emptied of ‘“‘wastebasket”’ taxa. Second, far too many of these same 
fossils are of debatable age, or are dated only to within the broadest 
of time zones. Given these considerations, it is obviously premature 
to attempt to determine the actual pattern of hominid brain size 
increase with time, although the overall tendency to enlargement (at 
least among those fossils conventionally assigned to genus Homo) 
is clearly there. 
However all this may be, when evaluated by the criteria routinely 
applied to all other organisms, the fairly substantial fossil record of 
hominid evolution robustly declares that the human story has been 
vastly more eventful than the linear model suggests (Tattersall, 
1986). This is no story of straight-line progression; rather, it is one 
of diversification, with numerous speciations and extinctions right 
from the very first fossil intimations of our family. If there is con- 
sistency in this almost 5 million-year-long story, it is not to be found 
in a slow and steady grind but rather in the consistency of repeated 
evolutionary experimentation, both successful and otherwise. Bear- 
ing this in mind, let’s look briefly at the human fossil and archae- 
ological records with the aim of identifying major innovations 
whose accretionary history may help us to determine the pattern of 
modification in human evolution. 
Innovations in Human Evolution 
The earliest evidence we have of creatures who were exclusively 
our ancestors, and not those of apes as well, comes from sites in 
Kenya and Ethiopia dating to the period between about 4.4 and 3.9 
million years (myr) ago. The most convincing of these fossils have 
been allocated to the species Australopithecus anamensis, a form 
represented as yet only by a few fragments which include a couple 
of fairly decent jaws and part of a shin bone (M. Leakey et al., 
1995). Despite a few differences in detail, the jaws and teeth look 
comfortingly similar to those of the next-in-line species Australo- 
pithecus afarensis, known from sites in Ethiopia and Tanzania that 
date in the 3.8 to 3.0 myr range. And, tellingly, the shin bone shows 
unmistakable signs of uprightness in the part that contributes to the 
