Primates

As with essentially all experimental models, monkeys offer a variety of advantages and disadvantages. Clearly, the most pronounced of the former is their biological similarity to humans. It is estimated that the DNA of rhesus monkeys possesses approximately 90 percent similarity with that of man. Chimpanzees are almost 99 percent identical to humans. Consequently, it is not very surprising that so many aspects of aging are similar across the phylogenetic range of primates. Thanks to their relatively shorter life spans, monkey aging can be observed faster than that of humans. Other advantages include an ability to control experimental conditions (e.g., long-term diet, environment, etc.) more rigorously than would be possible in studies employing humans. In addition, interventions (such as evaluation of new drugs) that are not ethically acceptable in man can be applied to nonhuman primates.

Unfortunately, the length of the monkey life span can also be a disadvantage. Although considerably shorter than for humans, the twenty-five to forty-year longevity of a rhesus monkey is still too long to conduct many experiments. Moreover, the cost of such monkey studies, both in terms of labor and initial animal procurement, may also be prohibitive in many cases. Even the availability of many nonhuman primate species may preclude their experimental use, as increasing numbers of investigators recognize the unique value of well-controlled data in species so similar to humans. Furthermore, despite the widespread use of monkeys such as the rhesus, their genetic heterogeneity is far greater than in many shorter-lived, cheaper animal models (e.g., rats and mice). Lastly, the ever-increasing level of restrictions and regulations concerning the use of nonhuman primates in research constitutes a major burden for scientists desiring such models.