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PubMed2002

Relative placement of the mandibular fossa in great apes and humans.

Several researchers have investigated, or commented on, the relative placement of the hominin mandibular fossa with regard to brain expansion and masticatory function. Two confounding factors are identified in this previous work. First, a number of different measurement techniques have been applied, confusing comparisons between studies. Second, the effects of squamous thickening due to temporal bone pneumatization are shown to influence measurements based relative to the ectocranial margin of the skull. To investigate the influence of these factors, a sample of adult human (n=12), chimpanzee (n=12), gorilla (n=15), and orang-utan (n=8) skulls from the Cleveland Museum of Natural History, University of Wisconsin Zoology Museum, and University of Wisconsin Anthropology collections, were CT scanned. Coronal scans were horizontally aligned and measured on a personal computer using ImageJ (NIH). To identify fossa placement, fossa breadth was measured as the projected distance in the coronal plane between the tip of the entoglenoid to lateral margin of the articular surface. A second distance, from the tip of the entoglenoid to a sagittal plane, tangent to the lateralmost margin of the endocranial surface was taken to indicate the extent of medial placement of the fossa. By eliminating the influence of pneumatization, these data unambiguously confirmed the medial placement of the human fossa and show all great apes as having a laterally placed fossa. Similar measurements on three fossil hominins, KNM-BC 1 (Homo sp. indet.), OH 5 and KNM-ER 23000 (Paranthropus boisei) demonstrate that, while all specimens demonstrate a broad fossa, only KNM-BC 1 is characterized by a relatively medial placement while the latter two display lateral placement.

Adult↗

PubMed1985

The capacity of animals to acquire language: do species differences have anything to say to us?

Following the Gardners' discovery that an ape named Washoe could learn to produce and combine a number of hand movements similar to those used by deaf human beings, a variety of 'ape-language projects' sprang up. Some projects used different symbol systems, others used different training techniques, and others used different species of apes. While debate still rages regarding the appropriate way to interpret the symbolic productions of apes, three species of great apes (gorilla, orangutan, and chimpanzee) have now been credited with this capacity while no lesser apes or monkeys have been reported, at present, to have acquired such communicative skills. Among all of the claims made for the various animal species, the philosophers have entered the fray attempting to define the essence of what it is about language that makes it 'human'. This paper will compare and contrast the above positions to arrive at behavioural definitions of symbolic usage that can be applied across species. It will then present new data on a fourth ape species Pan paniscus which is proving to be the first non-human species to acquire symbolic skills in a spontaneous manner.

Animals↗

PubMed2003

Age at first molar emergence in early Miocene Afropithecus turkanensis and life-history evolution in the Hominoidea.

Among primates, age at first molar emergence is correlated with a variety of life history traits. Age at first molar emergence can therefore be used to broadly infer the life histories of fossil primate species. One method of determining age at first molar emergence is to determine the age at death of fossil individuals that were in the process of erupting their first molars. This was done for an infant partial mandible of Afropithecus turkanensis (KNM-MO 26) from the approximately 17.5 Ma site of Moruorot in Kenya. A range of estimates of age at death was calculated for this individual using the permanent lateral incisor germ preserved in its crypt, by combining the number and periodicity of lateral enamel perikymata with estimates of the duration of cuspal enamel formation and the duration of the postnatal delay in the inception of crown mineralization. Perikymata periodicity was determined using daily cross striations between adjacent Retzius lines in thin sections of two A. turkanensis molars from the nearby site of Kalodirr. Based on the position of the KNM-MO 26 M(1)in relation to the mandibular alveolar margin, it had not yet undergone gingival emergence. The projected time to gingival emergence was estimated based on radiographic studies of M(1)eruption in extant baboons and chimpanzees. The estimates of age at M(1)emergence in KNM-MO 26 range from 28.2 to 43.5 months, using minimum and average values from extant great apes and humans for the estimated growth parameters. Even the absolute minimum value is well outside the ranges of extant large Old World monkeys for which there are data (12.5 to <25 months), but is within the range of chimpanzees (25.7 to 48.0 months). It is inferred, therefore, that A. turkanensis had a life history profile broadly like that of Pan. This is additional evidence to that provided by Sivapithecus parvada (Function, Phylogeny, and Fossils: Miocene Hominoid Evolution and Adaptations, 1997, 173) that the prolonged life histories characteristic of extant apes were achieved early in the evolutionary history of the group. However, it is unclear at present whether life-history prolongation in apes represents the primitive catarrhine pace of life history extended through phyletic increase in body mass, or whether it is derived with respect to a primitive, size-adjusted life history that was broadly intermediate between those of extant hominoids and cercopithecoids. Life history evolution in primates as a whole may have occurred largely through a series of grade-shifts, with the establishment of fundamental life-history profiles early in the histories of major higher taxa. These may have included shifts that were largely body mass dependent, as well as those that occurred in the absence of significant changes in body mass.

Adaptation, Physiological↗

PubMed2006

Relationship between formation of the femoral bicondylar angle and trochlear shape: independence of diaphyseal and epiphyseal growth.

During hominin evolution, an increase in the femoral bicondylar angle was the initial change that led to selection for protuberance of the lateral trochlear lip and the elliptical profile of the lateral condyle. No correlation is found during ontogeny between the degree of femoral obliquity and of the prominence of the lateral trochlear lip. Might there be a relationship with the elliptical profile of the lateral condyle? On intact femoral diaphyses of juvenile humans and great apes, we compared the anteroposterior length of the lateral and medial sides of the distal metaphysis. The two diaphyseal pillars remain equal during postnatal growth in great apes, while the growth of the lateral pillar far exceeds that of the medial pillar in humans. Increase in bicondylar angle is correlated with disproportionate anteroposterior lengthening of the lateral pillar. The increased anteroposterior length of the lateral side of the metaphysis would contribute to increasing the radius of the curvature of the lateral condyle, but not to the projection of the lateral trochlear lip. The similar neonatal and adult femoro-patellar joint shape in humans prompted an assessment of the similarity during growth of the entire neonatal and adult epiphyses. We showed that the entire epiphysis undergoes drastic changes in proportions during postnatal growth. Finally, we emphasize the need to distinguish the cartilaginous phenotype and the ossified phenotype of the distal femoral epiphysis (and of any epiphysis) during postnatal growth. This crucial distinction applies to most postcranial bones, for they almost all develop following the process of endochondral ossification.

Adaptation, Physiological↗

PubMed2005

Comparative anatomy of the facial motor nucleus in mammals, with an analysis of neuron numbers in primates.

The facial motor nucleus (VII) contains motoneurons that innervate the facial muscles of expression. In this review, the comparative anatomy of this brainstem nucleus is examined. Several aspects of the anatomical organization of the VII appear to be common across mammals, such as the distribution of neuron types, general topography of muscle representation, and afferent connections from the midbrain and brainstem. Phylogenetic specializations are apparent in the proportion of neurons allocated to the representation of subsets of muscles and the degree of differentiation among subnuclei. These interspecific differences may be related to the elaboration of certain facial muscles in the context of socioecological adaptations such as whisking behavior, sound localization, vocalization, and facial expression. Furthermore, current evidence indicates that direct descending corticomotoneuron projections in the VII are present only in catarrhine primates, suggesting that this connectivity is an important substrate for the evolution of enhanced mobility and flexibility in facial expression. Data are also presented from a stereologic analysis of VII neuron numbers in 18 primate species and a scandentian. Using phylogenetic comparative statistics, it is shown that there is not a correlation between group size and VII neuron number (adjusted for medulla volume) among primates. Great apes and humans, however, display moderately more VII neurons that expected for their medulla size.

Anatomy, Comparative↗

PubMed2002

Quantifying temporal bone morphology of great apes and humans: an approach using geometric morphometrics.

The hominid temporal bone offers a complex array of morphology that is linked to several different functional systems. Its frequent preservation in the fossil record gives the temporal bone added significance in the study of human evolution, but its morphology has proven difficult to quantify. In this study we use techniques of 3D geometric morphometrics to quantify differences among humans and great apes and discuss the results in a phylogenetic context. Twenty-three landmarks on the ectocranial surface of the temporal bone provide a high level of anatomical detail. Generalized Procrustes analysis (GPA) is used to register (adjust for position, orientation and scale) landmark data from 405 adults representing Homo, Pan, Gorilla and Pongo. Principal components analysis of residuals from the GPA shows that the major source of variation is between humans and apes. Human characteristics such as a coronally orientated petrous axis, a deep mandibular fossa, a projecting mastoid process, and reduced lateral extension of the tympanic element strongly impact the analysis. In phenetic cluster analyses, gorillas and orangutans group together with respect to chimpanzees, and all apes group together with respect to humans. Thus, the analysis contradicts depictions of African apes as a single morphotype. Gorillas and orangutans lack the extensive preglenoid surface of chimpanzees, and their mastoid processes are less medially inflected. These and other characters shared by gorillas and orangutans are probably primitive for the African hominid clade.

Adult↗

PubMed1998

Short adolescence in early hominids: infantile and adolescent growth of the human femur.

Did the first hominids have a short developmental period similar to that of the great apes or a longer period closer to that of modern humans? Evidence from studies on dental and facial growth favors the first point of view. Additional evidence presented in this report is provided by a morphogenetic analysis of the lower limb. Some morphological modifications undergone by the human femur during infantile and adolescent growth are shown to be excellent markers of different developmental stages. The angular remodelling of the femoral diaphysis, which results in femoral bicondylar angle, is a marker of infancy, while the reshaping of the distal femoral epiphysis is a marker of adolescence. This reshaping of the bony epiphysis consists of the strong projection of the external lip of the femoral trochlea, the increase of the radius of curvature of the external condyle, and the anteroposterior lengthening of the whole epiphysis. The growth spurt in linear dimensions of the femur, characteristic of human adolescence, is shown to be associated with qualitative changes of the distal femoral epiphysis engendered by the late closure of the distal epiphysis. The femur of the first hominids (Australopithecus afarensis) shows only features of infantile growth, whereas characters of both precocious and later growth are typical of later hominids (Homo). The absence of the derived epiphyseal features in Australopithecus would be linked to their early epiphyseal closure and short adolescent growth period; their presence in Homo would have been promoted by their delayed epiphyseal closure and prolonged adolescent growth period. The transition from Australopithecus to Homo appears to have involved a heterochronic process of time hypermorphosis (Gould, [1977], Ontogeny and Phylogeny [Cambridge: Harvard University Press]) in which the size of the femur increases, the epiphysis is modified, and the period of peripubertal growth is prolonged. The shape of the distal epiphyses of KNM-WT 15000, an immature Homo erectus (Brown et al. [1985] Nature 316:788-792), lies clearly within the range of modern human adolescents. In contradiction to Smith's ([1993] in A. Walker and R. Leakey [eds.]: The Nariokotome Homo erectus Skeleton [Cambridge: Harvard University Press], pp. 195-220) hypothetical reconstruction of life span of Homo erectus, we infer that a growth spurt had begun with Homo erectus but was probably less pronounced and of shorter duration than in modern humans. Our findings on the femur are consistent with studies of the growth on the hominid pelvis (Berge [1996] in LF Marcus, M Corti, A Loy, G Naylor, and DE Slice [eds.]: Advances in Morphometrics [Chicago: Plenum Publishing Corp.], pp. 441-448). It is suggested that the lengthening of the adolescent growth period, from Australopithecus to Homo, would have been also associated with the shape changes of the pelvis and with the lengthening of the lower limbs.

Adolescent↗

PubMed2006

DNA sequence and analysis of human chromosome 8.

The International Human Genome Sequencing Consortium (IHGSC) recently completed a sequence of the human genome. As part of this project, we have focused on chromosome 8. Although some chromosomes exhibit extreme characteristics in terms of length, gene content, repeat content and fraction segmentally duplicated, chromosome 8 is distinctly typical in character, being very close to the genome median in each of these aspects. This work describes a finished sequence and gene catalogue for the chromosome, which represents just over 5% of the euchromatic human genome. A unique feature of the chromosome is a vast region of approximately 15 megabases on distal 8p that appears to have a strikingly high mutation rate, which has accelerated in the hominids relative to other sequenced mammals. This fast-evolving region contains a number of genes related to innate immunity and the nervous system, including loci that appear to be under positive selection--these include the major defensin (DEF) gene cluster and MCPH1, a gene that may have contributed to the evolution of expanded brain size in the great apes. The data from chromosome 8 should allow a better understanding of both normal and disease biology and genome evolution.

Animals↗

PubMed2002

Complex SNP-based haplotypes in three human helicases: implications for cancer association studies.

We have initiated a candidate gene approach to study variation and predisposition to cancer in the four major ethnic groups that constitute the U.S. population (African Americans, Caucasians, Hispanics, and Asians). We resequenced portions of three helicase genes (BLM, WRN, and RECQL) identifying a total of 37 noncoding single nucleotide polymorphisms (SNPs). Haplotype inference predicted 50 haplotypes in BLM, 56 in WRN, and 47 in RECQL in a sample of 600 chromosomes. Approximately 10% of the predicted haplotypes were shared among all ethnic groups. Linkage disequilibrium and recombination effects showed that each locus has taken a diverse evolutionary path. Primate DNA analysis of the same loci revealed one human haplotype per gene shared with the great apes, indicating that the observed diversity occurred since the divergence of humans from the last common ancestor. In BLM, we confirmed the presence of a founder haplotype among Ashkenazi Jews homozygous for the blm(Ash) mutation. The cosegregating haplotype was seen in all (6/6) samples of Ashkenazi descent, whereas in the general population it has a low frequency (0.02) and was not found in African Americans. In WRN, ethnic samples were studied for their haplotype content and the presence or absence of six previously described coding SNPs (cSNPs). Hispanic individuals carrying two of these cSNPs showed a 60% increase in the frequency of a common haplotype (haplotype No. 28). In the pooled sample, no association was found. Because (1) the majority of the haplotypes are population specific and (2) the patterns of linkage disequilibrium, recombination, and haplotype diversity are markedly different between gene regions, these data show the importance of either ethnically matched controls or within-family-based disease-gene association studies.

Alleles↗

PubMed2003

The human mind: building bridges between neuroscience and psychiatry.

This essay proposes the existence of four unique behavioral characteristics that distinguish Homo sapiens from its nearest evolutionary kin, the great apes. These are inventiveness, capacity for language, curiosity, and self-reflection or self-analysis. Some would counterargue that none of these features are "unique" to humans. Examples would be given of animal "intelligence" involving at times surprising problem-solving abilities. Even "conversations" between humans and parrots might be cited. However, this is to misunderstand what the focus is in the article. This is not a thesis on the continuity or discontinuities of evolution. Every well-trained biologist learns about evolution and understands that the most complex human traits have some hint of related traits in nearest relatives. Rather, the emphasis of this article has been to select and emphasize certain distinctive aspects of human behavior that are the most important features distinguishing human "uniqueness." Uniqueness may be quantified by the number and complexity of processes within the four attributes presented in this article. While this may be an interesting mathematical exercise, the author would rather take it for granted that the outcome would be that humans are significantly more complex in each of the four features referred to than the great apes. For those in the mental health field, one would hope that this overview of the most highly evolved systems in human brain may provide a useful framework where creative therapeutic processes can be applied to the ultimate beneficiary, the client or patient. This article proposes that psychosis can be considered the impossibility of conflict resolution among the special neuronal assemblies that separately mediate feelings of attachment versus abandonment, security versus anxiety, calmness versus anger, fulfillment versus helplessness, and satisfaction of sexual needs. Given this model, the role of the therapist is to consider whether the client is in touch with the various equilibrium points in their current life situation or crisis. A questionnaire designed to help access information on these internal states may work better than an oral interview because it forces the client to reflect. How much conflict does the client feel in sorting out personal priorities? Does the client have any practice at resolving internal conflicts? If unpracticed, is the client likely to act out in destructive ways to self or others to resolve the pressure of internal conflicts? I am sure that we can all think of current well-publicized destructive acts in which one has to wonder precisely what model of mind the psychotherapists were using to assist the client. At a higher level, each human has the potential to be creative. Whether expressed as curiosity about the universe and nature or inventiveness, as in improving the quality of one's life or by the use of gifted language as in art and music, the therapist needs to determine how to assist the client into these kinds of self-defined fulfillments, which one hopes will reduce the other tensions of conflict resolution. There is no doubt that the journey for both the client and therapist will be challenging. Ultimately, the journey is the reward for both the client and therapist. In closing, the following quotation seems appropriate. Sydney Brenner (2002), a pioneer in molecular biology, reviewed a current book on the Science, Politics, and Ethics of the Human Genome Project (Sulston and Ferry 2002). He states, "What I found interesting in the account is that Sulston doesn't tell us anything about the genomes he has sequenced. What did he find there that excited him? What did he learn about genes, about life, about evolution, about worlds to come? It is the play of Hamlet without Hamlet" (p. 794).

Animals↗