S4.3.3 For the adult
New species and extinction
How can one kind of animal become two kinds, and why do some kinds disappear for ever?
What this chapter teaches
A species is a group that can breed together to give fertile young. If a barrier keeps two groups apart and their conditions differ, selection and mutation can make them so different that they can no longer interbreed. Extinction has natural causes, such as an asteroid, and causes from people, such as habitat loss.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does a barrier alone not make a new species?
- Why are a small dog and a large dog still one species?
- What caused the extinction about 66 million years ago, and what causes extinction today?
After the chapter, the learner can
- Explain how isolation can lead to a new species
- Give causes of extinction, past and present
What they copy into their notebook
A species breeds to give fertile young. A barrier plus different conditions can make two species. Past causes of extinction: an asteroid, volcanoes, climate. Today: habitat loss, hunting, invasive species, pollution, climate change.