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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
Amber, sap from
ancient trees, hardens
and encases soft-bodies
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
• Half Life = time it takes for
half of a radioactive element
to decay.
• Radioactive Decay = isotope
breaking down into another
substance.
Radioisotope
Half-life
Polonium-215 0.0018 seconds
Bismuth-212 60.5 seconds
Sodium-24
15 hours
Iodine-131
8.07 days
Cobalt-60
Radium-226
Uranium-238
5.26 years
1600 years
4.5 billion years
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
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
Darwin
• 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
DNA analysis has confirmed that a bear shot in the Canadian Arctic last month is a halfpolar bear, half-grizzly hybrid. While the two bear species have interbred in zoos, this is
the first evidence of a wild polar bear-grizzly offspring.
Wildlife officials seized the bear after noticing its white fur was interspersed with brown
patches. It also had long claws, a concave facial profile, and a humped back, which are
characteristic of a grizzly.
Now the genetic tests have confirmed that the hybrid's father was a grizzly and its
mother was a polar bear.
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
– 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.
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.
• Animals that use mimicry use colors
and markings to look like another
animal.
–Example) the Monarch Butterfly and
the Viceroy
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 (have chloroplast)
– 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 = occurs slowly and
continuously over time
•Punctuated equilibrium =
evolution can occur
quickly