What is evolution?

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What is evolution?
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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

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• 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

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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.

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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 1900s 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.

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• 1950s
• 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

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• How do peppered moths support evolution?
• 1. 1850s moths in England were mostly flecked
  (some were black) flecked ones survived because
  they were camouflaged
• 2. 1900s air pollution made trees black. Black
  moths were able to survive
• 3. 1950s saw pollution controls and now the
  flecked moth is surviving again

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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
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• 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.

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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

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• 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

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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

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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
  Noahs flood or droughts
• Developed the theory of catastrophism
• Catastrophes account for the disappearance and
  appearance of new species in the fossil record

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Charles Lyell (1797-1875)

• Expanded on Hutton's idea of Gradualism
• Gradualism-
• idea that earths 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

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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

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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

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• 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

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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.

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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

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Natural Selection and Evolution
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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

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Darwins Finches
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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

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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

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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

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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

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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.

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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
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• 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
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C 14
C14
N14
N14
C14
C14
5730 years One ½ life
5730 years 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 25 12.5 6.25 3.125 1.56
1 half life
2 half life
3 half life
4 half life
5 half life
6 half life
1
1/2
1/4
1/8
1/32
1/64
1/16
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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

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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

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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

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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)

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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

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Homologous structures
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Analogous structures
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Vestigial
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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

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Comparative embryology
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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

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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

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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

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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

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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.

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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
• 1100
• 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

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• P2 2pq q2 1
• P2 frequency of Homozygous dominant genotype
• 2pqfrequency of heterozygous genotype
• q2 frequency of homozygous recessive genotype

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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 of gerbils (19216836) 400 400 400 400
Genotype frequency (BB,Bb,bb) BB 196/4000.49 Bb168/400 0.42 BB 36/4000.09
Allele frequency (B and b) B 196
168/8000.07 b 168 36/800 0.03
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• 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 0.09q2
• 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

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More on Evolution

• Microevolution - population change in allele
  frequencies
• Macroevolution grand scale changes as seen in
  the fossil record

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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

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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

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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

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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

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• 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

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Polydactyl in Quakers
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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

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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

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Non-Random Mating
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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

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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

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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

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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

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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

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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

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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

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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
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Types of Speciation

• Allopatricseparation 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.

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• ParapatricOccurs 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.
• Sympatricis 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.

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Allopartric vs. Sympatric
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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

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• Biological Barriers
• These are barriers that keep species
  reproductively isolated
• These barriers may be Pre-zygotic barriers or
  Post zygotic Barriers

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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.

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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 donkeymule(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

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Patterns of Evolution

• Convergent Evolutionbecome more alike due to
  environment. Aquatic mammals and fish.
• Divergent EvolutionShare a common ancestor, but
  evolve differently.
• CoevolutionPlants and pollinators parasites and
  hosts.

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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
• Ancestral species
• Ex. Galapagos finches from one common ancestor on
  islands

Species 1 Species 2 Species 3
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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)

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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

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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

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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

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Pace of evolution

• How fast does evolution occur?
• There are two theories that explain how fast
  evolution occurs. Both examine the fossil record.

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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

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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

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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

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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

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• 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

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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

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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

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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

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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

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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