7.1 Classification organises our world

In this topic, you will learn that:

• classification systems help scientists to communicate • scientists identify all living things through scientific names • Carolus Linnaeus developed the modern Linnaean classification system.

Figure 1 The mature pine tree looks very different from its sapling.

a

b

Early classification methods

Early humans first classified plants by learning which plants were edible and which were poisonous. A new plant or animal discovered by humans was (and still is) studied and put into a group. Some plants were found to help sick people and others were poisonous. Some animals could produce food, such as milk and eggs. Each generation of scientists worked to improve how these groups were classified.

Common names or scientific names

Scientists try to communicate with each other regularly to help with their research. Before the existence of photographs or computers, scientists would have to draw creatures, such as birds, by hand and describe them in as much detail as they could. This was difficult, and it was easy to make mistakes as the photographs of the American magpie and the Australian magpie show (Figure 2). Both birds looked so similar that they were given the same common name, ‘magpie’. However, their scientific names are different. The name Cracticus tibicen for the Australian magpie means the same to scientists in every country around the world.

The Linnaean classification system

Greek philosopher Aristotle (384–322 bce) was the first scientist to start using systems to describe plants and animals. By the 17th century the early classification systems used a hierarchy list of names, starting with large general groups (such as plants and animals) and then dividing each group into smaller and smaller groups based on their characteristics. Each organism ended up with a long Latin name that described the characteristics of each level of the hierarchy. Swedish botanist Carolus Linnaeus (1707–1778) tried these classification systems but found their descriptions to be too long. He decided that a simpler system was needed. He changed the descriptions to single words and reduced the number of classification groups to seven.

Figure 4 Part of Linnaeus’s classification system

Figure 2 a The American magpie Pica hudsonia and b the Australian magpie Cracticus tibicen

Aristotle (384–322 BCE) sent his students out to gather local samples and stories. He ordered the samples and stories from least important (rocks) to the most important (wild animals, men, kings, fallen angels, angels and God).

Andrea Cesalpino (1519–1603) suggested classifying plants into groups according to their trunks and fruits. John Ray (1627–1705) suggested that organisms needed to be observed over the whole of their lifespans.

Augustus Quirinus Rivinus (1652–1723) and Joseph Pitton de Tournefort (1656–1708) suggested using a hierarchy of names. Each organism had a long Latin name that described the characteristics of each level of the hierarchy.

Finding new species

There are many living things that are still to be discovered or named. In 2020, seven new species of peacock spiders were identifi ed in Australia. These spiders are the same size as a grain of rice. During their courtship dance, they wave their brightly coloured abdomens. Small groups of scientists are trying to fi nd undiscovered plants in Brazilian rainforests before they are destroyed by logging and farming. Often the scientists are supported by large pharmaceutical companies from other countries in the hope that it may lead to the discovery of new medications. The antibiotic

Figure 5 Peacock spiders are unique to Australia.

7.1 Check your learning

Remember and understand

1 Explain why Linnaeus simplifi ed the classifi cation system used by previous scientists.

2 Suggest two reasons why scientists still classify organisms today.

Apply and analyse

3 Explain why it would be diffi cult to classify frogs and tadpoles using the early methods of classifi cation. penicillin was discovered from a type of mould; aspirin comes from a substance in the bark of willow trees. The next painkiller could come from a small fungus in the rainforest or an insect that relies on the fungus for food. Without a name, the new discoveries would be lost and forgotten.

Figure 6 The rainforests of Brazil contain many undiscovered plant species.

Evaluate and create

4 The earliest scientists did not have pens or paper. Describe how they would have passed on the information they discovered. Discuss the accuracy of this approach (by describing the advantages and disadvantages of using this method). 5 Aristotle was one of the fi rst scientists to gather information from wide regions. Propose the method he might have used to tell the differences between a horse and a fl y.

Figure 7 Carolus Linnaeus

Carolus Linnaeus (1707–1778) introduced the Linnaean classification system. Thomas Cavalier-Smith (1942–2021) suggested the kingdom Plantae be split into two kingdoms because of differences in their cells.

Carl Woese (1928–2012) suggested that the bacterial kingdom Monera be split into two domains, and the third domain contain all other organisms.