What You Need to Know about Gene Mutations and Evolution
With over 6,000 recognized genetic diseases, the link between gene mutations and disease is well established, with some genetic conditions causing debilitating and even life-threatening symptoms. Since the Human Genome Project, scientists have been learning more and more about the role of DNA in the health and function of our bodies. Not all gene mutations produce negative results. In this article we examine some of the more positive consequences of genetic mutations, including their role in human evolution.
The link between cystic fibrosis and cholera resistance
Cystic fibrosis is a debilitating condition that is most common in people of Northern European descent. It causes the body to produce thicker secretions of mucus that can accumulate in the lungs and other vital organs, causing obstruction, infection, and ultimately organ failure. It is inherited in an autosomal recessive manner; both parents must carry the cystic fibrosis gene mutation for a child to inherit the disorder. As many as one in 20 people of European descent carry the mutation, making cystic fibrosis the most common genetic disorder in the U.S.
One might assume that a genetic mutation causing such a serious, fatal condition would eventually be “weeded out” of the gene pool over the generations. However, scientists from the University of North Carolina recently discovered that the gene mutation associated with cystic fibrosis also offers a degree of resistance to cholera. In evolutionary terms, scientists theorize that the beneficial effect of providing cholera resistance to the many carriers of the mutation vastly outweighed the negative effect of causing cystic fibrosis in the fewer numbers of people who actually inherit the disorder. This positive effect may have allowed the genetic disorder to persist through the generations.
Genetics and increased bone density
In 1994, physicians referred a young man to the Yale Bone Centre following a car accident. He had no injuries, but X-rays revealed that the man had unusually dense bones. Karl Insogna of the Yale Bone Center reported that the man’s bone density was eight times higher than that usually found in a man of his age. Tests revealed a link between this positive trait and a genetic anomaly affecting chromosome 11. The same gene mutation was found in several other patients who had abnormally dense bones.
DNA changes and altitude tolerance
Since many Tibetans breathe easily at altitudes in excess of 4,000 meters (13,000 feet), where most people struggle to function normally, much research has been carried out on altitude tolerance in the peoples of the Himalayas. Scientists have traced the genetic mutation responsible for altitude tolerance in Tibetans back to a subspecies of ancient humans called Denisovans, who became extinct when they interbred with proto-European and Asian populations around 40,000 years ago. Researchers discovered that Tibetans carry less hemoglobin in their blood, which helps them to avoid altitude-exacerbated problems like blood clots and strokes.
Lactose tolerance in Ancient Europe
Though it may seem surprising, genetic mutations are thought to be responsible for the ability to easily digest milk beyond infancy — an ability that not all people have. Scientists believe a genetic mutation allowed early Europeans to produce lactase even after being weaned, which enabled them to digest milk into adulthood. In the 1970s, archaeologists excavating an ancient Polish settlement discovered that communities in the area were making cheese some 7,000 years ago. Experts believe that the genetic mutation that enabled adults to digest milk spread throughout Europe thousands of years ago, opening up the local diet to a nutrient-rich food source that could be transported with communities as they migrated throughout the continent and beyond.
Genetic mutations and the migration of ancient humans from Africa
A team of scientists from Wake Forest Baptist Medical Center, Johns Hopkins University, and the University of Washington hypothesize that Homo sapiens’ migration from Africa was ultimately spurred by a genetic mutation that first occurred more than 85,000 years ago. Researchers have discovered a link between a genetic abnormality on chromosome 11 and the ability to convert certain fatty acids found in plants to a form that promotes increased brain size and complex functioning.
Archeological studies reveal the existence of Homo sapiens in African some 180,000 years ago. However, these early humans appear to have remained in the same general location for almost 100,000 years, never straying far from bodies of water. The scientists involved in the research suggest that this could be because ancient humans were reliant on fish for vital enzymes. The genetic mutation conferring the ability to derive these nutrients from a plant-based diet facilitated the great expansion, removing early Homo sapiens’ reliance on fish and allowing the population to migrate across Africa and further afield.
The link between sickle cell disease and malaria protection
Sickle cell is a debilitating disease that affects the blood. A link has long been established between elevated incidence of sickle cell disease and areas with a high prevalence of malaria. Studies have recently revealed that the genetic mutation associated with sickle cell may also be responsible for providing a degree of malaria resistance. Similar to theories about the relationship between cystic fibrosis and cholera resistance, experts believe that the benefit provided to the many in terms of malaria resistance far outweighed the risk to the few of sickle cell disease, in evolutionary terms. Scientists believe that in this way, the genetic mutation associated with sickle cell flourished over thousands of years in many African countries because it conferred protection against malaria, which remains one of the biggest killers today in the developing world.
