AUSTRALOPITHECINES — ROBINSON 493 



possible that Paranthropus is a comparatively little-modified de- 

 scendant of the original australopithecine stock. Evidence thus far 

 shows that Paranthropus occurs under at least reasonably wet condi- 

 tions, whether in the Sterkfontein Valley, Olduvai, or Java. This, 

 and its dietary specialization, probably indicates that it lived in fairly 

 well-wooded country. However, there certainly will not have been 

 true dense forest over the whole of the Sterkfontein area. It is likely 

 that their habitat consisted of broken forest country with grassland. 



ADAPTIVE RADIATION IN THE AUSTRALOPITHECINES 



There is no obvious reason why Paranthropus should have altered 

 its way of life significantly as long as it was able to continue living 

 in the sort of habitat in which it had originated. It was adapted to a 

 vegetarian diet, and as long as its needs in this direction were met 

 there is no reason why it should have changed. Nor does this way of 

 life bring challenges which would tend to promote evolutionary 

 change, as can be seen in the modem pongids. For example, the 

 capabilities of the chimpanzee in the direction of tool using and even 

 primitive toolmaking find little outlet in its natural habitat and 

 way of life. If the new Olduvai dating is correct, then Paranthropus 

 is known in essentially the same form over considerably more than 

 a million years across the width of the Old World. During this time 

 considerable change occurred in the hominine line. 



But clearly adaptive radiation did occur within the hominid group 

 after Paranthropus came into existence and a very good reason for 

 this seems to be present during the latter half of the Tertiary (Robin- 

 son, 1962). This was the very considerable desiccation undergone 

 by a large part of the African continent. In the early Tertiary the 

 relatively moist conditions resulted in the expansion of the forests 

 and therefore m spread over much of the continent south of the 

 Sahara of conditions suitable for a form such as Paranthropus. But 

 with the onset of desiccation the forests contracted, grass savanna 

 spread, and by the end of the Tertiary, Kalahari conditions existed 

 over a large part of southern Africa, extending at least into the 

 Congo Basin. At this time areas suitable for Paranthropus will have 

 been very much scarcer. 



It is not difficult, then, to visualize the steady but slow progress of 

 the desiccation process. After a while australopithecine groups 

 would begin to find it less easy to survive the critical time of the 

 year — the latter end of the dry season — because of food shortage. 

 Under these circumstances they will almost certainly have supple- 

 mented their diet with insects, birds, reptiles, and small mammals 

 such as rodents. As aridity increased they will have had to rely on 

 this supplement to their diet more and more. In some areas the 



