The human adaptations to meat eating: a reappraisal

In this paper we discuss the hypothesis, proposed by some authors, that man is a habitual meat-eater. Gut measurements of primate species do not support the contention that human digestive tract is specialized for meat-eating, especially when taking into account allometric factors and their variations between folivores, frugivores and meat-eaters. The dietary status of the human species is that of an unspecialised frugivore, having a flexible diet that includes seeds and meat (omnivorous diet). Throughout the various time periods, our human ancestors could have mostly consumed either vegetable, or large amounts of animal matter (with fat and/or carbohydrates as a supplement), depending on the availability and nutrient content of food resources. Some formerly adaptive traits (e.g. the “thrifty genotype”) could have resulted from selective pressure during transitory variations of feeding behaviour linked to environmental constraints existing in the past.     

Intracellular parasitism: cell biological adaptations of parasitic protozoa to a life inside cells

Several protozoan parasites evade the host's immune defence because most of their development takes place inside specific host cells. Only a few of these protozoa live within the host cell cytosol. Most parasites are sequestered within membrane-bound compartments, collectively called ‘vacuoles’. Recent advances in the cell biology of intracellular parasites have revealed fundamental differences in the strategies whereby such organisms gain entry into their respective host cells. These differences have important implications for host-parasite interaction and for nutrient acquisition by the parasite. Leishmania spp. take advantage of the phagocytic properties of their host cells and presumably contribute little to the uptake process. In contrast, apicomplexan parasites have developed highly specialised organelles, called micronemes and rhoptries, to actively invade a variety of nucleated cells and, in the case of Plasmodium falciparum, human erythrocytes. Following invasion, parasites use a multitude of strategies to protect themselves from the defence mechanisms of the parasitized cells. In addition, they induce novel pathways within the infected cell that allow a most efficient nutrient acquisition both from the host cell cytoplasm and from the extracellular environment. Parasite-induced changes of host cells are most apparent in erythrocytes infected with Plasmodium spp. Mammalian erythrocytes are deficient in de novo protein and lipid biosynthesis and, consequently, pathways which allow the transport of macromolecules and small solutes are established by metabolic activities of the parasite. Research into the cell biology of intracellular parasitism has identified fascinating phenomena some of which we are beginning to understand at a molecular level. They are fascinating because they allow insights into a very intimate interaction between two eukaryotic cells of entirely different phylogenetic origins.     

Luteal phase immunosuppression and meat eating.

Immunosuppression during pregnancy makes the mother vulnerable to pathogens. Because meat is the principal source of ingestible pathogens, pregnancy raises the costs of meat eating. Natural selection has crafted a mechanism involving changes in nausea susceptibility and olfactory perception that reduces meat consumption during pregnancy. Evidence is presented showing that the luteal phase is marked by both immunosuppression and changes in nausea susceptibility and olfaction; meat consumption may be reduced during this period, suggesting a mechanism similar to pregnancy sickness. Constraints on compensatory increases in meat consumption outside of the luteal phase explain why women eat less meat than men. Meat is the principal target of acquired aversions. Women possess more aversions than men, suggesting that prophylactic mechanisms sometimes result in longstanding dietary changes. Reproductive immunosuppression explains many aspects of dietary behavior and sheds light on factors that may have contributed to gender-based divisions of labor during hominid evolution.     

Human skeletal remains from Cossack,Western Australia

Human remains of a male individual from Cossack, northwestern Australia are described. Absolute dating is not possible but site geomorphology restricts the upper limit to 6500 B.P. Morphologically and metrically the skull differs from those of recent Western Australian male Aborigines, but it is very similar to that of Kow Swamp I and others included in the “robust” prehistoric Australian Aboriginal group (Thorne, 1977). The specimen is important as indicating the widespread nature and probable recency of a large, robust Australian Aboriginal population demonstrably different to recent populations.     

Alternative adaptations, sympatric speciation and the evolution of parasitic, inquiline ants

Inquiline ant species are workerless social parasites whose queens reproduce in colonies of other species alongside the host queens. Inquilines arise either when one non-parasitic species evolves into an inquiline parasite of another non-parasitic species (the interspecific hypothesis), or by the speciation of intraspecific inquilines from their host stock (the intraspecific hypothesis): it is unlikely that inquilines evolve from other forms of social parasite. This paper reviews the evidence for and against the inter-and intraspecific hypotheses. All inquilines are close phylogenetic relatives of their host species (loose ‘Emery's rule’), and some are their host's closest relative (strict ‘Emery's rule’). A problem for the interspecific hypothesis is how to explain the strict Emery's rule, because phylogenetic constraints on host choice are probably quite weak. By contrast, the intraspecific hypothesis has difficulty accounting for the parasites' sympatric reproductive isolation. Facultative polygyny, in which queens may found colonies alone or by adoption into an existing multi-queen colony, should promote the evolution of small intraspecific inquilines. This is because small colony-founding queens should preferentially seek adoption, which provides the opportunity to produce a sexual-only brood. We suggest that microgynes, i.e. miniature queens found in some polygynous ants, represent such parasites. We review the evidence that inquiline species have evolved intraspecifically from microgynes in Myrmica ants. The coexistence within a species of a monogynous (singly-queened) and a polygynous form is probably a phenomenon usually unconnected with inquiline evolution. The reproductive isolation of intraspecific inquilines plausibly arises from divergent breeding behaviour associated with the parasites' small size. Such divergence could involve either a temporal separation in mating episodes, with small parasites maturing early, or a spatial separation, with small males being sexually-selected to mate near the nest with small queens seeking adoption, instead of in mating aggregations. We conclude that inquiline species strictly following Emery's rule could have evolved by the intraspecific route. If so, such species provide evidence for West-Eberhard's “alternative adaptation” hypothesis that between-species diversity frequently stems from diversity within species. They also represent likely cases of sympatric speciation. We suggest work on the parasites' phytogeny, genetics, behaviour and mating biology to test these conclusions further.     

Neuromuscular adaptations to training

The purpose of this experiment was to determine whether there is a central adaptation to resistance overload. The right adductor pollicis muscle of each subject was trained with either voluntary (n = 9) or electrically stimulated contractions (n = 7), the contralateral muscle acted as an internal control, and seven other subjects acted as a control group. Training was the same in both groups: 15 contractions at 80% maximal voluntary contraction (MVC), 3 days/wk for 5 wk. Trained muscles in both groups increased MVC by approximately 15% (voluntary, P less than 0.01; stimulated, P less than 0.05). There was a small (9.5%) but significant (P less than 0.05) increase in MVC of the untrained muscles in the voluntary group. MVC did not change in the control group. Maximal electromyogram (EMG) was highly reproducible pre-to posttraining in the control group (r = 0.92, slope = 0.995) and did not change pre- to posttraining in the trained groups. Sensory adaptation to training caused a reduction in force sensation in the stimulated group (P less than 0.05) but not in the voluntary group. Because there was a small increase in MVC of the untrained muscle of the voluntary group (9.5%, P less than 0.05) but not in the stimulated group, it is possible that there is a central motor adaptation, but it is not manifested in increased neural drive (EMG). Moreover, this central adaptation may be responsible for the decrease in force sensation that follows training.     

Vertebrate predation in Cebus capucinus: meat eating in a neotropical monkey

A long-term study of two groups of white-faced capuchins (Cebus capucinus) in Santa Rosa National Park in Costa Rica provides evidence of unusually high levels of vertebrate predation compared to those reported in other field studies of Cebus. The hunting techniques for different prey types are described, and several questions concerning vertebrate predation in primates are addressed. Why is there variation between individuals and between groups in the rate of predation? Why do males hunt more than females? Previous hypotheses to explain hunting in Old World primates are applied to this Neotropical example. Finally, I argue that successful vertebrate predation can readily arise in species like Cebus, which are characterized by opportunistic foraging patterns, manipulative and cognitive skills and well-developed techniques for locating and subduing invertebrate prey.     

The O.H.7 (Olduvai Gorge, Tanzania) parietal fragments and their reconstruction: a reply to Wolpoff

Given Wolpoff's (1981) dimensions for lambda-bregma and biparietal breadth, it was possible to reconstruct a new version of the O.H.7 hominid parietals. The constraints of the anatomical features of the original parietal fragments plus Wolpoff's constraints from his own reconstruction, permit testing his claims as a hypothesis. By comparing the resulting distortion of Wolpoff's proposed reconstruction with that of the original reconstruction by Tobias, it is clear that the latter's is far superior to the former's, and that the cranial capacity of O.H.7 of roughly 700 ml is most probable.     

The hunters and the hunted revisited

The dietary niches of extinct animals, including hominids and predators, may be constrained using stable carbon isotope ratios in fossil tooth enamel.(13)C/(12)C ratios of many of the primates abundant in the faunal assemblages of Members 1 and 2 at Swartkrans, including cercopithecoids and Australopithecus (Paranthropus) robustus, and a range of other possible prey species, have been reported previously. Resulting suggestions of a mixed, or omnivorous, diet for A. robustus raise questions about niche overlap with coeval, larger brained Homo. Here we present(13)C/(12)C data from Homo and several large predators including Panthera pardus, Dinofelis sp., Megantereon cultridens and Chasmoporthetes nitidula in Member 1, and P. pardus and P. leo in Member 2, in order to compare the two hominid species and to determine likely predators of the various primates and other macrovertebrates. Results for three Homo cf. ergaster individuals are indistinguishable from those of A. robustus, showing that proportions of C(3)- and C(4)-based foods in their diets did not differ. P. pardus, Megantereon and Crocuta are shown to be likely predators of the hominids and Papio baboons in Member 1, while the Dinofelis individual concentrated on prey which consumed C(4)grasses. The hunting hyaenid C. nitidula preyed on either mixed feeders or on a range of animals across the spectrum of C(3)and C(4)variation. The data from Members 1 and 2 confirm a shift in leopard diets towards animals that consumed C(4)grasses.     

Cardiovascular adaptations to mechanical overload

The cardiac changes resulting from mechanical overload of the left ventricle have been well documented and a variety of compensatory mechanisms described. These include a decrease in maximum velocity (V₀) of shortening in the absence of reduction in active tension (P₀), and a reversible decrease in myofibrillar adenosine triphosphatase activity resulting from isoenzymic shift from, predominantly, a form of myosin with high ATPase activity (V₁) to another with low (V₃). The thermodynamic advantage of the transition is the hypertrophied muscle possesses a more energy-efficient form of contraction. These reversible transitions resulted from altered gene expression of isoenzymic forms of myosin heavy chain. It must be borne in mind that the adaptational modifications just described appear to occur only in smaller animals such as the rat, that possesses several myosin isozymes. In large mammals it is mainly the V₃ form of myosin that is present, which does not change with altered contractile state. Responses of the large arteries to hypertension have been poorly studied. This is surprising when one recalls that degenerative disease of such vessels, that include the aorta, carotids and ileo-femoral arteries is almost an obligatory concomitant of hypertension. Such studies as have been carried out indicate that hyperplasia is specific for abdominal aortic stenosis while hypertrophy is found in aortic smooth muscle in rats with systemic hypertension. Mechanically, an increase in V₀ with no change in P₀ have been reported; an increase in myofibrillar ATPase activity was also reported. Though two myosin heavy chain isozymes have been found in aortic smooth muscle densitometry did not reveal any difference in distribution between tissues from control and hypertensive rats. The cause of the increased ATPase activity must be in increased phosphorylation of the muscles' 20,000 dalton light chain.     

Gorilla adaptations to naturalistic environments

In the past few decades there have been increased investigations into the effects of captive environments on behavior. Simultaneously, zoological gardens have undergone a revolution in philosophy and design, resulting in a proliferation of “naturalistic” habitats. Complex environments such as these have been found to affect the behavior of captive animals favorably, including increasing reproductive and rearing success, encouraging the expression of species-typical behavior patterns, and decreasing abnormal behaviors. In June 1988, Zoo Atlanta completed four naturalistic habitats for western lowland gorillas (Gorilla gorilla gorilla). These new habitats afforded a unique opportunity to study the adaptation of lowland gorillas to novel, naturalistic habitats. During the first year of habitation, a total of 451 hours of data were collected on 11 gorillas housed in three harem groups. Focal animal sampling with a behavioral change scoring system was used to obtain information on behavior, substrate, environmental components utilized, and location in sun or shade. Instantaneous scans at 15 minute intervals provided information on location and behavior of all individuals. Adaptation to the environments was assessed by using the indices of: time spent manipulating objects across the course of the study, the percent of the habitats utilized, and the dispersal of individual animals over the habitats. Trends in these behaviors indicated that exploration of the environments significantly decreased, but that this decline in exploration took over six months to occur. Several interpretations of these findings are presented including the unfamiliarity of these naturalistic habitats to these subjects.     

Erythropoietic adaptations to endurance training

Erythropoietic adaptations involving the oxygen dissociation curve (ODC) and erythropoietin production have been implicated in the etiology of reduced blood haemoglobin concentrations in sportspersons (known as sports anaemia). A significant increase in the half-saturation pressure indicating a right-shift in the ODC was measured in 34 male [25.8-27.4 mmHg (3.44-3.65 kPa)] and 16 female (25.8-27.7 mmHg (3.44-3.69 kPa)] trained distance runners (P less than 0.01 for both genders) after completing a standard 42-km marathon. Erythrocyte 2,3-diphosphoglycerate concentrations measured concurrently were unaltered by exercise, although consistently higher in the female compared to the male athletes (P less than 0.05). The serum erythropoietin (EPO) concentrations of 15 male triathletes (26.3 U.ml-1) were significantly lower than those of 45 male distance runners (31.6 U.ml-1; P less than 0.05). However, the mean serum EPO concentrations of male and female athletes engaged in a variety of sports were not different from those of sedentary control subjects of both sexes (26.5-35.3 U.ml-1). Furthermore, the serum EPO concentrations were unaltered after prolonged strenuous exercise in 20 male marathon runners. These data suggest that the haematological status of these endurance athletes is in fact normal and that the observed shift in the ODC, while providing a physiological advantage during exercise, has no measurable effect on the erythropoietic drive.     

Sire breed comparisons for meat and eating quality traits in Australian pig populations

Sire breed comparisons for carcase (n = 1169), meat and eating quality (n = 686) traits were obtained using data recorded on progeny of known pedigree sired by Duroc (DU), Large White (LW), Landrace (LR) and Duroc Synthetic (DS) boars from crossbred (LW/LR) sows. Animals were reared in eco-shelters in large single-sex contemporary groups and slaughtered on an age constant basis at 22 weeks of age. Compared to progeny from other sire groups, animals sired by purebred Duroc boars tended to have improved eating quality traits (higher intramuscular fat and lower shear force) at the expense of poorer carcase characteristics (higher subcutaneous and belly fat). Animals sired by DS boars tended to be heavier and leaner than those sired by LW, LR or DU boars; intramuscular fat but not belly fat was correspondingly lower, while tenderness was generally consistent with that of the DU progeny. Significant variability of sire progeny groups within sire breed suggests that sire breed selection, potentially used for improving traits such as meat quality in commercial progeny, will be less accurate in the absence of sire-specific information, which is typically poorly recorded in this class of traits.     

A Survey of Tetrapod Tracksites Preserved in Pyroclastic Sediments,with Special Reference to Footprints of Hominids,Other Mammals and Birds

Pyroclastic sediments provide an unusual and favorable medium for the recording, burial, and preservation of tetrapod tracks and other traces. Twenty-two tracksites were reviewed for the purpose of determining how these deposits contribute to track formation, burial, and preservation. These include Jurassic sites in Argentina and Mexico, Cretaceous sites in Korea, Miocene sites in Mexico and the United States, Pliocene sites in Tanzania, Pleistocene sites in Mexico, Korea, and Italy, and Holocene sites in Mexico, Turkey, Italy, Japan, New Zealand, Nicaragua, and the United States. Twelve of the sites contain hominid tracks.

Tracksites occur most commonly in reworked tephra on the shorelines of rivers, lakes, and seas. They also occur on pyroclastic falls, flows, and surges, and on lahars. Most tracksites are in volcanic arcs, especially around the Pacific Rim. A few occur in continental rifts or near intraplate volcanoes. Most older tracksites (Jurassic, Cretaceous, and Miocene) occur in silicic tephras such as rhyolite and dacite. The younger tracksites are mostly associated with basaltic tephra, though other compositions are also represented.

Volcanic eruptions contribute to formation of substrates suitable for recording tracks by producing abundant fine-grained pyroclasts that interact physically and chemically with water to become cohesive. Hiatuses between eruptions provide time for tracks to accumulate, and in some cases, to lithify rapidly. Both physical processes (drying and compaction) and chemical processes (mineral precipitation) appear to be involved in early lithification. Eruptions also contribute to burial of tracks through rapid sedimentation and aggradation that typically follow a pyroclastic eruption. Multiple, closely spaced track horizons are common in pyroclastic sequences. Most tracksites are buried by either fallout tephra or reworked, waterlain deposits. Others are buried by lahars, pyroclastic flows and surges, or windblown ash. Upon exhumation pyroclastic deposits contribute to the formation of bedding planes through clay drapes, friable ash layers, and biotite-rich layers. Precipitation of authigenic minerals contributes to erosional resistance within beds. Bedding plane formation and erosional resistance facilitate discovery and study of tracks.     

Host–parasite interactions and vectors in the barn swallow in relation to climate change

Recent climate change has affected the phenology of numerous species, and such differential changes may affect host–parasite interactions. Using information on vectors (louseflies, mosquitoes, blackflies) and parasites (tropical fowl mite Ornithonyssus bursa, the lousefly Ornithomyia avicularia, a chewing louse Brueelia sp., two species of feather mites Trouessartia crucifera and Trouessartia appendiculata, and two species of blood parasites Leucozytozoon whitworthi and Haemoproteus prognei) of the barn swallow Hirundo rustica collected during 1971–2008, I analyzed temporal changes in emergence and abundance, relationships with climatic conditions, and changes in the fitness impact of parasites on their hosts. Temperature and rainfall during the summer breeding season of the host increased during the study. The intensity of infestation by mites decreased, but increased for the lousefly during 1982–2008. The prevalence of two species of blood parasites increased during 1988–2008. The timing of first mass emergence of mosquitoes and blackflies advanced. These temporal changes in phenology and abundance of parasites and vectors could be linked to changes in temperature, but less so to changes in precipitation. Parasites had fitness consequences for hosts because intensity of the mite and the chewing louse was significantly associated with delayed breeding of the host, while a greater abundance of feather mites was associated with earlier breeding. Reproductive success of the host decreased with increasing abundance of the chewing louse. The temporal decrease in mite abundance was associated with advanced breeding of the host, while the increase in abundance of the lousefly was associated with earlier breeding. Virulence by the tropical fowl mite decreased with increasing temperature, independent of confounding factors. These findings suggest that climate change affects parasite species differently, hence altering the composition of the parasite community, and that climate change causes changes in the virulence of parasites. Because the changing phenology of different species of parasites had both positive and negative effects on their hosts, and because the abundance of some parasites increased, while that of other decreased, there was no consistent temporal change in host fitness during 1971–2008.     

The energetic cost of locomotion: humans and primates compared to generalized endotherms

A wide range of selective pressures have been advanced as possible causes for the adoption of bipedalism in the hominin lineage. One suggestion has been that because modern human walking is relatively efficient compared to that of a typical quadruped, the ancestral quadruped may have reaped an energetic advantage when it walked on two legs. While it has become clear that human walking is relatively efficient and human running inefficient compared to "generalized endotherms", workers differ in their opinion of how the cost of human bipedal locomotion compares to that of a generalized primate walking quadrupedally. One view is that human walking is particularly efficient in comparison to other primates. The present study addresses this by comparing the cost of human walking and running to that of the eight primate species for which data are available and by comparing cost in primates to that of a "generalized endotherm". There is no evidence that primate locomotion is more costly than that of a generalized endotherm, although more data on adult Old World monkeys and apes would be useful. Further, human locomotion does not appear to be particularly efficient relative to that of other primates.