Biomedical subjects
Publications and source records attributed to Peter W Lucas.
One of the defining characteristics of humans, one that could also explain our species' success, is probably our ability to cook food. A brief review of the literature suggests several adaptations of the mouth can be interpreted to support this. All probably enhance the efficiency of the physical treatment of food in the mouth.
Broad-edged 'spatulate' upper and lower incisors are distinctive of catarrhines and platyrrhines who use them in various ways to peel fruits, remove bark, and strip leaves from branches. The incisors of modern humans not only control the bite size of foods during ingestion, but often grip items in a number of non-food related tasks. Such uses have long been implicated for Neandertals as well. Despite the evolutionary importance of incision and the fact that the incisors feature prominently in clinical dentistry (via orthodontic practices designed both to correct incisal misalignments and adjust their orientation), little is known about what affects their functional efficiency. Few mechanical analyses of incisal action have been published and none that seem to take note of the mechanisms of both fracture and friction at the tooth-food interface. Here, we modeled the incisal tip as a wedge, finding that the efficiency of biting foods that fracture elastically is strongly dependent on both the apex angle of the incisor and the coefficient of friction. Based on apex angle measurements from a small sample of human central incisors, the overall efficiency of upper central incisors is predicted to be greatest when the angle between the apex bisector and the direction of applied force is zero. However, this is complicated greatly by friction, particularly for the lower incisors. The analysis probably applies not only to the use of incisors by humans, but also to some extent to frugivorous primates. This model should clarify the mechanics behind incision and can provide a basic foundation upon which more advanced models can be built on in the future.
Previous studies suggest the orientation of the incisor teeth to the path of jaw movement pronouncedly affects their efficiency of action. To test this hypothesis, upper and lower incisal portions of a study model with ideal Asian occlusion were mounted on a mechanical tester and impressed into rectangular blocks made of 15.3% w/w starch gels or Cheddar cheese. At varying angulations of attack between the long axis of the teeth (defining the orientation of the tooth crown) and force direction, the teeth were driven into the blocks for 4-6mm until fractures had grown in the foods. Both the angle of attack and the work divided by fractured area produced in the food, termed 'work to fracture', were measured. The food type (cheese or gel), incisal type (upper or lower pair) and angle of inclination were significant effects on the works to fracture. The minimal work was for angles slightly proclined to the vertical, although only angles of proclination >40 degrees were significantly higher than all other angles. Retroclination or large angles of proclination made little difference to the work done, but produced markedly off-axis cracks. It is suggested that human incisors act most efficiently at small gapes and that orthodontic corrections will thus offer definite functional benefits.
Ateles spp. and Alouatta spp. are often sympatric, and although they are mainly frugivorous and folivorous, respectively, they consume some of the same fruit species. However, they differ in terms of color vision, which is thought to be important for fruit detection. Alouatta spp. have routine trichromatic color vision, while Ateles spp. presents the classic polymorphism of platyrrhines: heterozygous females have trichromatic color vision, and males and homozygous females have dichromatic vision. Given these perceptual differences, one might expect Alouatta spp. to consume more reddish fruits than Ateles spp., since trichromats have an advantage for detecting fruits of that hue. Furthermore, since Ateles spp. have up to six different color vision phenotypes, as do most other platyrrhines, they might be expected to include fruits with a wider variety of hues in their diet than Alouatta spp. To test these hypotheses we studied the fruit foraging behavior of sympatric Alouatta palliata and Ateles geoffroyi in Costa Rica, and modeled the detectability of fruit via the various color vision phenotypes in these primates. We found little similarity in fruit diet between these two species (Morisita = 0.086). Furthermore, despite its polymorphism, A. geoffroyi consumed more reddish fruits than A. palliata, which consumed more greenish fruits. Our modeling results suggest that most fruit species included in the diet of A. geoffroyi can be discriminated by most color vision phenotypes present in the population. These findings show that the effect of polymorphism in platyrrhines on fruit detection may not be a disadvantage for frugivory. We suggest that routine trichromacy may be advantageous for other foraging tasks, such as feeding on young leaves.
Although most arguments explaining the predominance of polymorphic color vision in platyrrhine monkeys are linked to the advantage of trichromacy over dichromacy for foraging for ripe fruits, little information exists on the relationship between nutritional reward and performance in fruit detection with different types of color vision. The principal reward of most fruits is sugar, and thus it seems logical to investigate whether fruit coloration provides a long-distance sensory cue to primates that correlates with sugar content. Here we test the hypothesis that fruit detection performance via trichromatic color vision phenotypes provides better information regarding sugar concentration than dichromatic phenotypes (i.e., is a color vision phenotype with sufficient red-green (RG) differentiation necessary to "reveal" the concentration of major sugars in fruits?). Accordingly, we studied the fruit foraging behavior of Ateles geoffroyi by measuring both the reflectance spectra and the concentrations of major sugars in the consumed fruits. We modeled detection performance with different color phenotypes. Our results provide some support for the hypothesis. The yellow-blue (YB) color signal, which is the only one available to dichromats, was not significantly related to sugar concentration. The RG color vision signal, which is present only in trichromats, was significantly correlated with sugar content, but only when the latter was defined by glucose. There was in fact a consistent negative relationship between fruit detection performance and sucrose concentration, although this was not significant for the 430 nm and 550 nm phenotypes. The regular trichromatic phenotypes (430 nm, 533 nm, and 565 nm) showed higher correlations between fruit performance and glucose concentration than the other two trichromatic phenotypes. Our study documents a trichromatic foraging advantage in terms of fruit quality, and suggests that trichromatic color vision is advantageous over dichromatic color vision for detecting sugar-rich fruits.
Here we describe correlations among visual ecology and the physiochemical properties of fruits and leaves consumed by four species of catarrhine primate: Cercopithecus ascanius, Colobus guereza, Pan troglodytes, and Piliocolobus badius. Collectively, their diet was diverse, with each species relying on fruits and leaves to different extents. The mean chromaticity of both foods, as perceived by the green-red and yellow-blue signals that catarrhines decode, was distinct from background foliage. However, selection on the basis of color was evident only for leaves. Primates consumed leaves with higher green-red values than the leaves they avoided-sensory mechanism that correlated with key nutritional variables, such as increased protein and reduced toughness. Moreover, the monkeys ingested leaves near dusk, when reddish targets may be more salient. Similar patterns were never observed with respect to edible fruits, the chromaticities of which did not differ from unconsumed fruits or correlate with nutritional properties. We also found that primate biomass is higher in seasonal sites. We conclude that these findings are consistent with the notion that routine trichromatic vision evolved in a context where seasonal folivory was pivotal to survival.
Despite the potential for changes during transit or preservation, the physicochemical properties of leaves are typically measured in a laboratory setting. A suite of laboratory methods adapted for use in the field is described here. The equipment is portable and operable in remote environments. Each technique has been validated against laboratory standards and has been tested throughout the tropics in a variety of ecological contexts. The properties of canopy and understorey leaves from Central Panama are reported here. The results show clear differences between leaves growing in different light regimes. Canopy leaves are tougher and possess greater concentrations of protein, phenols, and tannins. The implication of these results to the resource availability hypothesis, which proposes trade-offs between physiology and defences against herbivory, is discussed.
An analysis of the action of the incisor teeth in humans is presented in terms of the fracture of food particles. It is predicted that the resistance of foods with an essentially linear elastic response to an initial bite by the incisors will depend on the square root of the product of two food properties, Young's modulus and toughness. This quantity should be approximately equal to the product of the stress at cracking during a bite, and the square root of the length of a notch or indentation from which that crack initiates. As a test of the theory, the relationship between in vivo stresses and the depth of incisal penetration, measured during bites on seven 'snack' foods by 10 subjects, and food properties established from mechanical testing, was investigated. Theory and experiment were found to be in excellent agreement. A dimensionless index of the efficiency of incision is suggested, relating fracture performance by subjects to values from a testing machine. This appears to have a high level of inter-subject discrimination with efficiencies varying about threefold. The method appears to have potential applications in dentistry, food science and studies of human and primate evolution.
Evolution of the red-green visual subsystem in trichromatic primates has been linked to foraging advantages, namely the detection of either ripe fruits or young leaves amid mature foliage. We tested competing hypotheses globally for eight primate taxa: five with routine trichromatic vision, three without. Routinely trichromatic species ingested leaves that were "red shifted" compared to background foliage more frequently than species lacking this trait. Observed choices were not the reddest possible, suggesting a preference for optimal nutritive gain. There were no similar differences for fruits although red-greenness may sometimes be important in close-range fruit selection. These results suggest that routine trichromacy evolved in a context in which leaf consumption was critical.
PURPOSE: To elucidate the characteristics and location of the supraorbital and frontal exits of the supraorbital nerve in Chinese skulls and to compare these findings with other ethnic populations. METHODS: The anatomy of the supraorbital nerve exits was studied in 97 adult Chinese skulls (194 orbits). The characteristics and location of the supraorbital nerve exits were determined. Analyses were performed to compare differences between sexes and sides. Data were then compared with those of the other populations. RESULTS: Supraorbital exits were found in all 194 orbits. Among these, 89 (45.9%) were foramina. Frontal exits were found in 69 of the 194 (35.6%) orbits in which 18 were foramina (9.3%). The location of the supraorbital exits showed a skewed distribution toward the medial aspect of the superior orbital rim. The median distance between the supraorbital exits and the facial midline was 24.56 mm. Eighty percent of the supraorbital exits lay between 20.77 mm and 30.52 mm from the facial midline. The mean frontal exit was 7.02 mm medial to the supraorbital exits. Compared with other populations, a higher proportion of Chinese have foramina above the superior orbital rim as the exits for the supraorbital neurovascular bundle. The location of the supraorbital nerve exit is highly variable in all studied populations. CONCLUSIONS: In a significant proportion of Chinese, the supraorbital nerve exits are located toward the medial aspect of and above the superior orbital rim. Extra care should be taken during dissection around this region to avoid damage to the supraorbital nerve.