5. Early hominins

During the period from 8–5 million years ago, the Earth experienced the beginning of a long-term drying and cooling trend. Due to the increasing dryness, forests were replaced with open woodland, and areas of grassland began to appear. Hominin evolution began in Africa at the time of these climatic changes. ‘Early hominins: possible and probable’ reviews four collections of fossils that represent each of the ‘candidate’ species that have been put forward for being at the base of the hominin clade: Sahelanthropus tchadensis dated to 7.2–6.8 mya; Orrorin tugenensis dated to round 6 mya; Ardipithecus kadabba dated to 5.7–5.2 mya; and Ardipithecus ramidus from round 4.5 mya.