Classification

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Slide 1

In this lesson, we’re going to talk about why scientists classify organisms. The organisms that have lived on the Earth in the past, and that continue to live on the Earth today form a diverse group with many different characteristics. Scientists believe that there are over 50 million different species of organisms alive on the Earth today.

In order to study them, scientists need to group or classify them so that they can make sense of the things that different species have in common, and the differences
between them.

We’ll begin this lecture by talking about the reasons why we classify animals and plants. We’ll be particularly interested in classifying animals. Afterwards, we’ll talk about the different approaches to classification and the problems that scientists may encounter when classifying organisms into groups.

Slide 2

First, What is classification?

Each of the organism in the world is unique (whether it is plant or an animal) These unique characteristics form the basis of diversity.

Because there are so many different organisms, scientists need to arrange them into groups in an effective way, based on their similarities and differences. This helps scientists to work more efficiently as they will no longer need to study the functions and reasons for a particular, common characteristic again and again as they study each different organism.

The method scientist use to arrange organisms into groups or sets on the basis of their similarities and differences is called classification

Slide 3

Let’s talk a little more about the reasons why scientists classify organisms. There are over 50 million species of organisms. If we group them together, it will make it quicker and easier to study them. Classification helps us in the following ways. First, it can allow us to identify evolutionary links. Next it can help us to identify known
Organisms from their characteristics. Finally it can help us to predict which characteristics an organism will possess, based on the characteristics of the other organisms in its class. We’ll have a look at a few examples showing how classification helps scientists to do each of these things.

Slide 4

The first reason why scientists use classification is that it helps them to identify evolutionary links between past and present organisms.

Species classified into the same group often share characteristics which they have inherited from a common ancestor. Scientists can thus use the characteristics of organisms to predict evolutionary links between them.
Early classification systems only used the physical appearances of organisms to classify them. Today, scientists look more deeply to find the reasons for these characteristics before assigning them to groups. Organisms in the same group are likely to share characteristics because they have evolved from a common ancestor.

For example, chickens are believed to have evolved from dinosaurs similar to the tyrannosaurus rex because they share a number of characteristics such as hollow bones, air sacs and a configuration of wrist bones with them.

The characteristics of organisms can be used to predict the evolutionary link.

The example on the right shows that some reptiles evolved from a common ancestor as certain species of fish.
(Click)---- Classification also shows that Humans and chimpanzees have evolved from the same common ancestor. Note: humans did not directly evolve form chimpanzees, but they shared a common ancestor about 6.5 million years ago (some time before the first upright walking organism in this diagram).
These evolutionary theories are based on the classification of organisms, and are illustrated in a type of evolutionary tree called a cladogram.

Slide 5

Scientists also use classification to identify organisms. This helps them to organize and streamline their studies of different species. Each of these cats on the right lives in a different environment, and looks different, but the bottom two belong to the same species. The top one belongs to a different species.
If scientists know, for example, that the cat on the top right belongs to a species that eats small mammals, lizards, birds, eggs, invertebrates, and the occasional tree frog, they will not waste time trying to work
Out what its diet is like.
(click) Let’s look at another example. Suppose you were walking in the bush, and saw a pretty parrot. In order to understand the parrot, its habitat, its
Diet and its behavior it would be useful to identify it. Classification helps us to do precisely that. However, parrots all belong to the order Psittaciformes, so all of the parrots shown below share some characteristics, and hence some biological properties. This classification helps us to streamline our study of parrots as it helps us to identify and understand some basic characteristics that are common to all parrots.

Slide 6

Another reason to classify organisms is so that we can predict what their characteristics might be.
If several members of a group share the same characteristics, we can predict that the remaining members might also share these characteristics.
For example the birds in the picture on the right share several characteristics: their bone structure is similar, they all have feathers, they all have hollow bones, they can all
Fly and so on.
Click--- The cow and the buffalo shown also have many biological characteristics in common.

Slide 7

Classification has many different benefits for scientists. It helps them to study a huge variety of organisms, and to understand the relationships between different groups
Of organisms. It also helps them to identify the species of a given organisms. Classification is useful in helping scientists to understand the evolutionary relationship between past and present organisms. Through studying the characteristics of living organisms, scientists can form hypotheses about the characteristics of extinct organisms that are related to them through evolution. Classification means that scientists don’t need to study the characteristics of every single member of a group.
They can predict the characteristics of all members of that group by studying just a few of its members.
Finally, classification is a valuable tool in several fields of applied biology. For example, agriculture, public health and environmental biology depend on the ability of scientists to classify pests, disease vectors, pathogens and other components of an ecosystem. By knowing that the mosquitoes in a given environment are anopheles mosquitoes, doctors are aware that the mosquitoes may carry malaria and that they need to take measures to prevent the transmission of malaria, and to treat its victims.

Slide 8

As we expand our scientific knowledge, we begin to realise that many past classifications have actually been incorrect. For example, at one stage bats and
Pigeons were placed in the same group because both could fly. However, we now know that bats are mammals, and pigeons are birds, and that they have quite different
Anatomy and mechanisms for achieving flight. Because of this knowledge, we have now placed bats and pigeons into two different groups. Since the discovery of
DNA, we have gained the ability to extract and examine DNA. This new knowledge has allowed us to realise that many of our past classifications were incorrect – that animals we previously thought were similar are not related at all. For example, DNA testing of sea slugs with different appearances from different parts of the world helps scientists to decide whether they do, in fact, belong in the same group. When we realise that a previous classification was incorrect, we need to change the nomenclature – or the conventions by which we name species to accurately reflect the changes that need to be made.