Key Idea 3:  Individual organisms and species change over time.
3.1  Describe sources of variation in organisms and their structures, and relate the variations to survival.
Major Understandings	Suggested Activity
3.1a  The processes of sexual reproduction and mutation have given rise to a variety of traits within a species.
3.1b  Changes in environmental conditions can affect the survival of individual organisms with a particular trait.  Small differences between parents and offspring can accumulate in successive generations so that descendants are very different from their ancestors.  Individual organisms with certain traits are more likely to survive and have offspring than individuals without these traits.
3.1c  Human activities such as selective breeding and advances in genetic engineering may affect the variations of species.
3.2  Describe factors responsible for competetion within species and the significance of that competition
Major Understandings	Suggested Activity
3.2a  In all environments, organisms with similar needs may compete with one another for resources.
3.2b  Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to permit its survival.  Extinction of species is common.  Fossils are evidence that a great variety of species existed in the past.
3.2c  Many thousands of layers of sedimentary rock provide evidence for the long history of Earth and for the long history of changing lifeforms whose remains are found in the rocks.  Recently deposited rock layers are more likely to contain fossils resembling extinct species.
3.2d  Although the time needed for change in a species is usally great, some species of insects and bacteria have undergone significant changes in just a few years.