Selection pressures in the evolution of morphological characters which are exclusive to primates were discussed. While the evolutionary change in some morphological characters of primates can be explained by natural or sexual selection, there are also morphological characters of primates, such as some regions of neocortices, which are involved in social interactions and whose evolutionary changes can hardly be explained by natural or sexual selection alone. Furthermore, recent studies have demonstrated that relative sizes of brain, neocortex and some thalamic nuclei of brains differ significantly by social structure in primates. Based on these and other findings, we propose here that “active” selection pressures may have favored a variety of morphological characters related to social interactions, the selection pressures which are derived from social interactions and are operative within animals or troops. The introduction of concept of active selection will be useful in developing conceptual frameworks for understanding of the mechanism of evolution of primates, in particular, of hominids.

The original hominoid brachiators probably used typical terrestrial quadrupedalism as their alternate mode of ground locomotion. The development of knuckle walking made possible a shortening of the flexor muscles to improve the hand grip for more efficient arm-swinging. Bipedalism equally served to free the hands from palmar application to the ground, and likewise permits manual flexor shortening. Recently discovered australopithecine limb bones may be interpreted as indicating a primarily arboreal adaptation, emphasizing brachiation, with bipedalism being no more than an alternate mode. Thus the origin of bipedal adaptations might be viewed not as a means of leaving the trees, but rather as a step in perfecting brachiation.

In recent years, comparative observations of primate anatomies have been extended using measurements and computer analyses: morphometrics. A question then follows. Can we extend field observations of animal lifestyles using measurement and computer analysis, using, in other words, a new «niche metrics», for comparison with the morphometrics of animal anatomies? This has been attempted (Oxnard, Crompton & Lieberman, 1990) by «measuring» 17 lifestyle variables (on locomotion, environment and diet) for 28 prosimian primate species. These data have been analysed by multivariate statistical methods entirely similar to those used in morphometrics. The results define groups of prosimian species that seem not to be related directly with taxonomy and evolution, but with functional adaptation to lifestyle. Comparisons between the morphometric and niche metric results reveal a degree of similarity of species grouping in each that is apparently related to adaptation and remarkably detailed. But further study of both the morphometric and niche metric results suggests that questions pertaining to evolution may also be asked. Thus, both morphometric investigations seeking clusterings of anatomical variables and niche metric studies seeking clustering of higher taxonomic groups of species produce results that seem to be of developmental and phylogenetic rather than directly adaptive import. Through the combination of these two approaches, it may eventually be possible to partition both evolutionary and adaptive components, even though, of course, there must always be overlap between them.

The measurement of biological forms has traditionally relied on metric measurements analyzed in terms of a suitable Cartesian space. Yet biological forms are not produced in such a framework and consequently there may be disjunction between analytical framework and biological process. A number of systems for the representation of form are examined and it is argued that all are defective, to one degree or another, at the level of congruence with biological process. Metric frameworks, it is suggested may not be sufficient and representations based on the concept of grammars and fractals are also briefly reviewed. It is concluded that representation of form in accordance with underlying structuring processes is still lacking.

Using samples of skulls of early and modern hominids and modern pongids we compare the plausibility of Evolutionist and Creationist viewpoints. Multivariate methods are used to assess the corollary of Creationism that all fossil specimens which Evolutionists consider to be hominids are either apes or humans. We conclude that the results of this study cannot easily be accommodated within a Creationist framework, and, therefore, contribute substantial evidence for the Evolutionist viewpoint.

It has been repeatedly suggested that twinning frequency in most catarrhine primates is approximately the same as in humans, whereas the frequency in the chimpanzee and the gorilla might be higher. This study presents a re-evaluation of the evidence from the pertinent literature. It can be demonstrated that most data on twinning frequency in Old World monkeys and apes should not be used because of their small sample size. A lower limit of 1500 pregnancies is suggested here. If all frequency estimates taken from smaller samples are rejected, only four estimates forMacaca mulatta andPapio hamadryas remain. The estimates range from 0.19 to 0.35% and are in fact lower than the frequencies of most (but necessarily all) human populations. The published birth samples for apes are, however, relatively small, and the resulting twinning rates may not be reliable.

The paper deals with a new form ofSinoadapis from the Lufeng hominoid Locality, assigned toSinoadapis shihuibaensis sp. nov. Holotype PA 882 A fragment of right mandible with C,−M3. Other materials. PA 903 A fragment of left maxilla with P3−M3. PA 959 Left lower tooth row with I1−P2, P4. PA 902 Right upper tooth row with C′−P3. PA 964 An isolated left I1. PA 907 An isolated right I3. PA 972 An isolated right M3.