Lesson 42: What Is a Species?
Biologists use ancestry, genes, reproduction, and other evidence to classify species. The lesson covers variation, breeds, cultivated varieties, hybrids, and why species boundaries can be difficult to define.
Key Ideas
- A species is a group of closely related living things. Scientists use several kinds of evidence to decide which things belong together.
- Looking alike is not enough to prove two living things are the same species. Scientists also study their bodies, genes, family history, and reproduction.
- Members of one species can have different traits. Both inherited information and the environment can affect how they develop.
- Breeds of domestic animals and cultivated plant varieties are groups within a species. People select traits when breeding them.
- Different species can sometimes reproduce together and have hybrid young. This is one reason species can be tricky to classify.
Vocabulary
- Species: A group of closely related living things classified using evidence such as shared features, ancestry, and reproduction.
- Offspring: The young produced by parents, such as puppies, chicks, and seedlings.
- Interbreed: To reproduce together.
- Hybrid: Young produced by parents from different groups, often different species.
- Breed: A group within a domestic animal species that people have bred for particular traits.
- Cultivated Variety: A kind of plant people grow for selected traits, such as a particular apple variety.
Discussion Questions
- Scientists find two fossil skeletons that look slightly different. They cannot watch the animals mate, because both died millions of years ago. How could they decide whether they were one species or two?
- A group of birds gets blown out to an island and never meets the rest of its kind again. After thousands of years, how would you find out whether they are still the same species?
- If every member of a species were exactly identical, what might happen to that species the first time a new disease came along?
Supplies
- A ruler or tape measure, paper, and everyone in the house