Mutation: Induction by Ionizing Radiation and Chemicals

Lessons to be learned from a contentious challenge to mainstream radiobiological science (the linear no-threshold theory of genetic mutations)

There are both statistically valid and invalid reasons why scientists with differing default hypotheses can disagree in high-profile situations. Examples can be found in recent correspondence in this journal, which may offer lessons for resolving challenges to mainstream science, particularly when adherents of a minority view attempt to elevate the status of outlier studies and/or claim that self-interest explains the acceptance of the dominant theory. Edward J. Calabrese and I have been debating the historical origins of the linear no-threshold theory (LNT) of carcinogenesis and its use in the regulation of ionizing radiation. Professor Calabrese, a supporter of hormesis, has charged a committee of scientists with misconduct in their preparation of a 1956 report on the genetic effects of atomic radiation. Specifically he argues that the report mischaracterized the LNT research record and suppressed calculations of some committee members. After reviewing the available scientific literature, I found that the contemporaneous evidence overwhelmingly favored a (genetics) LNT and that no calculations were suppressed. Calabrese's claims about the scientific record do not hold up primarily because of lack of attention to statistical analysis. Ironically, outlier studies were more likely to favor supra-linearity, not sub-linearity. Finally, the claim of investigator bias, which underlies Calabrese's accusations about key studies, is based on misreading of text. Attention to ethics charges, early on, may help seed a counter narrative explaining the community's adoption of a default hypothesis and may help focus attention on valid evidence and any real weaknesses in the dominant paradigm.

Implications of research in male-mediated developmental toxicity to clinical counsellors, regulators, and occupational safety officers

In closing, let me return to the somewhat irreverent question that I asked at the beginning: Apart from what we learn about fundamentally important biological processes, does male-mediated developmental toxicity make any practical difference? The answer is no, yes, and we don't know. No: The risk of serious birth defects in the future children of a man who is concerned about exposure to radiation or chemicals in the remote past does not appear to be measurably increased in comparison to the background. Yes: Male-mediated developmental toxicity may be of sufficient concern to restrict certain exposures in the population as a whole, but in order for male-mediated developmental toxicity to be determinative, these conditions will have to be otherwise non-toxic. To date, no exposures have been identified that produce substantial male-mediated developmental toxicity in the complete absence of other kinds of toxicity. We don't know how big a problem male-mediated developmental toxicity really is because we have not studied a large enough number and variety of exposures. We don't know if our perspective will change as we begin to understand the importance of individual susceptibility better. We don't know all of the mechanisms that may be involved in male-mediated developmental toxicity or their general biological importance. We don't know more than we do know about male-mediated developmental toxicity, and we are anxious to learn more.