The study's authors researched 96 peer-reviewed studies documenting SSB to compile one of the most comprehensive datasets for primates to date. The study found that SSB are a "persistent and integral component of primate social [practices]." In fact, the prevalence of SSB across a variety of closely related primate species - and over several lines of descendants - "indicates a deep evolutionary root or multiple independent evolutionary origins," the study's authors wrote.
When you learned about the history of human evolution in school, there's a good chance you were shown one all-too-familiar image. That picture probably showed a conga line of human-like creatures, from a primitive ape at one end to a modern man proudly strolling into the future at the other. For many people, this iconic image captures evolution's slow but inevitable march from the simple to the complex.