A common ancestor refers to an organism from which two or more different species have evolved. This concept is fundamental in the study of evolution, as it helps scientists understand how diverse life forms are related. For example, humans and chimpanzees share a common ancestor that lived millions of years ago. The idea of a common ancestor is supported by various fields, including genetics and paleontology. By examining DNA similarities and fossil records, researchers can trace back the lineage of species, revealing how they have diverged over time from their common ancestor. This understanding enhances our knowledge of biodiversity and the evolutionary process.