Download Heterotroph Theory

A history of life and natural
selection
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Early predictions
 Imagine you live in the 1600s- so you
have no modern technology and no
way to see microscopic organisms.
 You see maggots growing on raw meat
and mold growing on old bread.
 You know these organisms are alive,
so where did they come from?
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Where did life come from?
 Before the 1700s, people believed in
spontaneous generation
 The idea that life can come from
nonliving things
 This is mainly due to people not being
able to observe how things like
maggots were created
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Redi’s experiment
 Around 1650, Francesco Redi performed an
experiment to see how maggots were created
 He used covered and uncovered meat in jars and found
maggots came from flies NOT MEAT!!!
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Pasteur’s Experiment
 In the mid 1800’s, Louis Pasteur performed another
experiment looking at where bacteria came from, but
instead he used a flask with a curved neck- so air could
get in but bacteria could not
 He found bacteria did not spontaneously generate
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Biogenesis
Soon after Pasteur, spontaneous
generation was rejected and
biogenesis (the principle that
states all living things come
from other living things) was
accepted
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The origin of organic
compounds
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First Organic Compounds
 The estimated age of the Earth is over 4 billion years
old
 This was found by radiometric dating (which we will
learn about another day)
 All elements found in organic compounds today are
thought to have existed on earth and in the rest of the
solar system when the Earth formed
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First Organic Compounds
 We know Earth’s early atmosphere contained
ammonia, hydrogen gas, water, and compounds made
of hydrogen and carbon (like methane) – NO
OXYGEN
 In the 1920s, two scientists, Alexander Oparin and
John Haldane proposed that with heat, these
compounds would form simple organic compounds
(like amino acids)
 Oparin also thought over time these compounds may
react to form more complex compounds (like proteins)
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First Organic Compounds
 In 1953, Stanley Miller
and Harold Urey
experimented with and
confirmed Oparin and
Haldane ideas
 Organic compounds
were produced using the
same gases that were
found in Earth’s early
atmosphere and heat
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First Organic Compounds
 Many similar experiments have been done, and the
following have been produced with similar conditions
to Early Earth:
 Amino acids
 ATP
 nucleotides
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First Organic Compounds
 We also know the Earth’s
atmosphere contained a lot of
CO2, which interferes with
the formation of organic
compounds
 So, scientists believed these
compounds were created in
places not exposed to CO2 ,
like undersea hot springs
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First Organic Compounds
 Another explanation is that organic
compounds could have been carried to
Earth by debris from space (like meteorites)
 We have recently found meteorites covered
in organic material
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Heterotroph Theory
 How might the first cells have been created?
 Microspheres and Coacervates have been produced
from mixtures of organic chemicals (similar to the
one’s produced in the previous experiments)
 Microsphere: a very small spherical vessicle that is
bound by a membrane-like layer of amino acids
 Coacervates: collection of droplets made of many
different organic compounds (lipids, amino acids,
sugars)
 How are they like cells?
 Both can take in materials from there surroundings,
grow, and reproduce
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The First Life Forms
 RNA came before DNA!!!
 In the 1980s, Thomas Cech found that there
is a type of RNA that acts as a chemical
catalyst (like an enzyme)
 He called it a ribozyme
 Other studies based on his work have
concluded that ribozymes also direct their
own replication
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Hammerhead Ribozyme
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The First Life Forms
 So…the ingredients – RNA, Microspheres, and
Coacervates – formed the first cells
 RNA was the genetic material and probably acted like
an enzyme
 Microspheres and coacervates were the membrane and
organelles.
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Heterotroph theory
 What did the first cells look like?
 We know there was little to no oxygen in the early
atmosphere
 The oldest fossils we have resemble prokaryotes
(bacteria)
 The only food available would have been organic
molecules
 From this evidence, we conclude the first organisms
would have been anaerobic, heterotrophic
prokaryotes
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The First Life Forms
 Eventually, the heterotrophs used up most or all of
the organic molecules and would die unless…
 Autotrophs evolved and multiplied
 These organisms would have been
chemosynthetic, not photosynthetic
 Chemosynthesis is much simpler than
photosynthesis (photosynthesis is very
complicated and uses many enzymes-which were
not around at this time)
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The First Life Forms
 Chemosynthesis
 CO2 serves as the carbon source to create
organic molecules
 Energy is obtained from the various
inorganic substances-like sulfur (hot spring)
 Archaea are modern day bacteria that most
likely resemble the first life forms
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The First Life Forms
 From fossils, we know that photosynthetic
organisms developed about 3 bya and were
unicellular
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The First Life Forms
 Photosynthesis produces oxygen, which was deadly
to some of these unicellular organisms.
 So, these organisms must have chemically bound
oxygen to other molecules to make it harmless
 This is thought to be involved in the development
of aerobic respiration, because the first step is
binding oxygen
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The First Life Forms
 As the photosynthetic organisms
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developed, oxygen in the atmosphere
increased
This oxygen rose into the upper
atmosphere, where it was hit with
sunlight
Sunlight splits O2atoms into 2 O atoms
These single O atoms reacted with O2to
produce O3-which is ozone
Soon an ozone layer formed, which
shielded the Earth from UV rays (which
are deadly to life on land)
This allowed life on land to further
develop.
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The First Life Forms
 How did eukaryotes develop?
 Endosymbiosis-States mitochondria and
chloroplasts were once free living
prokaryotic cells that were ingested by
bigger prokaryotes
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Radiometric Dating
 This is how we know how old things are
 Remember back to the Periodic Table
 The atomic number of an element is the number of
protons (p) in an element.
 This number is unique for each element-change the #
and change the element
 Atoms of the same element CAN have a different
number of neutrons (n).
 These are called isotopes
 Most elements have several isotopes
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Radiometric Dating
 Carbon-12(isotopes are listed with their
mass next to the element name-12 in
this case)
 Atomic # of carbon is 6
 This isotope has 6 neutrons
 6 + 6 = 12 (mass)
 Carbon-14 would have how many
neutrons?
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Radiometric Dating
 Some isotopes are not stable and may undergo
radioactive decay, in which their nuclei will release
particles and/or energy until it becomes stable
 Isotopes that go through radioactive decay are called
radioactive isotopes
 The rate of the decay of many radioactive isotopes has
been determined
 The rate of time it takes for ½ of the sample of isotope
to decay enough to become stable is called the half
life of that substance
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Radiometric Dating
 How does half life relate to dating?
 Organic matter contains a known amount of
carbon-14
 Carbon-14 is radioactive and decays into carbon-12,
which is stable
 When an organism dies, carbon-14 continues to
degrade, so that over time, there is less carbon-14
 By measuring the change in carbon-14, we can
deduce the age of dead organisms
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Radiometric Dating
 The half-life of carbon-14 is 5,730 years
 If you find an organism that originally had 10 grams of
carbon-14 and it has 5 grams when you find it…how
old would it be?
 About 5,730 years old (1 half life of carbon-14 means
50% of the sample will be left)
 Carbon-14 is only good for dating organisms less than
60,000 years old
 After that time, the carbon-14 left would be too small
to measure (or none at all)
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Radiometric Dating
Radioactive Istotope
 Potassium-40
 Uranium-235
 Uranium-238
 Rubidium-87
Product (decays to…)
Argon-40
Lead-207
Lead-206
Strontium-87
)
1.25 billion
7.04 million
4.5 billion
48.8 billion
Half-life (years
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Radiometric Dating
 If 1/8 of the original amount of Potassium-
40 is left in a sample, how old is it?
 1/8 means 3 half lives ( ½ x ½ x ½ = 1/8 )
 Half life of potassium-40 is 1.25 billion
 3 x 1.25 billion years = 3.75 billion years
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Who is involved and what did
they think?
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What is evolution?
 Evolution is development of new types of organisms
from preexisting types of organisms over time
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Timeline of Theory of Evolution
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In the 1800s
 Before the 1800s most people thought all
species were permanent and did not change
 They also thought the Earth was only
thousands of years old
 The following slides list scientists that
helped to change these ideas
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James Hutton (1726-1797)
 Geologist that came up with the
concept of Gradualism:
 a) Processes today are the same
as in the past
 b) Large changes are the
accumulation of slow,
continuous processes.
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Thomas Malthus (1766-1834)
 Published essay on human population
where he said limited resources control
populations
 It influenced Darwin on his ideas about
organism’s struggle for existence
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Charles Lyell (1800’s)
 Geologist
 Proposed Uniformitarianism= Processes
that occur today have always occurred
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Jean BaptisteLamarck (1744-1829)
 Naturalist
 Inheritance of acquired
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characteristics
Organisms change in
response to the
environment.
Structures that are used
become stronger, and
structures that are not
used become weaker.
Pass new trait to kids
NOT TRUE!!!
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In the 1800s
 Scientists began to
study rock layers
(strata) in the 1800s
 They found that
different strata formed
at different times and
generally the oldest
layers were found at
the bottom
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In the 1800s
 Georges Cuvier was able to find and piece
together some fossils.
 He found many extinct (no longer exist)
species
 He also found that some strata had very
different organisms than the strata above or
below them
 This showed that species on Earth had
changed and become extinct over time
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Charles Darwin
 In the 1830s, Charles
Darwin took a trip
around the world in
the HMS Beagle, his
observations on this
trip led him to write
theories about how
organisms change over
time
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Darwin’s Voyage
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Galapagos islands are located
off the coast of South America
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Charles Darwin
 Scientists before Darwin had hypothesized
about evolution, but no one was able to
explain HOW it happened
 Alfred Russel Wallace went on a sea voyage
and had very similar ideas around the same
time as Darwin, but since Darwin published
his findings first, he is credited with the
discovery of natural selection
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Charles Darwin
 On the Galapagos Islands, Darwin saw many
animals, such as finches, that seemed to
have a lot in common, but were also
different in many ways
 Darwin found 13 species of finches on the
islands, all of which looked similar to a finch
he observed in South America
 This led him to believe the island finches
had an ancestor in South America
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Darwin’s Finches
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Charles Darwin
 Darwin began to ponder how so many species of
finches could have “descended with modifications”
from one ancestral species
 He came up with the theory of natural selection to
explain decent with modification
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Natural Selection
The theory had 4 main parts:
Overproduction
Genetic variation
Struggle to survive
Differential reproduction
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Overproduction
 Organisms tend to produce more offspring than
can possibly survive in any given environment
 This idea actually came from Thomas Malthus-
who pointed out that the human population is
growing much faster than the environment can
withstand. Malthus pointed out that
populations are often limited by things like
disease, or lack of food.
 Darwin realized that the environment limits all
organisms-there is not an unlimited supply of
resources in any environment
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Overproduction
 Example Clown fish lay hundreds of eggs (remember
Nemo)-much more than can possibly survive
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Genetic variation
 Darwin noticed that within a population,
individuals had different traits (caused by
genetic variation)
 Also, these variations are passed on to
offspring
 Continuing the Nemo example, let’s say
some of the babies are fast swimmers and
some are slow swimmers
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Struggle to survive
 Individuals compete with each other to get
the resources necessary for survival
 Some variations improve an organisms
chances for survival/reproduction and some
reduce an organisms chances for
survival/reproduction
 A trait that makes an individual successful
in its environment is called an adaptation
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Struggle to survive
 Continuing the Nemo example-Let’s say the clown fish
offspring must swim away from the angler fish, which
will eat them
 The slow ones tend to be eaten
 The fast ones tend to get away
 So being a fast swimmer is an adaptation
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Differential reproduction
 Darwin concluded that organisms with the best
adaptations are most likely to survive and
reproduce.
 Then those that survive will pass on their
adaptations to their offspring
 So, the FAST clown fish in our example will
survive, reproduce, and pass their “fast” genes
on to their offspring
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Natural Selection
 This theory is often called “Survival of the Fittest”
 BUT fitness does not necessarily mean strongest
 Fitness is a measure of an individual's hereditary
contribution to the next generation
 So if an organism is able to produce many offspring (in
other words, pass on its hereditary information) and
those offspring survive to reproduce, it is considered FIT
 Having lots of babies AND grandbabies means an
organism is FIT
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Lamarck vs. Natural Selection
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Another Example
 A population of
cockroaches living in a
field is sprayed with
pesticide
 A few of the cockroaches
are resistant and survive
 Those survivors pass on
the resistance to their
offspring, so now the
pesticides no longer kill
the population
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Peppered Moths
 Peppered moths rest on bark of
oak trees. Birds eat the ones they
can see
 During early 19th century,
most moths blended in with
the oak bark (light brown/
green specks)
 Post Industrial Revolutionsoot and pollution stained
the tree bark dark brown.
 Population of dark moths
grew- light colored moth
population shrank.
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Types of Natural Selection
 Predation selection
 Speed
 Mimicry- copying
 Camouflage- blending in
 Physiological selection: body functions
 use of O2; efficiency
 disease resistance
 Sexual Selection- mating
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Natural Selection and Evolution
 Natural Selection can only work on expressed
phenotypes!!!
 Natural selection over many generations can lead to
evolution
 Survival AND reproduction are important for natural
selection
 Organisms DON’T TRY TO CHANGE…they cannot
“develop an adaptation” or “become immune”
 Natural Selection does NOT always lead to organisms
adapting- 99% of species that have ever lived on earth
are now extinct.
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Types of Natural Selection
 Stabilizing selection- favors average individuals;
reduces variation in a population
 Directional selection- favors one of the extreme
variations of a trait and can lead to rapid evolution
of a population
 Disruptive selection- favors both extreme
variations of a trait, resulting in no intermediate
forms of the trait and leading to the evolution of 2
new species.
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What types are these?
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Types of Natural Selection
 Let’s say a fish can be small, medium or
large. Generation 1 has more medium fish
(average) than small or large fish (extremes)
 Example 1: There are 2 predators, one eats
only small fish and one eats only large
fish. So, the frequency of medium fish
would go up in generation 2 and this
would be stabilizing selection
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Types of Natural Selection
 Let’s say a fish can be small, medium or
large. Generation 1 has more medium fish
(average) than small or large fish (extremes)
 Example 2: There is 1 predator, and it can
only eat the small and medium fish. So,
the frequency of large fish would go up in
generation 2 and this would be directional
selection
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Types of Natural Selection
 Let’s say a fish can be small, medium or
large. Generation 1 has more medium fish
(average) than small or large fish (extremes)
 Example 3: There is 1 predator, and it only
eats the medium fish. So, the frequency of
medium fish would go down and small or
large fish would go up in generation 2; and
this would be disruptive selection
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