Different genetic traits can be beneficial (for example, fending off disease) or harmful (making humans more susceptible to illness), depending on the environment. The theory behind these evolutionary trade-offs is called balancing selection. In new research, University at Buffalo evolutionary biologist Omer Gokcumen and colleagues scoured the genomes of hundreds of modern humans from around the world and four groups of ancient human ancestors, including Neanderthals and Denisovans. They looked for structural changes in genes, like deletions, that date back to more than 700,000 years ago — before modern humans split from their ancestors, and found large numbers of such ancient genes in modern humans.
The persistence of versions of genes that cause severe disease in human populations has long perplexed scientists. It is common for many versions of a gene to exist.
But scientists expect that over time natural selection will eliminate versions of genes harmful to human health.
Sometimes, there are good reasons that a disease-causing gene may persist.
For example, having two copies of a particular gene variant causes a condition, called sickle cell disease.
But having one sickle cell-causing copy of the gene and one non-disease-causing copy protects against malaria.
As a result, the version of the gene that causes sickle cell is more common in people from areas where malaria is prevalent despite the risks to people who end up with two copies.
Researchers call this phenomenon balancing selection because trade-offs in the gene’s benefits and risks cause it to persist in the population.
Dr. Gokcumen and colleagues explored the phenomenon by analyzing thousands of modern human genomes alongside ancient hominin groups, such as Neanderthal and Denisovan genomes.
“Our research has implications for understanding human diversity, the origin of diseases, and biological trade-offs that may have shaped human evolution,” Dr. Gokcumen said.
“The study shows that…
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