D1Origin of life on Earth
Assessment statement
D.1.1
Describe four processes needed for the
spontaneous origin of life on Earth.
Teacher’s notes
Obj
2
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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 into membranes
with an internal chemistry different from their
surroundings.
TOK: We could question whether any investigation
of the history of evolution of life on Earth can be
scientific. The concept of falsifiability could be raised
here.
D.1.2
Outline the experiments of Miller and Urey into
the origin of organic compounds.
2
TOK: Scientific progress often depends upon model
building, a working hypothesis and possible
falsification. In this case, we may be able to show
that organic compounds could arise under certain
conditions, but we should consider whether we can
show that they did at some time in the past, or
whether they certainly did not.
D.1.3
State that comets may have delivered organic
compounds to Earth.
1
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.
D.1.4
Discuss possible locations where conditions
would have allowed the synthesis of organic
compounds.
3
Examples should include communities around deepsea hydrothermal vents, volcanoes and
extraterrestrial locations.
D.1.5
Outline two properties of RNA that would have
allowed it to play a role in the origin of life.
2
Include the self-replicating and catalytic activities of
RNA.
D.1.6
State that living cells may have been preceded
by protobionts, with an internal chemical
environment different from their surroundings.
1
Examples include coacervates and microspheres.
D.1.7
Outline the contribution of prokaryotes to the
creation of an oxygen-rich atmosphere.
2
D.1.8
Discuss the endosymbiotic theory for the origin
of eukaryotes.
3
TOK: As with other theories that aim to explain the
evolution of life on Earth, we can obtain evidence for
a theory and we can assess the strength of the
evidence. However, can we ever be sure that the
theory explains what actually happened in the past?
For something to be a scientific theory, we must also
be able to test whether it is false. Can we do this if
the theory relates to a past event? Is a special
standard required for claims about events in the past
to be scientific? If they cannot be falsified, is it
enough if they allow us to make predictions?
D2Species and speciation
Assessment statement
Obj
D.2.1
Define allele frequency and gene pool.
1
D.2.2
State that evolution involves a change in allele
frequency in a population’s gene pool over a
number of generations.
1
Teacher’s notes
D.2.3
Discuss the definition of the term species.
3
D.2.4
Describe three examples of barriers between
gene pools.
2
Examples include geographical isolation, hybrid
infertility, temporal isolation and behavioural
isolation.
D.2.5
Explain how polyploidy can contribute to
speciation.
3
Avoid examples involving hybridization as well as
polyploidy, such as the evolution of wheat.
D.2.6
Compare allopatric and sympatric speciation.
3
Speciation: the formation of a new species by
splitting of an existing species.
Sympatric: in the same geographical area.
Allopatric: in different geographical areas.
D.2.7
Outline the process of adaptive radiation.
2
D.2.8
Compare convergent and divergent evolution.
3
D.2.9
Discuss ideas on the pace of evolution,
including gradualism and punctuated
equilibrium.
3
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.
D.2.10
Describe one example of transient
polymorphism.
2
An example of transient polymorphism is industrial
melanism.
D.2.11
Describe sickle-cell anemia as an example of
balanced polymorphism.
2
Sickle-cell anemia is an example of balanced
polymorphism where heterozygotes (sickle-cell trait)
have an advantage in malarial regions because they
are fitter than either homozygote.
D3Human evolution
Assessment statement
Obj
Teacher’s notes
Knowledge of the degree of accuracy and the choice
of isotope to use is expected. Details of the
apparatus used are not required.
D.3.1
Outline the method for dating rocks and fossils
using radioisotopes, with reference to 14C and
40
K.
2
D.3.2
Define half-life.
1
D.3.3
Deduce the approximate age of materials
based on a simple decay curve for a
radioisotope.
3
D.3.4
Describe the major anatomical features that
define humans as primates.
2
D.3.5
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.
2
Knowledge of approximate dates and distribution of
the named species is expected. Details of
subspecies or particular groups (Cro-Magnon,
Peking, and so on) are not required.
D.3.6
State that, at various stages in hominid
evolution, several species may have
coexisted.
1
An example of this is H. neanderthalensis and
H. sapiens.
D.3.7
Discuss the incompleteness of the fossil
record and the resulting uncertainties about
human evolution.
3
Reasons for the incompleteness of the fossil record
should be included.
TOK: Paleoanthropology is an example of the
diverse aspects of science, in that it is a data-poor
science with largely uncontrollable subject matter.
Paradigm shifts are more common in a data-poor
science. The discovery of small numbers of fossils
has caused huge changes in theories of human
evolution, perhaps indicating that too much has
been constructed on too little.
Conversely, discoveries such as those made in
Dmanisi, Georgia provide examples of falsification of
earlier held positions, indicating why
paleoanthropology can be considered a science.
D.3.8
Discuss the correlation between the change in
diet and increase in brain size during hominid
evolution.
3
D.3.9
Distinguish between genetic and cultural
evolution.
2
D.3.10
Discuss the relative importance of genetic and
cultural evolution in the recent evolution of
humans.
3
TOK: This is an opportunity to enter into the
nature/nurture debate. There is clear causation
when a genetic factor controls a characteristic.
Cultural factors are much more complex, and
correlation and cause are more easily confused.