Why aren’t there two-headed mutants running around after Chernobyl?
Because the relevant embryos with developmental defects were not embedded in the uterus and were aborted. This process has been studied in detail in rodents and in cattle exposed to high radiation levels in the vicinity of the Chernobyl nuclear power plant. These animals did not produce more deformed young, but their fertility was substantially reduced. And that is not all. It was found that, under the new conditions of elevated radiation, heterozygote individuals very frequently produced, with different probability, descendants with one or the other allele – i.e. exactly that phenomenon that we discussed in connection with the S allele. By the way, infant mortality increased substantially in Eastern Europe after the Chernobyl nuclear power plant exploded. It can be expected that a similar change (in this case, on the other hand, a decrease) could be found in the fertility of the inhabitants of Europe (e.g. in the average period of time that a pair waited for a child). It is quite probable that, in addition to reducing the population growth, the explosion of the Chernobyl power plant was also manifested in the composition of the gene pool of the European population (because of the above-mentioned changes in the probability of transmission of the individual alleles to the next generation).