by Kevin Schofield

Do you remember the “tree of life” that we all studied in high school biology classes, the one that documented how the species on Earth today descended from common ancestors? For hundreds of years, species ancestry was pieced together the hard way: by comparing the phenotypes of organisms. A phenotype is the set of observable characteristics of a species, everything from basic size, shape, and color to specific body parts, such as fingers, toes, wings, and eyes. Understanding that evolution is a long series of small adjustments, rather than large leaps, biologists looked for physical resemblances to make judgments about how closely related two species are.