The world's "better" countries, with greater access to healthcare, experience much higher rates of cancer incidence than the world's "worse off" countries, according to new research from the University of Adelaide.
Researchers say this is the result of relaxed "natural selection", because modern medicine is enabling people to survive cancers, and their genetic backgrounds are passing from one generation to the next.
The researchers say the rate of some cancers has doubled and even quadrupled in the world over the past 100-150 years, and that human evolution has changed away from "survival of the fittest".
Comparative anatomy and human evolution expert Professor Maciej Henneberg and PhD student Wenpeng You, both from the University's Adelaide Medical School, have been studying 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 results of their studies, now published in the journal Evolutionary Applications, show an accumulation of cancer incidence over four to five generations.
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.
The 10 countries with highest opportunities for natural selection (among the "worse off" countries of the world): Burkina Faso, Chad, Central African Republic, Afghanistan, Somalia, Sierra Leone, Democratic Republic of the Congo, Guinea-Bissau, Burundi, and Cameroon.
The researchers found that the rate of most cancers in the 10 best countries was greater than in the 10 worst countries:
Testicular cancer 14 times higher incidence in the top 10 best countries
Lung cancer 12 times higher (smoking accounts for 50% of this cancer, the researchers say)
Skin melanoma 10 times higher
Brain cancer 6.5 times higher
Pancreatic cancer 5.1 higher
Prostate cancer 3.5 higher
Leukemia 3.5 higher
Breast cancer 2.7 times higher
Ovarian cancer 2 times higher