Fig. 5. Upper dentition of a “gracile” australopith, Australopithecus africanus 
(Sts 52a), from Sterkfontein Member 4, South Africa. About 2.5 myr old. Scale is 1 cm. 
that are often dubbed “‘robust’’ versus “‘gracile.’’ The robust forms 
differentiated before about 2.6 myr ago and typically showing huge 
cheek teeth—molars and premolars—in contrast to tiny front teeth— 
incisors and canines—(fig. 4) are widely thought to have specialized 
in exploiting the tough roots and tubers of the grasslands, though 
there is little direct evidence for this. The “‘gracile’’ forms (fig. 5), 
on the other hand, are believed to have hewed to a more opportu- 
nistic, omnivorous diet. Significantly, though, it’s clear that each 
lineage made its own evolutionary experiments, each spinning off 
separate species or species groups in southern and eastern Africa 
(and presumably elsewhere in the continent, did we but have the 
fossil evidence to show it; the lone such fossil comes from Chad). 
Presumably it was one such experiment within the gracile lineage 
that gave rise to the first members of the genus Homo. The earliest 
widely recognized species of Homo, H. habilis (““handy man’’) was 
described in 1964 from Olduvai Gorge in Tanzania (L. Leakey et 
al., 1964). The handful of fossils (e.g., fig. 6) on which this new 
i 
