measured in humans from collections of the Cleveland Museum of
Natural History who certainly had language.
From these data it is clear that modern humans differ markedly from
modern chimps in mean values and in the range of variation for the
external cranial base angle.It is also clear that many extinct hominid
forms have an external cranial base angle that fits within the modern
human range and lies totally beyond the chimpanzee range.For example,
all the Neanderthals have external cranial base angles well above
the chimp range and none are substantially different from Skhul 5,a
specimen considered by many to be closer to living humans than any
Neanderthal.Some expressed no doubts about the ability of Skhul
5 to produce the full range of human linguistic sounds (Lieberman 1975;
Crelin 1987) based on soft tissue vocal tract reconstruction.If this is the
case,it is difficult to deny similar linguistic capacities to Neanderthals
who had virtually identical external cranial base angles.
Early Homo from Africa also have flexed cranial bases that fall above
the chimpanzee range.Specimens ER 3733 from east Turkana and OH
24 from Olduvai Gorge both show considerable flexion,substantially
greater than chimpanzees and fully within the modern human range.
On the contrary,for the five australopithecines,the external cranial base
is generally flatter than that of later hominids and within the chimp
range.This is true for all but specimen ER 406 that is a hyperrobust
australopithecine from east Turkana.This specimen,dated to about
1.6 million years ago,is identified as a member of a splinter group of
hominids that went extinct without issue by about 1 million years ago
(Wolpoff 1996).These hominids split from the one leading to Homoby
about 2.5 million years ago based on fossil ancestors as represented by
WT 17000,an early robust australopithecine from west Turkana (Walker
et al.1986).Without getting bogged down in taxonomic issues,it is impor-
tant to recognize that if WT 17000 (or specimens like it) are broadly
ancestral to ER 406 (or specimens like it),a trend for increased exter-
nal cranial base flexion occurs in a line of hominids that no one consid-
ers to be in even the same genus as living humans let alone ancestral to
them.But the same may be true for OH-24,who most consider belongs
to Homo habilis,which also is probably an extinct side branch of the
human line (Wolpoff 1996).Moreover,it likely derived from populations
represented by forms like Sterkfontein 5,which have a flat,apelike exter-
nal cranial base.
The implication of these patterns is that marked flexion of the exter-
nal cranial base occurred in three separate hominid lines.If this flexion
is related to a lowered larynx and increased supralaryngeal vocal tract,
does this mean that speech capacity also evolved independently three
separate times? It is an intriguing question and is made more provoca-224 David W.Frayer and Chris Nicolay