Some teachers may wish to assess students' current understanding of evolution with a pretest and then select teaching materials based on areas of weakness. For test items that can be used for this purpose, check out the evolution items on the AAAS Science Assessment website. Access to items is free, but teachers will have to register with the site.

Biological evolution accounts for diversity over long periods of time. Through billions of years of evolution, life forms have continued to diversify in a branching pattern, from single-celled ancestors to the diversity of life on Earth today. Life forms of the past were in some ways very different from living forms of today, but in other ways very similar. Present-day life forms are descended from past life forms; all life is related. Geological change and biological evolution are linked. Tectonic plate movement has affected the distribution and evolution of living things. Living things have had a major influence on the composition of the atmosphere and on the surface of the planet. Most species that once lived on Earth have gone extinct. Background extinctions are a normal occurrence. Mass extinctions occur. Extinction can result from environmental change. Extinction can stimulate evolution by opening up resources.

Evidence of Evolution concepts for 6-8

The patterns of life's diversity through time provide evidence of evolution. An organism’s features reflect its evolutionary history. There is a fit between organisms and their environments, though not always a perfect fit. There is a fit between the form of a trait and its function, though not always a perfect fit. Some traits of organisms are not adaptive. Fossils provide evidence of past life. The fossil record contains organisms with transitional features. The sequence of forms in the fossil record is reflected in the sequence of the rock layers in which they are found and indicates the order in which they evolved. There are similarities and differences among fossils and living organisms. All life forms share fundamental similarities. Anatomical similarities of living things reflect common ancestry. There are similarities in the cell function of all organisms. All life forms use the same basic DNA building blocks. Not all similar traits are homologous; some are the result of convergent evolution. Artificial selection provides a model for natural selection. People selectively breed domesticated plants and animals to produce offspring with preferred characteristics.

Mechanisms of Evolution concepts for 6-8

Evolution results from natural selection acting upon variation within a population There is variation within a population. Variation is the result of genetic recombination or mutation. The variation that occurs within a population is random. Offspring inherit many traits from their parents, but are not identical to their parents. Traits that are advantageous often persist in a population. Individual organisms with advantageous traits are more likely to survive and have offspring. Natural selection is dependent on environmental conditions. The number of offspring that survive to reproduce successfully is limited by environmental factors. Organisms with similar requirements may compete with one another for limited resources. Environmental changes affect opportunities and can influence natural selection.

Nature of Science concepts for 6-8

Science focuses on natural phenomena and processes. Scientific knowledge is open to question and revision as we come up with new ideas and discover new evidence. A hallmark of science is exposing ideas to testing. Scientists test their ideas using multiple lines of evidence. Scientists use multiple research methods (experiments, observations, comparisons, and modeling) to collect evidence. Scientists can test ideas about events and processes long past, very distant, and not directly observable. The real process of science is complex, iterative, and can take many different paths. Accepted scientific theories are not tenuous; they must survive rigorous testing and be supported by multiple lines of evidence to be accepted. Science is a human endeavor.

Studying Evolution concepts for 6-8

Our knowledge of the evolution of living things is always being refined as we gather more evidence. Scientists use multiple lines of evidence to study life over time. Scientists use anatomical features to infer the relatedness of taxa. Scientists use fossils to learn about past life. Scientists use geological evidence to establish the age of fossils. Scientists use artificial selection as a model to learn about natural selection. Classification is based on evolutionary relationships. Evolutionary relationships may be represented by branching trees (i.e. phylogenies or cladograms).