Transcript - SlideBoom

Mr. Lajos Papp
The British International School, Budapest
2011/2012
By evolution we mean the development of life in geological time. The term comes
from the Latin word evolvere, meaning to unroll. Today the word implies "origin
from earlier forms" and is used widely in the English language, not only in
reference to a complex biological process. In biology the term is used specifically
for the processes that have transformed life on Earth from its earliest beginnings to
the vast diversity of fossilised and living forms we know today. The idea of
biological evolution is linked to the name of Charles Darwin, but in fact it was
discussed by several biologists and geologists long before the publication of
Charles Darwin's theory in 1859 (On the origin of species by means of natural
selection or the preservation of favoured races in the struggle for life).
http://www.literature.org/authors/darwin-charles/the-origin-of-species/
D1. Origin of life on Earth
Pasteur showed in an experiment in the 19th century that
spontaneous generation of life from inorganic matter does not
take place – cells can only be formed from other cells.
http://www.accessexcellence.org/RC/AB/BC/Spontaneous_Gener
ation.php
http://www.talkorigins.org/faqs/abioprob/spontaneousgeneration.html
When the Earth was formed there were no living cells on it,
so at some stage the first living cells must have appeared.
The oldest bacterial fossils date from 1.9 billion years ago.
1. chemical reactions to produce simple organic molecules,
such as amino acids, from inorganic molecules, such as
water, carbon dioxide and ammonia,
2. assembling of these simple organic molecules into
polymers, for example polypeptides from amino acids,
3. formation of polymers that can self-replicate – that
allows inheritance of characteristics,
4. development of membranes, to form spherical
droplets, with an internal chemistry different from the
surroundings, including the polymers that held the
genetic information.
The product of these four processes would have been cell-like
structures. Natural selection could have operated on them,
allowing evolution to begin.
http://www.answersingenesis.org/docs2002/dw_origin.asp
http://www.nwcreation.net/abiogenesis.html
Describe four processes needed for the spontaneous origin of
life on Earth. Include: the non-living synthesis of simple
organic molecules; the assembly of these molecules into
polymers; the origin of self-replicating molecules that made
inheritance possible; the packaging of these molecules with an
internal chemistry different from their surroundings.
The concept that simple organic molecules such as sugars,
nucleotide bases, and amino acids could form spontaneously
from simpler raw materials was first hypothesised in the
1920s by two scientists working independently: A. I. Oparin,
a Russian biochemist, and J. B. S. Haldane, a Scottish
physiologist. Their hypothesis was tested in 1953 by Stanley
Miller and Harold Urey, who designed an apparatus that
stimulated conditions thought to be common on early Earth.
They exposed an atmosphere rich in hydrogen, methane,
water vapour, and ammonia to an electrical discharge
that stimulated lightning. Their analysis of the
chemicals produced in a week revealed that amino acids
and other organic molecules had formed.
Although more recent data suggest that Earth's early atmosphere
was not rich in methane or ammonia, similar experiments using
different combinations of gases have produced a wide variety of
organic molecules, including the nucleotide bases of RNA and
DNA. When laboratory conditions become oxidising, no amino
acids are formed, suggesting that reducing conditions were
necessary for prebiological organic synthesis.
http://www.postmodern.com/~jka/rnaworld/nfrna/nf-millered.html
Outline the experiments of Miller and Urey into the origin of
organic compounds.
Various possible locations have been suggested for the
synthesis of the organic compounds needed for the
origin of life.
1. Miller and Urey's experiments suggest that organic
compounds could have been synthesized by chemical
reactions in the atmosphere and in water, on the
surface of the Earth.
2. There are hydrothermal vents (openings on the ocean
floor that emit hot water and dissolved minerals) deep in
the ocean, with chemicals welling up from the rocks
below. Around these vents, there are very unusual
chemical conditions, which might have allowed the
spontaneous synthesis of the organic compounds from
which the first organisms evolved.
3. Some theories involve an extraterrestrial origin for organic
compounds. Experiments have shown that organic compounds and
proto-cells could have formed in cold interstellar space. They
might then have been delivered to the Earth by meteorites or
comets. There was a heavy bombardment (flood, shower) of the
Earth by meteorites 4 000 million years ago, which might have
brought the organic compounds that became organized into the
first living organisms.
http://universe-review.ca/F11-monocell.htm
Discuss possible locations where conditions would have allowed
the synthesis of organic compounds. Examples should include
communities around deep-sea hydrothermal vents, volcanoes
and extraterrestrial locations. Comets may have delivered
organic compounds to Earth. Comets contain a variety of
organic compounds. Heavy bombardment about 4,000 million
years ago may have delivered both organic compounds and
water to the early Earth.
In modern prokaryotes, the various parts of the genetic
mechanism cannot function without each other. For example,
genes cannot be replicated without enzymes and enzymes cannot
be made without genes. It seems inconceivable that the whole
mechanism could have evolved at once, but gradual evolution
would have required simpler intermediate stages. One possibility
is the use of RNA may have had a very significant role in the
origin of life. It has two properties that would have allowed it to
do this – catalysis and self-replication.
1. RNA catalyses a broad range of chemical reactions. It
could therefore have taken the role that is carried out by
proteins (enzymes) in the organisms that now exist on
Earth. RNA still catalyses some reactions, for example
peptide bond formation during protein synthesis in the
ribosome.
2. RNA is capable of self-replication – one molecule can form
a template for the production of another molecule, following
the rules of complementary base pairing. If the newly
synthesized molecule is then used as a template, a replicate
of the original molecule will be produced.
No biological mechanisms now exist for self-replication by
RNA molecules, but this is not surprising as RNA was
replaced by DNA as the genetic material and by proteins as the
catalysts of life.
There are various reasons for the DNA-protein world replacing
the RNA world. One possibility is that the maximum length of
RNA molecules is about 1500 nucleotides – this places a severe
restriction on the amount of genetic information that can be held.
http://bill.srnr.arizona.edu/classes/182/RNAWorld.HTM
http://bill.srnr.arizona.edu/classes/182/Lecture%202009-04.htm
Outline two properties of RNA that would have allowed it to
play a role in the origin of life. Include self-replicating and
catalytic activities of RNA.
To form the first cells, membranes were needed to separate
cytoplasm and its metabolism from the surrounding fluid.
Phospholipids naturally group together to form bilayers in water.
These bilayers form spherical structures enclosing a droplet of fluid,
similar to the vesicles that are now found in cells. Water containing
these membrane-bound microspheres is called coacervate and is
viscous and cloudy in appearance. Because of their hydrophobic
properties, bilayers of phospholipid would have allowed an internal
environment
environment.
to
develop,
different
from
the
surrounding
These primitive cell-like structures, that may have preceded
living cells, are called protobionts. To become cells, they
would have had to develop genetic mechanisms to allow
reproduction and the transmission of characteristics to
offspring. The details of this transition are not yet
understood.
The formation of protobionts
Protobionts
are
aggregates
of
abiotically
produced
molecules able to maintain an internal environment different
from their surroundings and exhibiting some life properties
such as metabolism, excitability and self-replication. These
protobionts were probably antecedents of first true cells.
Evidence to support this hypothesis:
1. When mixed with cool water, proteinoids (thermal proteins,
protein-like molecules formed inorganically from amino acids)
self-assemble into microspheres surrounded by a selectively
permeable membrane.
2. Liposomes can form spontaneously when phospholipids form
a bilayered membrane similar to those of living cells.
3. Coacervates (colloidal drops of polypeptides, nucleic acids
and polysaccharides) self-assemble.
http://www.biog11051106.org/demos/106/unit04/3a.protobionts.html
Living cells may have been preceded by protobionts, with
an internal chemical environment different from their
surroundings.
microspheres.
Examples
include
coacervates
and
The first organisms on Earth to use photosynthesis for the
synthesis of organic compounds were prokaryotes. When these
organisms started to use water as the source of hydrogen in
photosynthesis, oxygen started being released as a waste product
into the atmosphere. Concentrations of oxygen built up over a
hundred million years. This was probably due to the activity of
photosynthetic prokaryotes. Other prokaryotic organisms were
able to use aerobic cell respiration, once the atmosphere
contained oxygen.
Outline the contribution of prokaryotes to the creation of an
oxygen-rich atmosphere.
The fossil evidence shows that not only were the first cells
prokaryotic, but that it was thousands of millions of years
before eukaryotic cells joined them. The difference in the
levels of organisation of these two types of cell is greater
than that between plants and animals. There is NO fossil
record of the event. The eukaryotic cell is characterised by a
range of organelles not present in prokaryotes, most being
membranous structures.
Cell organelles, such as endoplasmic reticulum and
nuclear envelope, may have originated as infoldings of
the plasma membrane. Simple infoldings are found in
some present-day bacteria and it is not difficult to
imagine in various ways and eventually pinching off
from the plasma membrane to become separate
structures. But chloroplasts and mitochondria almost
certainly have an entirely different origin.
One possibility is that a heterotrophic prokaryote may have
ingested an autotrophic prokaryote which, instead of being
digested, became a symbiont inside the heterotroph,
enabling it to carry out photosynthesis. Equipped with its
own DNA, the symbiont may have divided inside the host
cell every time the host cell itself divided, and in this way
the symbiont may have become a chloroplast inside the host
cell.
This endosymbiotic theory may also explain the origin of
mitochondria. The ancestors of mitochondria may have been
bacteria that were aerobic heterotrophs. Perhaps they first gained
entry into a larger prokaryote as undigested prey or internal
parasites. One can imagine how the 'capture' of appropriate
prokaryotes
might
lead
to
a
large
prokaryote
having
protochloroplasts and protomitochondria. The endosymbiotic theory
has been advocated over the last 25 years by Lynn Margulis. There
are several lines of evidence for it:
1. It explains why mitochondria and chloroplasts, unlike
other organelles, have a double membrane. The inner
membrane in each case presumably belonged to the
original free-living organism. The outer membranes
assumed to be comparable to the membrane that surrounds
a food particle in phagocytosis.
2. Mitochondria and chloroplasts have their own DNA and
this is in the form of a ring, just as in present day
prokaryotes.
3. The inner membranes of mitochondria and chloroplasts
have several enzymes and transport systems that closely
resemble those found in the cell membranes of modern
prokaryotes.
4. Mitochondria and chloroplasts divide by a splitting
method reminiscent of binary fission in bacteria.
The ribosomes in mitochondria and chloroplasts are the
same size as those found in modern prokaryotes, and
significantly smaller than those found in the cytoplasm of a
eukaryote.
Discuss the endosymbiotic theory for the origin of
eukaryotes.
D2. Species and speciation
Many genes have different alleles. In a typical interbreeding
population, some alleles will be commoner than others. How
common an allele is can be assessed using allele frequency.
Allele frequency can range from 0.0 to 1.0.
Allele frequency: the frequency of an allele, as a proportion
of all alleles of the gene in the population.
A new individual, produced by sexual reproduction, inherits
genes from its two parents. If there is a random mating, any
two individuals in an interbreeding population could be the
two parents, so the individual could inherit any of the genes
in the interbreeding population. These genes are called the
gene pool.
Gene pool: all the genes in an interbreeding population.
Define allele frequency and gene pool.
Evolution involves a change in allele frequency in a
population’s gene pool over a number of generations.
Species: a group of organisms that differ from all other groups of
organisms and that are capable of breeding and producing fertile
offspring. This is the smallest unit of classification.
The biological definition of a species: a group of actually or
potentially interbreeding populations, with a common gene pool,
which are reproductively isolated from other such as groups.
This definition causes some problems.
1. Many sibling species have been found. These are species
that cannot interbreed, but show no significant differences
in appearance. Although separate species, they are very
difficult for ecologists to identify.
2. Some pairs of species that are clearly different in their
characteristics will interbreed. Many plant species
hybridize.
3. Some species always reproduce asexually, so the
members of a population do not interbreed. The biological
species definition is therefore unusable.
4. Fossils cannot be classified according to the definition,
as it is impossible to decide with which organisms they
would have been able to interbreed.
Discuss the definition of the term species.
The formation of a new species is called speciation. New
species are formed when a pre-existing species splits. This
usually involves the isolation of a population from the
remainder of its species and thus the isolation of its gene
pool. The isolated population will gradually diverge from
the rest of the species if natural selection acts differently on
it.
Eventually the isolated population will be unable to
interbreed with the rest of the species – it has become a new
species.
Speciation via polyploidy: a diploid cell undergoes failed
meiosis (non-disjunction), producing diploid gametes, which
self-fertilize to produce a tetraploid zygote.
Explain how polyploidy can contribute to speciation. Avoid
examples involving hybridization as well as polyploidy,
such as the evolution of wheat.
Allopatric speciation occurs when members of a species
migrate to a new area, forming a population that is
geographically isolated from the rest of the species.
Interbreeding is impossible – geographical isolation acts as
a barrier between the gene pools of the populations. The
populations can therefore split to form separate species.
Sympatric speciation occurs when two varieties of a
species live in the same geographical area, but do not
interbreed. Reasons can be: behavioural (temporal) barrier,
hybrid infertility (polyploidy, in plants).
The apple maggot fly of North America used to lay its
eggs only on hawthorn fruits, which were the food of its
larvae. It now also infests non-native apple trees as well.
One strain of this species now lays its eggs on apple fruits
and other strains on hawthorn fruits. Because the fruits
ripen at different times, adult of the two strains emerge
and mate at different times, so there is a behavioural or
temporal barrier between the gene pools.
Barriers between gene pools can also occur by hybrid
infertility, often due to polyploidy. If there are some
tetraploid individuals in a population, the gametes that they
produce will be diploid. Hybrids produced when diploids
mate with tetraploids will be triploid. These hybrids will
always be sterile as meiosis fails in triploid cells. So,
diploids can only produce fertile offspring by mating with
diploids and tetraploids by mating with other tetraploids.
Compare allopatric and sympatric radiation. Speciation:
the formation of a new species by splitting of an existing
species. Allopatric: in different geographical areas.
Sympatric: in the same geographical areas.
Describe three examples of barriers between gene pools.
Examples include geographical isolation, hybrid infertility,
temporal isolation and behavioural isolation.
An adaptive radiation is a rapid evolutionary radiation
characterized by an increase in the morphological and ecological
diversity of a single, rapidly diversifying lineage. Phenotypes
adapt in response to the environment, with new and useful traits
arising. This is an evolutionary process driven by natural
selection.
1. Species A migrates from the mainland to the first
island.
2. Isolated from the mainland, species A evolves to
species B
3. Species B migrates to the second island.
4. Species B evolves in species C.
5. Species C recolonizes the first islands, unable to
reproduce with species B.
6. Species C migrates to the third island.
7. Species C evolves into species D.
8. Species D migrates to the first and second island.
9. Species D evolves to species E.
This process could go on indefinitely until a large
diversity is reached.
Darwin's Finches
They illustrate adaptive radiation. This is where species all
deriving from a common ancestor have over time successfully
adapted to their environment via natural selection.
Previously, the finches occupied the South American
mainland, but somehow managed to occupy the Galapagos
Islands, over 600 miles away. They occupied an ecological
niche with little competition.
As the population began to flourish in these advantageous
conditions, intraspecific competition became a factor, and
resources on the islands were squeezed and could not sustain the
population of the finches for long. Due to the mechanisms of
natural selection, and changes in the gene pool, the finches
became more adapted to the environment.
Outline the process of adaptive radiation.
Convergent evolution describes the acquisition of the same
biological trait in unrelated lineages. Although their last common
ancestor did not have wings, birds and bats do, and are capable of
powered flight. The wings are similar in construction. Similarity can
also be explained by shared ancestry, as evolution can only work
with what is already there - thus wings were modified from limbs, as
evidenced by their bone structure.
http://en.wikipedia.org/wiki/List_of_examples_of_convergent_evol
ution
Divergent evolution is the accumulation of differences
between groups which can lead to the formation of new
species. The vertebrate limb is one example of divergent
evolution. The limb in many different species has a common
origin, but has diverged somewhat in overall structure and
function.
Compare convergent and divergent evolution.
Gradualism states that the evolution proceeds very slowly,
but large changes can gradually take place over long periods
of time. This does not fit in with the fossil record, which
shows periods of stability, with fossils showing little
evolution followed by periods of sudden major change. The
periods of stability may be due to equilibrium where living
organisms have become well adapted to their environment
so natural selection acts to maintain their characteristics.
The periods of sudden change that occasionally occur, may
correspond with rapid environmental change, caused for
example by volcanic eruptions or meteor impacts. New
adaptations would be necessary to cope with changed
environmental conditions.
Punctuated equilibrium theory implies that there were long
periods with no change and short periods of rapid evolution.
Periods of mass extinctions were caused by environmental
disruption (meteors, earthquakes, volcanoes, etc.) or by a rapid
environmental change in short periods.
This theory is based on fossil evidence rather than biochemical
evidence and is supported by lack of fossils showing gradual
changes.
Discuss ideas on the pace of evolution including gradualism
and punctuated equilibrium. Gradualism is the slow change
from one form to another. Punctuated equilibrium implies long
periods without appreciable change and short periods of rapid
evolution. Volcanic eruptions and meteor impacts affecting
evolution on Earth could also be mentioned.
Polymorphism is the word used to describe the presence of
genetically determined differences between large groups in the
same population.
The peppered moth (Biston betularia) is very common in
Britain and normally rests in shaded sites on trees. Here it
depends on its cryptic coloration to blend in with the background.
The normal form of the moth is speckled white, but another form
is very much darker. This is called the melanic form.
The black variety of moth arose as a result of a mutation called
polymorphism. Black form is caused by a dominant allele and the
frequency of it increases or decreases quickly with environmental
change. It is caused by production of melanin. The first melanic
moths were reported in 1848 in Manchester. In the 1950s
scientists conducted an extensive survey on the relative
abundance and distribution of the normal and melanic forms in
different parts of the country.
The interesting fact that emerged was that the melanic form abounded
in industrial regions where smoke and soot from factory chimneys had
blackened the bark of trees and killed off pale lichens. Around
Manchester, for example, the frequency of the melanic form exceeded
95 per cent. In non-polluted areas, however, the light form
predominated. In the north of Scotland and the extreme south-west of
England it even reached 100 per cent. How can we explain this
distribution? The peppered moth is preyed upon by birds, such as great
tits, which peck them off the trees. In polluted areas the dark form is
almost invisible against the darkened branches, whereas the light form
stands out like a beacon.
In clean areas the reverse is true: the light form is admirably
camouflaged against the background of unsooted lichens, but the
dark form is very clearly seen. The scientists showed that in
polluted woods, such as occurred near Birmingham, far more
light moths were picked off the trees by birds than the better
camouflaged dark forms. As a result the frequency of dark moths
was significantly higher. In non-polluted Dorset woods, however,
it was mainly the dark moths that fell prey to birds, so the
frequency of the light moths was higher. In each case differential
mortality was achieved by selective predation.
The darkening of trees with the coming of the industrial
revolution meant that the dark body colour was favoured
over light. In the last thirty years, however, there has been a
significant reduction in industrial pollution in Britain. As a
result the frequency of melanic moths has started to decline
in industrial areas. This phenomenon is called industrial
melanism.
Transient polymorphism: industrial melanism: black
variety of moth arose as a result of a mutation (in the light
form); phenomenon is called transient polymorphism; black
form is caused by a dominant allele; black colour is caused
by production of melanin; industrial pollution caused death
of lichens on trees and rocks; many trees, rocks and
buildings became blackened; melanic variety became better
camouflaged than light form; resulted in less predation by
birds;
black variety increased at the expense of the light variety; as
pollution decreased the lichens recovered and conditions
favoured the light form; light variety increased at the
expense of the dark variety.
Describe one example of transient polymorphism. An
example of transient polymorphism is industrial melanism.
Sometimes two alleles of gene can persist indefinitely in the gene
pool of a population. It is not therefore a transient polymorphism
and instead is called balanced polymorphism (sickle cell
anaemia)
Individuals with the genotype HbAHbA do not develop sickle cell
anaemia but are susceptible to malaria.
Individuals with the genotype HbSHbS are resistant to malaria,
but develop severe sickle cell anaemia.
Heterozygous individuals HbAHbS do not develop sickle cell
anaemia and are resistant to malaria. They are therefore the
best adapted in areas where malaria is found.
http://www.sicklecellsociety.org/healthpr.htm
Describe sickle cell anaemia as an example of balanced
polymorphism. Sickle cell anaemia is an example of
balanced polymorphism where heterozygotes (sickle cell
trait) have an advantage in malarial regions because they
are fitter than either homozygote.
D3. Human evolution
Half life: the time during which the radioactivity falls to
half its original level.
The most useful fossil evidence comes from rocks that
have been accurately dated. Radioactive isotopes (called
radioisotopes) present in a rock give us an accurate
measure of its age. Radioisotopes emit powerful, invisible
radiations.
As a radioisotope emits radiation, its nucleus changes
into the nucleus of a different element in a process
known as radioactive decay. Each radioisotope has its
own characteristic rate of decay.
The period of time required for one half of the atoms of a
radioisotope to change into a different atom is known as its
half-life.
Different radioisotopes have enormous variations in their
half-lives. For example, the half-life of iodine-132 is only
2.4 hours, whereas the half-life of uranium-235 is 704
million years.
The half-life of a particular isotope is constant and does not
vary with temperature, pressure, or any other environmental
factor. The age of a fossil is estimated by measuring the
relative proportions of the original radioisotope and its
decay product.
For example, the half-life of potassium-40 is 1.3 billion years,
meaning that in 1.3 billion years half of the radioactive potassium
will have decayed into its decay product, argon-40. The
radioactive clock begins ticking when the rock solidifies. The
rock initially contains some potassium, but no argon. Because
argon is a gas, it escapes from hot rock as soon as it forms, but
when potassium decays in rock that has cooled and solidified, the
argon accumulates in the crystalline structure of the rock. If the
ratio of potassium-40 to argon-40 in the rock being tested is 1:1,
the rock is 1.3 billion years old.
Several different radioisotopes are commonly used to date fossils.
These include potassium-40, uranium-235, and carbon-14 (halflife 5730 years). Potassium-40, with its long half-life, can be used
to date fossils that are many hundreds of millions of years old.
Radioisotopes other than carbon-14 are used to date the rock
in which fossils are found, whereas carbon-14 is used to date
the carbon remains of anything that was once living, such as
wood, bones, or shells. Whenever possible, the age of a fossil is
independently verified using two or more different radioisotopes.
Carbon-14, which is continuously produced in the atmosphere
from nitrogen-14 (by cosmic radiation), subsequently decays
back to nitrogen-14. Because the formation and the decay of
carbon-14 occur at constant rates, the ratio of carbon-14 to
carbon-12 (the more abundant, stable isotope of carbon) is
constant in the atmosphere. Since each living organism absorbs
carbon from the atmosphere (either directly or indirectly), its ratio
of carbon-14 to carbon-12 is the same as the atmosphere. When
an organism dies, however, it no longer absorbs carbon and the
proportion of carbon-14 in its remains declines as carbon-14
decays to nitrogen-14.
Because of its relatively short half-life, carbon-14 is useful
for dating fossils that are about 100,000 years old or less.
Radioactive isotopes decay at a constant rate producing
radioactive radiation and a non-radioactive isotope:
6C
 7 N + -1 e
14
40 K
19
14
0
+ 0e  40 Ar
-1
18
A method that can be used to date fossils up to 100 000 years old:
use radioisotope;
14C;
extract isotopes from fossil; measure
amount/proportion of 14C; compare with decay curve.
Outline the method for the dating of rocks and fossils using
radioisotopes, with reference to
14C
and
40K.
Knowledge of the
degree of accuracy and the choice of isotope to use is expected.
Worksheet.
Deduce the approximate age of materials based on a simple decay
curve for a radioisotope. Look on the graph at how many times the
concentration of the original isotope has halved then multiply that
by the half-life.
The characteristics of the primates
1.
adaptation for a tree-living (arboreal) existence with prehensile
(grasping) hands, five digits (four fingers plus an opposable thumb)
manipulating objects
2.
long, slender limbs that rotate freely at shoulders and hips
3.
nail instead of claws, and sensitive touch pads at the ends of the
digits
4.
an increasingly forward-facing position of the eyes with the
development of stereoscopic vision and both sides of the brain
receive images from the two eyes, enabling accurate depth perception
5. an expansion and elaboration of the parts of the brain,
especially the parts associated with muscular coordination, colour vision, tactile senses, memory, thought,
learning, sound processing
6. a tendency to hold the head erect and to sit upright
Describe the major anatomical features that define
humans as primates.
In 1924 Raymond Dart announced the discovery of a fossil skull
from a Southern African quarry. The fossil was named
Australopithecus
africanus
(Southern
ape).
Subsequent
discoveries indicated that Australopithecus walked fully erect and
had human-like hands and teeth. The brain of Australopithecus
was about one-third the size of a modern human's. The genus has
by now been split into several species. One of these is called
Australopithecus afarensis because the first fossil of this species
was found in Ethiopia. This fossil was discovered in 1974.
Its significance lies partly in the fact that it is 40 per cent intact,
making it one of the most complete fossil hominids known. The
fossil is known as 'Lucy'. Lucy lived some three million years
ago. She stood only 110 cm tall and weighed about 30 kg. The
shape of her pelvis identifies her as an adult female. Her cranial
capacity was only about 400 cm3 and, although she was bipedal,
her walk was probably more rolling than ours. Between
Australopithecus and us - Homo sapiens - lie a number of other
species including Homo habilis and Homo erectus.
H. habilis is the older, existing about 1.5 million years ago,
in Africa, from where it migrated to Asia, where the first
fossils were found (Java Man and Peking Man). Judging by
the artefacts, both species used tools. H. erectus individuals
seem to have lived in huts and caves, built fires and clothed
themselves in animal skins.
The oldest fossils classified as Homo sapiens date from
about 130 000 years ago. H. sapiens is distinguished from
H. erectus by a number of precise anatomical differences,
including the possession of a significantly larger brain. In
addition archaeological remains show that the early
members of H. sapiens buried their dead.
Ardipithecus ramidus
http://humanorigins.si.edu/evidence/humanfossils/species/ardipithecus-ramidus
Ardipithecus ramidus was named in September 1994.
The first fossil find was dated to 4.4 million years ago.
Its
distinguishing
characteristics
are
bipedalism
incorporating a big toe, reduced canine teeth and a
smaller brain size comparable to that of the modern
chimpanzee.
Ardipithecus ramidus had a small brain, measuring
between 300 and 350 cm3. This is about the same size as
a female common chimpanzee brain, but much smaller
than the brain of Australopithecines like Lucy (~400 to
550 cm3) and roughly 20% the size of the modern Homo
sapiens brain.
Australopithecus afarensis
http://humanorigins.si.edu/evidence/humanfossils/species/australopithecus-afarensis
The earliest evidence of fundamentally bipedal hominids
can be observed in Tanzania. This site contains hominid
footprints that are remarkably similar to those of modern
humans and have been dated to as old as 3.6 million years.
The brains of most species of Australopithecus were roughly
35% of the size of that of a modern human brain. Most
species of Australopithecus were gracile, usually standing
between 1.2 to 1.4 m tall.
In several variations of Australopithecus there is a considerable
degree of sexual dimorphism, in this case males being larger than
females. Modern hominids do not appear to display sexual
dimorphism to the same degree — particularly, modern humans
display a low degree of sexual dimorphism, with males being
only 15% larger than females, on average. In Australopithecus,
however, males can be up to 50% larger than females.
Australopithecus africanus
http://humanorigins.si.edu/evidence/humanfossils/species/australopithecus-africanus
Australopithecus fossils
found in East and South Africa; app. 2-4 million years old;
small size; erect, biped position; small brain and skull;
humanoid teeth.
Australopithecus culture
uses objects as tools; makes very simple tools; no evidence
of fire cooking; gatherers, killers of very small animals; low
cultural evolution.
Homo habilis
http://humanorigins.si.edu/evidence/humanfossils/species/homo-habilis
Homo habilis
"Handy-man” is a species of the genus
Homo, which lived from approximately 2.3 to 1.4 million
years ago. H. habilis was short and had disproportionately
long arms compared to modern humans; however, it had a
less protruding face than the australopithecines from which
it
is
thought
to
have
descended.
Compared
to
australopithecines, H. habilis's brain capacity of 363 and
600 cm³ was on average 50% larger than australopithecines,
but considerably smaller than the 1350 to 1450 cm³ range of
modern Homo sapiens.
These hominids were smaller than modern humans, on
average standing no more than 1.3 m (4 ft 3 in) tall. Despite
the ape-like morphology of the bodies, H. habilis remains
are often accompanied by primitive stone tools.
Homo erectus
http://humanorigins.si.edu/evidence/humanfossils/species/homo-erectus
Homo erectus is an extinct species of hominid that
originated in Africa and spread as far as China and Java
about 1.8 to 1.3 million years ago. H. erectus originally
migrated from Africa around 2.0 million years ago.
Fossilized remains 1.8 and 1.0 million years old have been
found in Africa, Europe, Indonesia and China.
H. erectus had a cranial capacity greater than that of Homo
habilis: the earliest remains show a cranial capacity of
850 cm³, while the latest Javan specimens measure up to
1100 cm³, overlapping that of H. sapiens; the face is less
protrusive than either the australopithecines' or H. habilis's,
with large brow-ridges and less prominent cheekbones.
These early hominids stood about 1.79 m and were more
robust than modern humans. The sexual dimorphism
between males and females was slightly greater than seen in
H. sapiens, with males being about 25% larger than females.
Homo erectus
found in Africa, Asia and Europe; app. 200,000-1 million
years old; erect, biped position; larger brain than
Australopithecus and larger skull; medium size.
Homo erectus culture
tool maker; more elaborated tools; use of fire for cooking;
hunters and gatherers.
Homo neanderthalensis
http://humanorigins.si.edu/evidence/humanfossils/species/homo-neanderthalensis
Homo neanderthalensis is an extinct member of the Homo genus
found in Europe and parts of western and central Asia. The first protoNeanderthal traits appeared in Europe as early as 600,000–350,000
years ago. By 130,000 years ago, complete Neanderthal characteristics
had appeared. These characteristics then disappeared in Asia by 50,000
years ago and in Europe by about 30,000 years ago.
Current genetic evidence suggests interbreeding took place with Homo
sapiens between 80,000 and 50,000 years ago in the Middle East,
resulting in 1–4% of the genome of people from Eurasia having been
contributed by Neanderthals.
Neanderthal stone tools provide further evidence for their
presence where skeletal remains have not been found.
Neanderthal cranial capacity is thought to have been as large as
that of Homo sapiens, perhaps larger, indicating their brain size
may have been comparable, as well. On average, the height of
Neanderthals was comparable to contemporaneous Homo
sapiens. Neanderthal males stood about 165–168 cm, and were
heavily built with robust bone structure. They were much
stronger than Homo sapiens, having particularly strong arms and
hands. Females stood about 152–156 cm.
Homo sapiens
http://humanorigins.si.edu/evidence/humanfossils/species/homo-sapiens
Humans, known taxonomically as Homo sapiens (Latin for "wise man" or
"knowing man"), are the only living species in the Homo genus of bipedal
primates in Hominidae. Anatomically modern-appearing humans originated in
Africa about 200,000 years ago, reaching full behavioural modernity around
50,000 years ago. Humans have a highly developed brain, capable of abstract
reasoning, language and problem solving. This mental capability, combined
with an erect body carriage that frees the hands for manipulating objects, has
allowed humans to make far greater use of tools than any other living species
on Earth. Other higher-level thought processes of humans, such as selfawareness, rationality are considered to be defining features of what
constitutes a person.
Like most higher primates, humans are social animals. However,
humans are uniquely adept at utilizing systems of communication
for self-expression, the exchange of ideas, and organization.
Humans create complex social structures composed of many
cooperating and competing groups, from families to nations.
Social interactions between humans have established an
extremely wide variety of values, social norms, and rituals, which
together form the basis of human society.
With individuals widespread in every continent except
Antarctica, humans are a cosmopolitan species. Humans are
noted for their desire to understand and influence their
environment, seeking to explain and manipulate phenomena
through science, philosophy, mythology, and religion. This
natural curiosity has led to the development of advanced
tools and skills, which are passed down culturally; humans
are the only species known to build fires, cook their food,
clothe themselves, and use numerous other technologies.
Homo
sapiens
evolved
from
Australopithecus
as
illustrated by the fossil record:
anatomy of Australopithecus is intermediate between human
and ape;
legs/pelvis adapted to upright walking;
short ileum;
position of femur altered/hip above knee/ knee can lock;
canines smaller than apes/intermediate between humans and
apes;
brain/cranium larger than ape/intermediate;
arms longer than human/intermediate;
ribcage stronger than in humans;
foramen magnum/hole in skull for spinal cord is forward.
http://www.mnh.si.edu/anthro/humanorigins/
The fossils show trends:
including increasing adaptation to bipedalism;
increasing brain size in relation to body size.
Australopithecus and Homo habilis fossils were all found in
Southern or Eastern Africa. Homo erectus fossils were found in
Eastern Africa, but also in Asia, indicating that there was
migration out of Africa. Homo neanderthalensis fossils were
found in Europe and Homo sapiens in many parts of the world
indicating further migrations.
Outline the trends illustrated by the fossils of Ardipithecus
ramidus, Australopithecus including A. afarensis and A.
africanus, and Homo including H. habilis, H. erectus, H.
neanderthalensis and H. sapiens. Knowledge of approximate
dates and distribution of the named species is expected. Details
of subspecies of particular groups are not required.
At various stages in hominid evolution, several species may
have coexisted. An example of this is H. neanderthalensis and
H. sapiens.
http://www.mnsu.edu/emuseum/biology/humanevolution/fosrec.h
tml
Palaeontology is the study of plants and animals of the geological past,
as represented by their fossil remains. Fossils are the dead remains of
plants and animals, preserved in sedimentary rocks (most are found in
limestones, chalks and clays, rather than in sandstones or gravels,
which are too porous), in waterlogged peat or in the sticky gum that
exudes from certain trees. Fossils are virtually the only source of
information about forms of life that are now extinct. But only a tiny
proportion of the organisms living at any time will become fossilised;
of those that are formed, very few will ever be discovered by a human
and their secrets recorded for posterity.
Fossils are formed by chance, depending on where the organism
dies and on the extent to which it remains escape being eaten by
scavengers, rapid decay by microorganisms and dispersal by
wind or rain. Although most fossils are preserved in rock strata
(layers), some more recent remains have been exceptionally well
preserved in bogs, tar, amber, or ice. For example, the remains of
a woolly mammoth deep-frozen in Siberian ice for more than
25,000 years were so well preserved that part of its DNA could
be analysed. The most common vertebrate fossils are bones and
teeth.
From the shapes of the bones and the positions of the bone scars
indicating points of muscle attachment, biologists can infer an animal's
posture and style of walking, the position and size of its muscles, and
the contours of its body. By a careful study of fossil remains, biologists
can often reconstruct what an animal probably looked like in life.
Fossils provide a record of animals and plants that lived earlier and
some understanding of where and when they lived. Using fossils of
organisms from different geological ages, the lines of descent that gave
rise to modern-day organisms can often be inferred. Sometimes fossils
provide direct evidence of the origin of new species from pre-existing
species, including intermediate forms.
The formation and preservation of a fossil require that an
organism be buried under conditions that slow or prevent the
decay process. This is most likely to occur if an organism's
remains are covered quickly by sediment of fine soil
particles suspended in water. In this way remains of aquatic
organisms may be trapped in bogs, mud flats, sand bars, or
deltas. Remains of terrestrial organisms that lived on a flood
plain may also be covered by water-borne sediments or, if
the organism lived in an arid region, by wind-blown sand.
Over time, the sediments harden to form sedimentary rock, and
the organism's remains are usually replaced by minerals so that
many details of its structure remain. Layers of sedimentary rock
occur naturally in the sequence of their deposition, with the more
recent layers on top of the older, earlier ones.
However, geological events that occurred after the rocks were
initially formed occasionally change the relationships of some
rock layers.
Geologists identify specific sedimentary rocks not only by their
positions in layers but also by features such as mineral content,
and by the fossilised remains of certain organisms, known as
index fossils, that characterise a specific layer over large
geographical areas. Index fossils are fossils of organisms that
existed a relatively short geological time but were preserved as
fossils in large numbers. With this information, geologists arrange
strata and the fossils they contain in chronological order, and
identify comparable layers in widely separated locations.
Because of the conditions required for preservation, the fossil
record is not a random sample of past life, but instead is biased
toward aquatic organisms and those living in the few terrestrial
habitats conductive to fossil formation. For example, relatively
few fossils of tropical forest organisms have been found because
plant and animal remains decay extremely rapidly on the forest
floor, before fossils can form. Another reason for bias is that
organisms with hard body parts such as bones and shells are more
likely to form fossils than those with soft body parts.
Fossilisation: when the organism dies, the organic material
breaks down in the hard parts (skeleton) as well  becomes
porous if the body is buried in mud or sand that can turn into
mud, mineral particles infiltrate the bones and fill up the
pores. If then the mud turns into rock, the skeleton hardens
as well and will be preserved (mineralization). The rock
(matrix) surrounding the fossil is usually softer (sedimentary
rock).
1. sometimes the whole animal decays but the space it
occupied gets filled with another material e.g.; silicate 
mould (shells,).
2. impressions (footprints, leaves, scales, feathers): mud on
which the animal has been walking becomes covered over
by successive layers of deposit which harden, a line of
weakness between the layers splits revealing them.
3. only a few organisms get fossilised and then many get
destroyed + geological distortion.
Evidence from fossils:
1. demonstrates progression in geological time from the
simple towards the complex
2. ecological aspects: land plants before land animals;
insects before insect pollinated plants
3. coincides with the classification of the recent species of
certain groups: what we now consider to be more
developed, appeared later.
Organisms can become fossilised:
 - mineral infiltration of body parts, hardening of body
parts, hardening and later petrifaction;
 - remains buried, decay and the space is occupied by
another material 'moulds';
 - footprints covered by deposits which harden
'impressions‘;
 - organisms immerse in natural substances that act as
preservatives;
 - tar pits and asphalt fields as preserving areas;
 - not all organisms fossilise.
Discuss the incompleteness of the fossil record and the
resulting
uncertainties
about
human
evolution.
Reasons for the incompleteness of the fossil record
should be included.
The brains of early hominids were only slightly larger than in
relation to body size than the brains of apes. The powerful jaws
and teeth of Australopithecus indicate a mainly vegetarian diet.
About 2.5 million years ago Africa became much cooler and
drier. Savannah grassland replaced forest. This change of habitat
may have prompted the evolution of the first species of Homo,
with the development of increasingly sophisticated tools and a
change to a diet that included meat obtained by hunting and
killing large animals. This change in diet corresponds with the
start of the increase in brain size of hominids. This was due to
continued rapid brain growth after birth.
In apes and early hominids, brain growth slows after birth. The
correlation between the change in diet and the increase in brain
size can be explained in two ways:
1.
Eating meat increases the supply of protein, fat and energy in
the diet, making it possible for the growth of larger brains.
2.
Catching and killing prey on the savannas is more difficult
than gathering plant foods, so natural selection will have
favoured hominids with larger brains and greater intelligence.
Discuss the correlation between the change in diet and increase
in brain size during hominid evolution.
Genetic evolution: gradual change through time of
morphological and physiological characteristics due to the
interaction of factors (mutation, isolation, natural selection).
Cultural evolution: gradual development of speech and
communication, skills and attitudes, social grouping,
parental care, ideas, rules, laws, values.
The large brains of Homo sapiens and other species of Homo
allow much to be learned, both during the long period of
childhood and during adulthood. Language, tool making skills,
hunting techniques, methods of agriculture, religion, art and
many other forms of behaviour are passed on from one
generation of a tribe or other group to the next by teaching and
learning. These things are the culture of the group. New methods,
inventions or costumes can be incorporated into what is passed
on. This is called cultural evolution and is different from the type
of evolution that involves natural selection between inherited
differences – genetic evolution.
Cultural evolution does not involve changes in allele frequencies
in the gene pool.
Changes due to cultural evolution can happen during one human
lifetime, whereas genetic evolution happens over generations, so
cultural can be much more rapid than genetic evolution.
Cultural evolution involves characteristics acquired during a
person’s life (nurture) whereas genetic evolution involves
characteristics that are inherited (nature).
Distinguish between genetic and cultural evolution.
Cultural evolution is significant for Homo sapiens, base for
the development of the characteristics that identify "human
culture". It passes down knowledge between generations
(e.g. agriculture, language, etc.). It is possibly more
important than genetic evolution. Knowledge increases
survival chances. Cultural evolution is rapid. Human
lifestyles therefore change rapidly. Some traditions have
been lost. Cultural evolution was not as important in early
evolution.
In the recent evolution of humans, cultural evolution has been
very important and has been responsible for most of the changes
in the lives of humans over the last few thousand years. This is
much too short a period for genetic evolution to cause much
change. Also some aspects of cultural evolution, for example the
development of medicine, have reduced natural selection between
different genetic types and therefore genetic evolution.
Discuss the relative importance of genetic and cultural
evolution in the recent evolution of humans.
ONLY HIGHER LEVEL STUDENTS!
D4. The Hardy- Weinberg principle
Consider a pair of alleles, A and a, where the gene frequency in
the population of A is represented by p and frequency of a is
represented by q (the frequency of alleles must add up to 1, so p +
q = 1). There are only three gene combinations possible in the
offspring: AA, Aa, aa. Hardy and Weinberg found that the
proportions of each type of offspring will depend upon the way
gametes fuse and the gene frequency in the population.
Punnett square diagram: p2: frequency of dominant
homozygous
individuals;
2pq:
frequency
of
heterozygous individuals; q2: frequency of homozygous
recessive individuals.
Explain how the Hardy-Weinberg equation is derived.
1. calculate allele frequencies if phenotype frequencies
are known e.g. frequency of recessive allele is square
root of frequency of recessive phenotype;
2. calculate phenotype frequencies if allele frequencies
are known;
3. calculate genotype frequencies if allele frequencies are
known;
4. quotation and use of Hardy-Weinberg equation to
deduce genotype / phenotype frequencies.
Calculate allele, genotype and phenotype frequencies for
two alleles of a gene, using the Hardy-Weinberg equation.
http://www.misterabrams.com/biosite/biopages/changethruti
me/Hardy%20Weinberg%20Exercises%20set%202%20with
%20answers.htm
http://shs.westport.k12.ct.us/mjvl/biology/genetics/hardy.ht
m
Assumptions
made
when
the
Hardy-Weinberg
equation is used. It must be assumed that a population
is large, with random mating and a constant allele
frequency (no natural selection) over time. This
implies no allele-specific mortality, no mutation, no
emigration and no immigration.
D5. Phylogeny and systematics
Classification in biology is arranging living organisms into groups. In
an artificial classification some prominent and easily observed feature
is taken as the mark of resemblance or dissemblance; while, in a natural
classification, the things classified are arranged according to the totality
of their morphological resemblances, and the features which have been
ascertained by observation to be the indications of many likenesses or
unlikenesses.
There are many advantages (of natural classification):
1. species identification – it is easier to find out to which
species an organism belongs with organisms classified rather
than forming a disorganized catalogue.
2. predictive value – if several members of a group have a
characteristic, another species in this group will probably
also have this characteristic.
3. evolutionary links – species that are in the same
group probably share characteristics because they
have evolved from a common ancestor, so the
classification of groups can be used to predict how
they evolved.
Outline the value of classifying organisms. This refers
to natural classification. Include how the organization
of data assists in identifying organisms, suggests
evolutionary
links,
and
allows
prediction
characteristics shared by members of a group.
of
Evidence
for
evolutionary
relationships
is
provided
by
similarities and differences in the biochemistry and molecular
biology of various organisms. Indeed, lines of descent based on
biochemical and molecular characters closely resemble lines of
descent based on structural and fossil evidence. Molecular
evidence for evolution includes the genetic code and the
conserved sequences of amino acids and of nucleotides in DNA.
The genetic code is universal
All living things have DNA as their genetic material, with a
genetic code which is almost universal. The processes of
'reading' the code and protein synthesis, using RNA and
ribosomes, are very similar in prokaryotes and eukaryotes,
too. The universality of the genetic code is compelling
evidence that organisms arose from a common ancestor. The
genetic code has been passed along through all branches of
the evolutionary tree.
Proteins contain a record of evolutionary change
Investigations of the sequence of amino acids in proteins
playing the same roles in different species have revealed
both great similarities and certain specific differences.
Even organisms that are remotely related, such as humans,
oaks, and Escherichia coli, have some proteins such as
cytochrome c in common.
In order to survive, all aerobic organisms need a respiratory protein
with the same basic structure and function as the cytochrome c of
their common ancestor. Consequently, not all of the amino acids that
give the protein those features are free to change.
However, in the course of evolution of different organisms,
mutations have resulted in the substitution of many amino acids at
less important locations in the cytochrome c protein.
The longer it has been since two organisms diverged,
the greater the differences in the amino acid sequences
of their cytochrome c molecules. A phylogenetic tree, a
diagram showing lines of descent, can be derived from
differences in the amino acid sequence of a common
protein like cytochrome c.
Genetic distance; differences between DNAs
Comparing DNA from a variety of living species can indicate
quantitatively the degree of relatedness of their genes. To
quantify the relatedness of two species (for example, humans and
chimpanzees), DNA strands from both species are extracted and
separated (hydrogen bonds between the complementary base
pairs are broken by heat treatment). Then restriction enzymes are
used to cut single-stranded DNA into fragments about 500
nucleotides long.
If the fragments from the two species are mixed, double-stranded
DNA
is
formed
by
hydrogen-bond
formation
between
complementary base pairs. Some of the double strands are of
DNA from the same species but others are from different species
(hybrid DNA). On heating, double-stranded DNA will
separate; the hybrid DNA, however, separates at a lower
temperature. The closer the temperature at which hybrid
DNA separates to the temperature at which single-species
DNA separates, the more closely related are the two species.
The degree of relatedness of various Primates to
humans estimated in this way gives results as follows:
chimpanzee (an ape)
97.6%
rhesus monkey
91.1%
vervet monkey
84.2%
galago (a prosimian)
58.0%
These results tie in with other evidence about the
evolution of the Primates.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/T/Ta
xonomy.html#DNA_DNAHybridization
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Pr
imates.html
There are remarkable similarities between living organisms
in their biochemistry.
1. All use DNA (or RNA) as their genetic material.
2. All use same universal genetic code, with only a few
insignificant variations.
3. All use the same 20 amino acids in their proteins.
4. All use left and right-handed amino acids.
The similarities in amino acid composition are striking because
many other amino acids, in both left and right-handed versions,
were available when life evolved, according to Miller’s
experiments. These biochemical similarities suggest very strongly
that all organisms have evolved from a common ancestor, which
had all of these characteristics.
Explain the biochemical evidence provided by the universality
of DNA and protein structures for the common ancestry of
living organisms.
Tracing evolutionary links and origins is called phylogeny.
The phylogeny of many groups has been studied by
comparing the structure of a protein or other biochemical
that they contain. Usually the results match the existing
classification of the group.
Explain how variations in specific molecules can indicate
phylogeny.
In the mid-1960s techniques like electrophoresis became
available for the study of differences among proteins. The
application of these techniques to evolutionary problems
made possible the pursuit of issues; for example, exploring
the extent of genetic variation in natural populations (which
sets bounds to their evolutionary potential) and determining
the amount of genetic change that occurs during the
formation of new species.
Comparisons of the amino acid sequences of proteins in different
species provided quantitatively precise measures of species
divergence, a considerable improvement over the typically
qualitative evaluations obtained by comparative anatomy and
other evolutionary disciplines. In 1968 the Japanese geneticist
Motoo Kimura proposed the neutrality theory of molecular
evolution, which assumes that at the level of DNA and protein
sequence many changes are adaptively neutral and have little or
no effect on the molecule's function.
If the neutrality theory is correct, there should be a
"molecular clock" of evolution; that is, the degree of
divergence between species in amino acid or nucleotide
sequence would provide a reliable estimate of the time since
their divergence. This would make possible a reconstruction
of evolutionary history that would reveal the order of
branching of different lineages, such as those leading to
humans, chimpanzees, and orangutans, as well as the time in
the past when the lineages split from one another.
The techniques of DNA cloning and sequencing have provided a
new and more powerful means of investigating evolution at the
molecular level.
Differences in the base sequence of DNA and therefore in the
amino acid sequence of proteins, accumulate gradually over long
periods of time. There is evidence that differences accumulate at
a roughly constant rate. They can therefore be used as an
evolutionary clock. The number of differences in amino acid
sequence can be deduced how long ago species split from a
common ancestor.
For example, mitochondrial DNA from three humans and
four related primates has been completely sequenced.
From the differences in base sequence, a hypothetical
phylogeny has been constructed. Using the numbers of
differences in base sequence as an evolutionary clock,
these approximate dates for splits between groups have
been deduced:
70 000 years ago, Europeans – Japanese split
140 000 years ago, African – European/Japanese split
about 5 million years ago, human – chimpanzees split.
http://www.youtube.com/watch?v=mcAq9bmCeR0
Discuss how biochemical variations can be used as an
evolutionary clock.
Clades can be large groups, with a common ancestor far back in
evolution, or smaller groups with a more recent common
ancestor.
Clade: a group of organisms that evolved from a common
ancestor.
http://en.wikipedia.org/wiki/Clade
Cladograms have been used to re-evaluate the classification of
many groups of organisms. A new name has been given to this
type of classification – cladistics.
http://en.wikipedia.org/wiki/Cladogram
Cladistics is the hierarchical classification of species based
on evolutionary ancestry. Cladistics is distinguished from
other taxonomic systems because it focuses on evolution
rather than similarities between species, and because it
places heavy emphasis on objective, quantitative analysis.
Cladistics generates diagrams called cladograms that
represent the evolutionary tree of life. DNA and RNA
sequencing data are used in many important cladistic efforts.
Define clade and cladistics.
An example of an artificial classification is putting insects, birds and
bats into one group because they can fly. The wings of these animals
are examples of analogous structures – structures with a common
function, but a different evolutionary origin. Natural classification is
based on homologous structures – structures that have a common
evolutionary origin, even if their function is different. The pentadactyl
limb is an example of homologous structure in mammals.
Distinguish, with examples, between analogous and homologous
characteristics.
Outline the methods used to construct cladograms and the
conclusions that can be drawn from them.
http://www.eeescience.utoledo.edu/Faculty/Dwyer/Biodiver
sity/ConstructingCladograms.htm
http://www.indiana.edu/~ensiweb/lessons/mclad.ws.pdf
http://www.brooklyn.cuny.edu/bc/ahp/CLAS/CLAS.Clad.ht
ml
http://www.mhhe.com/biosci/pae/zoology/cladogram/
Construct
a
simple
cladogram.
Morphological
or
biochemical data can be used.
Analyse cladograms in terms of phylogenetic relationships.
The classification of many groups has been re-examined
using cladograms. In many cases, cladograms have
confirmed existing classifications. This is not surprising as
both traditional classification and cladistics are attempting to
reflect phylogenetic relationships – the evolutionary origins
of groups of living organisms. Cladograms can be difficult
to reconcile with traditional classifications, because the
nodes can occur at any point.
It can therefore seem rather than arbitrary how the hierarchy of
taxa is fitted to the clades. In some cases, cladistics suggests
radically different phylogenies. Should the existing classifications
be trusted in these cases, or the new ones based on cladistics?
The strength of cladistics is that the comparisons between
organisms are objective, based, as they are, on molecular
differences.
The weakness is that these molecular differences are analysed on
the basis of probabilities. Occasionally
improbable events occur, making the analysis wrong. So,
although cladistics should not be treated as infallible, in many
cases it stimulates a reinterpretation of the data on which
traditional classifications have been based.
Discuss
the
relationship
between
classification of living organisms.
cladograms
and
the