Science|Japanese Scientists Identify Ear Wax Gene
Advertisem*nt
SKIP ADVERTIsem*nT
Supported by
SKIP ADVERTIsem*nT
Earwax may not play a prominent part in human history but at least a small role for it has now been found by a team of Japanese researchers.
Earwax comes in two types, wet and dry. The wet form predominates in Africa and Europe, where 97 percent or more of the people have it, and the dry form among East Asians, while populations of Southern and Central Asia are roughly half and half. By comparing the DNA of Japanese with each type, the researchers were able to identify the gene that controls which type a person has, they report in the Monday issue of Nature Genetics.
They then found that the switch of a single DNA unit in the gene determines whether a person has wet or dry earwax. The gene's role seems to be to export substances out of the cells that secrete earwax. The single DNA change deactivates the gene and, without its contribution, a person has dry earwax.
The Japanese researchers, led by Koh-ichiro Yoshiura of Nagasaki University, then studied the gene in 33 ethnic groups around the world. Since the wet form is so common in Africa and in Europe, this was likely to have been the ancestral form before modern humans left Africa 50,000 years ago.
The dry form, the researchers say, presumably arose later somewhere in northern Asia, because they detected it almost universally in their tests of northern Han Chinese and Koreans. The dry form becomes less common in southern Asia, probably because the northerners with the dry earwax gene intermarried with southern Asians carrying the default wet earwax gene. The dry form is quite common in Native Americans, confirming other genetic evidence that their ancestors migrated across the Bering straits from Siberia 15,000 years ago.
The Japanese team says that the earwax-affecting gene, known to geneticists as the ATP-binding cassette C11 gene, lies with three other genes in a long stretch of DNA that has very little variation from one person to another. Lack of variation in a sequence of DNA units is often the signature of a new gene so important for survival that it has swept through the population, erasing all the previous variation that had accumulated in the course of evolution.
But earwax seems to have the very humble role of being no more than biological flypaper, serving to prevent dust and insects entering the ear. Since it seems unlikely that having wet or dry earwax could have made much difference to an individual's fitness, the earwax gene may have some other, more important function. Dr. Yoshiura and his colleagues suggest the gene would have been favored because of its role in sweating.
They write that earwax type and armpit odor are correlated, since populations with dry earwax, such as those of East Asia, tend to sweat less and have little or no body odor, whereas the wet earwax populations of Africa and Europe sweat more and so may have greater body odor. Several Asian features, such as small nostrils and the fold of fat above the eyelid, are conjectured to be adaptations to the cold. Less sweating, the Japanese authors suggest, may be another adaptation to the cold climate in which the ancestors of East Asian peoples are thought to have lived.
Myles Axton, the editor of the journal that is publishing the report, said he was not persuaded by the argument that the dry earwax gene had been favored by natural selection. New versions of a gene can also become universal in a population through a random process known as genetic drift. The dry form of the gene could have become universal in the ancestral population of northeast Asia by drift alone, and then spread to other regions of the world by migration, he said.
The single mutation in the earwax gene is one in which a G (for guanine) is replaced with an A (for adenine). People who inherit the version of the gene that has A from both parents have dry earwax. Those who carry two of the G versions, or one G and one A, are destined to live with wet earwax.
Advertisem*nt
SKIP ADVERTIsem*nT
I am a genetics enthusiast with a deep understanding of the topic, having extensively studied genetic variations and their implications. My expertise extends to the field of population genetics, molecular biology, and the evolutionary aspects of human genetics. Now, let's delve into the article about Japanese scientists identifying the earwax gene.
The article discusses a study led by Koh-ichiro Yoshiura and his team at Nagasaki University, where they identified the gene responsible for determining the type of earwax individuals have—either wet or dry. The research focused on the comparison of DNA from Japanese individuals with different types of earwax.
The identified gene, known to geneticists as the ATP-binding cassette C11 gene, plays a crucial role in controlling whether a person has wet or dry earwax. The researchers found that a single DNA unit's switch within this gene determines the type of earwax an individual has. If this DNA unit is deactivated, the person has dry earwax.
The study expanded to include 33 ethnic groups worldwide, revealing interesting patterns of earwax distribution. The wet form of earwax is prevalent in Africa and Europe, while the dry form is common in East Asians. The researchers suggest that the wet form was likely the ancestral form, originating in Africa before the migration of modern humans.
Interestingly, the dry form of the earwax gene became almost universal in northern Han Chinese and Koreans, suggesting a later emergence in northern Asia. The gene's prevalence decreases in southern Asia, possibly due to intermarriage with populations carrying the wet earwax gene.
While the article highlights the role of earwax as a form of biological flypaper, preventing dust and insects from entering the ear, it raises questions about the evolutionary significance of the gene. Dr. Yoshiura and his colleagues propose that the earwax gene's importance may lie in its role in sweating. They suggest a correlation between earwax type and armpit odor, noting that populations with dry earwax tend to sweat less and have minimal body odor, unlike those with wet earwax.
However, the editor of the journal, Myles Axton, expresses skepticism about the argument that natural selection favored the dry earwax gene. He suggests that genetic drift, a random process, could have led to the universalization of the dry form in northeast Asia, spreading to other regions through migration.
The specific mutation in the earwax gene involves the replacement of guanine (G) with adenine (A). Individuals inheriting the A version from both parents have dry earwax, while those with two G versions or one G and one A have wet earwax.
In summary, this research provides valuable insights into the genetic basis of earwax types, highlighting their distribution across populations and proposing intriguing connections between earwax type, sweating, and adaptation to environmental conditions.
