University of Adelaide

Cancer incidence increasing globally: The role of relaxed natural selection

From Cancer incidence increasing globally: The role of relaxed natural selection – You – 2017 – Evolutionary Applications

Cancer incidence increase has multiple aetiologies. Mutant alleles accumulation in populations may be one of them due to strong heritability of many cancers. The opportunity for the operation of natural selection has decreased in the past ~150 years because of reduction in mortality and fertility. Mutation-selection balance may have been disturbed in this process and genes providing background for some cancers may have been accumulating in human gene pools. Worldwide, based on the WHO statistics for 173 countries the index of the opportunity for selection is strongly inversely correlated with cancer incidence in peoples aged 0–49 years and in people of all ages. This relationship remains significant when gross domestic product per capita (GDP), life expectancy of older people (e50), obesity, physical inactivity, smoking and urbanization are kept statistically constant for fifteen (15) of twenty-seven (27) individual cancers incidence rates. Twelve (12) cancers which are not correlated with relaxed natural selection after considering the six potential confounders are largely attributable to external causes like viruses and toxins. Ratios of the average cancer incidence rates of the 10 countries with lowest opportunities for selection to the average cancer incidence rates of the 10 countries with highest opportunities for selection are 2.3 (all cancers at all ages), 2.4 (all cancers in 0–49 years age group), 5.7 (average ratios of strongly genetically based cancers) and 2.1 (average ratios of cancers with less genetic background).

Cancer treatment is a ‘double-edged sword’ by allowing survivors to pass on their tumour-causing genes

From Cancer treatment lets survivors pass on their tumour genes | Daily Mail Online

Because of the quality of our healthcare in western society, we have almost removed natural selection as the “janitor of the gene pool”.
‘Natural selection in the past had an ample opportunity to eliminate defective genes introduced by mutations.
He said: ‘However, natural selection has been significantly reduced in the past 100 to 150 years, and the direct consequence of this process is that nearly every individual born into a population can pass genes to the next generation, while some 150 years ago, only 50 per cent or less of individuals had this chance.
‘Unfortunately, the accumulation of genetic mutations over time and across multiple generations is like a delayed death sentence.
‘Allowing more people with cancer genes [to] survive may boost cancer gene accumulation. Patients who survive it will have a chance to pass this predisposition to the next generation.

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Rather than just removing cancers, the researchers add patients should undergo genetic engineering that ‘turns off’ their tumour-causing genes.
Professor Henneberg added: ‘Assuming that the increasing genetic load underlies cancer incidence as one of the contributing factors, the only way to reduce it remains genetic engineering- repair of defective portions of the DNA or their blockage by methylation and similar approaches.
‘These techniques, though theoretically possible, are not yet practically available.
‘They will, however, need to be developed as they provide the only human-made alternative to the disappearing action of natural selection’.

Fascinating perspective and research. I think we are totally unequipped to understand the long-term implications of how we are changing the human body.