In males, the canine teeth tend to be longer, and sharper. Additionally, there appears to be greater variation in size and shape of male canines, in comparison to the relatively stable size and shape of the female canine. Often, the size differences between male and female teeth are seen more in the height of the crown of the tooth than in the length or width of the lower portions of the tooth (Plavcan, 29).
Further dimorphism can be seen in the anterior surface of the canine teeth. Researchers note that, in males, there is a groove that runs the length of the tooth, whereas in females, this groove in generally absent. Additionally, even in cases where the female tooth does have this groove, it is much less pronounced than that of the male primate (Plavcan, 29).
The mandibular premolar also appears to show signs of dimorphism. In males, this tooth is longer, and overlaps with the canine teeth, acting as a sharpening tool. While this can also be true for females, the evidence suggests that, in females, the overlap appears to be a response to the male overlap, rather than a functional tool for sharpening the teeth (Plavcan, 30).
It is not just the size and shape of the canine teeth that shows sexual dimorphism in primates. Researchers have also found that the non-canine teeth of males are approximately seven to ten percent larger than those of the female primate. Furthermore, the density of the teeth in males tends to be far lower than that of females, generally due to the smaller jaw size of the female primate (Plavcan, 31).
Again, there are many theories as to the reasoning for the sexual dimorphism in tooth development in primates. One such theory relates to body mass. According to some, body mass is directly related to tooth size. Since the female primate tends to be much smaller in body mass than the male primate, it follows that the female would have smaller teeth in general. This relationship between body mass and dentition is easily explained, in that larger mass requires more energy to move. With larger teeth, male primates would be able to chew meat more effectively, thus equating to higher levels of protein, carbohydrate, and caloric intake (Plavcan, 32).
Another theory of tooth sexual dimorphism is related to alterations in diet. According to some researchers, the addition of meat to the diet of primates was relatively simple for the males, in comparison to the female. While the male primate could certainly create tools, and overpower smaller meat sources, the female primate had far more obstacles. Since the female primate is primarily responsible for the care of her young, she is less able to spend time hunting, or even scavenging. This may have equated to a female diet higher in plant and vegetation, simply out of necessity. Additionally, the female body requires far different nutrients when preparing for labor, and while nursing young, which may also have contributed to a differentiation of diet between the female and male primate (Oxnard, 35).
It is obvious that there are vast differences in the dentition of primates, both in terms of evolution of the species, and in terms of sexual dimorphism. While the first primates probably lived on fruits and vegetables, their incisors and canines were sharp, allowing for the ripping of plant materials and the enamel was thin. Later primates show molars of duller cusps, and thicker enamel, indicating a change to include nuts and seeds, which require stronger molars to allow for the breakage of such foods. Finally, the most recently developed primates show a further dulling of the molars, thicker enamel on all teeth, and a sharpening, reshaping of the incisor, which allows for the tearing of meat. These changes are more pronounced in female primates than in males.
It is still unclear as to why these changes occurred, but evidence suggests many possible solutions. Changes in environment, changes in food availability, body mass increase, greater brain capacity, and nutrient adaptation may have all played a part in the evolution of diet and dentition of primates. Further distinction between male and female primates may have also been due to body size, or limitations of female dietary intake based on reproductive cycles.
More research will need to be done in this area to fully explain the changes in dietary evolution of primates. Gaining an understanding of this evolution can assist researchers in discovering the origin of human consumption, and can help evaluate current recommendations for food intake. It is only by studying the precursors to humankind that scientists can fully understand the evolutionary process.
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