How many kinds of living thing?
Life is believed to have arisen on Earth about 3.6 billion years ago. The accepted view is that the simple unicellular organisms that arose first evolved gradually into complex multicellular ones.
Today about 8.7 million species are thought to live on Earth, and among them there is enormous variety.
Activity 13.1
- Identify the animal species shown in figure 13.1.
- Group those species using a criterion of your own choosing.
- Compare the way you grouped them with the way the other students in your class did.
Figure to be added
Observation
No two students will have produced quite the same answer. One will have split them by winged and wingless, another by living in water and living on land. What this shows is that living things can be classified in many ways, on many different characteristics.
Which leaves the question: with so many ways of grouping available, which do scientists choose, and why? That is what the next few pages are about.