Key Idea: Similarities and differences in inherited characteristics of organisms alive today or in the past can be used to infer the relatedness of any two species, changes in species over time, and lines of evolutionary descent.

Students are expected to know that:

  1. The similarities among living things suggest relatedness.
  2. The fact that organisms retain some of the inherited characteristics and DNA of their ancestors from many generations ago makes it possible for scientists to identify both recent and past ancestors of those organisms.
  3. Inherited characteristics (both internal and external) of species alive today, including their DNA and the proteins needed to carry out basic life functions, can be compared to determine how similar the species are. Organisms with more similarities are usually more closely related to each other than organisms with fewer similarities, i.e., organisms that have more similarities tend to have a more recent common ancestor than those with fewer similarities.
  4. Inherited characteristics (both internal and external) of species alive today can be compared to the characteristics of species that lived in the past, including their DNA if available and , to determine how similar they are. Organisms with more similarities are usually more closely related to each other than organisms with fewer similarities, i.e., organisms that have more similarities tend to have a more recent common ancestor than those with fewer similarities.
  5. Some structures that do not seem similar in gross structure and function (e.g. the hand of a human and the front flipper of a whale) may after closer analysis of the detailed anatomy and their DNA sequences be shown to have the same origin. A comparison of these homologous structures and the embryonic structures from which they arise can help to infer lines of evolutionary descent.
  6. Many of the same genes code for homologous structures across different species.
  7. The relative ages of fossils can be used to help infer lines of evolutionary descent. Relative ages of fossils are determined by their relative positions in the earth's rock layers.
  8. Fossils, anatomy, and embryos provide corroborative lines of evidence for common ancestry. DNA underlies the similarities and differences in fossils, anatomy, and embryos.
  9. Cladograms and tree diagrams can be used to represent lines of evolutionary descent and to organize hypotheses about the relationships among living things.
  10. Evidence for common ancestry across a wide variety of species provides support for the idea that all multi-cellular organisms (including humans) share a common ancestor. Evidence also indicates that life began as single-celled organisms and that complex multi-cellular organisms evolved from them.
  11. The similarities and differences in all living organisms are explained by their evolution from common ancestors.
  12. Because all organisms share an ancient common ancestor, all organisms, no matter how different they appear to be, have some features in common.

Boundaries:

  1. Students are not expected to know about convergent evolution.
  2. Students are not expected to know about Archae bacteria and the possible multiple origins of life.
  3. Students are not expected to know methods of dating.
  4. Students are not expected to know the approximate date of the origin of life or when any particular species or type of organism originated.