Natural selection opportunities tied to cancer rates

^{Photo by Rhoda Baer}

Cancer patient receiving chemotherapy

Countries with the lowest opportunities for natural selection have higher cancer rates than countries with the highest opportunities for natural selection, according to a study published in Evolutionary Applications.

Researchers said this is because modern medicine is enabling people to survive cancers, and their genetic backgrounds are passing from one generation to the next.

The team said the rate of some cancers has doubled and even quadrupled over the past 100 to 150 years, and human evolution has moved away from “survival of the fittest.”

“Modern medicine has enabled the human species to live much longer than would otherwise be expected in the natural world,” said study author Maciej Henneberg, PhD, DSc, of the University of Adelaide in South Australia.

“Besides the obvious benefits that modern medicine gives, it also brings with it an unexpected side-effect—allowing genetic material to be passed from one generation to the next that predisposes people to have poor health, such as type 1 diabetes or cancer.”

“Because of the quality of our healthcare in western society, we have almost removed natural selection as the ‘janitor of the gene pool.’ Unfortunately, the accumulation of genetic mutations over time and across multiple generations is like a delayed death sentence.”

Country comparison

The researchers studied global cancer data from the World Health Organization as well as other health and socioeconomic data from the United Nations and the World Bank of 173 countries. The team compared the top 10 countries with the highest opportunities for natural selection to the 10 countries with the lowest opportunities for natural selection.

“We looked at countries that offered the greatest opportunity to survive cancer compared with those that didn’t,” said study author Wenpeng You, a PhD student at the University of Adelaide. “This does not only take into account factors such as socioeconomic status, urbanization, and quality of medical services but also low mortality and fertility rates, which are the 2 distinguishing features in the ‘better’ world.”

“Countries with low mortality rates may allow more people with cancer genetic background to reproduce and pass cancer genes/mutations to the next generation. Meanwhile, low fertility rates in these countries may not be able to have diverse biological variations to provide the opportunity for selecting a naturally fit population—for example, people without or with less cancer genetic background. Low mortality rate and low fertility rate in the ‘better’ world may have formed a self-reinforcing cycle which has accumulated cancer genetic background at a greater rate than previously thought.”

Based on the researchers’ analysis, the 20 countries are:

Cancer incidence

The researchers found the rates of most cancers were higher in the 10 countries with the lowest opportunities for natural selection. The incidence of all cancers was 2.326 times higher in the low-opportunity countries than the high-opportunity ones.

The increased incidences of hematologic malignancies were as follows:

• Non-Hodgkin lymphoma—2.019 times higher in the low-opportunity countries
• Hodgkin lymphoma—3.314 times higher in the low-opportunity countries
• Leukemia—3.574 times higher in the low-opportunity countries
• Multiple myeloma—4.257 times higher in the low-opportunity countries .

Dr Henneberg said that, having removed natural selection as the “janitor of the gene pool,” our modern society is faced with a controversial issue.

“It may be that the only way humankind can be rid of cancer once and for all is through genetic engineering—to repair our genes and take cancer out of the equation,” he said.