The Dark Side of Our Genes
The Industrial Revolution has made it easier for humanity to access food and clean water, as well as the emergence of antibiotics, vaccines and modern medical approaches. However, modern technologies have not just reduced the number of infectious diseases and increased life expectancy, they have also formed an environment radically different from the one in which human evolution took place. Genes useful in our evolutionary past may cause a predisposition to the development of chronic diseases in old age, such as diseases of the cardiovascular system and cancer.
An international team of researchers has conducted a detailed comparison of the data supporting the existence of such a discrepancy between evolutionary adaptations and modern life. They also suggested that natural selection associated with modernization processes can reduce the burden of a number of chronic diseases on a global scale.
Over the past four centuries, human ecology, lifestyle options and life history have undergone very strong changes. The new lifestyle has also made adjustments to the main causes of death of people. Infectious diseases prevalent in childhood have given way to chronic diseases associated with old age. All people are destined to die, so it is obvious that with a decrease in the number of deaths from some causes, the frequency of deaths from others should increase proportionally. However, the increasing differences between the environment to which our genes have adapted and the modern environment also play an important role.
Aging is partly due to the combined influence of many genes that are beneficial to the body at a young age and have negative effects in old age. Genes can influence various traits, while their level of expression may change as they age (pleiotropy). The term "antagonistic pleiotropy" applies to genes that can have both positive and negative effects. To some extent, contrary to common sense, evolution occurring through natural selection can lead to the spread of antagonistic pleiotropy in populations: the positive influence at a young age may outweigh the evolutionary disadvantages in old age. For example, certain variants of the BRCA1 gene are favorable for fertility. However, women who carry one of these options will almost certainly develop breast cancer before reaching the age of 90.
According to Professor Virpi Lummaa from the University of Turku, Finland, Angelina Jolie's decision to amputate both mammary glands (double mastectomy) is due to the high risk of cancer due to the carrier of the corresponding variant of the BRCA1 gene. Evolution did not remove this gene from the population earlier precisely because of its positive effect on fertility. Currently, the situation is much worse. Due to low birth rates and higher life expectancy, the positive influence of such genes is becoming obsolete.
Jacob Moorad from the University of Edinburgh, UK adds that such genes are very likely to contribute to an increase in the incidence of chronic diseases in modern people, but today it is unclear whether they are the main cause of this or just a minor contributing factor.
At the same time, it is very difficult to establish the evolutionary burden of modern life on human health: it often takes many generations for evolutionary changes to leave a clear trace in our genome. During their analysis, the authors received "suggestive, but not unambiguous" evidence that natural selection, which is the engine of evolution, is changing its direction in modern conditions. For example, the results of a number of studies conducted on pre- and post-industrial populations indicate selection in favor of increasing the period of fertility in women.
However, Stephen Stearns, a professor at Yale University, USA, warns that caution should be exercised in this regard. Changes in human biology are formed by two processes that do not exclude each other. The environment has a direct effect on gene expression. For example, poor nutrition in childhood can cause growth to slow down. However, the environment also generates natural selection. Over time, this can lead to an increase in the frequency of occurrence of some genes and a decrease in the frequency of occurrence of other genes in the population. An example is a gene that causes lactose intolerance in adults. When identifying any change, I really want to indicate natural selection as the reason. However, especially with regard to recent changes, the most likely cause is a change in gene expression, and not changes in the genes themselves as a result of adaptation to new environmental conditions.
Associate Professor Stephen Corbett from the University of Sydney, Australia explains that future research and methodological improvements will help us assess the degree of relationship between chronic diseases and gene expression, as well as confirm or refute the assumption that natural selection is already beginning to resist the increasing burden of chronic diseases. He believes that in order to obtain clear evidence, it is absolutely necessary to conduct large cohort studies involving many generations.
Dr. Alexandre Courtiol from the Leibniz Institute of Zoology and Wildlife Studies in Berlin, Germany also believes that genes play an important role, but it is impractical to expect that natural selection will adapt our great-great-great-grandchildren to the conditions of our modernity. This may not work, as the environment is currently changing at a tremendous rate. A more rational response to an increase in the frequency of chronic diseases is to change our social environment and lifestyle. The recipe is known to all of us: sleep more, give up fast food, do not forget about regular physical activity and pollute the environment less. Of course, this is a very difficult task for many, but there is nothing impossible about it.
Article by Corbett S et al. The transition to modernity and chronic disease: mismatch and natural selection is published in the journal Nature Reviews Genetics.
Evgenia Ryabtseva, portal "Eternal Youth" http://vechnayamolodost.ru based on the materials of Forschungsverbund Berlin: The dark side of our genes – healthy ageing in modern times.