1. Exploring Change Unity and Diversity

2. Classification Introduction How many species are there? Why should we be interested in learning about the diversity of life? When did scientists begin classifying living things? Why do we classify living things today?

3. Introduction Scientists like to classify organisms in order to study them better. The Linnaean system of classification is used in the biological sciences to describe and categorize all living things.

4. How Many Species are There? About 1.8 million have been given scientific names. Thousands more are added to the list every year. Over the last 50 years, estimates have ranged from 3 to 100 million.

5. How Many Species are There? Tropical forests and deep ocean areas likely hold the highest number of still unknown species.

6. How Many Species are There? We may never know how many there are because it is probable that most will become extinct before being discovered and described.

7. How Many Species are There? It is estimated that 99% of all plant and animal species that have existed have already become extinct with most leaving no fossils.

8. How Many Species are There? Humans and other large animals are freakishly rare life forms, given that 99% of all known animal species are smaller than bumble bees.

9. Why Should We Care About Diversity? In order to fully understand our own biological evolution, we need to be aware that humans are animals and that we have close relatives in the animal kingdom.

10. Why Should We Care About Diversity? Grasping the comparative evolutionary distances between different species is important to this understanding. It is interesting to learn about other animals.

11. When did scientists begin classifying living things? Before genetically based evolutionary studies, biology consisted primarily of classification of organisms based on their physical characteristics.

12. When did scientists begin classifying living things? One of the most important 18 th century naturalists was Carolus Linnaeus. He published Systema Naturae in 1735, which he outlined his scheme for classification of organisms according to extent of their similarities.

13. When did scientists begin classifying living things? This Linnaean system of classification is still the basic framework for all taxonomy in the biological sciences today.

14. When did scientists begin classifying living things? Uses two Latin name categories, genus and species, to designate each type of organism.

15. Linnaean System of Classification Nature was viewed as unchanging, static. This static view of nature was challenged by a small number of radical naturalists, most notably Charles Darwin.

16. Linnaean System of Classification Darwin provided evidence that evolution of life forms had occurred. He proposed natural selection as the mechanism responsible for these changes.

17. Why do we classify things today? Since Darwin's time, biological classification has come to be understood as reflecting evolutionary distances and relationships between organisms.

18. Why do we classify things today? The creatures of our time have had common ancestors in the past. The great diversity of life is largely a result of branching evolution or adaptive radiation.

19. Adaptive Radiation This is the diversification of a species into different lines as they adapt to new ecological niches and evolve into distinct species. Natural selection is the principal mechanism driving adaptive radiation.