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N G Jablonski

Publications and source records attributed to N G Jablonski.

At least 19 recordsLinked to original sources
PubMed2000

The evolution of human skin coloration.

Skin color is one of the most conspicuous ways in which humans vary and has been widely used to define human races. Here we present new evidence indicating that variations in skin color are adaptive, and are related to the regulation of ultraviolet (UV) radiation penetration in the integument and its direct and indirect effects on fitness. Using remotely sensed data on UV radiation levels, hypotheses concerning the distribution of the skin colors of indigenous peoples relative to UV levels were tested quantitatively in this study for the first time. The major results of this study are: (1) skin reflectance is strongly correlated with absolute latitude and UV radiation levels. The highest correlation between skin reflectance and UV levels was observed at 545 nm, near the absorption maximum for oxyhemoglobin, suggesting that the main role of melanin pigmentation in humans is regulation of the effects of UV radiation on the contents of cutaneous blood vessels located in the dermis. (2) Predicted skin reflectances deviated little from observed values. (3) In all populations for which skin reflectance data were available for males and females, females were found to be lighter skinned than males. (4) The clinal gradation of skin coloration observed among indigenous peoples is correlated with UV radiation levels and represents a compromise solution to the conflicting physiological requirements of photoprotection and vitamin D synthesis. The earliest members of the hominid lineage probably had a mostly unpigmented or lightly pigmented integument covered with dark black hair, similar to that of the modern chimpanzee. The evolution of a naked, darkly pigmented integument occurred early in the evolution of the genus Homo. A dark epidermis protected sweat glands from UV-induced injury, thus insuring the integrity of somatic thermoregulation. Of greater significance to individual reproductive success was that highly melanized skin protected against UV-induced photolysis of folate (Branda & Eaton, 1978, Science201, 625-626; Jablonski, 1992, Proc. Australas. Soc. Hum. Biol.5, 455-462, 1999, Med. Hypotheses52, 581-582), a metabolite essential for normal development of the embryonic neural tube (Bower & Stanley, 1989, The Medical Journal of Australia150, 613-619; Medical Research Council Vitamin Research Group, 1991, The Lancet338, 31-37) and spermatogenesis (Cosentino et al., 1990, Proc. Natn. Acad. Sci. U.S.A.87, 1431-1435; Mathur et al., 1977, Fertility Sterility28, 1356-1360).As hominids migrated outside of the tropics, varying degrees of depigmentation evolved in order to permit UVB-induced synthesis of previtamin D(3). The lighter color of female skin may be required to permit synthesis of the relatively higher amounts of vitamin D(3)necessary during pregnancy and lactation. Skin coloration in humans is adaptive and labile. Skin pigmentation levels have changed more than once in human evolution. Because of this, skin coloration is of no value in determining phylogenetic relationships among modern human groups.

Adaptation, Physiological↗
PubMed2000

The influence of life history and diet on the distribution of catarrhine primates during the Pleistocene in eastern Asia.

Environmental changes during the Pleistocene in eastern Asia had profound impacts on the distributions of mammalian groups. Critical for many mammals were the southward latitudinal shifts of the tropical and subtropical vegetational zones, and decreases in the areas of these zones. Examination of the responses of members of a single clade, the Catarrhini, indicates that the main catarrhine genera of eastern Asia responded individually to the environmental changes in the Pleistocene. These responses were influenced by the life history parameters and diets of the genera involved. Those animals (macaques, langurs) with shorter gestation times, shorter weaning periods, shorter interbirth intervals, higher intrinsic rates of increase of population, and abilities to survive on a wider variety of vegetation in seasonal habitats were less adversely affected than those (gibbons, orangutans and the giant extinct hominoid, Gigantopithecus) with more protracted reproductive schedules, lower intrinsic rates of population increase and preferences for the higher quality foods (especially ripe fruits) of less seasonal environments. Hominids, while displaying "hyper-ape" life history parameters, increasingly overcame the constraints of these parameters through extrasomatic means not available to other catarrhines. This ability made possible their colonization, by the Late Pleistocene, of highly seasonal habitats such as tundra, which were off-limits to non-culture-bearing catarrhines.

Animals↗
PubMed1999

A possible link between neural tube defects and ultraviolet light exposure.

The protective role of folate in preventing neural tube defects is now well established. The hypothesis is advanced here that photolysis of folate by ultraviolet (UV) light may, in some women, precipitate a folate deficiency sufficient to cause a neural tube defect (NTD) during the first few weeks of pregnancy. This hypothesis is supported by the demonstration of in vitro photolysis of folate by simulated strong sunlight (1), a decline in folate levels in light-skinned subjects exposed to UV light for dermatological conditions (1), and the occurrence of NTDs in the offspring of women who exposed themselves to high levels of UV light on the sunbeds of tanning salons (2). If established, a connection between in vivo folate photolysis by UV light, clinical folate deficiency and NTDs would suggest that intense or prolonged periconceptual exposure of women to UV light for recreational or therapeutic reasons should be avoided.

Female↗
PubMed1995

Sexual dimorphism in the snub-nosed langurs (Colobinae: Rhinopithecus).

Sexual dimorphism in the dentition and skeleton of the four extant species of snub-nosed langurs, Rhinopithecus (R.) bieti, R. (R.) brelichi, R. (R.) roxellana and R. (Presbytiscus) avunculus, was studied. The species shared a similar general pattern of sexual dimorphism, but were found to differ in respects that appear to reflect the influence of disparate socioecological and environmental factors. All the species showed marked canine dimorphism but the very high degree of canine dimorphism in R. bieti appeared to be due to the intensity of intermale competition for mates during a temporally restricted breeding season, and possibly also to the intensity of competition between males for other resources during other times of the year. Sexual dimorphism in the postcranial skeleton of Rhinopithecus species was also most pronounced in R. bieti and may be related to the relatively higher frequency of terrestrial locomotion in males of the species.

Animals↗
PubMed1994

New fossil cercopithecid remains from the Humpata Plateau, southern Angola.

The aim of the present investigation was to describe and identify the well-preserved cranial remains of a fossil cercopithecid recently recovered from sites on the Humpata Plateau in southern Angola. In the past, papionin fossils recovered from the Angolan site of Tchiua (Leba) have been referred to various taxa, including Dinopithecus ingens, Parapapio sp., and Papio (Dinopithecus) quadratirostris. Comparison of the new Angolan papionin cranial remains with those previously described from the Humpata Plateau and a large range of living and fossil Papionini revealed that the range of metrical and morphological variation present in the Humpata papionin sample was consistent with that found in a single extant papionin species. The Humpata cranial remains bear the largest number of similarities to Theropithecus baringensis R. Leakey, 1969, and it is to this species that the remains are hereby referred. This assignment is based on a suite of 11 shared attributes of the Humpata papionin fossils and the type specimen of T. baringensis, KNM BC2, which include: large molar teeth of relatively low relief with pinched cusps and with a prominent distal fovea on M3; a small, low cranial vault with little mid-parietal expansion; a bow-shaped supraorbital torus; trapezoidal, inferiorly tapering orbits; a functional complex related to the presence of a large and vertically oriented anterior temporalis muscle; a large infratemporal fossa with an anteromedially oriented posterior border; a long muzzle with a steep interorbital drop, shallow incisive arc, flattened dorsum, and rounded maxillary ridges; nasal bones that extend across the breadth of the posterior margin of the nasal aperture and then taper markedly as they approach nasion; prominent, inferiorly divergent mental ridges; and relatively shallow mandibular fossae that are long, elliptical in shape, and extend to the level of the M3. The results of the current study suggest that T. baringensis (now including the Humpata papionin sample) and T. quadratirostris occupy a position at the base of the Theropithecus radiation very close to the origin of Dinopithecus ingens and Gorgopithecus major. The species of the genera Theropithecus (including its Humpata representatives) and Papio, along with D. ingens and G. major, form a cluster of taxa that are more closely related to each other than they are to other extant or extinct papionins.

Age Factors↗
PubMed1993

A comparative study of the elbow joints in five species of Chinese macaques.

In this paper, we report the findings of a comparative study of the elbow joints of five species of macaque that inhabit China: Macaca assamensis, M. arctoides, M. mulatta, M. thibetana and M. nemestrina. Results of multivariate analyses of size-related variables and indices of the elbow joint suggested that the breadths of the ventral aspect of the trochlea and of the medial epicondyle of the humerus as well as indices describing the head of the radius are important factors for discriminating these species. The elbow joint of M. arctoides was most similar to that of M. thibetana, no doubt reflecting recency of common ancestry and similarity in terrestrial locomotion. The structures of the elbow joints in M. nemestrina and M. assamensis seemed more adapted to arboreal quadrupedalism. The elbow joint of M. mulatta, however, appears intermediate between the most terrestrial and the most arboreal forms.

Animals↗
PubMed1993

The phylogenetic relationships and classification of the doucs and snub-nosed langurs of China and Vietnam.

The taxonomy of the douc and snub-nosed langurs has changed several times during the 20th century. The controversy over the systematic position of these animals has been due in part to difficulties in studying them: both the doucs and the snub-nosed langurs are rare in the wild and are generally poorly represented in institutional collections. This review is based on a detailed examination of relatively large numbers of specimens of most of the species of langurs concerned. An attempt was made to draw upon as many types of information as were available in order to make an assessment of the phyletic relationships between the langur species under discussion. Toward this end, quantitative and qualitative features of the skeleton, specific features of visceral anatomy and characteristics of the pelage were utilized. The final data matrix comprised 178 characters. The matrix was analyzed using the program Hennig86. The results of the analysis support the following conclusions: (1) that the douc and snub-nosed langurs are generically distinct and should be referred to as species of Pygathrix and Rhinopithecus, respectively; (2) that the Tonkin snub-nosed langur be placed in its own subgenus as Rhinopithecus (Presbytiscus) avunculus and that the Chinese snub-nosed langur thus be placed in the subgenus Rhinopithecus (Rhinopithecus); (3) that four extant species of Rhinopithecus be recognized: R. (Rhinopithecus) roxellana Milne Edwards, 1870; R. (Rhinopithecus) bieti Milne Edwards, 1897; R. (Rhinopithecus) brelichi Thomas, 1903, and R. (Presbytiscus) avunculus Dollman, 1912; (4) that the Chinese snub-nosed langurs fall into northern and southern subgroups divided by the Yangtze river; (5) that R. lantianensis Hu and Qi, 1978, is a valid fossil species, and (6) the precise affinities and taxonomic status of the fossil species R. tingianus Matthew and Granger, 1923, are unclear because the type specimen is a subadult.

Animals↗
PubMed1993

Scaling of limb proportions and limb bone diameters in three species of Chinese snub-nosed langurs (genus Rhinopithecus).

In this study, aspects of the structural mechanics of the upper and lower limbs of the three Chinese species of Rhinopithecus were examined. Linear regression and reduced major axis (RMA) analyses of natural log-transformed data were used to examine the dimensions of limb bones and other relationships to body size and locomotion. The results of this study suggest that: (1) the allometry exponents of the lengths of long limbs deviate from isometry, being moderately negative, while the shaft diameters (both sagittal and transverse) show significantly positive allometry; (2) the sagittal diameters of the tibia and ulna show extremely significantly positive allometry--the relative enlargement of the sagittal, as opposed to transverse, diameters of these bones suggests that the distal segments of the fore- and hindlimbs of Rhinopithecus experience high bending stresses during locomotion; (3) observations of Rhinopithecus species in the field indicate that all species engage in energetic leaping during arboreal locomotion. The limbs experience rapid and dramatic decelerations upon completion of a leap. We suggest that these occasional decelerations produce high bending stresses in the distal limb segments and so account for the hypertrophy of the sagittal diameters of the ulna and tibia.

Animals↗
PubMed1993

Classification and evolution of Asian colobines.

In order to study the differentiation of Asian colobines, 14 variables measured on 123 skulls, including Rhinopithecus, Presbytis, Presbytiscus (Rhinopithecus avunculus), Pygathrix and Nasalis were analyzed by one-way, cluster and discriminant function analyses. Information on paleoenvironmental changes in China and southeast Asia since the late Tertiary was used to examine the influences of migratory routes and range of distribution in Asian colobines. A cladogram for 6 genera of Asian colobines was constructed from the results of various analyses. Some new points or revisions were suggested: (1) Following one of two migratory routes, ancient species of Asian colobines perhaps passed through Xizang (Tibet) along the northern bank of the Tethys sea and through the Heng Duan Shan regions of Yunnan into Vietnam. An ancient landmass linking Yunnan and Xizang was already present on the east bank of the Tethys sea. Accordingly, Asian colobines would have two centers of evolutionary origin: Sundaland and the Heng Duan Shan regions of China. (2) Pygathrix shares more cranial features with Presbytiscus than with Rhinopithecus. This differs somewhat from the conclusion reached by Groves. (3) Nasalis (karyotype: 2n = 48) may be the most primitive genus among Asian colobines. Certain features shared with Rhinopithecus, e.g. large body size, terrestrial activity and limb proportions, can be interpreted as symplesiomorphic characters. (4) Rhinopithecus, with respect to craniofacial features, is a special case among Asian colobines. It combines a high degree of evolutionary specialization with retention of some primitive features thought to have been present in the ancestral Asian colobine.

Animals↗
PubMed1993

Quaternary environments and the evolution of primates in East Asia, with notes on two new specimens of fossil Cercopithecidae from China.

Primate faunas in East Asia since the mid-Tertiary have undergone a series of major changes in response to a complex sequence of environmental changes. As a consequence of the Himalayan orogeny and the rapid, episodic uplift of the Tibetan plateau, the climate of East Asia during the late Tertiary became monsoonal and thus more strongly seasonal. This led to the expansion of seasonal tropical forests and, in some areas, grasslands. During the Pleistocene, the climatic consequences of continued rapid uplift of the Tibetan plateau and other land masses (e.g. the Qinling mountains) were combined with those of glaciations, resulting in dramatic climatic oscillations between warm-humid and cold-dry phases. The contraction of tropical environments that began in the late Tertiary reached its peak at the last glacial maximum (LGM) and was responsible for the decline in the distribution and diversity of hominoids in East Asia. Cercopithecids, which were only minor elements of the late Tertiary primate faunas, colonized tropical, subtropical and temperate environments in the Pleistocene and were able to reradiate into those environments after the LGM. The abilities of monkeys to populate a wide range of terrestrial environments (eurytopy) contrast with those of apes, which are restricted to tropical forest environments (stenotopy).

Animals↗
PubMed1992

Age estimation from the structure of adult human teeth: review of the literature.

The literature on age estimation from the structure of adult human teeth is reviewed. Several anatomic changes of teeth have been shown to be valuable in age determination, but there is still controversy concerning the accuracy of cemental annulation. It is believed that improvements in age estimation can be made using direct measurement rather than scoring systems.

Age Determination by Teeth↗
PubMed1991

Preliminary report on a new method of human age estimation from single adult teeth.

A total of 317 upper and lower third molars were randomly divided into working and control samples and used to estimate chronological age employing a method which combined multiple regression analysis of data from Gustafson's and Maples's scoring system, direct morphological measurements obtained with a Kontron image analysis system and logarithmic data transformation. The standard errors of estimate were 2.4-6.8 years in the working sample and 1.9-7.5 years when the derived formulae were tested on the control sample, respectively. Compared to previous studies, this method provides a smaller standard error of estimate from a single molar tooth. The method is presently being tested on other tooth categories, like premolars, canines and other types of molars.

Adolescent↗
PubMed1989

Identification of unknown human remains by comparison of antemortem and postmortem radiographs.

The identification of unknown human remains by comparison of ante mortem and post mortem radiographs has found wide acceptance in recent years. This report documents two recent cases in Hong Kong in which unequivocal positive identifications were achieved by comparison of radiographs. In both cases, comparison of radiographs was the only available means of establishment of personal identity. The first case involved the identification of a very badly burned body of a 22-year-old male by the matching of the ante mortem and post mortem radiographic images of the cranial base (in particular the sella turcica), hard palate, paranasal air sinuses, mastoid air cells, the lambdoid suture, and the upper molar teeth as revealed on comparable lateral skull films. The second was the identification of a deliberately mutilated torso of a 28-year-old female by comparison of the radiographic images of the lumbar spine, pelvis, and head of the femur as revealed on plain abdominal films taken before and after death. While evidence of injury or surgery did not figure in either of the identifications, the presence of a mild scoliosis and the absence of the twelfth ribs aided identification in the latter case. Emphasis is placed in this account on the value of radiographic comparison as a means of identification because it draws upon the matching of intricate and highly individual patterns of external and internal bony anatomy that are stable over long periods of time. In cases where ante mortem radiographs and photographs are available, establishment of personal identity by comparison of radiographs is deemed preferable to identification by photographic superimposition because radiographic comparison permits the matching of a potentially larger number of unique anatomical features and is less time consuming and technically exacting.

Adult↗