6.4 Classification of Living Organisms

The system of classification of organisms devised by Carl Linnaeus can be described as follows:

A hierarchical classification system of organisms in biology that is used to organise and group similar organisms together so that they can be more easily understood. A hierarchical system is one in which larger groups contain smaller groups with no overlap between groups.

Explain why it is important for there to be no overlap between groups. 

Observers looking at the Linnaean hierarchy of organisms could criticise the system as just being one that sorts organisms into convenient groups with no apparent scientific benefit. 

On the other hand, evolutionists would disagree strongly with that point of view.

Suggest the benefits to evolutionists (and to biology in general) of classifying organisms in a hierarchical system like the Linnaean system. 

Scientists investigating extinct species have used the fossil record to piece together evolutionary timelines for those organisms. 

On occasions, the bodies of well-preserved animals are discovered, such as the woolly mammoth, Yuka, found in ice in Siberia in 2012. 

Suggest the possible benefits of having a well-preserved animal carcass to examine, as opposed to fossils alone. 

Explain why, in evolutionary terms, the more recent a common ancestor between two species, the more closely related those two species are. 

A group of students were investigating fruit flies for a school project.

Fruit flies belong to the classification kingdom ‘Animalia’.

What type of cells are found in a fruit fly?

The way that scientists classify organisms has changed over time.

In the 1970’s Carl Woese developed a classification system called the ‘three-domain system’.

Name the three domains.

State and explain which domain fruit flies belong to in the three-domain system.

The students collected three different types of fruit fly to study.

The three species of fruit fly were Ceratitis capitata, Dacus dorsalis and Dacus oleae.

What do these names suggest about the evolutionary relationships between these fruit fly species?

Explain your answer.

In 1753, the Swedish botanist Carl Linnaeus published his book Species Plantarum.

Every known species of plant known at the time was listed in this book.

The plants were classified into groups called genera and each individual species was given a binomial name.

Name the two classification groups that are identifiable in a binomial name.

Scientists have been classifying organisms into groups for centuries.

Modern technological developments have enhanced the ability of scientists to classify organisms into groups and to understand the evolutionary relationships between them.

Describe how the process of classifying organisms has changed over time.

Figure 1 shows part of the evolutionary tree for penguins.

Figure 1

What does the evolutionary tree in Figure 1 tell us about the evolution of the Emperor and King penguins in relation to other species of penguin?

What evidence is used by scientists to build an evolutionary tree to show the relatedness of organisms?

Suggest why scientists view evolutionary trees as “a hypothesis of the evolutionary past”.

Evolutionary trees are a method to show how scientists believe organisms are related.

Part of the evolutionary tree for the Canidae family, which includes the domestic dog, is shown in Figure 2 below.

Figure 2

Draw a line and mark an ‘X’ on Figure 2 to show where the last common ancestor for the species’ Canis latrans and Canis lupus is.

In the evolutionary tree shown in Figure 2, the domestic dog has the same binomial name as the gray wolf, but has been given an additional subspecies name, familiaris.

Suggest why domestic dogs might be classified in this way.

Five million years of evolution is represented by the evolutionary tree in Figure 2.

Explain how several different species of canine could have evolved from a common ancestor over 5 million years.

Scientists use molecular data and DNA analysis to develop evolutionary trees such as those shown in Figure 2.

The enzymes involved in aerobic respiration can be studied to determine the relationships between different members of the canine family.

Explain how DNA sequencing of an enzyme involved in aerobic respiration could have been used to determine the relationship between the domestic dog, grey wolf and coyote.