3. INTRODUCTION
• Classification – a system of naming objects or
entities by common characteristics.
• In a biological sense, classification is the
systematic grouping of organisms based on
structural or functional similarities or
evolutionary history.
• A process of establishing, defining, and
ranking taxa within hierarchical series of
groups.
4. INTRODUCTION
• Not surprisingly, biologists classify organisms into
different categories mostly by judging degrees of
apparent similarity and difference that they can
see.
– The assumption is that the greater the degree of
physical similarity, the closer the biological
relationship.
• To discover unknown organism, taxonomists do
the following:
i. They begin their classification by looking for
anatomical features that appear to have the same
function as those found on other species.
5. ii. They determine whether or not the
similarities are due to an independent
evolutionary development or to descent
from a common ancestor.
• If the latter is the case, then the two species are
probably closely related and should be classified
into the same or near biological categories.
• Natural selection and other processes have
led to a staggering diversity of organisms.
• Biologists have identified and named about
1.5 million species so far and 2-100 million
additional species are yet to be discovered
6. • To study the diversity of life, biologists use a
classification system to name organisms and
group them in a logical manner.
–In the discipline of taxonomy, scientists
classify organisms and assign each organism
a universally accepted name.
–When taxonomists classify organisms, they
organize them into groups that have
biological significance.
7. Related terminologies with
classification
1. Homologies-are anatomical features, of different
organisms, that have a similar appearance or
function because they were inherited from a
common ancestor that also had them.
– E.g. the forelimb of a horse, the wing of a bird, and
your arm have the same functional types of bones as
did our shared reptilian ancestor. Therefore, these
bones are homologous structures.
– The more homologies two organisms possess, the
more likely it is that they have a close genetic
relationship.
9. 2. An individual living thing, such as an animal or
a plant , is called an organism. The term
‘living organism’ is usually used to describe
something which displays all the
characteristics of living things.
3. Analogies- are anatomical features that have
the same form or function in different species
that have no known common ancestor.
– E.g., the wings of a bird and a butterfly are
analogous structures because they are
superficially similar in shape and function.
10. • Analogies may be due to homologies ,but the
common ancestor, if any, is unknown.
4. Taxonomy – the classification of organisms into a
system that indicates natural relationships
(evolutionary relationships); the theory and
practice of describing, naming, and classifying
organisms.
5. Systematics – the systematic classification of
organisms and the evolutionary relationships
among them; taxonomy.
6. Phylogeny – the evolutionary history of a group
or lineage.
11. Problems in Classifying Organisms
1. Defining species difficulties -Species are
always changing
– Listing characteristics that distinguish one
species from another has the effect of making it
appear that the species and their distinctive
attributes are fixed and eternal. These
distinguishing characteristics were due to
evolutionary processes that occurred in the
distant past and is still occurring now that may
be expected to give rise to new forms in the
future.
12. – that most species are physically and genetically
diverse. Many are far more varied than humans.
• Species Concept: meaning “problems”
(a). evolutionary species concept
A species is a lineage of ancestral descendant
populations which maintains its identity from
other such lineages and which has its own
evolutionary tendencies and historical fate.
– This definition suffice the current knowledge of
evolutionary processes
– The reasons to support this current defintion of
species are:
13. i. all organisms, past and present, belong to
some evolutionary species;
ii. reproductive isolation must be effective
enough to permit maintenance of identity
from other contemporary lineages;
iii. morphological distinctiveness is not
necessary; and
iv. no presumed (hypothesized) single lineage
may be subdivided into a series of ancestral-
descendant “species.”
14. (b). Biological Species concept
• The biological species concept is the most widely
accepted species concept. It defines species in
terms of interbreeding. For instance, Ernst Mayr
defined a species as follows:
– "species are groups of interbreeding natural
populations that are reproductively isolated from
other such groups."
• The biological species concept explains why the
members of a species resemble one another, i.e.
form phenetic clusters, and differ from other
species.
15. • When two organisms breed within a species,
their genes pass into their combined offspring.
– As this process is repeated, the genes of different
organisms are constantly shuffled around the
species gene pool.
– The shared gene pool gives the species its identity.
By contrast, genes are not (by definition)
transferred to other species, and different species
therefore take on a different appearance.
– Interbreeding between species is prevented by
isolating mechanisms.
16. ( c) Ecological species concept
• The ecological species concept is a concept of
species in which a species is a set of organisms
adapted to a particular set of resources, called
a niche, in the environment.
• According to this concept, populations form
the discrete phenetic clusters that we
recognize as species because the ecological
and evolutionary processes controlling how
resources are divided up tend to produce
those clusters.
17. 2. determining the specific characteristics that
actually distinguish it from all other types of
organisms.
– Debate among taxonomists over defining new
species
3.
18. Why Classification of living things
• Taxonomy (Gk. Taxis, arrangement, and
nomy, science of),
– classification of organisms into different categories
based on their physical characteristics and
presumed natural relationship
•
19. Importance of classification
• It makes the study of such a wide variety of
organisms easy.
• It projects before us a good picture of all life
forms at a glance.
• It helps us understand the interrelationship
among different groups of organisms.
• It serves as a base for the development of other
biological sciences such as biogeography etc.
• Various fields of applied biology such as
agriculture, public health and environmental
biology depends on classification of pests,
disease vectors, pathogens and components of
an ecosystem.
20. • Classification is important because it helps
scientists to clearly identify species, study and
observe them, and organize concentrated
conservation efforts.
• It also assists as a way of remembering and
differentiating the types of organisms, making
predictions about organisms of the same type,
classifying the relationship between different
organisms, and providing precise names for
organisms.
21. Linneaus classificication system
• The first individual to propose an orderly
system for classifying the variety of organisms
found on our planet was Linnaeus (1753).
• In his system of classification, the finest unit in
the organization of life is the species. .
• In the Linnaean classification system, all
organisms are placed in a ranked
hierarchy. His system was one of small groups
building into larger ones.
22. The Linnaean Classification System
• The current groupings of organisms from
largest to smallest are: kingdom, phylum,
class, order, family, genus, species.
• Within these groups, the higher you go, the
less similar organisms in the group may
appear.
• Few organisms, however, may share some
similar characteristics.
23. • Alternately, as you move
downward, the organisms
become more and more
similar.
• There are 3 domains of
life:
– Bacteria,
– Archaea, and
– Eukarya.
• These domains
encompass the six
kingdoms.
24. Classification Systems
• There are two main types classification
systems:
i. Artificial classification system
– Which place organisms into groups for purposes
of convenience.
– These groups are usually based on one or a few
easily observed features.
– E.g. where they live, how they move, or their
size.
25. • Classification without basing on relationship
among organism
• Based on one or two superficial morphological
characters
• Characters chosen were arbitrary, sexual and
for sake of convenience only
• Does not give any idea on origin and evolution
of different taxa.
• Example: Linnaean system
26. • Example: Theophrastus (370‐300 BC)
classified plants into:
• Trees
• Shrubs
• Undershrubs
• Herbs
– these systems lack any predictive value since they
are not concerned about real (biological)
relationships between groups.
27.
28. • Aristotle (384‐322 BC) classified animals
into:
– • Enaima (Animals with red blood)
– • Anaima (Animals without red blood)
– • Ovipary (Egg laying)
– • Vivipary (Giving birth to young ones)
29. Merits of artificial classification
• Only few characters are considered
• It is easy to use and reproducible
• Stable in classification
30. Demerits of Artificial classification
• The criteria used for classification are superficial
and do not reflect the natural relationships
• The system does not reflect the evolutionary
relationship between the organisms
• Many unrelated organisms are placed in the same
group on the basis of their habitats(dwelling
place). E.g whales and fish in the same group
• Closely related organisms have been placed in
different groups because of the differences in
their habitat, feeding habits,etc.
• Provide only limited information
• Cannot add new discoveries
31. ii. Natural classification system
– It is a system of classification based on natural
similarities/relationship
– The grouping is based on many features, internal
as well as external
– Uses information from many branches of biology
– Most classification in use today are natural and
they aim to reflect phylogenic relationships, i. e.
historical evolutionary relationships between
organisms
32. • Based on similarities and differences in the
large number of characters
• Classification basing on form or natural
relationship between organisms
• Based on one or more natural characters
• Characters chosen were permanently retained
sexual or vegetative characters
• Also does not give any idea on origin and
evolution of different taxa, but gives some
idea on their natural relationship.
• Almost all the characters are considered
33. Merits of natural classification
• It avoids the heterogeneous grouping of
unrelated organisms
• It helps in placing only related groups of
organisms together
• It indicates the natural relationships among
organisms
• It also provides a clear view on the
evolutionary relationship between different
groups of living organisms
• New advancement in the field can be added
34. Demerits of natural classification
• sometimes closely related organisms can
differ in important properties.
– An example of this is pathogenic bacteria that are
very closely related to non-pathogenic strains
• it can be quite difficult to determine how
organisms are related; consequently natural
classification systems tend to change as new
information becomes available.
– May change with advancement of knowledge
35. Taxonomy and Carolus Linnaeus
• A Swedish naturalist named Carolus Linnaeus
is considered the 'Father of Taxonomy'
because, in the 1700s, he developed a way to
name and organize species that we still use
today. His two most important contributions
to taxonomy were:
1. A hierarchical classification system
2. The system of binomial nomenclature (a 2-part
naming method
36. 1. Categories of classification
• Are levels of classification
• Also known as Linnaean hierarchy- a system
of categories that connote taxonomic rank
• Every organism can be classified at 7 different
levels - kingdom, phylum, class, order, family,
genus and species.
• Each level contains organisms with similar
characteristics.
• The kingdom is the largest group and very
broad.
37. • Each successive group contains fewer
organisms, but the organisms are more
similar.
• The species is the smallest group and is very
narrow.
– Organisms within a species are able to mate and
produce fertile offspring.
38.
39. 2. Nomenclature
• Nomenclature
– Nomen- name and calare- to call by name.
– System of giving names to living organism
• Nomenclature is not an end to systematics
and taxonomy but it is necessity in organizing
information about biodiversity.
• It functions to provide labels(names) for all
taxa at levels in the hierarchy of life.
40. Binomial nomenclature
• Linnaeus also developed a two-word naming
system called binomial nomenclature.
• In the binomial nomenclature system, each
species is assigned a two-part scientific name.
– The scientific name is always written in italics.
– The first word is a 'generic name,' which is called
the genus (pl. genera) and is always capitalized.
– The second word is the 'specific name,' the
species and is written lowercase. It might tell you
something about the organism-what it looks like,
where it is found, or who discovered it.
41. • Both the genus and species names are written
in Latin because that was the language used
by scientists during Linnaeus's time.
– A complete scientific name is written in Italics or
underlined.
• For example: Canis latrans
• The genus is capitalized - Canis
• The species is in lower case - latran
• This is true ALL THE TIME !!!!
• So don't forget.
42. Significance of nomenclature
• Universality-It is the language we use to communicate
ideas and information about the diversity of life
• Uniqueness: It is an information retrieval system
conveying information about diversity and
relationships.
• Stability: it maintains names of organisms to be useful
rather than changing them frequently and arbitrarily
• Avoid the use of common names which are in the
normal languages. These names can often be
misleading
• Scientific names are Latin names that are standardized
by a series of rules and are applicable Worldwide
43. Taxonomic keys
• Aka dichotomous key
• A key is a convenient method of enabling a
biologist to identify an organism.
• It involves listing the observable features of
the organism and matching them with those
features which are diagnostic of a particular
group.
• Features used are based on the easily
observable features such as shape, colour, and
number of appendages , segments, etc.
44. • A key provides a structure for sorting through
a great deal of information, so that the user
can quickly and automatically skip over many
species that do not resemble the organism.
• A key is written as a series of couplets.
• Each couplet consists of two opposing
descriptions of some features of an organism.
• The user chooses the description that best fits
the unknown organism, and is guided by that
choice to another couplet or to an answer.
45. • The two halves of the couplet lead the user to
different parts of the key, dealing with
different subgroups of the organisms included
in the key.
• All of the organisms in the half that was not
chosen are instantly rejected.
• Because the key is constructed of pairs of
contrasting choices, it is often referred to as a
dichotomous key.
46. • A taxonomic key begins by looking at large,
important features that can divide the
possible answers into a few large groups, thus
quickly ruling out most of them.
• Later couplets, which divide those groups into
smaller and smaller subgroups, use tiny details
to help the user tell the difference between
very similar species.
47. Types of dichotomous key
• There are two types:
1. Indented keys
– Indents the choices(leads) of the couplet an equal
distance from the left margin.
e.g
1a. Plant either a tree or shrubs
2a. Leaves compound ------------Tipuana
2b. Leaves simple------------------Hibiscus
1b. Plant herbaceous
3b. Leaf net-veined-----------------Salvia
3b. Leaf parallel-veined------------Kikuyu grass
48. 2. Bracketed(parallel) keys
– Provide both choices side-by-side.
– The choices of the couplet must be numbered(or
lettered).
– NB In some bracketed keys alternate couplets are
indented; in others, all couplets begin at the left
margin.
– The user proceeds to the couplet that is indicated
by the lead selected.
49. 1a. Skin of fruit is thin, soft or at least flexible,
edible …………………………………….2
1b. Skin of fruit is thick, leathery or hard,
inedible ………………………………….4
2a. Seeds in several liquid-filled chambers; fruit
soft throughout … …………………….Tomato
2b. Seeds in hard or papery structure in center
of fruit …………………………………… 3
3a. Seed enclosed in hard, stone-like pit; flesh
soft … ………………………………..Peach
50. 3b. Seeds enclosed in, papery core; flesh crisp
………………………………………. Apple
4a. Fruit weighs more than 0.5 kg; skin does not
peel off …………………………… Watermelon
4b. Fruit weighs less than 0.5 kg; skin can be
peeled ………………………………. 5
5a. Fruit long and narrow, yellow; flesh not
divided into sections …………………….Banana
5b. Fruit round, orange; inner flesh divided into
several segments …………………………..Orange
51. Constructing a taxonomic key
• A taxonomic key is designed to look at the
similarities and differences between objects using
a series of paired statements.
• The paired statements describe contrasting
characteristics (it is best to use observable,
physical characteristics).
• You choose one statement out of the pair that
happens to be true of the object you are trying to
identify.
• The statement you choose may ask you to go on
to another pair of statements or it may give you
the name of the object.
52. Instructions
• Make sure there are two leads or choices at
each point.
– Do not use body as a characteristic
• Since the key must be useful for small specimens of
species that do become large
– Limit the use of colour as a character . Colour may
fade in preserved specimens, and may vary among
individuals
– Use morphological characters such as body shape,
position of fins, presence or absence of scales or
spines in fin supports,etc
53. • Keep each of the leads parallel in
construction, that is, start each lead with the
same noun and describe the same feature in
each.
– (e.g., leaves ovate vs. leaves elliptic contrasts leaf
shapes; leaves ovate vs. leaves opposite should
not be used as it contrasts leaf shape with leaf
arrangement).
• Be sure to give alternate conditions or states
of the same character when constructing a
couplet.
54. • Give exact measurements or ratios; the terms
large and small have no meaning in the
absence of quantitative values.
• If possible, use several easily seen and
interpreted morphological characters in each
lead
