A genetic mutation is a spontaneous random change in the chemistry of DNA. The word mutation is related to the Latin verb mutare meaning “to change.” Mutagenesis is the process by which mutations arise, and a product of mutagenesis is sometimes referred to as a mutant. Science fiction frequently has popularized mutants as negative beings, but in reality genetic mutations actually can have positive, neutral, or negative results. During the past few decades, DNA research, with much attention to genetic mutations, has greatly expanded as a research area.
Some mutations are not only positive but also crucial because if there were no mutations, there would be no changes in the chemistry of DNA and, hence, no evolution. Of the four evolutionary forces important to the survival and distribution of genes (mutation, natural selection, genetic drift, and gene flow), only mutation is a source of new genetic material. Natural selection does help to increase more favorable mutations in the gene pool (as well as remove less favorable mutations), whereas genetic drift and gene flow affect the distribution of genetic variations.
Mutations can occur in all cells in the body, but only mutations in the germ cells (sperm and eggs) can be inherited and perhaps passed on to future generations. Although mutations in nongerm cells, somatic cells, are frequent and occur throughout life, they are not inherited. These mutations affect only a relatively small number of the billions of somatic cells and usually are neutral and insignificant. However, some somatic mutations can be very serious. A mutation can cause a cell to grow and divide uncontrollably, leading to a tumor and possibly cancer.
During human reproduction, the four building blocks of DNA are adenine, cytosine, thymine, and guanine. They are referred to by their initials, ACTG (the language of DNA), and usually are copied exactly for the next generation. But occasionally an error or mutation occurs. An analogy may be made between a typist making a simple random retyping error and the genes making a copying error with these four letters, with varying consequences in both cases. For example, an original police report might state that cake was in the bag that the suspicious person was carrying, but the retyped report that the judge sees might state that coke was in the bag. Simple errors can have serious consequences. Because some genetic mutations can have very serious consequences, such as disease or death, natural selection has ensured that the number of mutations remain low.
In addition to spontaneous natural mutations, external agents, called mutagens, also can cause mutations, referred to as induced mutations. The two major mutagens are radiation and chemicals. For example, ultraviolet radiation from the sun is mostly absorbed by the ozone layer, but as the ozone hole grows, the odds of being afflicted with skin cancer and melanoma increase. Radiation from X rays also causes controversy. Toxic chemicals from cigarette smoke, many industrial pollutants, and an increasingly recognized number of other sources also can cause harmful mutations. As the overall mutation rate in DNA from mutagens is increased, the odds of a mutation occurring in a cancer-causing gene are increased. The number of known factors that can cause mutations is increasing as more research is being conducted. For example, it has been suggested that increasing the temperature of the male testes, such as can occur by wearing tighter pants, can also increase the mutation rate.
Especially since the 1960s, more understanding of the importance of mutations has led to more interest in medical anthropology. Controlling communicable diseases, making advances in reproductive technology, and understanding the effects of environmental destruction on possible medical advances are examples of ways in which anthropology intertwines with genetic research.
Research advances in genetic mutations have affected previous anthropological explanations of ancient history in different parts of the world. For decades, physical anthropologists who accept the multiregional school of history have said that historical changes in human physical characteristics are the result of slow adaptation happening simultaneously at different rates in different parts of the world. With support from research on mitochondrial (female) DNA mutations, replacement school researchers have been able to estimate the number of generations it takes for a mutation to occur and, therefore, have been able to go backward in time to estimate the time period of major migrations and settlements in different parts of the world. Using their dates, they argue that mutational changes could not have occurred within the time periods suggested by the multiregionalists.
Genealogy, using the anthropological concept of kinship, also has benefited much from the study of mutations. Mitochondrial DNA mutates too slowly to provide much help for recent genealogical knowledge for females on female lines, but it has been used to classify nearly all women into one of seven genetic groups in the world, referred to by Bryan Sykes as the seven daughters of Eve. The male Y chromosome mutates more rapidly. Using the male Y chromosome to study how closely two males are related, for example, one can count the number of mutations between two males to determine how many generations one needs to go back to find the most recent common direct male ancestor (MRCA). For example, if two males match on 12 of 12 markers (positions tested on the DNA chain), there is a 50% probability that their most recent common direct male ancestor is 500 years in the past.
Forensic anthropology, a specialization area within physical or biological anthropology, continues to put much emphasis on osteology or skeletal biology. But it also has benefited much from recent DNA research based on mutations. Similar to genealogical matches, DNA from a suspect is matched with DNA results from a number of people who have been tested to see whether the DNA of a suspect matches the DNA of any of the people tested or vice versa.
The relationship among linguistics, archaeology, and differential DNA distributions as related to national, ethnic, and other groups received major attention during the 1990s with the work of Luigi Luca Cavalli-Sforza.
DNA research is starting to make major advancements. As academicians studying ancient migration and settlement patterns, or as applied anthropologists concerned with medicine, forensics, or genealogy, anthropologists can make major contributions.
References:
- Cavalli-Sforza, L. L., & Cavalli-Sforza, F. (1995). The great human diaspora: The history of diversity and evolution. Reading, MA: Addison-Wesley.
- Cavalli-Sforza, L. L., Menozzi, P., & Piazza A. (1994). The history and geography of human genes. Princeton, NJ: Princeton University Press.
- Sykes, B. (2001). The seven daughters of Eve: The science that reveals our genetic ancestry. New York: Norton.
