Download File

What is evolution?
Evolution
• The relative change in the characteristics of
a population over successive generations
– Changes in traits etc. As time goes by.
• Ruffled grouse has changed to become well
camouflaged enabling it to survive
• A population is the smallest unit that can
evolve
• Any shift in a gene pool is called evolution
If evolution is the change in characteristics of
a population over successive generations,
then how do these characteristics change?
• With the help of Adaptations and Variations
Some Causes of evolution
• 1. Adaptation
– A particular structure, physiology or behavior
that helps an organism survive and reproduce in
a particular environment
• Ex. Camouflage of tiger, excellent sense of smell,
hearing, vision, etc
• 2. Variation
– A significant deviation from the normal
biological form, function or structure
• Ex. Albino moose, striped zebra.etc.
Peppered Moth – Case of adaption (p.644)
“Industrial Melanism
• Peppered moth cones in two variations
– Black( wing color is black
– Flecked moths( light white wings with flecks of black)
• Pre-mid 1900’s many more flecked moths than lack moths
– Flecked moths would rest on lichens that provided camouflage.
Black moths were easily seen and eaten
• Industrial Revolution 'factories in England started producing black
smoke that covered trees and killed lichens
– Flecked moths were seen and eaten
– Black moths survived long enough to reproduce and pass on their
genes
– Many more black moths than flecked moths. Frequency of genes
has changed in the population.
• 1950’s
– England introduced the Clean Air policy ‘, less
soot, lichens began to grow on trees again
– 1959- 9/10 moths are black
– 1985 5/10 moths are black
– 1989 3/10 are black
– 2010 black peppered moth will be as rare as
before industrial revolution
• How do peppered moths support
evolution?
– 1. 1850’s moths in England were mostly
flecked (some were black) flecked ones
survived because they were camouflaged
– 2. 1900’s air pollution made trees black.
Black moths were able to survive
– 3. 1950’s saw pollution controls and now
the flecked moth is surviving again
Time line of evolution!
• Evolution has taken a loooog time to occur.
If 24hrs. Represented the entire evolutionary time scale.
Humans would show up about 3 seconds before midnight
• How long has it taken for evolution to occur
and from what did it start?
• Life is believed to have begun over 3500
million years ago with the earliest of cells.
Mechanisms of evolution
• Natural Selection
– Proposed by Darwin
– Idea where characteristics of a population
change because individuals with certain
heritable traits survive local environmental
conditions and pass their traits onto their
offspring
– The environment determines which individuals
are most fit to survive and pass on genes
– Fitness- how well an organism fits its
environment
– Ex. Peppered moth, leaf bug
Artificial Selection
• Human selection of particular traits by
breeding
– Ex. Faster horses, disease resistant
plants, dogs, etc
• Humans determine the traits to be
passed on to future generations
• Population evolves in the direction man
wishes it to
• Not all breeding( artificial selection) is
good. Breeding Pekinese and British
bulldogs for flat face produces
respiratory problems
History of evolution. Who gave us what?
• While we generally accept Darwin's theory
of Natural selection as the mechanism of
evolution several people have had an
influence in evolutionary thought.
1. Greek philosophers
• Greek philosophers such as Aristotle and
Plato did not believe in evolution. They
said all organisms which could exist were
already created
Georges Cuvier (1769-1832)
• Founder of Paleontology(the study of fossils)
• Fossil record revealed that something was
causing species to appear and disappear
• Thought that boundaries between fossils layers
corresponded to catastrophic events such as
Noah’s flood or droughts
• Developed the theory of catastrophism
• Catastrophes account for the disappearance and
appearance of new species in the fossil record
Charles Lyell (1797-1875)
• Expanded on Hutton's idea of Gradualism
• Gradualism– idea that earth’s geological features are in a
slow continual cycle of change
• Developed the theory of Uniformitarianism
– Idea that geological processes operated at the
same rates in the past as they do today.
• He rejected the idea of catastrophism, etc
• He said the world was millions of years old
and not 6000 years as believed
Thomas Malthus (1789)
• Looked at plants and animals
• Said that plants and animals grow faster
than their food supply
• Causes a population to be reduced by
starvation, disease, etc.
• Crowding and struggle for food and
resources is what kept population from
exploding
• Darwin borrowed ideas on struggle for
survival and realised those with the
best traits for survival would pass on
their gene
Jean Baptiste Lamarck (1744-1829)
• Published a theory of evolution in 1809 the year
Darwin was born
• Believed that organisms came from nonliving
sources
• Said that organisms respond to the needs in their
environment
• Proposes the idea that body parts used extensively
to cope in the environment would be come
stronger and stronger (idea of use and disuse)
– Examples biceps of blacksmiths ,giraffes neck
• He based his theory on two observations thought to
be true in his day
– 1. use and disuse• individuals lose characteristics they do not
require and develop those which are useful.
– Examples such as the black smith biceps
– 2. Inheritance of acquired traits
• Individuals inherit the acquired traits of their
ancestors
– Ex. A child would be strong because their
dad was a weightlifter
– A person who accidentally lost a finger
would produce offspring with nine fingers
Alfred Wallace (1858)
• British Naturalist developed same theory as Darwin
• Wallace did extensive fieldwork, first in the Amazon River and
the Malay Archipelago, where he identified the Wallace Line that
divides the Indoneaian archipelago into two distinct parts: a
western portion in which the animals are largely of Asian origin,
and an eastern portion where the fauna reflect Australasia
• He was considered the 19th century's leading expert on the
geographical distribution of animal species and is sometimes
called the "father of biogeography“.]
• Wallace was one of the leading evolutionary thinkers of the 19th
century and made many other contributions to the development of
evolutionary theory besides being co-discoverer of natural
selection. These included the concept of warning coloration in
animals, and the Wallace effect, a hypothesis on how natural
selection could contribute to speciation by encouraging the
development of barriers against hybridization.
Charles Darwin
• In 1831 he left on a 5 year voyage on board the beagle
• He stopped in the Galapagos islands where the
diversity of tortoises and birds amazed him
• His theory of Descent with Modification had two
main ideas
– 1. present life forms have risen by descent and
modification from an ancestral species
– 2. Natural selection is the mechanism of
modification over long periods of time
• He returned to England in 1836
• He wrote the book `the origin of the Species` in which
he published his theory of evolution
Natural Selection and Evolution
•
•
•
•
Summary of Darwin's Findings on
Galapagos Islands
Noticed that each island had finch birds that
were different from each other
Noticed that tortoises were different on each
of the islands
If these were the products of creation, how
could such variations have occurred in such
a small area
Darwin thought that these organisms must
have evolved from a common ancestor
Darwins Finches
Darwin's Theory of Natural Selection
• Main points
– 1. organisms produce more offspring than can
survive
– 2. competition occurs between individuals for
limited resources. This causes a struggle to
survive
– 3. There are variations in individuals in a given
population and these traits can be passed on.
Variations are often caused by Mutations
– 4. only the individuals that are better suited to
local environmental conditions survive to
reproduce
What Darwin could not Explain
• Darwin was not able to explain how the
favorable traits were passed on to the
offspring
• why
– He knew nothing of Mendel (heredity) and
Mutations(producing variations) that could be
passed on
– However Mendel's ideas supported Darwin's
ideas. This produced a revised theory of
evolution
Theory of Modern Evolution or Modern
synthesis
• This is the theory of evolution commonly
accepted today.
• 1. This is a meshing of Mendel's and
Darwin's ideas
• 2. Darwin says that variations exist in a
population allowing certain organisms to
adapt to their environment. These traits can
then be passed on to offspring
• 3. Mendel's work points out that mutations
are the cause of variation within a
population and it is the DNA that helped
carry these best traits onto the next
generation
Evidence Supporting the Modern Theory
of evolution
• The following are pieces of evidence that supports
the modern theory of evolution
– 1. Fossil record
– 2. Biogeography
– 3. Comparative Anatomy
• A. Homologous structures
• B. Analogous structures
• C. Vestigial structures
– 4. comparative embryology
– 5. heredity
– 6. Molecular biology
1. Fossil Record
Fossil: remains or traces of once living organism. Often
preserved in rock.
• Fossil evidence supports evolution in the following ways
– A. Fossils from more recent geological eras are more similar
to present day organism than older fossils
• This supports the idea that life evolve over time
– B. Fossils appear in chronological order in sedimentary rock.
Younger fossils appear higher in sedimentary layers and are
more complex than older fossils appearing in deeper layers
• This supports the idea that has evolution has occurred , species of
organisms have become more complex
– C. Transitional Fossils make links between different sets of
related organisms within differing fossil layers
• Ex. Archaeopteryx shows a relationship between reptiles and birds.
• This suggests that evolution is occurring over time from less complex
to more complex life forms.
Finding the Age of Fossils Dating Fossils
• There are two methods to determine the age
of fossil.
• A. Relative Dating; Judging the age of a
fossil according to its position in the layer of
rock.
– Ex. Fossil B is younger than C but older than
Fossil A
A
B
C
• B. Absolute Dating-finding the exact age of a fossil using
radioactive dating
– Radioactive dating- a method of finding the age of a
fossil using half life of certain radioactive substances
that decay over time
– Note: The radioactive substances decays into a more
stable daughter element
– Half Life: period of time required for 1./2 of a
radioactive isotope to decay into a more stable element
• Representative radioactive isotopes with half life
Radioactive
Parent
Stable daughter
Half Life (years)
C14
N14
5730
U235
Pb 207
713000000
K40
Ar 40
1250000000
Rb 87
Sr 87
48800000000
C 14
C14 N14
N14 C14 C14
5730 years
5730 years
One ½ life
One ½ life
Notice after each half life only ½ the original C14 sample
remains. The other ½ has been changed into N14( the more
table form
Percentage of original sample remaining
100%
50%
1 half life
1
25%
2 half life
1/2
12.5% 6.25% 3.125%
3 half life
1/4
4 half life
1/8
5 half life
1/16
1/32
1.56%
6 half life
1/64
Calculations involving half life
• A. Finding amount of sample remaining
• Procedure: use ½ n (where n=# half flies) to find
multiplication factor. Then multiply total by
original mass
– Ex. A 10 kg sample of C14 has underwent 4 half life's.
How much of the original sample remains?
• Ans. ½ n = ½ 4 = ½ x ½ x ½ x 1/2 = 1/16
• Now multiply 1/16 x original mass
• 1/16 x 10kg= .625 kg remaining
Finding the half life( time required for a
substance to deacy1/2 its original amount
• Ex. A rock is found to be 33000000 years old and contains
1/64 of the original sample. What is the half life of the
rock/
• First find the number of half life's it took to reduce the
sample to 1/64
• To do this we ask the question, ½ to what power =1/64/ the
easiest way to find this is to ask the question , 2 to what
power is 64. In this case 26 =2x2x2x2x2x2, so we
conclude that the number of half life's =6
• Next divide the age of the rock by the number of half life's
and you will find the value of 1 half life
• In this case 33000000/6 half-life's = 5500000/ half life's
Finding the age of the fossil
• Ex. A fossil contains 1/32 of the original U-235. what is the age
of the fossil if the half life of u-235 is 713000000?
• Answer
– First we need the number of half life's that reduces the fossil to
1/32 of its original amount
– To do this we as the question ½ to what power is 1/32.
Obviously it would be ½ to the power of 5. This means that 5
half life's have passed.
• Next we use the 5 half life's and multiply the value of a single half
life to get fossil age. In this case we have the following
• 5 half lifes X 713000000yrs/ half life= 3565000000 yrs old
2. Biogeography
• This is the study of the geographical distribution
of species
• Darwin noticed that the birds on the Galapagos
islands were similar to those on the mainland of
South America
• Geographically close environments (desert and
jungles of south America) are more likely to be
populated by related species rather than locations
that are geographically separate but
environmentally similar ( desert of Australia and a
desert in Africa)
3. Comparative Anatomy
• This is a comparison of physical structures in differing organisms
that may suggest a common ancestor. These methods are looked at:
• Homologous Structures: these are body structures in different
species which have the same origin but differ in structure and
function.
– Ex. Human arm, frog leg, bat wing, horse leg
• These structures all have a similar number of bones/ ligaments
suggesting they came from a common ancestor, but they all have a
different structure and function
• Analogous structures: these structures that have different origins
but similar functions
– Ex. Bird and incest wings
• Vestigial structures: these are structures that were functional in
ancestors, but have no current function
– Ex. Pelvic bone in baleen whales, wings in ostriches, appendix in humans
Homologous structures
Analogous structures
Vestigial
4. Comparative Embryology
• This is a comparison of embryos from
various species to indicate relationships
among organisms
• Many embryos have similar stages of
development
– Ex. All vertebrates go through a stage having a
gill pouch
Comparative embryology
5. Heredity
• Knowledge of heredity can explain how
variations can occur in a population
allowing members of that population to be
better suited to their environment and thus
undergo natural selection
6. Molecular Biology
• This is a comparison of the DNA and
proteins within various species to indicate
relationships/ similarities
• The closer the DNA sequences are between
organism the more closely related the
species are. This may suggest a common
ancestor
• Ex. Humans and chimpanzee differ by only
2.5%
Population Genetics and Hardy Weinberg
• Population genetics
– This is a study of the genes in a population and how
they may or may not change over time
• Recall: if there is a shift in the gene pool of a
population them we know evolution is happening
• Population
– A localized group of a single species occupying a
particular area
• Gene pool
– This is the total of all genes within a population
Hardy-Weinberg Principle
• Proposed by Hardy and Weinberg
• A model of a population that is not changing to help
understand a population that is changing
• Premise of the principle
– The principle states that in a population under certain conditions
the frequency of alleles will remain stable from generation to
generation
• In other words, under certain conditions a populations
genetic makeup will not change meaning it is not
evolving. It is in Genetic Equilibrium
• The principle explains why recessive alleles do not
disappear in a population over time and to helps explain
why dominant traits do not become more widespread
Conditions necessary to establish a
population hardy Weinberg equilibrium
•
•
•
•
Requirements
1. No mutations occur in the population.
2. No immigration or emigration.
3. There must be a very large population in
order to avoid genetic drift.
• 4. There must be no natural selection No
genotype has an advantage over another.
• 5. There must be no sexual selection
mating is random.
Formula
• 1. p+ q= 1
• P= frequency of dominant allele(how often the
dominant allele shows up in the total population
• q= frequency of the recessive allele(how often
the recessive allele shows up in the total
population
• 1=100%
• Since there are only ever two alleles for a trait ,
the total amount of the allele always has to add up
to be 100% or 1
• P2 + 2pq +q2 = 1
• P2 = frequency of Homozygous dominant
genotype
• 2pq=frequency of heterozygous genotype
• q2 frequency of homozygous recessive
genotype
example
• Suppose we have a population of Gerbils
with he following conditions
Phenotype
Black
Black
White
Genotype
BB
Bb
Bb
Number of
gerbils
196
168
36
Total number 400
of gerbils
(192+168+36)
= 400
400
400
Genotype
frequency
(BB,Bb,bb)
Bb=168/400=
0.42
BB=
36/400=0.09
BB=
196/400=0.49
Allele frequency (B and b)
B= 196 + 168/800=0.07
b= 168 + 36/800 = 0.03
• The table above shows the frequencies and
genotypes frequencies . Notice how they are
calculated
• Now lets look at formula
• we know BB = 0.49= p2
• Bb = 0.42= 2pq
• Bb = 0.09=q2
• According to the formula
• If we find want to find the frequencies of
the alleles B and b we need to find the
square root of p2 and q2 so
More on Evolution
• Microevolution - population change in allele
frequencies
• Macroevolution – grand scale changes as
seen in the fossil record
Mechanisms of evolution
• The following are mechanisms that cause
genetic variation in a population and thus move
them away from Hardy – Weinberg equilibrium
• In other words the following cause populations
to evolve
–
–
–
–
–
–
Mutations
Genetic drift
Gene flow
Non-random mating
Natural selection
Sexual selection
Mutations
• Changes in the DNA that bring new alleles in a
population
• New alleles provide variations that cause
evolution
• Mutations can be harmful, neutral or beneficial
• Mutations are beneficial if they provide a
selective advantage which allows certain
organisms to adapt to their environment
• Ex. California ground squirrel having the ability
to break down rattlesnake poison
Genetic Drift
• Change in allele frequencies in small populations
caused by chance alone
– For example in a small population mutations can
cause allele frequencies to change whereas in a
large population the mutations may have little to
no effect on the frequencies. The gene pool will
not shift if the population is large
• The allele frequencies in small populations can
change over time and this can lead to evolution.
Remember: in a non evolving population ( hardy
Weinberg equilibrium) the allele frequencies remain
unchanged
Causes of Genetic drift
• A. Bottleneck effect: a situation in which as a
result of chance some alleles are
overrepresented and others are
underrepresented because a population has
been reduced through natural disasters etc.
– Ex. Elephant seals have passed through a bottleneck. They
have been overhunted causing their numbers to be
reduced to about 20. because of this certain alleles have
been eliminated)( variety reduced). The population has
since grown to 30000 having little variation. This has
resulted in a change in the allele frequency
• Founder effect
• When a small amount of organisms (called
a founder population) move into a new area,
chances are they do not contain the entire
population in the parent population this
results in a changes in allele frequencies
– Ex. Hawaiian honey creeper birds migrated
from north America
Polydactyl in Quakers
Gene Flow
• This is the movement of genes into or out of
a gene pool
• This causes a change in the gene pool
resulting in evolution
• If gene flow happens enough between two
neighbouring populations they may
eventually merge into one population with a
common genetic structure
Non Random Mating
• If a population mates on a random basis genetic equilibrium is
maintained and the population does not evolve
• Normal populations do not undergo random mating. For
example individuals will mate more with their neighbours rather
than distant organisms there are two types of non random
mating
• Inbreeding- mating between closely related organism
– This will cause a loss in variety in the population and the allele
frequencies will change
• Assortive Mating- this is where organisms choose mates that
are similar to themselves
– Artificial selection ( breeding of certain dogs) is an example of assertive
mating. The dogs being mated are choosing (or are chosen for them)
mates that are similar to themselves
– This causes a reduction in variety in the population causing allele
frequencies to change
Non-Random Mating
Natural selection
• A populations characteristics can change
because certain individuals within the
population have heritable traits that allow
them top adapt to and survive local
environmental conditions
• There are 3 types of Natural Selection
– Stabilizing selection
– Directional selection
– Disruptive selection
Stabilizing
• Natural selection where an intermediate or
normal phenotype is favored over the
extremes
– Ex. Birth weight( most babies born today are of
average or normal weight because the extreme
(low or high) birth weight babies are selected
against(we do not see many low birth weights
or high birth weights babies anymore) The
middle intermediate phenotype is favored
Directional
• Selection where one extreme phenotype is
favored over the other. This causes a shift
in the phenotypes in that direction
• This type of selection is common during
environmental change or when population
migrates to a new habitat
– Ex modern horse (adapted to a grassland
habitat) adapted from an ancestral horse
(adapted to a forest habitat). Most horse today
resemble the modern horse and not the forest
horse
Disruptive
• Selection where both extremes of the
phenotype are selected rather than the
middle (intermediate phenotype)
• The intermediate phenotype may be
eliminated from the population
– Ex. Coho salmon. Males are either small (jack
salmon) or very large. No real medium size
male salmon found in the population
Sexual Selection
• This is selection on the basis off being able to
find a suitable mate in which to produce
offspring. Having the ability to choose a mate
helps ensure genetic information is passed on as
well as introduces variety into the population
• Finding a suitable mate is based on 2 main
characteristics
– Male competition- male competition can determine
who gets the chance to mate with female
– Female choice-females choose who they mate with
Sexual Selection
• Sexual selection acts on an
organism's ability to obtain
or successfully copulate
with a mate.
• Selection makes many
organisms go to extreme
lengths for sex:
Speciation
• Formation of a species
• Biological species: a group of organisms
able to interbreed and produce fertile
offspring
– Ex. Horses and donkeys are separate species.
They are able to interbreed, but the offspring
produced are not fertile
How do species form?
There are generally two pathways in which species are
formed
• 1. Transformation- the formation of a species because of
a series of accumulated changes over time. One species
changes into another in this way.
– Species
changes
new species
• 2. Divergence- the formation of species from a parent
species/ ancestor
– Parent
species
» Species
Speciation occurs when two groups become isolated from each other
Types of Speciation
• Allopatric—separation of members of the same species by a
physical barrier. The separate populations over time may evolve
distinctly different characteristics. If the geographical barriers
are later removed, members of the two populations may be
unable to successfully mate with each other, at which point, the
genetically isolated groups have emerged as different species.
• Allopatric isolation is a key factor in speciation and a common
process by which new species arise.[
• Parapatric—Occurs in adjacent populations
due to local environment problems. is the
relationship between organisms whose ranges
do not significantly overlap but are
immediately adjacent to each other; they only
occur together in a narrow contact zone.
• Sympatric—is the process through which
new species evolve from a single ancestral
species while inhabiting the same geographic
region
• individuals continue to live with each other.
Mostly in plants. Due to polyploidy.
Allopartric vs. Sympatric
What causes species to become
isolated?
Barriers
• Types of barriers
– Geographical Barriers- when a population
becomes divided by a geographical boundary
such as a canyon, river, etc. This prevents
interbreeding. Over time natural selection
causes genetic differences to become so large
two species form.
• Ex. Giraffes that become separated by mountains
will eventually develop into separate species
Biological Barriers
• These are barriers that keep species
reproductively isolated
• These barriers may be Pre-zygotic barriers
or Post zygotic Barriers
Pre zygotic Barriers
These are known as pre-fertilization barriers that either impede
mating or prevent fertilizations
• a. Behavioural isolation- bird songs, courtship rituals pheromones, etc. Are
all species specific and prevent fertilization
• b. Temporal isolation; these are usually timing barriers. Several species mate
at different times during the year and as such are not able to mate
• c. Habitat isolation-some species live in the same area but have different
habitats
– Ex. North American garter snakes. One prefers open areas while the other
prefers water
• d. Mechanical isolation- some species are automatically incompatible thus
not allowing them to exchange sperm and egg
– Ex. The genitals on certain species on insects work on a lock and key
hypothesis. If the lock does not fit the key, no fertilization can happen
• e. Gametic Isolation-sometimes the gametes from species do not even meet.
This prevents fertilisation.
– Ex. Sea urchins release eggs into the water but chemicals on the surface of
the eggs prevent sperm from as different species to fertile them.
Post Zygotic Barriers
These are barriers that prevent a zygote from developing
into a fertile organism
• a. Hybrid Invariability-incompatibility of two species
may cause the zygote to stop embryonic development.
– Ex. Embryos of sheep/goats do not survive
• b. Hybrid sterility- this is the production of an
organism but it is sterile
– Ex. Horse + donkey=mule(sterile)
• c. Hybrid Breakdown-sometimes the first generation
of offspring are viable and can reproduce, but when
their offspring reproduce their offspring are sterile or
weak.
– Ex. Cotton plants produce generations of seeds that die
Patterns of Evolution
• Convergent Evolution—become
more alike due to environment.
Aquatic mammals and fish.
• Divergent Evolution—Share a
common ancestor, but evolve
differently.
• Coevolution—Plants and
pollinators; parasites and hosts.
Adaptive Radiation
• The diversifying of an ancestral species into
a variety of species
• This usually occurs after a novel
characteristic has evolved or if there is a
mass extinction
Species 1
Species 2
• Ancestral species
Species 3
– Ex. Galapagos finches from one common
ancestor on islands
Adaptive Radiation
• The finches of the Galapagos Islands provide a
classic example this evolutionary process - a single
lineage gives rise to species occupying diverse
environmental niches. (13 species)
Divergent evolution
• This is where species that were once similar
to an ancestral species diverge to become
different species
• Note: Adaptive radiation is an example of
Divergent Evolution
Convergent evolution
• This is evolution where two completely
unrelated species have similar traits
– Ex. Birds and bees have wings (similar trait)
• Each species develops the same traits
because they adapt to the same type of
environmental conditions
• The species do not come from a common
ancestor
Co evolution
• This is evolution where two species change
together where each species responds to
changes in the other
– Ex. Milkweed plants and monarch butterflies.
The milkweed plant has toxins in their leaves.
Monarch butterfly eats the leaves and absorbs
the toxins making them toxic. Most birds avoid
monarch butterflies for this purpose
Pace of evolution
• How fast does evolution occur?
• There are two theories that explain how fast
evolution occurs. Both examine the fossil
record.
Gradualism
• A model that says change occurs slowly and
steadily before and after a divergence
• Fossils show a slow and repeated change
through the fossil record
Punctuated equilibrium
• A model; proposed by Gould and Eldridge
• A model that proposes evolution happens in
spurts
• The model says that species undergo long
periods of stasis where they remain unchanged
followed by short periods of very rapid change
(spurts)
• The changes are usually brought about by
sudden environmental changes such as volcanoes
earthquakes etc.
• Species previously disadvantaged could now be
advantaged and new species could develop
quickly
Origins of the World and Life
• Many theories exist that try to explain the origin and
development of life on earth
• The following will be considered
–
–
–
–
–
–
Chemical evolution’
Panspermia
Gaia hypothesis
Heterotroph hypothesis
Symbiogensis (symbiotic theory)
Intelligent design
Chemical Evolution
• A theory of evolution created by Oparin-Haldane
• They said that organic molecules (the building blocks of
life) could develop from inorganic compounds present on
the surface of the early earth
– The earth had an atmosphere that consisted of no oxygen, but
plenty of hydrogen, Ammonia(NH3 , Methane and water
vapour(inorganic molecules)
– These gases condensed and formed a primordial soup
– Energy from, lightening and UV radiation caused organic
molecules to develop from inorganic molecules in the soup
– Overtime the organic molecules combined to become an early life
form
• Miller Urey
• Two scientists who designed an experiment to
prove Oparin-Haldanes theory. Here is what they
did
• They combined methane, ammonia, water vapour
and hydrogen in a flask and exposed the gases to
an energy source simulating lightening
• The liquid inside the flask changed color and
when examined contained several organic
compounds including amino acids
– Amino acids make up protein which make up the
structure of most living things
Panspermia
• A theory that suggests life began elsewhere
in the universe and migrated to our plant
• For example it is believed that life
originated from bacterial cells elsewhere
and travelled from outer space to earth on
meteorites
Gaia Hypothesis
• theory put forward by James Lovelock
• Idea that earth is a super organism called
Gaia
• The earth has systems that keep a balance
between temperature and atmosphere
• After life originated on earth, Gaia came
alive and began to regulate earth systems
• The systems help provide an environment
where life could exist and survive
Heterotroph Hypothesis
• Theory put forth by Oparin
– Said that firs cells on earth had to be heterotrophs that eventually
developed into autotrophs
• Primordial soup existed of organic molecules
• The environment was oxygen poor
• Heterotrophs such as anaerobic bacteria fed on the organic
molecules
• The hetrotrophs began to release carbon dioxide into the
atmosphere, The heterotrophs developed into autotrophs
and began using carbon dioxide
• The autotrophs began to release oxygen into the
atmosphere
• This made the atmosphere oxygen rich that could now
support life
Symbiogensis
• Put forth by Lynn Margulis
– Theory that attempts to explain the development of
mitochondria and chloroplasts as organelles that appear
in eukaryotic cells
– Chloroplasts and mitochondria have their own DNA
and come from the symbosis (working together) of
prokaryotic cells
– Here is how she said eukaryotic organisms developed
• An anaerobic bacterium ate but did not digest an aerobic
bacterium(called a guest bacterium)
• The guest bacterium provided oxygen to the bacterium. The
guest bacterium eventually became a mitochondrion
• Other bacteria ate photosynthesizing bacteria. The
photosynthesizing bacteria became chloroplasts
Intelligent Design
• Theory suggests that life and mechanism of
life are too complex to have evolved by
chance
• Believed that the generation and evolution
of life must have been directed by some
unidentified supernatural intelligence