|376 HETEROCHRONY AND PAEDOMORPHOSIS
occur.* Given the fact of this matrix, it would be surprising indeed if paedomorphosis had not played a dominant role in human evolution (Table 9).
Morphology in the Matrix of Retardation
Although I have tried to establish general retardation as an enabling criterion for massive human paedomorphosis, an assessment of our neoteny still requires a discussion of morphological features. I shall not pursue this subject in the enumerative tradition. Rather, I shall treat morphology in the context of three objections that have unjustifiably weakened the theory of our paedomorphic origins and relegated one of the major factors of human evolution to short and ambiguous paragraphs in text books. I believe that these objections are both ill-founded in theory and untenable in fact.
The most popular argument for denying our paedomorphic nature rests upon the enumeration of specific features that do not fit the hypothesis. This contention takes two forms: (1) An external similarity in form between juvenile primates and adult humans need not reflect a "passive" paedomorphic retention; it may signify the active acquisition of a new feature yielding the same result. (2) Many important human features do not resemble the juvenile stages of primates. I shall deal with the first contention by discussing the specific issue— cranial flexures—that led to its assertion; I shall treat the second by attempting to show that many nonpaedomorphic features are, nonetheless, direct consequences of retardation in development.
CRANIAL FLEXURES. The literature on orientation of the parts of the skull with respect to each other and of the entire skull to the rest of the body is among the most confusing that I have ever encountered. Conclusions depend strongly on which points or planes are taken as references (Frankfort horizontal versus basicranial axis, for example), and a bewildering array of angles have been proposed and inconsistently used. Yet the subject is of great importance, since the relative
* As I have emphasized continually, not all types of retardation imply paedomorphosis; hypermorphosis (with recapitulation) is also an aspect of retardation. But hypermorphosis involves a delay in reproductive maturation alone, dissociated from all other aspects of somatic development. Human retardation is a pervasive phenomenon of almost all systems, somatic and germinal. General retardation of this sort entails extensive paedomorphosis as an almost ineluctable consequence.