The distribution of sequences complementary to human satellite DNAs I,II and IV in the chromosomes of chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla) and orang utan (Pongo pygmaeus)

Human satellite DNAs I, II and IV were transcribed to yield radioactive complementary RNAs (cRNAs). These cRNAs were hybridised to metaphase chromosomes of man, chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla) and orang utan (Pongo pygmaeus). The results of this in situ hybridisation were analysed quantitatively and compared with accepted chromosome homologies based on Giemsa banding patterns. The cRNA to satellite II (cRNAII) did not hybridise to chimpanzee chromosomes, although its hybridisation to chromosomes of gorilla and orang utan yielded more autoradiograph grains than hybridisation to human chromosomes, and cRNAIV hybridised to many chromosomes of gorilla and chimpanzee but was almost entirely restricted to the Y chromosome in orang utan. Most sites of hybridisation were located on homologous chromosomes in all four species, but there were a number of sites which showed no correspondence between satellite DNA location and chromosome banding patterns, and others where a given chromosomal location hybridised with different cRNAs in each species. These results are in contrast to those found for many transcribed DNA sequences, where the same sequence is usually located at homologous chromosome sites in different species, and appear to cast doubt on many proposed models of satellite DNA function.     

Did knuckle walking evolve twice?

Although African great apes share a similar quadrupedal locomotor behaviour, there are marked differences in hand morphology and size between the species. Hence, whilst all three species (two genera) of African ape frequently knuckle walk as adults, debate remains as to whether this behaviour is derived from a common ancestor or whether it evolved in parallel in chimpanzees and gorillas. This exploratory morphometric study of the sub-adult and adult wrist of these two genera aims to contribute to this debate. A total of twenty-seven dimensions of the lunate, triquetral, hamate and capitate of sub-adult and adult Pan troglodytes and Gorilla gorilla were analysed in order to determine whether carpal dimensions are generally ontogenetically scaled, and whether differences in growth trajectories, or length of growth, and adult morphologies can be explained by behavioural differences between the two species. Only 56% of all dimensions studied were ontogenetically scaled in sub-adults and some of these dimensions exhibit differing adult proportions between the two species. In general, the dimensions analysed fell into two categories: Pan and Gorilla either follow the same growth trajectories (Pattern A) or the Pan reduced major axis (RMA) regressions were significantly transposed above those of Gorilla (Pattern B). Additionally, it was found that Gorilla carpals appear to cease growing relatively earlier than those of Pan. While a small number of differences, notably those of the lunate, can be accounted for by differences in behaviour between the species, the majority of differences indicate heterochronic modifications of development during evolution, which correspond to kinematic differences in knuckle walking between the African great apes. In light of morphological, behavioural and ecological data currently available it is parsimonious to suggest that knuckle walking has evolved in parallel in the two lineages.     

Patterns of mandibular variation in Pan and Gorilla and implications for African ape taxonomy

Pan and Gorilla taxonomy is currently in a state of flux, with the number of existing species and subspecies of common chimpanzee and gorilla having been recently challenged. While Pan and Gorilla systematics have been evaluated on the basis of craniometric and odontometric data, only a handful of studies have evaluated multivariate craniometric variation within P. troglodytes, and none have evaluated in detail mandibular variation in either P. troglodytes or Gorilla gorilla. In this paper, we examine ontogenetic and adult mandibular variation in Pan and Gorilla. We test the hypothesis that patterns and degrees of mandibular variation in Pan and Gorilla closely correspond to those derived from previous analyses of craniometric variation. We then use these data to address some current issues surrounding Pan and Gorilla taxonomy. Specifically, we evaluate the purported distinctiveness of P.t. verus from the other two subspecies of Pan troglodytes, and the recent proposals to recognize Nigerian gorillas as a distinct subspecies, Gorilla gorilla diehli, and to acknowledge mountain and lowland gorillas as two separate species. Overall, patterns and degrees of multivariate mandibular differentiation parallel those obtained previously for the cranium and dentition. Thus, differences among the three conventionally recognized gorilla subspecies are somewhat greater than among subspecies of common chimpanzees, but differences between P. paniscus and P. troglodytes are greater than those observed between any gorilla subspecies. In this regard, the mandible does not appear to be more variable, or of less taxonomic value, than the face and other parts of the cranium. There are, however, some finer differences in the pattern and degree of morphological differentiation in Pan and Gorilla, both with respect to cranial and dental morphology, and in terms of the application and manner of size adjustment. Mandibular differentiation supports the conventional separation of bonobos from chimpanzees regardless of size adjustment, but size correction alters the relative alignment of taxa. Following size correction, intergroup distances are greatest between P.t. verus and all other groups, but there is considerable overlap amongst chimpanzee subspecies. Amongst gorillas, the greatest separation is between eastern and western gorillas, but adjustment relative to palatal vs. basicranial length results in a greater accuracy of group classification for G.g. gorilla and G.g. graueri, and more equivalent intergroup distances amongst all gorilla groups. We find no multivariate differentiation of the Nigerian gorillas based on mandibular morphology, suggesting that the primary difference between Nigerian and other western lowland gorillas lies in the nuchal region. Though intergroup distances are greatest between P.t. verus and other chimpanzee subspecies, the degree of overlap amongst all three groups does not indicate a markedly greater degree of distinction in mandibular, as opposed to other morphologies. Finally, mandibular differentiation corroborates previous craniodental studies indicating the greatest distinction amongst gorillas is between eastern and western groups. Thus, patterns and degrees of mandibular variation are in agreement with other kinds of data that have been used to diagnose eastern and western gorillas as separate species.     

The location of DNA homologous to human satellite III DNA in the chromosomes of chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla) and orang utan (Pongo pygmaeus)

Radioactive RNA with sequences complementary to human DNA satellite III was hybridised in situ to metaphase chromosomes of the chimpanzee (Pan troglodytes), the gorilla (Gorilla gorilla) and the orangutan (Pongo pygmaeus). A quantitative analysis of the radioactivity, and hence of the chromosomal distribution of human DNA satellite III equivalent sequences in the great apes, was undertaken, and the results compared with interspecies chromosome homologies based upon Giemsa banding patterns. In some instances DNA with sequence homology to human satellite III is present on the equivalent (homologous) chromosomes in identical positions in two or more species although quantitative differences are observed. In other cases there appears to be no correspondence between satellite DNA location and chromosome homology determined by banding patterns. These results differ from those found for most transcribed DNA sequences where the same sequence is located on homologous chromosomes in each species.     

Conservation of pericentromeric duplications of a 200-kb part of the human 21q22.1 region in primates

We analyzed the conservation of large paralogous regions (more than 200 kb) on human chromosome regions 21q22.1 and 21q11.2 and on pericentromeric regions of chromosomes 2, 13, and 18 in three nonhuman primate species. Orthologous regions were found by FISH analysis of metaphase chromosomes from Gorilla gorilla, Pan troglodytes, and Pongo pygmaeus. Only one orthologous region was detected in chromosomes of P. pygmaeus, showing that the original locus was at 21q22.1 and that the duplication arose after the separation of Asian orangutans from the other hominoids. Surprisingly, the paralogous regions were more highly conserved in gorilla than in chimpanzee. PCR amplification of STSs derived from sequences of the chromosome 21 loci and low-stringency FISH analysis showed that this duplication occurred recently in the evolution of the genome. Different rates of sequence evolution through substitutions or deletions, after the duplication, may have resulted in diversity between closely related primates.     

The articular surface of the temporal bone in certain fossil hominoids

Although quantitative variations exist between living Man ( Homo sapiens sapiens ) and the extant great apes ( Pongo, Pan, Gorilla ) in such features of the articular surface of the temporal bone (a part of the temporomandibular joint) as the proportionate development of the postglenoid tubercle, the relative prominence of the articular tubercle and the slope of its posterior face, these do not individually effect a clear differentiation between the four extant genera. But in multivariate combination of these features, although Pan and Pongo are relatively closely associated, Gorilla and Homo sapiens sapiens are distinct, and also clearly differentiated from each other. The differences between genera of extant apes are, on average, as great as those between extant Man and individual apes.
As portrayed by such multivariate compound, this anatomical region in four fossil groups displays a unique configuration differentiating Homo sapiens neanderthalensis, Homo erectus pekinensis, Australopithecus africanus and Australopithecus robustus both from one another and from extant types. The differences are such that the fossil species lie uniquely and not intermediate between extant groups.
Definable age changes in this multivariate compound occur in both Man and apes but neither these, nor overall differences between adults, appear to be associated with marked contrasts in the pattern of jaw movement. It would thus seem improbable that inferences can be made from these features about the type of jaw movement that characterized the several fossil groups.     

Comparative mapping of human alphoid satellite DNA repeat sequences in the great apes

Heterochromatic regions of chromosomes contain highly repetitive, tandemly arranged DNA sequences that undergo very rapid variation compared to unique DNA sequences that are predominantly conserved. In this study the chromosomal basis of speciation has been looked at in terms of repeat sequences. We have hybridized twenty-one chromosome-specific human alphoid satellite DNA probes to metaphase spreads of the chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla), and orangutan (Pongo pygmaeus) to investigate the evolutionary relationship of heterochromatic regions among such hominoid species. The majority of the probes did not hybridize to their corresponding equivalent chromosome but presented hybridization signals on non-corresponding chromosomes. Such observations suggest that rapid changes may have occurred in the ancestral alphoid satellite DNA sequence, resulting in divergence among the great ape species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of cranial ontogenetic trajectories among great apes and humans

Molecular data suggest that humans are more closely related to chimpanzees than either is to the gorillas, yet one finds the closest similarity in craniofacial morphology to be among the great apes to the exclusion of humans. To clarify how and when these differences arise in ontogeny, we studied ontogenetic trajectories for Homo sapiens, Pan paniscus, Pan troglodytes, Gorilla gorilla and Pongo pygmaeus. A total of 96 traditional three-dimensional landmarks and semilandmarks on the face and cranial base were collected on 268 adult and sub-adult crania for a geometric morphometric analysis. The ontogenetic trajectories are compared by various techniques, including a new method, relative warps in size-shape space. We find that adult Homo sapiens specimens are clearly separated from the great apes in shape space and size-shape space. Around birth, Homo sapiens infants are already markedly different from the great apes, which overlap at this age but diverge among themselves postnatally. The results suggest that the small genetic differences between Homo and Pan affect early human ontogeny to induce the distinct adult human craniofacial morphology. Pure heterochrony does not sufficiently explain the human craniofacial morphology nor the differences among the African apes.     

A complete sequence of the mitochondrial genome of the western lowland gorilla

The complete mitochondrial DNA (mtDNA) molecule of the gorilla was sequenced. The entire sequence, 16,412 nucleotides, was determined by analysis of natural (not polymerase chain reaction) restriction fragments covering the whole molecule. The sequence was established from one individual and thus nonchimeric. After comparison with the COII gene of gorilla specimens with known geographical origin, the sequence was identified as characteristic of the Western lowland gorilla, Gorilla gorilla gorilla. With the exception of the NADH2 gene, all genes have a methionine start codon. The inferred start codon of NADH2 is ATT (isoleucine). The COIII, NASDH4, and cytochrome b genes are not terminated by a stop codon triplet, and the COI gene is probably terminated by an AAA triplet rather than by a regular stop codon. The great majority of genic sequences (rRNAs, peptide-coding genes, tRNAs) of the complete mtDNAs of Gorilla, Pan, and Homo show a greater similarity between Pan and Homo than between either of these genera to Gorilla. The analysis of the peptide-coding genes suggest that relative to comparison between Homo and Pan a certain degree of transition saturation has taken place in codon position 3 in comparisons between Gorilla to either Homo or Pan.      

Qualitative analysis of constitutive heterochromatin and primate evolution

The results of qualitative heterochromatin analysis in 16 species of primates: Homo sapiens , Pan troglodytes and Gorilla gorilla (F. Hominidae), Hylobates syndactilus (F. Hylobatidae), Macaca fascicularis , M. tibetana , Mandrillus sphinx , M. leucophaeus , Cercopithecus aethiops , C. sabaeus and C. albogularis (F. Cercopithecidae), Cebus apella , Ateles belzebuth hybridus , Aotus azarae , Saimiri sciureus and Lagothrix lagothricha (F. Cebidae) are presented in this work. We characterized heterochromatin using: (a) in situ digestion with restriction enzymes AluI, HaeIII, RsaI and Sau3A, and (b) chromosome staining with DA/DAPI on unbanded chromosomes, on C-banded chromosomes and on sequentially G-C-banded chromosomes. The aim of this work was to relate the qualitative characteristics of constitutive heterochromatin observed with the cytogenetic evolutive processes in the primate group. Results obtained show that (1) in the family Cercopithecidae, Papionini species do not present chromosomal rearrangements when their karyotypes are compared and the heterochromatin characteristics are uniform, while Cercopithecini species show a high number of chromosomal reorganizations, but they have the same heterochromatic characteristics; (2) the Platyrrhini species analysed show variability in their karyological and heterochromatic characteristics; (3) the Hominoidea present two different situations: Pan , Gorilla and Homo with few chromosomal reorganizations among their karyotypes but with a high variability in their heterochromatin characteristics, and Hylobates with low heterochromatin variability and a highly derived karyotype. Speciation processes related to chromosome changes and heterochromatin variations in different groups of primates are discussed.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 107–124.     

Photometric determination of the DNA distribution in the 24 human chromosomes

From five normal individuals the DNA content and the DNA arm ratios of the 24 metaphase chromosomes were determined by means of scanning densitometry of photographic negatives of Feulgen-stained metaphase preparations. The results showed high reproducibility of the measuring procedure. The obtained DNA values for the 24 chromosomes showed general correspondence between the individuals. No differences between males and females were found. The DNA arm ratios showed somewhat higher inter-individual variability, especially for the acrocentric chromosomes. Our data are in agreement with other data published so far, which were obtained with somewhat different techniques, indicating that the DNA content of the individual human chromosomes in general is highly constant. Attempts were made to distinguish chromosomes by their DNA content and DNA ratio. It appears that classification of chromosomes using these parameters cannot compete with classification according to the banding patterns. Determination of the total DNA content and DNA distribution along the metaphase chromosomes may, however, provide a frame of reference for cytochemical methods directed towards the localization and quantification of molecular properties of the chromosome.     

Ontogeny of canine dimorphism in extant hominoids.

Many behavioral and ecological factors influence the degree of expression of canine dimorphism for different reasons. Regardless of its socioecological importance, we know virtually nothing about the processes responsible for the development of canine dimorphism. Our aim here is to describe the developmental process(es) regulating canine dimorphism in extant hominoids, using histological markers of tooth growth. Teeth preserve a permanent record of their ontogeny in the form of short- and long-period incremental markings in both enamel and dentine. We selected 52 histological sections of sexed hominoid canine teeth from a total sample of 115, from which we calculated the time and rate of cuspal enamel formation and the rate at which ameloblasts differentiate along the future enamel-dentine junction (EDJ) to the end of crown formation. Thus, we were able to reconstruct longitudinal growth curves for height attainment in male and female hominoid canines. Male hominoids consistently take longer to form canine crowns than do females (although not significantly so for our sample of Homo). Male orangutans and gorillas occasionally take up to twice as long as females to complete enamel formation. The mean ranges of female canine crown formation times are similar in Pan, Gorilla, and Pongo. Interspecific differences between female Pan canine crown heights and those of Gorilla and Pongo, which are taller, result from differences in rates of growth. Differences in canine crown heights between male Pan and the taller, more dimorphic male Gorilla and Pongo canines result both from differences in total time taken to form enamel and from faster rates of growth in Gorilla and Pongo. Although modern human canines do not emerge as significantly dimorphic in this study, it is well-known that sexual dimorphism in canine crown height exists. Larger samples of sexed modern human canines are therefore needed to identify clearly what underlies this.     

Size and shape dimorphism in great ape mandibles and implications for fossil species recognition

Sexual dimorphism is an important source of morphological variation, and species differences in dimorphism may be reflected in magnitude, pattern, or both. While the extant great apes are commonly used as a reference sample for distinguishing between sexual dimorphism and intertaxic variation in the fossil record, few studies have evaluated mandibular dimorphism in these taxa. In this study, percentage, degree, and pattern of mandibular dimorphism are evaluated in Pongo, Gorilla, and Pan. Mandibular dimorphism patterns are explored to determine the extent to which such patterns accurately track great ape phylogeny. Pattern stability is assessed to determine whether there are stable patterns of mandibular size and shape dimorphism that may be usefully applied to hominoid or hominid fossil species recognition studies. Finally, the established patterns of dimorphism are used to address recent debates surrounding great ape taxonomy. Results demonstrate that mandibular dimorphism is universally expressed in size, but only Pongo and Gorilla exhibit shape dimorphism. Pattern similarity tends to be greater between subspecies of the same species than between higher-order taxa, suggesting that within the great apes, there is a relationship between dimorphism pattern and phylogeny. However, this relationship is not exact, given that dimorphism patterns are weakly correlated between some closely related taxa, while great ape subspecies may be highly correlated with taxa belonging to other species or genera. Furthermore, dimorphism patterns are not significantly correlated between great ape genera, even between Gorilla and Pan. Dimorphism patterns are more stable in Gorilla and Pongo as compared to Pan, but there is little pattern stability between species or genera. Importantly, few variables differ significantly between taxa that simultaneously show consistently relatively low levels of dimorphism and low levels of variation within taxa. Combined, these findings indicate that mandibular dimorphism patterns can and do vary considerably, even among closely related species, and suggest that it would be difficult to employ great ape mandibular dimorphism patterns for purposes of distinguishing between intra- and interspecies variation in fossil samples. Finally, the degree of pattern similarity in mandibular dimorphism is lower than previously observed by others for craniofacial dimorphism. Thus, the possibility cannot be ruled out that patterns of craniofacial dimorphism in great apes may be associated with a stronger phylogenetic signal than are patterns of mandibular dimorphism.     

Preliminary observations on increasing root length during the eruptive phase of tooth development in modern humans and great apes

Ground sections of incisors, canines, and molars were selected that showed clear incremental markings in root dentine. The sample comprised 98 Homo sapiens, 53 Pan troglodytes, and a more limited combined sample of 51 Gorilla and Pongo sections. Daily rates of root dentine formation, together with the orientation of incremental markings in roots close to the cement-dentine junction (CDJ), were used to calculate root extension rates for the first 10mm of root formed beyond the buccal enamel cervix. Modern human anterior tooth roots showed a more regular pattern of increase in root length than those in great apes. In Pan, root growth rose quickly to higher rates but then flattened off. The fastest extension rates in modern humans were in incisor roots (10-12 microm per day), followed by canines (8-9 microm per day). Extension rates in Pan rose to slightly greater values in canines ( approximately 12-14 microm per day) than in incisors ( approximately 10-11 microm per day). Molar tooth roots in both modern humans and great apes grew in a nonlinear manner. Peak rates in molars reduced from M1 to M3 (8, 7, and 6 microm per day, respectively). Like humans, root growth in Pan peaked earlier in M1s at rates of between 8 and 9 microm per day, and later in M3s at rates of 7 to 8 microm per day. The more limited data set for Gorilla and Pongo molars suggests that extension rates were generally higher than in Pan by approximately 1.0-1.5 microm per day. There were greater differences in peak extension rates, with Gorilla and Pongo extension rates being between 2.5 and 4.5 microm per day higher than those in Pan. These findings highlight for the first time that root growth rates differ between tooth types in both pattern and rate and between taxa. They provide the basis with which to explore further the potential comparative relationships between root growth, jaw growth, and the eruption process.     

Implications of body mass and predation for ape social system and biogeographical distribution

Despite the fact that all African great apes have overlapping diets, they differ substantially in both biogeographical distribution and social organisation: Gorilla lives in relatively small, cohesive groups within a small biogeographical area while Pan is much more widely distributed and lives in large, fluid groups in which the members are rarely all together. In this study we use a modelling approach to identify possible causes and consequences of these differences. We use a time budget model which is based on the relationship between time available for various activities, group size, body mass and climate. We demonstrate the importance of body mass as a critical determinant for maximum ecologically tolerable group size as well as ape distribution patterns. In addition, we show that predation pressure may play a strong role in limiting the distribution of smaller-bodied apes ( Pan ). Predation pressure appears to be especially important if the apes opt for a fission–fusion strategy because it obliges them to maintain larger (sub-) groups. In effect, the apes appear to face a tradeoff between solving the predation problem by increasing body size (at the expense of reduced ecological flexibility) and going for ecological flexibility (but at some cost in terms of how they handle predation).     

Ontogeny and the evolution of adult body size dimorphism in apes

This analysis investigates the ontogeny of body size dimorphism in apes. The processes that lead to adult body size dimorphism are illustrated and described. Potential covariation between ontogenetic processes and socioecological variables is evaluated. Mixed-longitudinal growth data from 395 captive individuals (representing Hylobates lar [gibbon], Hylobates syndactylus [siamang], Pongo pygmaeus [orangutan], Gorilla gorilla [gorilla], Pan paniscus [pygmy chimpanzee], and Pan troglodytes [“common” chimpanzee]) form the basis of this study. Results illustrate heterogeneity in the growth processes that produce ape dimorphism. Hylobatids show no sexual differentiation in body weight growth. Adult body size dimorphism in Pongo can be largely attributed to indeterminate male growth. Dimorphism in African apes is produced by two different ontogenetic processes. Both pygmy chimpanzees (Pan paniscus) and gorillas (Gorilla gorilla) become dimorphic primarily through bimaturism (sex differences in duration of growth). In contrast, sex differences in rate of growth account for the majority of dimorphism in common chimpanzees (Pan troglodytes). Diversity in the ontogenetic pathways that produce adult body size dimorphism may be related to multiple evolutionary causes of dimorphism. The lack of sex differences in hylobatid growth is consistent with a monogamous social organization. Adult dimorphism in Pongo can be attributed to sexual selection for indeterminate male growth. Interpretation of dimorphism in African apes is complicated because factors that influence female ontogeny have a substantial effect on the resultant adult dimorphism. Sexual selection for prolonged male growth in gorillas may also increase bimaturism relative to common chimpanzees. Variation in female growth is hypothesized to covary with foraging adaptations and with differences in female competition that result from these foraging adaptations. Variation in male growth probably corresponds to variation in level of sexual selection. © 1995 Wiley-Liss, Inc.     

Genome size and «C-heterochromatic-DNA» in man and the african apes

The genome sizes and the amounts of DNA after C-banding pretreatments (C-heterochromatic DNA) were measured by quantitative cytochemical methods in man and the African apes,Gorilla gorilla andPan troglodytes. As evaluated by flow cytometry on propidium-iodide-stained lymphocytes, gorilla and chimpanzee have genome sizes larger than man. On the basis of the different resistance of metaphase chromosome DNA to the C-banding procedure, two genome compartments were defined, i.e.,C-heterochromatic-DNA andeuchromatic-DNA. The latter proved to be fairly constant in man and the African apes (as well as in two hylobatid species), whereas the variable amounts ofC-heterochromatic-DNA account well for the interspecific differences of genome size among the hominoid species studied so far. During karyotype diversification, quantitative changes (with either gains or losses) ofC-heterochromatic-DNA seem to have taken place independently in the hylobatid and the man/African ape lineages.     

Parasitological evidence pertaining to the phylogeny of the hominoid primates

A systematic review of parasitological data pertaining to the phylogeny of hominoid primates revealed considerable internal consistency and congruence with non-parasitological data. Hylobatids are supported as the sister-group of Pongo + Pan + Gorilla , the 'Great Apes'. Within the Great Apes, Pan + Gorilla are sister taxa. Multiple analyses of presence/absence data place Homo with cercopithecids, probably an artefact of humans' widespread occurrence and polymorphic feeding and living habits. Explicit phylogenetic hypotheses are available for only two parasite groups. Hookworms of the genus Oesophagostomum subgenus Conoweberia place Homo as the sister-group of Pan + Gorilla , whereas pinworms of the genus Enterobius place Homo as the sister-group of Pongo + Pan + Gorilla . This disagreement among data sets with regards to the placement of Homo , combined with the complete agreement about the placement of the other hominoids, is consistent with uncertainties in current findings from other sets of data.     

Q and G banding patterns of the chromosomes of some Primates

A study of the Q (quinacrine fluorescence) and G (Giemsa) banding patterns of the chromosomes of Pan troglodytes and Gorilla gorilla gorilla shows that they are almost identical. The differences include a pericentric inversion in pairs 5, 9, 19 and the X-chromosome, a possible translocation between pairs 7 and 17 of gorilla and a deletion of part of the long arms of the Y-chromosome in the chimpanzee. Several species of the genera Macaca, Papio and Cercocebus have the same karyotype and identical banding patterns. This suggests that speciation in this group may have taken place on purely genic grounds, without, involving any karyological changes.     

Growth changes in internal and craniofacial flexion measurements.

Growth changes in both internal and craniofacial flexion angles are presented for Pan troglodytes, Gorilla gorilla, and modern humans. The internal flexion angle (IFA) was measured from lateral radiographs, and the craniofacial flexion angle (CFA) was calculated from coordinate data. Stage of dental development is used as a baseline for examination of growth changes and nonparametric correlations between flexion angles and dental development stage are tested for significance. In Gorilla, the IFA increases during growth. The IFA is relatively stable in Pan and modern humans. Pan and Gorilla display an increase in the CFA. However, this angle decreases during growth in modern humans. Flexion angles were derived from coordinate data collected for several early hominid crania. Measurements for two robust australopithecine crania indicate strong internal flexion. It has been suggested that cerebellar expansion in this group may relate to derived features of the posterior cranial base. In general, australopithecine crania exhibit craniofacial flexion intermediate between great apes and modern humans. The "archaic" Homo sapiens specimen from Kabwe is most similar to modern humans.