How many kinds of living things are there?

Count the kinds of life in a garden

Go out to a garden and count the different kinds of living things. You may find grass, a mango tree, a few weeds, an ant, a butterfly, a crow, an earthworm, a mushroom and some moss. After one hour you have counted thirty kinds. Now think about a forest, a pond, a desert and the sea. How many kinds of living things are there on Earth?

Nobody knows the exact number. The number of species that are known and described is between 1.7 and 1.8 million. Biologists find new ones every year, and they think that many more are still waiting to be found.

The number and the variety of the living organisms on Earth is called biodiversity. A species is one kind of organism; we define it more exactly in the third course.

You should find that with an estimate of $8.5$ million species and $18$ thousand new ones a year, naming the rest would take about $372$ years. The estimates are rough, but the message is clear: most of life is still unnamed.

A problem of names

How do you talk about so many organisms? You use names. But the names that we use every day have problems.

• One organism has many names. The plant called "tulsi" in Hindi is called holy basil in English. Every language has its own name, and often every region has one too.
• A name can mislead. A silverfish is an insect, not a fish. A jellyfish is an animal without a backbone, not a fish either.
• A name can mean different things in different places. The same common name can be used for two different organisms.

Imagine a scientist in one country who writes about the medicine in a plant, and a scientist in another country who wants to use it. If the plant has a local name only, they might never find that they mean the same plant.

One name for the whole world

So biologists need a system. It must give one name to each organism, the same everywhere, and it must put organisms with similar features in groups. These two jobs are called nomenclature (naming) and classification (grouping).

Why does this matter?

Taxonomic studies of plants, animals and other organisms are useful in agriculture, forestry and industry. They also help us to know our biological resources and their diversity. A farmer who asks whether a weed is harmful, or a forest officer who protects a rare tree, must first know exactly which organism it is.

Try it in Python

This program keeps a list of common names in two languages, and it gives the scientific name for each. It counts how many common names belong to one organism.

Practise with new numbers

Common mistakes

• Thinking all species are known. Only about $1.7$ to $1.8$ million are described, and many more wait.
• Trusting a common name. A silverfish is not a fish, and one name may stand for two plants.
• Mixing up nomenclature and classification. Nomenclature names; classification groups.
• Thinking taxonomy is only for scientists. It helps agriculture, forestry and industry too.

Remember these

• Between $1.7$ and $1.8$ million species are described, and many more are not.
• Biodiversity is the number and the variety of the organisms on Earth.
• Common names change with place and language, and they can mislead.
• A scientific name is one name for each organism, the same everywhere.
• Taxonomy helps agriculture, forestry and industry, and shows us our biological resources.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. About how many species have been described?

2. Give one example of a common name that misleads.

3. Why must two scientists in different countries use the same name for a plant?

4. What two jobs must a system of names do?