Exemplar: Atapuerca 5 [Sierra de Atapuerca, Spain] - c.400,000 y.a.HOMO HEIDELBERGENSIS, previously called archaic Homo sapiens, marks another increase in hominid size about 800,000 years ago. The designation heidelbergensis covers a diverse group of skulls which share features with Homo erectus, Homo neanderthalensis and modern humans.
The browridge is smaller and the angle of the rest of the face is more vertical than in erectus or ergaster. Males stood over 1.7 meters and weighed 62 kilos, females 1.6 meters and 51 kilos: bone mass indicates a significant increase in physical strength. In addition, brain size increases gradually up to 1600cc. Heidelberg skeletons and teeth are usually less robust than in erectus, but more robust than modern humans. Most have large browridges and receding foreheads and chins.
Heidelbergensis was apparently the next species, after ergaster and possibly erectus, to diffuse throughout the length and northern breadth of Africa, and from there into southern Europe and the Middle East. The causes of this human migration are not known, but increasing pursuit of large animal game may have played a role. Able to resist competition from any other large predator and to compete with those predators for a wide range of prey, heidelbergensis likely expanded the opportunities for human hunting. The richer diet that resulted may in turn have contributed significantly to the evolutionary scope for increased body mass.
Heidelberg fossils are also increasingly associated with dismembered and burned human remains that indicate cannibalism. It is not clear whether this was a response to ecological scarcity, a habitual diet, or a learned treatment of captives or the dead.
With the scaling up of physical size and brain capacity seems to have come a greater physical variability. Heidelbergs are almost certainly the ancestor to Homo neanderthalensis -- which is apparently an adaptation to more northern, colder habitats -- and they were probably direct descendants of the recently discovered and still controversial Homo antecessor. But there is sometimes no clear distinction between some western forms of erectus and heidelbergensis. Both used Acheulean tool industry until extinction, and many fossils from around 500,000 years ago are difficult to classify into one species or the other.
It's unfortunate that few hominid specimens survive from prior to about 800,000 years ago, because evolutionary relationships among habilis, rudolfensis, ergaster, erectus and heidelbergensis remain in many details controversial and difficult to fix.
In the descriptions of existing fossils, phrases such as "a curious mixture of primitive and advanced traits" or "a transitional form" too often signal that existing species designations -- and species concepts -- insufficiently characterize the diversity and plasticity of human evolution in the middle of its course between our origins and the present day.