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were more important than animal flesh. But what about disease and parasites?
    The sort of infections that prevail among monkeys and arboreal apes today may resemble the parasitic populations with which these remote ancestors of humankind co-existed. Though important details remain unclear, the array of parasites that infest wild primate populations is known to be formidable. In addition to various mites, fleas, ticks, flies, and worms, wild apes and monkeys apparently play host to an impressive roster of protozoa, fungi, and bacteria, not to mention more than 150 so-called arbo-viruses (i.e., arthropod-borne viruses, conveyed from one warm-blooded host to another by insects or other arthropods). 1
    Among the organisms that infect monkeys and apes in the wild are fifteen to twenty species of malaria. 2 Humankind normally supports only four kinds of malaria, but apes can be infected with human strains of malaria plasmodia, and people can likewise suffer from some of the kinds of malaria found among monkeys and apes. Such speciation, in addition to the specialization of habitat for different kinds of anopheles mosquitoes between the treetops, middle altitude and ground level of tropical rain forests, certainly suggests a very long evolutionary adjustment among the three parties concerned: primate, mosquito, and plasmodium. 3 Moreover, given the present-day distribution of malarial organisms, and what is known about the geography of malaria in older times, sub-Saharan Africa appears to have been a principal and perhapsthe exclusive center for the development of this form of parasitism. 4
    Among all the diverse natural environments of the earth, tropical rain forests are the most variegated in the sense that more diverse forms of life share this kind of habitat than occupy drier, cooler regions. A corollary to this fact is that no single species of plant or animal dominates the forest—not even humankind, at least until very recently. Many tiny organisms that cannot endure freezing temperatures or low humidity thrive in tropical rain forests. In the warmth and moisture of those environments, single-celled parasites can often survive for long periods of time outside the body of any host. Some potential parasites can exist as free-living organisms indefinitely. This means that scant populations of potential hosts can still experience widespread infection and infestation. Even if contacts between the parasite and a possible host are rare occurrences because there are few hosts to be found in the forest, the parasite can wait. Applied to human populations, this means that even when our ancestors were few and scarce in the balance of nature, it was possible for an individual to pick up a full complement of parasites in the course of a normal lifetime. This remains true today; so much so that the principal obstacle to human dominion over the rain forests is still the rich variety of parasites lying in wait for intruders. 5
    Does this mean that our pre- and proto-human ancestors were perpetually sick? Not really, for the myriad tropical forms of parasitism are characteristically slow to advance toward critical intensity, just as they are slow to recede. Another way of saying the same thing is that tropical rain forests support a highly evolved natural balance at every level: between parasites and hosts, among rival parasites, and between host and the things he eats. We may safely assume that millions of years ago, before humans began to alter the ecological context of the world’s tropical rain forests, the balance between eater and eaten was stable, or nearly so, for long periods of time.
    Hence the wide variety of foods our remote ancestors consumed was undoubtedly matched by the wide variety of para-sites that shared this food with them, in one way or another, without necessarily producing symptoms we would recognize as illness. Mild parasitic invasions may have, at times, diminished our ancestors’ strength and endurance. Low-grade