| A | B |
|---|
| primitive trait | a trait that evolved in an early, common ancestor |
| advanced trait | a trait that is modified by evolution to be different from the primitive trait it evolved from |
| relative dating | determining the age of a fossil by the layer in which it is found |
| absolute dating | determining the age of a fossil by radioactive dating techniques; more precise than relative dating |
| radioactive isotopes | certain atoms of an element that decay at a uniform rate |
| decay product | the atoms that result when a radioactive element decays |
| vestigial structure | a structure with little or no funciton in an organism that did have a function in its ancestors |
| embryos | an organism in an early stage of development before it is hatched, born, or germinated |
