Evolution occurs when heritable characteristics of a species change. The fossil record provides evidence for evolution. Selective breeding of domesticated animals shows that artificial selection can cause evolution. Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function. Populations of a species can gradually diverge into separate species by evolution. Continuous variation across the geographical range of related populations matches the concept of gradual divergence.

1. TOPIC 5: Evolution and
Biodiversity
IB Diploma Programm
By Mrs. Mariam Ohanyan

2. 5.1: Evidence for Evolution
Understandings:
• Evolution occurs when heritable characteristics of a species change
• The fossil record provides evidence for evolution
• Selective breeding of domesticated animals shows that artificial
selection can cause evolution
• Evolution of homologous structures by adaptive radiation explains
similarities in structure when there are differences in function
• Populations of a species can gradually diverge into separate species
by evolution
• Continuous variation across the geographical range of related
populations matches the concept of gradual divergence
12/21/2017 By Mrs. Mariam Ohanyan

3. Applications:
Development of melanistic
insects in polluted areas
Comparison of the
pentadactyl limb of
mammals, birds,
amphibians and reptiles
with different methods of
locomotion

4. Evolution
Cumulative change in the heritable characteristics of a population over
time.
In living organisms this change refers to the heritable characteristics of
a species (biological evolution)
Heritable characteristics are encoded for by genes and may be
transferred between generations as alleles
Hence biological evolution describes cumulative changes that occur
within a population between one generation and the next
A concise definition for biological evolution is:
A change in the allele frequency of a population’s gene pool over
successive generations
12/21/2017 By Mrs. Mariam Ohanyan

5. Briefly explain the theory of evolution
by natural selection. 4 marks
1
parents
produce more
offspring than
survive
2
there is
competition
among
members of a
species for
survival/strugg
le for
existence
3
species show
variation
4
certain
variations will
give a
selective
advantage/sur
vival of fittest
5
depending on
environment
6
these
variations will
be passed on
to the next
generation
7
leading to
change in allele
frequency

6. Darwin’s theory of evolution
Darwin’s theory of evolution entails the
following fundamental ideas.
12/21/2017 By Mrs. Mariam Ohanyan
Source: https://krishna.org/darwinism-a-crumbling-theory/

7. • Species (populations of interbreeding
organisms) change over time and space. The
representatives of species living today differ
from those that lived in the recent past, and
populations in different geographic regions
today differ slightly in form or behavior. These
differences extend into the fossil record,
which provides ample support for this claim.
12/21/2017 By Mrs. Mariam Ohanyan

8. All organisms share common ancestors
with other organisms. Over time,
populations may divide into different
species, which share a common
ancestral population. Far enough back
in time, any pair of organisms shares a
common ancestor.
For example, humans shared a
common ancestor with chimpanzees
about eight million years ago, with
whales about 60 million years ago,
and with kangaroos over 100 million
years ago. Shared ancestry explains
the similarities of organisms that are
classified together: their similarities
reflect the inheritance of traits from a
common ancestor.

9. Evolutionary change is gradual and slow in
Darwin’s view. This claim was supported by the
long episodes of gradual change in organisms in
the fossil record and the fact that no naturalist
had observed the sudden appearance of a new
species in Darwin’s time. Since then, biologists
and paleontologists have documented a broad
spectrum of slow to rapid rates of evolutionary
change within lineages.
12/21/2017 By Mrs. Mariam Ohanyan

10. Darwin’s process of
natural selection has four
components.
Variation.
Organisms (within populations) exhibit
individual variation in appearance and
behavior. These variations may involve body
size, hair color, facial markings, voice properties,
or number of offspring. On the other hand,
some traits show little to no variation among
individuals—for example, number of eyes in
vertebrates.
12/21/2017By Mrs. Mariam Ohanyan

11. Inheritance.
Some traits are consistently
passed on from parent to
offspring. Such traits are
heritable, whereas other
traits are strongly influenced
by environmental conditions
and show weak heritability.
12/21/2017

12. High rate of population growth.
Most populations have more
offspring each year than local
resources can support leading
to a struggle for
resources. Each generation
experiences substantial
mortality.

13. Differential survival
and reproduction.
Individuals
possessing traits well
suited for the
struggle for local
resources will
contribute more
offspring to the next
generation.

14. Outline four types of evidence which support
the theory of evolution by natural selection.
6 marks
• fossils/paleontological
– fossilized horse ancestors/other evidence
• homologous structures
– pentadactyl limb/vertebrate embryos/other
• geographic distribution
– ring species/other evidence from geographical
distribution
• recent observed evolution
– resistance to antibiotics/insecticides/heavy metal
tolerance/other recent example
12/21/2017 By Mrs. Mariam Ohanyan

15. Fossil
A fossil is the preserved remains or traces of
any organism from the remote past
Preserved remains (body fossils) provide direct
evidence of ancestral forms and include bones,
teeth, shells, leaves, etc.
Traces provide indirect evidence of ancestral
forms and include footprints, tooth marks,
burrows and faeces (coprolite)
The totality of fossils, both discovered and
undiscovered, is referred to as the fossil
record
The fossil record shows that over time changes
have occurred in the features of living
organisms (evolution).

16. Law of Fossil Succession
Three concepts
are important in
the study and use
of fossils:
01
Fossils represent
the remains of
once-living
organisms.
02
Most fossils
are the
remains of
extinct
organisms;
that is, they
belong to
species that
are no longer
living
anywhere on
Earth.
03
The kinds of
fossils found in
rocks of
different ages
differ because
life on Earth has
changed
through time.
04

17. If we begin at the present and examine older and older layers of
rock, we will come to a level where no fossils of humans are
present. If we continue backwards in time, we will successively
come to levels where no fossils of flowering plants are present, no
birds, no mammals, no reptiles, no four-footed vertebrates, no
land plants, no fishes, no shells, and no animals. The three
concepts are summarized in the general principle called the Law
of Fossil Succession: The kinds of animals and plants found as
fossils change through time. When we find the same kinds of
fossils in rocks from different places, we know that the rocks are
the same age.
12/21/2017 By Mrs. Mariam Ohanyan

18. 12/21/2017 By Mrs. Mariam Ohanyan
Source: https://en.wikibooks.org/wiki/High_School_Earth_Science/Relative_Ages_of_Rocks

19. Homologous structures
• Homologous structures are parts of the body
that are similar in structure to other species'
comparative parts. Scientists say these
similarities are evidence that life on earth
share a common ancient ancestor from which
many or all other species have evolved over
time. Evidence of this common ancestry can
be seen in the structure and development of
these homologous structures, even if their
function is different.
12/21/2017 By Mrs. Mariam Ohanyan

20. EXAMPLES
• The more closely organisms are related, the more similar the
homologous structures between organisms. Many mammals,
for example, have similar limb structures.
• The flipper of a whale, the wing of a bat, and the leg of a cat
are all very similar to the human arm, with a large upper arm
bone (the humorous on the human). The lower part of the
limb is made up of two bones, a larger bone on one side (the
radius in humans) and a smaller bone on the other side (the
ulna in humans).
12/21/2017 By Mrs. Mariam Ohanyan

21. • All of the species also have a collection of smaller
bones in the "wrist" area (these are called carpal
bones in humans) that lead into the long "fingers"
or phalanges.
• Even though bone structure may be very similar,
function varies widely. Homologous limbs can be
used for flying, swimming, walking, or everything
humans do with their arms.
12/21/2017 By Mrs. Mariam Ohanyan

22. Homologues
structures

23. HOMOLOGY AND EVOLUTION
When Swedish botanist Carolus Linnaeuswas
formulating his system of taxonomy to name
and categorize organisms in the 1700s, how the
species looked was the determining factor of the
group in which the species would be placed. As
time went on and technology became more
advanced, homologous structures became more
and more important in deciding the final
placement on the phylogenetic tree of life.
12/21/2017 By Mrs. Mariam Ohanyan

24. Carolus Linnaeuswas
12/21/2017 By Mrs. Mariam Ohanyan
Source: https://commons.wikimedia.org/wiki/File:LinnaeusWeddingPortrait.jpg

25. Linnaeus's taxonomy system places species into
broad categories. The major categories from
general to specific are
kingdom, phylum, class, order, family, genus,
and species. As technology has evolved,
allowing scientists to study life at the genetic
level, these categories have been updated to
include domain in the taxonomic hierarchy.
Domain is the broadest category, and organisms
are grouped primarily according to differences
in ribosomal RNA structure.
12/21/2017 By Mrs. Mariam Ohanyan

26. Outline one modern example of observed
evolution by natural selection. 3 marks
named example (this
must be a real example,
naming the species using
binomial nomenclature
or a full common name)
selective pressure (what
caused the change)
result (describing the
evolutionary change)
example
beaks of Galapagos
finches
competition for food
change in
numbers/proportion of
birds with different sized
beaks

27. Explain the evidence from homologous anatomical
structures that supports the theory of evolution. 6
marks
homologous structures
are various different
structures of the same
basic plan
derived from a similar
embryonic origin
variations on the basic
structure allow
different functions
permitting exploitation
of differnt ways of
life/adaptive radiation
the suggests
divergence from a
common ancestor
named example of a
homologous structure
(e.g. pentadactyl limb,
flower, birds` beaks)
description of basic
structure of this
example
variation related to
different functions of
this example

28. Outline how antibiotic resistance in bacteria
can arise in response to environmental
change. 5 marks
• antibiotic resistance can be inherited;
• alleles for resistance can be passed from one cell to another by
exchange of plasmids/conjugation;
• some varieties are more resistant than others;
• bacteria reproduce very rapidly and have high mutation rate;
• evolution can occur rapidly;
• increased exposure to antibiotics is the environmental change that
selects for resistant varieties;
• for example, in hospitals / animal feed / inappropriate prescriptions
/ not finishing prescriptions;
• bacteria without resistance die / resistant bacteria survive and pass
on genes to next generation;
• results in change in genetic makeup of population;
12/21/2017 By Mrs. Mariam Ohanyan

29. Antibiotic resistance
• Antibiotic resistance is one of the biggest threats to global
health, food security, and development today.
• Antibiotic resistance can affect anyone, of any age, in any
country.
• Antibiotic resistance occurs naturally, but misuse of
antibiotics in humans and animals is accelerating the
process.
• A growing number of infections – such as pneumonia,
tuberculosis, gonorrhoea, and salmonellosis – are
becoming harder to treat as the antibiotics used to treat
them become less effective.
• Antibiotic resistance leads to longer hospital stays, higher
medical costs and increased mortality.
12/21/2017 By Mrs. Mariam Ohanyan

30. 12/21/2017 By Mrs. Mariam Ohanyan
Source: http://biobunch.blogspot.am/2016/09/our-21st-century-apocalyse-rise-of.html

31. Bacteria resistant to antibiotics
• Some bacteria have developed resistance to antibiotics that were
once commonly used to treat them. For example, Staphylococcus
aureus (‘golden staph’ or MRSA) and Neisseria gonorrhoeae (the
cause of gonorrhoea) are now almost always resistant to benzyl
penicillin. In the past, these infections were usually controlled by
penicillin.
The most serious concern with antibiotic resistance is that some
bacteria have become resistant to almost all of the easily available
antibiotics. These bacteria are able to cause serious disease and this
is a major public health problem. Important examples are:
• methicillin-resistant Staphylococcus aureus (MRSA)
• vancomycin-resistant Enterococcus (VRE)
• multi-drug-resistant Mycobacterium tuberculosis (MDR-TB)
• carbapenem-resistant Enterobacteriaceae (CRE) gut bacteria
12/21/2017 By Mrs. Mariam Ohanyan

32. Ways to prevent antibiotic resistance
The most important ways to prevent antibiotic resistance
are:
• Minimize unnecessary prescribing and overprescribing
of antibiotics. This occurs when people expect doctors
to prescribe antibiotics for a viral illness (antibiotics do
not work against viruses) or when antibiotics are
prescribed for conditions that do not require them.
• Complete the entire course of any prescribed antibiotic
so that it can be fully effective and not breed
resistance.
• Practice good hygiene such as hand-washing and use
appropriate infection control procedures.
12/21/2017 By Mrs. Mariam Ohanyan

33. Alleles for resistance can be passed from one cell
to another by exchange of plasmids/conjugation
• This mechanism requires the presence of a special plasmid called
the F plasmid.
• Therefore, we will briefly review plasmid structure before
continuing.
– Plasmids are small, circular pieces of DNA that are separate and
replicate independently from the bacterial chromosome.
– Plasmids contain only a few genes that are usually not needed for
growth and reproduction of the cell.
– However, in stressful situations, plasmids can be crucial for survial.
– The F plasmid, for example, facilities conjugation.
• This can give a bacterium new genes that may help it survive in a changing
environment.
– Some plasmids can integrate reversibly into the bacterial
chromosome.
• An integrated plasmid is called an episome.
12/21/2017 By Mrs. Mariam Ohanyan

34. • Bacteria that have a F plasmid are referred to as as F+ or male.
– Those that do not have an F plasmid are F- of female.
• The F plasmid consists of 25 genes that mostly code for production
of sex pili.
• A conjugation event occurs when the male cell extends his sex pili
and one attaches to the female.
– This attached pilus is a temporary cytoplasmic bridge through which a
replicating F plasmid is transferred from the male to the female.
– When transfer is complete, the result is two male cells.
• The F plasmid can behave as an episome.
– When the F+ plasmid is integrated within the bacterial chromosome,
the cell is called an Hfr cell (high frequency of recombination cell).
– The F plasmid always inserts at the same spot for a bacterial species.
12/21/2017 By Mrs. Mariam Ohanyan

35. Antibiotic resistance in bacteria is an example of evolution in
response to environmental change. Using another example,
explain how an environmental change can lead to
evolution. 8 marks
natural selection
(in correct
context);
better-adapted
individuals
survive/more
likely to survive;
more
reproduction/gen
es passed on by
better adapted
individuals;
name of species;
(accept even if
remainder of
answer is invalid)
description of
original/decreasin
g phenotype;
type of
environmental
change that led to
evolution;
consequence of
environmental
change
description of
new/increasing
phenotype;
genetic basis of
phenotypes;
reason for new
phenotype being
better adapted;
detail of reason
for adaptedness of
new phenotype;

36. The
following
has been
provided
as an
example
answer.
great tit;
bird that lays its eggs in spring;
global warming/climate change;
more caterpillars (on trees) in early spring;
laying eggs earlier in spring;
time of egg laying is (partly) genetically
controlled;
eggs laid early hatch at start of period of
greatest food abundance;
more young can be fed/young grow
faster/fewer deaths;
12/21/2017By Mrs. Mariam Ohanyan

37. Discuss the definition of the term species. (8 max)
a species is a group of
organisms
a species shares a
common gene pool
showing similar
morphology /
characteristics
capable of
interbreeding
and producing fertile
offspring
but dissimilar
organisms sometimes
interbreed
mule formed by
crossing horse and
donkey / other example
of interspecific
hybridisation
interspecific hybrids
are sometimes fertile
sometimes organisms
that are very similar
will not interbreed
Drosophila
pseudoobscura and pe
rsimilis / other
example of sibling
species
reference to the
problem of defining
fossil species
reference to the
problem of species
that only reproduce
asexually
reference to the
problem of isolated
populations gradually
diverging

38. Outline allopatric and sympatric
speciation. 4 marks
• speciation is the formation of a new species by the splitting
of an existing species;
• allopatric speciation caused by geographical separation;
• sympatric speciation occurring within the same habitat
caused by different niches / caused by courtship/feeding
differences/behavioral differences;
• both processes lead to isolation of sub-populations;
• isolation favors certain genetic variations (within a species);
• over time this leads to genetic barriers/speciation;
• Both allopatric and sympatric speciation must be
mentioned. 3 max if only one mentioned.
12/21/2017 By Mrs. Mariam Ohanyan

39. Allopatric and
sympatric speciation
Source: http://www.old-
ib.bioninja.com.au/options/option-d-
evolution-2/d2-species-and-speciation.html

40. Allopatric speciation occurs when populations of a
species are separated by a physical barrier - this
could be a river for animals that cannot swim, for
example. Separation of the populations means that
there is very low or no gene flow between them -
the proportion of different genotypes in each
population is therefore able to change
independently of the other (there's no mixing up of
genes between the two populations). Over time,
these changes may be so drastic that the
populations become unable or unwilling to breed
with each other, and could therefore be described
as a pair of species.
12/21/2017 By Mrs. Mariam Ohanyan

41. Sympatric speciation occurs without a physical barrier to
gene flow. This is more common in plant species - plants
can mutate in a way which results in them producing
offspring with double or even quadruple the number of
chromosomes they normally do. The sex cells (sperm
and eggs) produced by these individuals cannot fuse
with sex cells from a "normal" plant - the plants with
unusually high numbers of chromosomes therefore
become isolated genetically from the "normal" plants,
even though they may be growing right next to each
other. This genetic isolation results in the two types of
plants developing into species due to lack of gene flow
and independent changes in the genotypes of plant
populations.
12/21/2017 By Mrs. Mariam Ohanyan

42. Discuss the theory that evolution occurs
by punctuated equilibrium. 3 marks
• long periods where there was no (apparent)
change/stasis
• short periods of rapid evolution
• periods of mass extinctions leading to
opportunities/caused by environmental
disruption/rapid environmental change in short
periods
• supported by lack of fossils showing gradual changes
• an example of such environmental disruption (meteors,
earthquakes, volcanoes, etc.)
• alternative theory is gradualism
• punctuated equilibrium is based on fossil evidence
rather than biochemical evidence
12/21/2017 By Mrs. Mariam Ohanyan

43. Theory is gradualism
Gradualism and punctuated equilibrium are two
ways in which the evolution of a species can
occur. A species can evolve by only one of these,
or by both. Scientists think that species with a
shorter evolution evolved mostly by punctuated
equilibrium, and those with a longer evolution
evolved mostly by gradualism.
12/21/2017 By Mrs. Mariam Ohanyan

44. Gradualism
Gradualism is selection and variation that
happens more gradually. Over a short period of
time it is hard to notice. Small variations that fit
an organism slightly better to its environment
are selected for: a few more individuals with
more of the helpful trait survive, and a few more
with less of the helpful trait die. Very gradually,
over a long time, the population changes.
Change is slow, constant, and consistent.
12/21/2017 By Mrs. Mariam Ohanyan

45. Gradualism
and
punctuated
equilibrium
12/21/2017 By Mrs. Mariam Ohanyan

46. Punctuated equilibrium
In punctuated equilibrium, change comes in spurts. There is a period of very
little change, and then one or a few huge changes occur, often through
mutations in the genes of a few individuals. Mutations are random changes in
the DNA that are not inherited from the previous generation, but are passed
on to generations that follow. Though mutations are often harmful, the
mutations that result in punctuated equilibrium are very helpful to the
individuals in their environments. Because these mutations are so different
and so helpful to the survival of those that have them, the proportion of
individuals in the population who have the mutation/trait and those who
don't changes a lot over a very short period of time. The species changes very
rapidly over a few generations, then settles down again to a period of little
change.
This explanation talks about punctuated equilibrium as the result of one or a
few mutations that cause large change. However, punctuated equilibrium is
any sudden, rapid change in a species and can also be the result of other
causes, such as huge and sudden changes in the environment that result in
more rapid changes in the organisms through harsher selection.
12/21/2017 By Mrs. Mariam Ohanyan

47. Compare evolution by punctuated equilibrium
with evolution by gradualism. 3 marks
• punctuated equilibrium involves faster mutation rates
• punctuated equilibrium involves more powerful natural
selection
• punctuated equilibrium implies that the environment
undergoes sudden changes
• punctuated equilibrium involves discontinuous
evolution
• gradualism implies continuous evolution
• punctuated equilibrium involves faster evolution rates
(when it occurs)
12/21/2017 By Mrs. Mariam Ohanyan