Scimex: The ratio of male cancer risk to female risk is significantly higher in
populations descended from societies that adopted the plough during the
Neolithic period, according to intriguing University of Otago research.
The ratio of male cancer risk to female risk is significantly higher
in populations descended from societies that adopted the plough during
the Neolithic period, according to intriguing University of Otago
research.
Otago Economics Professor David Fielding analysed international data
on cancer incidence for the 20 main non-sex-specific types of the
disease and found that the overall risk was higher for males, as is
generally thought.
However, the size of these sex differences in cancer risk showed
substantial international variation. Pursuing the hypothesis that there
could be an underlying evolutionary element behind this phenomenon, he
then examined anthropological data on the agricultural practices of the
ancestor societies of modern populations.
This further analysis revealed a significantly higher sex
differential in cancer risk in countries where most of the population
are descended from plough-using societies.
Professor Fielding says the effect remained even after controlling
for socio-economic factors, including sex differences in epidemiological
factors that are associated with higher cancer risk.
“All this suggests that a substantial portion of the higher male
cancer risk may be a consequence of something that occurred during
biological evolution,” he says.
“One plausible evolutionary mechanism is that plough agriculture,
which is more taxing than activities such as hoeing, created an economic
environment which favoured those males who possessed greater upper-body
strength.”
In plough societies then, males with genetic predispositions for
higher testosterone levels would be able to out-compete other men by
developing and maintaining stronger physiques.
The downside for their descendants is that raised testosterone is
known to be linked to a higher risk of many types of cancer, including
cancers of the bladder, kidney, liver, lung, and pancreas, he says.
“Countries where males and females were generally descended from
non-plough societies would then have a smaller difference in cancer
rates between the sexes, because there was less selective pressure in
those societies towards higher testosterone males.”
Professor Fielding likens this human evolutionary process, if it did
indeed take place, to the spread of a gene mutation in Neolithic dairy
farming peoples that extended lactose tolerance beyond childhood.
The study appears in the March issue of the Oxford University Press journal Social Forces.