6 IntroductionClassification, in biology, is identification, naming, and grouping of organisms into a formal system based on similarities such as internal and external anatomy, physiological functions, genetic makeup, or evolutionary history.With an estimated 10 million to 13 million species on Earth, the diversity of life is immense.Determining an underlying order in the complex web of life is a difficult undertaking that encompasses advanced scientific methods as well as fundamental philosophical issues about how to view the living world.
7 Classification-1Classification determines methods for organizing the diversity of life on Earth.It is a dynamic process that reflects the very nature of organisms, which are subject to modification and change over many, many generations in the process of evolution.Since life first appeared on Earth 3.5 billion years ago, many new types of organisms have evolved.Many of these organisms have become extinct, while some have developed into the present fauna and flora of the world.Extinction and diversification continue nonstop, and scientists are frequently encountering fluctuations that may affect the way an organism is classified.
8 Classification-2Taxonomy is part of a larger division of biology known as systematics.Determination of phylogeny is a goal of systematics.This is done by the construction of phylogenetic trees, which in a sense represent evolutionary hypotheses and attempts to define monophyletic groups.To build these trees, we must have data, which comes from the characteristics used in classification.There are several methods of classification: traditional, phentic, and cladistic.They differ in how they value certain characters.
9 Classifying Organisms-1 When classifying organisms, scientists study a wide range of features, including those visible to the naked eye, those detectable only under a microscope, and those that can be determined only by chemical tests.Scientists compare the external shapes and sizes of organisms as well as the anatomy and function of internal organs and organ systems, such as the digestive or reproductive systems.Biochemists study and compare the molecular interactions within an organism that enable it to grow, make and store energy, and reproduce.
10 Classifying Organisms-2 The early stages of an organism’s development, or embryology, as well as an organism’s behavior, or ethology, are also useful in grouping organisms.Even the role an organism plays in its habitat can help place it in a particular group.Scientists use the fossil record to learn how certain animals have changed and evolved through Earth’s history, which may provide clues for classification.
11 Classification Methods Grouping organisms according to shared characteristics is not a simple task, and scientists often disagree about the best way to classify organisms.Some think that organisms should be grouped according to differences or similarities in the way they look or act.Other scientists argue that classification should be based on characteristics derived from a shared evolution.Conflicting philosophies about classification have resulted in a variety of classification methods, each with their own set of assumptions, techniques, and results.
12 Types of Systems of Classification Three basic categories of systems of classificationArtificial systemsThese system use the habit and importance toman as taxonomic character.Natural systemsThese system used as many taxonomiccharacter as possible to group taxa.Phylogenetic systemThese system used as many taxonomic characteras possible to group taxa in addition to thephyologenetic [evolutionary] interpretations.
13 Traditional Approach to Classification of Organisms:1 Aristotle and Theophrastus used hierarchy in classification of organisms for the first time.Until relatively recently, all organisms placed in just two kingdoms, the animal and plant kingdom.This Two-kingdom system was mainly centered on the land organisms.Traditional classification, [Linnaeus’s system] did not dependent on evolutionary criteria.Traditional classification, [Linnaeus’s system] dependent on what seems natural.
14 Traditional Approach to Classification of Organisms:2 Data used in traditional systematics stresses both common ancestry (monophylesis) and the amount of divergence among groups.The traditional, dating to Linneaus view, is that birds have feathers, reptiles have scales, and mammals have hair.Using this as a major character, a classification like that above has been constructed.Fossils, evidence of past life, are not included in this classification.Since all of these groups have the amniotic egg, or a modification of it, they would be united in a larger taxon.
15 Traditional Approach to Classification of Organisms:3 Linneus placed each of these groups in a separate class within the Phylum Chordata.A primitive character is one present in the common ancestor and all members of the group, such as the amniotic egg.A derived character is one found only in a particular lineage within the larger group.In our example above, hair and feathers may be viewed as derived characters.A traditional view of our example group is that birds and mammals evolved from reptiles due to their unique derived characters.
16 Traditional Approach to Classification of Organisms:4 Figure 1. Traditional classification of reptiles, birds, and mammals
17 Phenetic classification:1 Phenetics is a noval phylogenetic method.Phenetic classification, applies numerical taxonomy to arranging groups into genera and higher ranks.The analysis of various types of taxonomic data by mathematical or computerized methods is called numerical taxonomy or taximetrics.Phenetics is a process by which taxa are clustered together based on the number of their similarities (or differences, depending on the numerical coefficient employed).
18 Phenetic Classification:2 Traits are measured and either converted into integers or input directly as numerical data.Theses data are then mathematically processed using an algorithm that generates a similarity (or distance as the case may be) matrixVarious graphical representations of this matrix include a phenogram, and principal coordinate plot.These characters are scored numerically and analyzed by rigorous methods.
19 Phenetic classification:3 Phenetics challenged the prevailing view that classification should be based on comparisons between a limited number of characters that taxonomists believed to be important for one reason or another.Phenetics argued that classification should encompass as many variable characters as possible.Phenetic classifications are plagued by problems of convergence and parallelism.but are useful in their attempt to objectify the classification process.
20 Numerical Taxonomy:1This approach of systematics involves the numerical evaluation of the similarities or affinities between taxonomic units, then arrangement of these units into taxa on the basis of their affinity.Numerical taxonomy is based on neo-Adansonian principles.Adanson , a French botanist, was the first to assign numerical values to the similarity between organisms.
21 Numerical Taxonomy: 2Groups of similar organisms recognized by numerical methods are called phenons.Phenons are equivalent to various taxonomic groups.
22 Cladistics:1Cladistics is the hierarchical classification of species based on evolutionary ancestry.Cladistics is distinguished from other taxonomic classification systems because it focuses on evolution (rather than focusing on similarities between species).It places heavy emphasis on objective, quantitative analysis.Cladistics generates diagrams called cladograms that represent the evolutionary tree of life.
23 Cladistics:2DNA and RNA sequencing data are used in many important cladistic efforts.Computer programs are widely used in cladistics, due to the highly complex nature of cladogram-generation procedures.Cladistics is a type of systematics developed by the late German biologist Willi Hennig, who attempted to formulate a more objective method of classifying organisms.
24 Cladistics:3Cladists group organisms based on the presence of shared derived characters, not the overall similarity of potential group members.In the example cited in Figure 1, the amniotic egg would be used to unite a group sharing common ancestry, since it would NOT be present in a group that was not in the lineageThe use of feathers and hair to separate birds and mammals from reptiles would NOT factor into a cladistic hypothesis, or cladogram, since these are characters unique to only one taxon in our group.
25 Figure 2. Dissected cladogram of repriles, birds, and mammals. Cladistics:4Figure 2. Dissected cladogram of repriles, birds, and mammals.
26 Cladistics:5Figure 2. Cladogram of the vertebrate chordates.
27 Cladistics:6The example used above, if treated cladistically, would produce a very different classification! Note that crocodiles have more in common (in a cladistic sense) with birds than they do with other reptiles.Birds and crocs form a clade, or monophyletic group united by shared derived characters not present in the other groups.If we construct a Linnean group from this cladogram, we have a class of birds and crocodiles, a second class of lizards, snakes, and turtles, and a third class of mammals, as shown in Figure 4.
28 Cladistics:7Figure 3. Cladistic-based classification of reptiles, birds, and mammals.
29 Cladistics compared with Linnaean Taxonomy Prior to the advent of cladistics, most taxonomists used Linnaean taxonomy to organizing lifeforms.That traditional approach used several fixed levels of a hierarchy, such as Kingdom, Phylum, Class, Order, and Family.Cladistics does not use those terms,becauseone of the fundamental premises of cladistics is that the evolutionary tree is very deep and very complex,and it is not meaningful to use a fixed number of levels.
30 Cladistics Compared to Phenetics Phenetics give equal weight to all characters where as cladistics did not.Cladistics is useful in order to infer the branching order in a phylogeny.It is necessary to distinguish those characters that provide a good indication of evolutionary relationships from other characters that might be misleading.
31 What we Learn ………. You have learnt : Different approaches to classificationNumerical taxonomyClassification methods
34 Study Tips Book Book Title: Plant taxonomy Author:O.P. sharma Book Title: Biological ScienceAuthor: Taylor, Green & StoutBookTitle: ABC Of BiologyPublisher :Holy FaithBookTitle: EvolutionAuthor: Monroe Strickberger