New research suggests that natural selection is an evolutionary process that guides which traits become more common in populations and has acted on us for the past 3,000 years to the present day.
And it seems to act in a surprising way on complex traits encoded by multiple genes, such as those associated with intelligence, psychosis, and even cancer.
In natural selection, genes that provide certain survival or reproductive benefits are inherited and survive within the population, but genes that lead to reduced survival or decreased progeny are less common. There is no doubt that natural selection has shaped the evolution of humans in our farther past. However, the impact of recent natural selection is a much more controversial issue.
John Novembre, a computational biologist at the University of Chicago who wasn’t involved in the new study, suggests that the new study is certainly an important factor in modern times. This means that the findings should not be taken as the last word of modern natural selection.
New research focuses on traits that result from a combination of multiple genetic mutations, such as intelligence and skin pigmentation.Complex Genetics Among these characteristics, it is difficult to elucidate the action of individual genes. To find these subtle effects, researchers perform genome-wide association studies (GWAS). In this study, we scan genetic markers throughout the genome to find shorter gene sequences that are more common than other traits for a particular trait.
These results can be difficult to interpret, even when comparing people at some point. In new research, not only genes associated with complex traits, but also Natural selection About these characteristics. In essence, genes that become more common over time are under a positive selection: they are somehow beneficial and therefore can be inherited. Genes that become less common over time are under negative choice. They are somehow harmful to survival and reproduction, so they are less likely to be inherited.
“There is a lot of controversy over whether GWAS can support this type of application,” November told Live Science.
Their study was published in the journal on November 15th. Behavior of natural humansResearchers have discovered a total of 755 traits that show signs of selection between the last 2,000 and 3,000 years.
For the latest sample, researchers used data from people of European descent at UK BioBank, a repository of genetic and health data from 500,000 participants. To explore history more deeply, researchers also used three datasets of ancient human DNA, consisting of a total of 512 people, before the Neolithic, the Neolithic, and after the advent of agriculture in the Near East. Did. Researchers have looked at three time frames: modern, past 2,000 to 3,000 years, and up to about 100,000 years ago. Guan Nin Ling, a research leader and professor of biomedical engineering at Shanghai Jiao Tong University, said the oldest data are the least reliable.
The researchers had detailed health and lifestyle information from UK BioBank, but the older samples had only partial genetics and no direct information such as the number of children or what they ate. .. Therefore, they used the gene itself to infer its properties. If the frequency of genes known to be involved in height increased over time, researchers regarded it as a signal that height may have been under positive natural selection.
The properties that appear to be selected range from skin properties such as “easiness to tan” to various anthropometric measurements. Somewhat surprisingly, genes associated with some seemingly unwanted traits increased in prevalence over time, including genes associated with the following conditions: Skin cancer, Inflammatory bowel disease When Anorexia nervosa.. This suggests that some of these disorders occur as side effects of beneficial genes for other reasons, the researchers suggested.
“If one mutation increases the risk of one disease and reduces the risk of another, natural selection will have little power to eliminate this mutation,” Lynn told Live Science.
Lynn and his colleagues were most interested in the question of why disorders with complex genetics, such as schizophrenia and attention deficit hyperactivity disorder (ADHD), persist despite natural selection. ..
However, GWAS could be a tricky tool for trying to unravel natural selection, November told Live Science. One of the biggest problems is what is called “hierarchy”. The difference between the two populations can appear genetic if they are actually environmental. Results can be strange and fast, as GWAS cannot show that genes cause traits, only that they are related.To use the classic example from 1994 paper, Chopsticks skills are obviously not a gift DNA: It is a problem of practice from an early age. However, GWAS studies in diverse populations such as San Francisco only reveal genes that are more common in East Asian populations than in European populations, and provide much easier evidence of genes associated with chopstick skills. May be revealed to.
This mistake actually happened. According to a study published in 2012, height-giving genetic variants have been more prevalent in Northern Europe than in Southern Europe over the past decade, and natural selection has led to an average height increase in Northern Europeans. Many papers have been published claiming to be.journal Nature Genetics..
However, the effects of these genetic variations turned out to be overestimated, Novembre said. Looking at those same genetic variations in less diverse populations (strategies to reduce stratification problems), evidence of natural selection disappeared. This study addressed previously unknown environmental differences between Northern and Southern Europe and mistaken them for purely genetic. According to the 2019 paper in the journal, researchers need to completely rethink the results, and it is still unclear whether natural selection is associated with height differences across Europe. eLife..
Genes and fate
The use of data from people of European ancestry only helps limit the problem of stratification, Novembre said. However, he warned that stratification problems could still occur.
Of the hundreds of traits researchers have discovered, some may have been naturally selected, some of which stood out. Focusing on modern data, researchers found that higher IQ was associated with more sexual partners but fewer children. On the other hand, ADHD and schizophrenia were both associated with having more sexual partners. Lin told Live Science that these two conditions are examples of traits that can be challenging in daily life but can improve mating success.
Looking back over 100,000 years of human history, researchers have found that properties related to skin color and body measurements are the most common to indicate selective pressure. These include face measurements, height, torso length, and more. For example, genes related to face shape and size appear to have been naturally selected over the last 100,000 years. This may be related to jaw and skull changes associated with diet and brain growth.
Looking back 3,000 years ago, researchers found that inflammatory bowel disease appeared to be favored by natural selection. This can be an example of a characteristic that is useful in one situation and harmful in another, Lin said.
“We assume that in ancient times when hygiene was poor, it was highly activated. Immune system It will protect us from infections in the gut, “he wrote in an email to Live Science. “But the highly activated immune system in modern society only attacks our intestines.”
However, it can be very difficult to show why a particular property is associated with successful evolution. Using height as an example, being tall may help reproduction by making someone more attractive to potential sexual partners. Alternatively, height is just a side effect of efficient metabolism that improves survival, and as the chances of survival to reproductive age increase, the gene may be passed on to the next generation. If genes tend to change together, and in many cases natural selection, it is possible that they are acting on properties that are completely different from what appears most intuitive. For example, according to Novembre, the skin tanning-prone variants revealed in a new study to include skin cancer incidence, freckles, hair color, and many other properties. It may be related. It is difficult to know exactly which genes lead to someone reaching reproductive age, attracting fertile buddies and giving birth to many babies, and the genes that make them lucky hangers in the process.
To complicate matters, the genetics of traits can be completely overwhelmed by the environment. This can theoretically happen with human intelligence. IQ is partially hereditary, so if it is true that there are few children with high IQ, it will undoubtedly depress the collective IQ of the population over time. However, if the environment promotes better nutrition, reduction of lead or other pollutants, and other brain development, the population may become brighter.
“A change in some obvious genetic basis does not even mean that the population is evolving in that direction,” Novemble said.
One approach to identify natural selection would combine large-scale GWAS with studies of single-family genomes, Novembre said. Families, especially siblings, usually grow up in fairly similar environments. Therefore, it is easy to tell when a gene is affecting a particular trait. These family studies can be used to assert truth from large GWAS samples and reveal which genes still show an effect when as many environments as possible are removed from the equation.
Lynn and his colleagues plan to conduct a family study to learn more about the genetics of complex conditions such as schizophrenia. They are also working to quantify genetic variation that can cause both beneficial and adverse effects at the same time, he said. According to Lin, the results of the new study are a starting point and remind us that natural selection is still human power. biology..
“Human evolution has been stopped by natural selection, changing the environment to promote and reduce physical work, minimizing energy costs to get better food, and achieving a better medical system. Even if given the ability to do, it’s not at all true, “Lin said.
Originally published in Live Science
Natural selection has acted on hundreds of human genes over the last 3,000 years.
https://www.livescience.com/natural-selection-human-genes Natural selection has acted on hundreds of human genes over the last 3,000 years.