Abstract Computer programs have been written to study the dynamic interaction in humans between environmental mutagenesis, the genomic load of deleterious mutations and the probability of zygote survival. The human genome is complex and highly redundant and as a consequence deleterious mutations accumulate. The computer programs are based on a model of the human genome in which deleterious mutations interact synergistically causing impaired performance in individual systems and this leads to a positive correlation between the total number of deleterious mutations in the genome and impaired performance across the whole spectrum of biological capability. This includes performance in intellectual tasks, sporting ability, the ability to fight disease and preserve health and the development of a symmetrical physical form. Sexual reproduction distributes deleterious mutations unequally amongst zygotes and the model predicts that zygote survival will correlate negatively with zygote mutational load. The computer simulation shows that rising environmental mutagenesis will lead to a rise in the human genomic mutational load and to decreased zygote survival, although the full effect would take several generations. If this occurred the health of future generations would suffer and methods to monitor environmental mutagenesis are required. The model also shows that a marked rise in environmental mutagenesis would lead to species extinction if mate choice were random, i.e., unrelated to the genomic mutational load. The biological imperfections caused by mutations, however, in health, intelligence and physical symmetry are all, to varying degrees, related to sexual attraction. The model shows that if mates are chosen in response to sexual attraction the species can be maintained in the presence of high environmental mutagenesis. A polygamous pattern in which females mate with a minority of males has the most marked effect in reducing the number of deleterious mutations in the next generation. The model also shows that as environmental mutagenesis falls the number of eligible males would increase and a species would change from a polygamous to a monogamous pattern of mating. These results imply that we are not attracted by good genes, but by a lack of bad genes. Sexual attraction is a force which counteracts genomic degradation.