Electromyography of the gluteal muscles in Hylobates,Pongo, and pan: Implications for the evolution of hominid bipedality

The gluteal musculature of primates has been a focus of great research interest among those who study human evolution. Most current theorists agree that gluteus superficialis (= maximus) need not have changed its action in the step from pongid to hominid, but dispute has arisen over a purported change in action and role of the gluteus medius. To clarify the functions of gluteus medius, gluteus superficialis, and tensor fasciae femoris during ape locomotion, we conducted a telemetered electromyographic study of these muscles in two gibbons, one orangutan, and four chimpanzees as they walked bipedally on the ground and on a horizontal tree trunk, walked quadrupedally on the same substrates, and climbed a vertical tree trunk. The results indicate that the gluteus medius of apes is not, as has been previously suggested, primarily an extensor of the thigh; its action is chiefly that of medial rotation. The role of the gluteus medius during bipedality is the same in apes and humans–to provide side-to-side balance of the trunk at the hip. The change in the hominid lateral balance mechanism can be viewed as primarily osteological, allowing preservation of the same muscle function with an extended thigh. As a result, the stride length is increased and there occurs a diminution of the demands placed on other muscles to maintain anteroposterior balance at the hip and knee. Our data also support the view that vertical climbing may be specifically preadaptive to bipedalism. One may picture the earliest hominid as part biped, when on the ground traveling between scattered food trees, and part climber, when moving from the ground to food.     

Reliance on head versus eyes in the gaze following of great apes and human infants: the cooperative eye hypothesis

As compared with other primates, humans have especially visible eyes (e.g., white sclera). One hypothesis is that this feature of human eyes evolved to make it easier for conspecifics to follow an individual's gaze direction in close-range joint attentional and communicative interactions, which would seem to imply especially cooperative (mututalistic) conspecifics. In the current study, we tested one aspect of this cooperative eye hypothesis by comparing the gaze following behavior of great apes to that of human infants. A human experimenter "looked" to the ceiling either with his eyes only, head only (eyes closed), both head and eyes, or neither. Great apes followed gaze to the ceiling based mainly on the human's head direction (although eye direction played some role as well). In contrast, human infants relied almost exclusively on eye direction in these same situations. These results demonstrate that humans are especially reliant on eyes in gaze following situations, and thus, suggest that eyes evolved a new social function in human evolution, most likely to support cooperative (mututalistic) social interactions.     

猿类胰腺的动脉分布模式初步研究

目的:对25例猿类胰腺及周围动脉进行解剖分析,研究猿类胰腺动脉的起源及肠系膜上动脉和腹腔干动脉的吻合关系。方法:对6例类人猿(Gorilla 1例,Pan troglodytes 3例和Hylobates lar 2例),13例狭鼻猿(Papio hamadryas 1例,Papio anubis 2例和Cercopithecus aethiops 10例)和6例阔鼻猿(Saimiri 6例)处死后取出内脏,用10%的福尔马林固定后储存在50%的酒精中,对胰腺、胃及脾脏的供应血管进行解剖游离和解剖分析,最后进行画图。结果:猿类胰腺动脉分布发源自腹腔干和/或肠系膜上动脉,胰腺接受腹腔干及肠系膜动脉的双向供应外,也有独自接受腹腔干动脉的血供,腹腔干动脉与肠系膜上动脉之间无任何吻合支存在者占总数的32%。结论:猿类胰腺形态与人类相似,其动脉分布来源比人类更有多样性。     

Reduced Polymorphism in the Chimpanzee Semen Coagulating Protein,Semenogelin I

The semen of many primate species coagulates into a mating plug believed to prevent the sperm of subsequent mating events from accessing the ova. The texture of the coagulum varies among species: from a semisoft mass in humans to a firm plug in chimpanzees. In humans, a component of the coagulum, semenogelin I, also inhibits sperm motility. We tested the hypothesis that polymorphism and divergence at semenogelin I differ among hominoid species with different mating systems. Sequence data for the semenogelin I locus were obtained from 12 humans, 10 chimpanzees, 7 gorillas, and 1 bonobo. Mitochondrial D-loop data were collected from a subset of individuals to assess levels of variation at an unlinked locus. HKA tests using D-loop sequence data revealed a significant reduction of polymorphism at semenogelin I in chimpanzees, consistent with predictions of a selective sweep at this locus. This result was supported by independent HKA tests using polymorphism data from a putatively neutral locus from the literature. Humans show a similar trend toward reduced polymorphism, although HKA tests were only marginally significant. Gorilla sequence data show evidence of functional loss at the semenogelin I locus, indicated by stop codons within the putative open reading frame as well as high levels of polymorphism. Elevated K _a/K _s ratios within the Pan–Homo clade suggest a history of positive selection at semenogelin I. Our results suggest that there is a positive relationship between the intensity of sperm competition in a species and the strength of positive Darwinian selection on the seminal protein semenogelin I.     

Behavioural responses to photographs by pictorially naïve baboons (Papio anubis), gorillas (Gorilla gorilla) and chimpanzees (Pan troglodytes)

This study assessed how pictorially naïve nonhuman primates understand pictures. Fifty-five baboons with no prior exposure to pictures were trained to grasp a slice of banana presented against a pebble in a two alternative forced choice task. Post-training testing involved three stimulus pairs: (1) real banana slice vs. its picture, (2) the banana picture vs. a real pebble and (3) banana picture vs. a pebble picture which were presented twice. Preliminary data were also collected on naïve gorillas (n = 4) and chimpanzees (n = 7) using the same procedure. Baboons revealed a preference for the food picture in (2) and (3) and often ate this stimulus, but the food item and its picture were accurately discriminated in (1). These results suggest that baboons mistook the pictorial stimulus and its referent, but processed the banana pictures as poor exemplars of the real banana category. Among apes, only gorillas ate the banana pictures, suggesting that picture–object confusion may also occur in this species. Findings are discussed as pertaining to the general issue of representational abilities in nonhuman primates, and its evolution.     

Cyclic development of contact behavior in apes and humans

Nursing and mother-infant distance were observed in three orangutans, two gorillas, one chimpanzee and four humans. All four species showed periods of a recurrence of greater time spent nursing and in contact with the mother. The initial regressive or reattachment period occurred similarly in all four species at between 6–12 months of age. An orangutan observed for two years showed a second period at 19–21 months. Other studies of weight gain in the three ape species coincidently peaked at the same time. When estimated peaks of individuals of each species were summed, the resulting graphs showed a differentiation of species rates of development. Gorillas developed most rapidly, orangutans developed most slowly, while chimpanzees and humans developed within the middle range.     

Experimental monkey hosts for human plasmodia

There has long been a need for a laboratory host of human plasmodia. Although certain of the anthropoid apes, especially Pan troglodytes (the chimpanzee) are susceptible to one or more species of these malarias, there are numerous difficulties in utilizing such animals as experimental subjects. Of the Old World monkeys, only macaques have shown some susceptibility to Plasmodium falciparum.With the demonstration in 1966 that P. vivax would develop in Aotus trivirgatus (the night monkey), New World monkeys became established as models for investigation. Later it was determined that vivax lines could be maintained in Saimiri, Saguinus, and Ateles spp. Adaptation of P. falciparum directly from man has been achieved in Aotus, with subsequent passage in Saimiri and Cebus; other Panamanian monkeys show only transitory parasitemias. Thus far, P. malariae has been infective only to Aotus.Infectivity of the gametocytes to mosquitoes has been retained in monkeys, with transmission back to man or to other monkeys, thus providing all stages of the parasites for biologic, chemotherapeutic, pathologic or immunologic studies.     

Distribution of dorsal carriage among simians

We surveyed the literature and obtained information from primate researchers and zookeepers to study the distribution of dorsal carriage among 77 simian species including New and Old World monkeys and apes in relation to arboreality and terrestriality, birth (litter) weight relative to maternal weight, and presence or absence of distinct natal coat colors. All New World monkeys are arboreal and commonly carry their infants dorsally. Conversely, arboreal Old World monkeys do not use dorsal carriage, and only some predominantly terrestrial Old World monkeys do so. Whereas lesser apes (which are highly arboreal) do not use dorsal carriage, arboreal as well as more terrestrial great apes commonly carry their infants dorsally. These findings indicate that simple arboreality or terrestriality is inadequate to explain dorsal carriage by monkeys. Infants of small- to medium-sized New World monkeys have relatively high birth weight compared with maternal weight, and are most likely to be carried dorsally than ventrally even on the first postnatal day. In contrast, infants of large-bodied New World monkeys are carried ventrally first and then dorsally up to the end of their second year, albeit increasingly infrequently. Among Old World monkeys, no association was found between mode of infant transport and birth weight relative to maternal weight, but some terrestrial Old World monkeys displaying dorsal carriage tend to do so with older infants, indicating that such behavior enables the mother to transport the infant with lower energy expenditure. Among terrestrial Old World monkeys, infants with distinctive natal coat colors are rarely carried dorsally until the natal coat color changes to adult coloration: infants with distinctive coat colors clinging to the backs of carriers could be highly visible and thus vulnerable to predation. Dorsal carriage by mothers may prolong the affiliative mother–infant relationship.     

Neural connectivity and cortical substrates of cognition in hominoids

Cognitive functions and information processing recruit discrete neural systems in the cortex and white matter. We tested the idea that specific regions in the cerebrum are differentially enlarged in humans and that some of the neural reorganizational events that took place during hominoid evolution were species-specific and independent of changes in absolute brain size. We used magnetic resonance images of the living brains of 10 human and 17 ape subjects to obtain volumetric estimates of regions of interest. We parcellated the white matter in the frontal and temporal lobes into two sectors, including the white matter immediately underlying the cortex (gyral white matter) and the rest of white matter (core). We outlined the dorsal, mesial, and orbital subdivisions of the frontal lobe and analyzed the relationship between cortex and gyral white matter within each subdivision. For all regions analyzed, the observed human values are as large as expected, with the exception of the gyral white matter, which is larger than expected in humans. We found that orangutans had a relatively smaller orbital sector than any other great ape species, with no overlap in individual values. We found that the relative size of the dorsal subdivision is larger in chimpanzees than in bonobos, and that the ratio of gyral white matter to cortex stands out in Pan in comparison to Gorilla and Pongo. Individual variability, possible sex differences, and hemispheric asymmetries were present not only in humans, but in apes as well. Differences in the distribution of neural connectivity and cortical sectors were identified among great ape species that share similar absolute brain sizes. Given that these regions are part of neural systems with distinct functional attributes, we suggest that the observed differences may reflect different evolutionary pressures on regulatory mechanisms of complex cognitive functions, including social cognition.