The idea that humans and chimps are more like siblings than cousins in the primate family initially shocked most people, who assumed that relationships mirrored physiques.
Gorillas look like the chimpanzees they sit next to in the zoo.
People assumed the cage bars drew hereditary lines as well. But genetic studies in recent years have drawn a different primate family tree. Off the original line of primates, the tree shows, gibbons and siamangs branched first. Yet when scientists compare hard tissues, such as bones and teeth, they sometimes find more similarities between chimps and gorillas than between chimps and people. Some scientists, therefore, doubt whether physical features can say anything about evolution at all.