United theory of biological evolution: Disaster-forced evolution through Supernova, radioactive ash fall-outs, genome instability, and mass extinctions

We present the disaster-forced biological evolution model as a general framework that includes Darwinian "phylogenic gradualism", Eldredge-Gould's "punctuated equilibrium", mass extinctions, and allopatric, parapatric, and sympatric speciation. It describes how reproductive isolation of organisms is established through global disasters due to supernova encounters and local disasters due to radioactive volcanic ash fall-outs by continental alkaline volcanism. Our new evolution model uniquely highlights three major factors of disaster-forced speciation: enhanced mutation rate by higher natural radiation level, smaller population size, and shrunken habitat size (i.e., isolation among the individual populations). We developed a mathematical model describing speciation of a half-isolated group from a parental group, taking into account the population size (N_e), immigration rate (m), and mutation rate (μ). The model gives a quantitative estimate of the speciation, which is consistent with the observations of speciation speed. For example, the speciation takes at least 10⁵ generations, if mutation rate is less than 10^-3 per generation per individual. This result is consistent with the previous studies, in which μ is assumed to be 10^-3-10^-5. On the other hand, the speciation is much faster (less than 10⁵ generations) for the case that μ is as large as 0.1 in parapatric conditions (m < μ). Even a sympatric (m ∼ 1) speciation can occur within 10³ generations, if mutation rate is very high (μ ∼ 1 mutation per individual per generation), and if N_e < 20-30. Such a high mutation rate is possible during global disasters due to supernova encounters and local disasters due to radioactive ash fall-outs. They raise natural radiation level by a factor of 100-1000. Such rapid speciation events can also contribute to macro-evolution during mass extinction events, such as observed during the Cambrian explosion of biodiversity. A similar rapid speciation (though in a much smaller scale) also has been undergoing in cichlid fishes and great African apes in the last several tens of thousand years in the current African rift valley, including the origin of humankind due to the radioactive ash fall-outs by continental alkaline volcanism.