Long-term survival mechanisms of human populations with low increase rates

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To clarify mechanisms of a human population's long-term survival through generations, this study constructed a set of three models in which its number changes and individual difference of reproduction rates exists. In the second step, our own data of demographic parameters, malaria prevalences according to geographic conditions, and various allele frequencies, which were obtained from a contemporary Gidra-speaking population in Papua New Guinea, were rearranged to be applicable to the models. The first model examined effects of individual difference of fertility. The results proved a markedly smaller number of maintained genes of the parent generation, in comparison with that in the previous gene-pool models : of 200 parents, only 26.5 had offspring at 30th generation ; and, the maximum number of offspring per parent was 300.2. The second model, in which gene diversity was examined among a initial population of 200 males and 200 females, demonstrated that it was significantly lower in the case of monogamy than in the case of polygyny. The third comprehensive model examined long-term human survival, taking into account the effects of infectious diseases on the stable population model. For instance, in cases that the initial population, 1,000 in number, inhabited the interior zone relatively free from such diseases and that individuals over the potential limit based on carrying capacity migrated to peripheral disease-prevalent zone and met with higher mortality, the gene pools differed between the two zones unless the difference of death rate from such diseases between them exceeded 1.0%. These results demonstrate that different gene structure in various loci between the two zones attributed to prevalence of diseases, malaria in particular. Our further analyzes make it possible to model long-term survival of human populations, including prehistoric ones, in more generalized conditions.