The Origin and Common Ancestry of Life

Life on Earth is astonishingly varied, yet beneath that variety lies a deep unity. Every organism ever studied, from a soil bacterium to a blue whale, shares a common set of molecular and cellular features. This shared toolkit is one of the strongest lines of evidence that all living things descend from a single ancestral population that existed billions of years ago.

Universal features of cellular life

When biologists compare organisms across every branch of the tree of life, certain features appear without exception. These universal characteristics point toward a common origin rather than repeated independent inventions.

• Cell structure: All organisms are built from one or more cells bounded by a phospholipid membrane. This membrane controls what enters and leaves, maintaining an interna