophs carry on photosynthesis in the
same way
Theories of Evolution
J.B. Lamarck
• Use and disuse
– Organisms can
change their body
structure over the
course of a lifetime
– ATROPHY – structure
decreases in mass
with disuse
– HYPERTROPHY –
structure increases in
mass with use
• Lamarck believed that
ACQUIRED TRAITS
could then be passed
to the offspring
– Example) the neck of
the giraffe
August Weissman
• Disproved Lamarck’s
theory of use and
disuse
– He cut off the tails of
mice then mated them
– All of the offspring had
long tails
– This experiment was
repeated for 22
generations
– All of the mice were
born with long tails!
Charles Darwin
• Theory of Natural
Selection
• Darwin served as a
geologist, botanist,
zoologist, and general
man of science
aboard the H.M.S.
Beagle from 18311836
• Overproduction – organisms produce
more offspring than can possibly survive
• Struggle for existence – there are only
limited resources available
– Not all offspring will survive
• Natural selection – those organisms with
advantages in a given environment are
most likely to survive and reproduce
– Those who survive and reproduce are the
FITTEST
• Variation – offspring tend to be different
from their parents and each other
• Speciation – after many generations are
involved in natural selection
– A population may be so different from the
original population that it can be classified as
a different species
– SPECIES = organisms who can mate and
produce fertile offspring
Speciation
• Involves isolation
– Anything which prevents two groups within a
species from interbreeding
Geographic isolation
• A population is divided by a natural barrier
– mountains
– Deserts
– Body of water
– Landslide cause by an earthquake
– Geographic isolation can instigate a
speciation event—but genetic changes are
necessary to complete the process
Reproductive isolation
• Differing selection pressures on the new
environments can complete the
differentiation of the new species.
• the differences between the isolated
groups become so great that they can no
longer interbreed
Microevolution
• Small, gradual changes which are
detectable within a few generations
• Industrial Melanism – changes in the
colors of a population as a result of human
industrial activity
Macroevolution
• Long term changes that make a new
species
General patterns for evolution
• Divergent evolution – different groups
evolve from one ancestor
• Convergent evolution – two or more
different groups evolve so that they
resemble one another strongly
• Adaptive radiation – organisms spread into
new environments and become adapted
through natural selection
Adaptations
• an anatomical structure, physiological
process or behavioral trait of an organism
that has evolved over a period of time by
the process of natural selection
– it increases the expected long-term
reproductive success of the organism
• Organisms that are adapted to their
environment are able to:
– obtain air, water, food and nutrients
– cope with physical conditions such as
temperature, light and heat
– defend themselves from their natural enemies
– reproduce
– respond to changes around them
• Camouflage and mimicry are adaptations
some animals use as protection from
predators.
• An animal that uses camouflage looks like
things in its environment. It might look like
a leaf, a twig, or a rock.
http://oncampus.richmond.edu/academics/education/projects/webunits/adaptatio
ns/mimicry.html
• Animals that use mimicry use colors and
markings to look like another animal.
– Example) the Monarch Butterfly and the
Viceroy
Symbiosis
• Two species live in close association with
each other
• In symbiosis, at least one member of the
pair benefits from the relationship. The
other member may be
– injured = parasitism
– relatively unaffected = commensalism
– may also benefit = mutualism
• Mutualism = (+) (+)
• Both organisms benefit
• Moray eel and
cleaner fish
• The eel gets clean
• The fish gets food
• Both organisms
benefit
• Parasitism = (+) (-)
• the parasite benefits while the host is
harmed
• (1) The hookworm latches on
the walls of the colon with
its sharp teeth where it feeds
on blood.
• (2) The tapeworm is the
longest parasite. A mature
adult can lay a million eggs a
day.
• (3) Tapeworm eggs
embedded in the colon.
• (4) The roundworm can grow
to be 20 inches (50 cm) long
and lay 200,000 eggs per
day.
• (5) Pinworms migrate
outside the colon during the
night to lay their eggs
around the anus. This
causes the nightly itching of
many unsuspecting victims.
• Commensalism = (+) (0)
• One organism benefits while the other is
neither helped or harmed
Heterotroph Hypothesis
• 1920-30s
• Formulated by a small group of scientists
• Suggests a probable sequence in which
organisms appeared
• Life on Earth began about 3.5 billion years
ago.
• The atmosphere was very different from
what it is today.
• The early Earth atmosphere contained
mostly hydrogen, water, ammonia, and
methane.
• There was very little oxygen
• There were abundant energy sources for
chemical reactions to occur
– Heat
– UV radiation
– Electrical activity
Primordial soup
• Gases in the atmosphere reacted with
each other to form simple organic
molecules
– Example ) Amino acids, nucleotides
Atoms combined to form molecules
Amino acids were formed
Stanley Miller
• Miller built an apparatus to test these
ideas in 1953
– A mixture of gases thought to resemble the
Earth’s primitive atmosphere was passed
through an electric spark
• After one week the contents were
analyzed
• Miller found that it contained organic
molecules
– Urea
– Amino acids
– Lactic acid
– Acetic acid
• The Heterotroph Hypothesis SUGGESTS
– The first organisms were anaerobic
• No O2 was available in Earth’s primitive
atmosphere
• The first organisms used the organic
molecules in the water for food
• They released CO2 as a waste product
• These organisms were ANAEROBIC
HETEROTROPHS
• Organisms that were able to use the CO2
evolved next
• These organisms were ANAEROBIC
AUTOTROPHS
– They used the CO2 for photosynthesis
– O2 was released as a waste product
• Organisms that were able to use O2
evolved next
• These were AEROBIC AUTOTROPHS
and AEROBIC HETEROTROPHS
Rate of Evolution
• Gradualism = evolution occurs slowly and
continuously over time
• Punctuated equilibrium = evolution can
occur quickly
• It can be followed by long periods of little
or no change at all
Population Genetics
• The study of the genes in an entire
population at one time
– Population = all of the members of one
species in a specific area
– Gene pool = all of the alleles within a
population
– Gene frequency = the % of all alleles for one
trait that are dominant or recessive
• The Hardy-Weinberg Law – based on
genetic equilibrium
– The condition where gene frequencies do not
change from one generation to the next
• The Hardy Weinberg Equation
–p+q=1
• Where p = dominant allele
•
q = recessive allele
– p2 + 2pq + q2 = 1
• Where p2 = homozygous dominant
•
2pq = heterozygous
•
q2 = homozygous recessive
• Example
– 30% of a population of banana-nose
hoseringers show the recessive phenotype of
yellow banana-nose as opposed to the
dominant phenotype of green banana-nose
•p + q = 1
• Where p = dominant allele
•
q = recessive allele
– 30% show the recessive phenotype
p + .3 = 1
p = .7
• What % of the banana-nose hoseringers
are heterozygous for nose color?
–p2 + 2pq + q2 = 1
– (.7)2 + 2 (.7)(.3) + (.3)2 = 1
– .49 + .42 + .09 = 1
– 42% are heterozygous
• For the Hardy-Weinberg law to be true five
conditions must be met
• 1) Large Populations
– In small populations alleles of low frequency
might be lost by the death of a few individuals
• 2) No Migration
– Individuals may not migrate into or out of the
population
• 3) No Mutations
– These will change the frequency of the alleles
in the population
• 4) No Natural Selection
– Each member of the population must survive
long enough to have offspring
• 5) Random Mating
– Each member of the population must have an
equal chance to reproduce
• The Hardy-Weinberg law does NOT
apply to situations in the real world!
• Mutations occur spontaneously
• Reproduction is NOT random
• Natural selection DOES occur
• The failure of Hardy-Weinberg Law is a
sign that evolution is occurring!
– There are changes in allele frequencies
– External factors cause the changes in
frequency