D. M. Avery South African Museum (Iziko: Museums of Cape Town), P.O. Box 61, Cape Town, 8000 South Africa. E-mail: mavery@samuseum.ac.za Received 14 August 1998 Revision received 23 April 2001 and accepted 24 April 2001 Keywords: Sterkfontein, Swartkrans, Plio-Pleistocene, micromammals, vegetation, climate, taphonomy. The Plio-Pleistocene vegetation and climate of Sterkfontein and Swartkrans, South Africa, based on micromammals Micromammalian remains from Oldowan and Acheulean horizons in Sterkfontein Member 5E (M5E-O and M5E-A) and Swartkrans Members 1–3 (SKX1–3) provide information for the period between about 2 and 1 Ma. Another small sample from Sterkfontein Member 4 (M4) refers to a short period around 2·8–2·6 Ma and material from Sterkfontein post Member 6 infill (post-M6) relates to the Middle Stone Age occupation around 100 ka. Virtual absence of evidence of digestion on in situ lower molars of the major prey species, Mystromys albicaudatus, indicates that one of the owls Tyto alba, T. capensis or Asio capensis was the responsible predator. Over-emphasis on riverine grassland supports this sugges- tion, as does faunal resemblance between the Sterkfontein Valley samples and modern prey samples for the three owl species con- cerned. The location of the roost and the range of prey species point to the barn owl T. alba. There is no indication of differential bias between samples. South African species of eagle owl (Bubo spp.) are ruled out. All samples appear to represent interglacial conditions. The Grassland—Savanna ecotone probably lay nearby, as did the border between Moist and Arid Savanna. Possible modern analogues occur about 200 km west and southwest of the valley more than 250 m lower in altitude. South of Mafikeng all three vegetation types intergrade but the rainfall is higher than that postulated for some of the units in the Sterkfontein Valley. Similar climatic conditions occur near Kuruman and Kimberley where Arid Savanna merges into Grassland. Landscape information indicates a succession from riverine grassland, sometimes with Acacia trees, through hillsides with bush, grass and some trees, to plains with open savanna woodland. The suggested climate for the Sterkfontein Valley varied between 310 mm and possibly 550 mm mean annual precipitation, summer aridity index 3·8–4·1 and percentage winter rainfall 23–24. Minimum and maximum monthly temperatures would have been higher than they are today but with the temperature range reduced.  2001 Academic Press Journal of Human Evolution (2001) 41, 113–132 doi:10.1006/jhev.2001.0483 Available online at http://www.idealibrary.com on Introduction In recent years increasing attention has been paid to understanding the impact of environmental conditions on human evolu- tion. Perhaps the most comprehensive treat- ment of the topic so far has been Vrba et al. (1995), which is notable for bringing together evidence deduced from a variety of datasets. Evolution is normally measured in terms of physical changes to the skeleton, from which can be extrapolated information on the ecology of the species concerned (e.g., Vrba, 1988). In the human case, how- ever, one must also consider technological and cultural development as well as the 0047–2484/01/080113+20$35.00/0  2001 Academic Press