According to most, ethnicity usually is displayed in the values, attitudes, lifestyles, customs, rituals, and personality types of individuals who identify with particular ethnic groups. Ethnic identifications and memberships in an ethnic group has farreaching effects on both groups and individuals, controlling assess to opportunities in life, feeling of well being and mastery over the futures of one's child and future. These feelings of belonging and attachment to a certain group of people for whatever reason are a basic feature of the human condition. These ties are called “ethnic ties” and the group of people that one is tied to is an “ethnic group.” In the general sense, an ethnic group consists of those who share a unique social and cultural heritage that is passed on from generation to generation.
I will begin to examine the Mexican American ethnic group, probing the historical circumstances that impelled them to come to America, focusing on the structure and functioning of their family life to determine or, at least, to raise clues about how and why they have been able or unable to maintain an ethnic identification over the generations, and take a brief look ahead to being to speculate what the future endeavors are for this ethnic group and their constitutive families.
The history of the Mexican American people predates by many years the incorporation of the Southwest into the United States. Native to the Southwest, the Mexican American people have a history marked by the Spanish and then by the Anglo Americans. This early history, perhaps because of the proximity of the southwestern states to the Mexican border, has left a legacy of conflict that is present today between Mexican Americans and Anglo Americans. The present position of Mexican Americans as a people, their family life, and effects of their position on their family life can best be understood through an understanding of their history as Mexicans and as North Americans.
The period of Spanish colonization began in the sixteenth century and lasted until 1821, when Mexico achieved independence from Spain. The first Spanish settlements in southwestern North America were in what is now known as New Mexico, where 25 missions were established between 1598 and 1630. Beginning in 1769, missions were established in California, and several in the areas of Texas and Arizona. The mission system helped to incorporate the Catholic Church into the region (McWilliams, 1988).
Because the Spanish conquerors were all men, they intermarried with the Mexicans and indigenous Indians. The mixed heritage of the Spanish, Mexicans, and Indians remains predominant among today's Mexican Americans. The Spanish heritage, language, and numerous other contributions, which were modified by time and the indigenous cultures of the Indians and Mexicans, constitutes the foundation of the unique Mexican American culture.
The history of the Southwest during the nineteenth century is a history of conflict between the United States and Mexico. The Mexican government had opened the area of Texas to settlers under the condition that they pledge allegiance to Mexico and agree to become Catholics. The Anglo Americans settlers, who were mostly United States citizens, resisted these conditions. At the same time, Mexicans of the territory resisted the Anglo American colonization through various forms of rebellion. Through the political process, Anglo Americans of the territory were able to pass laws favoring their minority group, and Mexicans were stripped of what little wealth they had and relegated to the lowest social and economic classes. Often, a small group of wealthier Mexicans collaborated with the Anglo Americans to maintain their own positions in the new order (Acuna, 1991).
Rebellions between the Anglo Americans and the Mexican government occurred throughout the territory of Texas between 1821 and 1848, setting the stage for the conquest of the rest of the Southwest. Until this time, the system ended the isolation of the Southwest from the rest of the country and brought larger numbers of Anglo Americans to the region (Acuna, 1991).
Over time there was a press for lifting the restrictions on Anglo American immigration and for the separate statehood, this occurred around the 1832. It was concluded that Anglo Americans in Texas saw separation from Mexico and eventual union with the United States as the most profitable political arrangement because the colonists had developed what appeared to be a strong economic trade arrangement with the United States. By 1825, 5,000 Mexicans resided in the Texas territory, and the Anglo Americans population had risen to 30,000. A fullscale rebellion escalated, and the Anglo Americans in Texas, with some Mexican supporters, declared war on Mexico. To diminish the rebellion, General Santa Anna led an army from the interior of Mexico. Then 187 Texans took refuge in a former mission, the Alamo. Although this was a lost battle for the Texans, much myth grows around the struggle and this continues to date. The forever cry "Remember the Alamo" prompted aid from the United States to assist the Texans, most of whom were United States citizens (Acura 1991). In the later part of 1836, Santa Anna was defeated at the Battle of San Jacinto. This defeat ended the era of the Texas revolution, or Texas's war for independence, and Texas became a United States territory. The Texas victory paved the way for the MexicanAmerican War.
This war (18461848) terminated with the Treaty of Guadalupe Hidalgo, in which Mexico accepted the Rio Grande River as the Texas border and ceded territory in the Southwest to the United States for many millions of dollars. The ceded territory incorporated the presentday states of California, New Mexico, and Nevada and some part of Colorado, Arizona and Utah. This begun the occupation of conquered territory (Acuna, 1991). In 1850, 13,300 persons of Mexican origin resided in the United States, and by the 1880's the figure was well of 65,000 (Jaffe, Cullen, and Boswell, 1990). Over the next 30 years, the Southwest was, for the most part, an isolated, selfcontained area that was culturally and economically removed from the rest of the United States. Most of the major movement between Mexico and the United States concentrated at the borders.
Due to the rapid economic development and commercialization of agriculture between 1880 and 1910, Mexican labor was highly sought by the United States. Mining, railroad and agriculture is where most of the interest lied. During these three decades, the population of Mexican origin grew threefold as Mexican immigrants gravitated toward the region's growing demands for lowwage labor. In approximately 1910, the U.S. Census recorded 220,000 Mexican born persons and 162,000 persons of Mexican parentage living in the United States (Jaffe, Cullen, and Boswell, 1990).
Between 1910 and 1930, the Mexican population in the United States continued to grow rapidly. By 1930, the population of Mexican origin exceeded one million persons. Emigration from Mexico continued to be spurred by a strong demand for labor, heightened by the entry of the United States into World War I. The 1910 Mexican Revolution and the Cristero Rebellion (19261929) in Mexico also served to heighten Mexican migration to the United States (Massey, 1992). However, due to the widespread of domestic unemployment and the demand for unskilled labor decreased more than 415,000 Mexicans were forcibly expelled from the United States. Another 85,000 left "voluntarily" (Hoffman, 1994). As a result the Mexican population dropped dramatically and 41% of Mexican born persons returned to Mexico (Jaffe, Cullen, and Boswell, 1990).
The Mexican American Family In Historical Perspective
Mexican American families consist largely of individuals who are descended from or who are themselves unskilled immigrants who come to the United States to work in lowwage sectors of the southwestern economy (McWilliams, 1998). Unlike the members of some other Hispanic groups, very few entered the United States as professional people. Due to the Southwest's geographic proximity to Mexico and its demand for low wage labor, the Mexican population is highly concentrated in the southwestern states. During most of their time in the Southwest, Mexicans have been the victims of prejudice and discrimination. Usually varying in intensity from time to time and placetoplace but always present (Hoffman, 1994). Because of their long history of settlement in the United States and continues emigration from Mexico, the Mexican American population is far more generationally diverse than other Hispanic groups. The generational diversity of the Mexican American people implies a corresponding diversity of social and economic statutes within the population.
It is often wondered what makes the situation of the Mexican American any different than that of other immigrating groups. Although change and presumptuous interaction, acculturation is taking place, Mexican Americans have more continues interaction with firstgeneration immigrants and proximity to their original homeland. First generation community members constantly reinforce traditional values. The rate and direction of acculturative change are thus greatly influenced and cause some cultural values to remain unchanged. The proximity of Mexico to the United States, regardless of the amount of flow back and forth, reinforces the family ties and the family values the span the two countries (Becerra, 1993).
Heterogeneity and Homogeneity
Due to the fact that family socialization takes root in the economic and political forces of society, the history of the Mexican American family must be anchored in the context of the American economy. Mexican Americans are a highly heterogeneous population. An important factor accounting for this variability is history. Mexican groups in the US have different histories of immigration and settlement. Some trace their roots to the Spanish and Mexican settlers who first settled the Southwest before the arrival of the pilgrims, whereas others are immigrants or children of immigrants who begun to arrive in large numbers by the beginning of the twentieth century (Marteniz, 1995). Saragoza (1993) points out that this history supports the fundamental cultural variation and social differentiation among Mexican American families. Crucial factors are variability across region and changes over time. Mexican American families in different historical periods have adapted differently to economic and political forces, and family socialization patterns have responded differently to societal pressures (BacaZinn, 1993).
The traditional structure of the Mexican family grew out of the socioeconomic needs dictated by the agrarian and craft economies of Mexico. For the traditional Mexican, the word family meant an extended, multi generational group of persons, among whom specific social roles were ascribed. By dividing functions and responsibilities among different generations of family members, the family was able to perform all the economic and social support chores necessary for survival in the relatively Spartan life circumstances of the rural Mexican environment. Mutual support, sustenance, and interaction among family members during both work and leisure hours dominated the lives of persons in these traditional Mexican families (Becerra, 1983)
After the conquest of the Southwest, Mexican families who remained or moved to the US out of necessity tended to work and live in ethnically homogenous settings. Minimally influenced by Anglo Americans culture, these communities supported the maintenance of Mexican familial structures as they might have been practiced in rural Mexico. The male took the role of authority figure and head of the household, and the female took the role of child bearer and nurture (Sanchez, 1994). This family form was a response to particular economic and political forces, as are all family forms, that resulted in the Mexican American family carrying both these ideals and values and the need for modification under new economic and political circumstances in the United States.
TRADITIONAL FAMILY STRUCTURE
Much has been written about the traditional structure of Mexican American families. Most of the information obtained these structures appear rigid, cold, and unstable on one end of the continuum or warm, nurturing, and cohesive on the other end. The three main characteristics of the Mexican American family that are usually are male dominance, rigid sex and age grading so that “the older order the younger, and the men the women”, and finally the strong family orientation. To better understand the structure I will begin to give an overview of the structure and how it affects the Mexican American.
The first of the three main characteristics, which is male dominance, is one of the popular stereotypes surrounding the Mexican American family. This has become a major part of American usage as the concept we know as machismo. Machismo is often equated with male dominance. Male dominance is the designation of the father as the head of the household, the major decision maker, and the absolute power holder in the Mexican American family setting. In his absence, this power position reverts to the oldest son. All members of the household are expected to carry out the orders of the male head.
This concept of machismo has various interpretations. For many, machismo is equated with excessive aggression, little regard for women, and sexual prowess. The macho demands complete allegiance, respect, and obedience from his wife and children. Madse (1993:20) states that the “ideally the Latin male acknowledges only the authority of his father and God. In case of conflict between these two sources, he should side with his father.”
On the flip side what is this teaching younger generations, especially boys, about becoming a man in a modern world? Is this adding to aggressive behavior, taking away from sharing of feelings and expressions, are we helping to develop more manifested negative qualities. According to Rothenberg (1998:563) it is important to instill masculinity traits in children, for the traditional Mexican American in their sons, however it is important to “father” by example. This will hope to promote positive change within the family setting.
In contrast, genuine machismo is characterized by true bravery, or valor, courage, generosity, and a respect for others. The machismo role encourages protection of and provision for the family members, the use of fair and just authority, and respect for the role of wife and children (Mirande 1995). Although, male dominance is a Mexican American cultural entity, as well as a structural component, its counterpart, the self-sacrificing, virtuous, and passive female, is no more true than the selfish, sexually irresponsible, and aggressive male. In the past many men have had, for economic reasons, had to leave the family home to search for work, leaving the women behind to head the household. Mexican American history is full of examples of women who have deviated from the submissive role. The ideals encompassed in the patriarchal tradition were often contradicted by the circumstances of day-to-day life. The types of jobs available to Mexican American men kept them away from their families for long periods of time as teamsters, wagon drivers, miners, and farm workers. Over a period of time, more and more women who were heads of households were forced into the work force, further changing the expected roles of women (Griswold del Castillo, 1994).
Patriarchal values did not disappear under the impact of economic and political changes. Mexican American men continued to expect women to be submissive, but in this respect, they were no different from other men. Family life became a mixture of the old and the new values regarding paternal authority and the proper role of women. Increasing poverty and economic insecurity intensified the pressures on Mexican American nuclear families and led to increased matriarchy and more working, single mothers. As a result, the ideology of patriarchy found less confirmation in everyday life. As a system of values and beliefs, however, the ideology of patriarchy continues to exist.
SEX AND AGE GRADING
Complementing the concept of male dominance is the concept of sex and age subordination, which holds that females are subordinate to males and the young to the old. In this schema, females are viewed as submissive, naive, and somewhat childlike. The older are viewed as wise, knowledgeable, and deserving of respect.
To some degree, these designations were derived from division of labor. Women as child bearers and child bearers did not perform the so-called more physically difficult jobs and therefore needed to be more protected by the man. If the women needed protection, the man took the role of overseeing the family. Yet, the power of the male was more apparent than real. Respect for the breadwinner and protector rather than dominance was more key to the family. Roles within the family system were stressed so that the constellation of the mini-system operated to the betterment of the individual and the family system (Mirande, 1995).
In the isolated rural areas where many of the Mexican American families lived, the coordination of role expectations facilitated survival on the frontier. Each person behaviorally and institutionally carried out those roles that would ensure family survival.
The female child learned the roles and skills of wife and mother early, because she would carry them both out in the absence of the mother and as a future wife and mother. The eldest female child was expected to oversee the younger children so that the mother could carry out her task and in the upkeep of the family. The oldest male, after passing through puberty, had authority over the younger children as well as his older female siblings. This because he would take on the responsibility for the family in the absence of his father and for his own family as a future father.
The oldest family members, after they physically could no longer work, assumed the role of assuring family continuity. They were the religion teachers, family historians, nurturer of small children and transmitter and guardians of accumulated wisdom. This wisdom and many years of labor for the family was repaid by the respect given for their years.
Therefore, although particular role expectations are based on gender and age, and these dictate relationships and interactions, these roles were originally developed in response to a means for family maintenance and survival.
The Mexican American family form was a result of a style that was brought from Mexico, modified in the United States, and adapted to fit a pattern of survival in the isolated, rural areas of the Southwest. Because of this history, there is an assumption that the Mexican family and the Mexican American family are isomorphic, allowing one to evaluate the Mexican American family from knowledge of the Mexican family, which is, in fact, misleading. However the importance of the family unit continues as a major characteristic among Mexican Americans to this day.
The family orientation continues because the family is viewed as a warm and nurturing institution for most Mexican Americans. It is a stable structure, in which the individual’s place is clearly established and secure. The family, indicates, offers emotional security and sense of belonging to its members, and offers support throughout the individual’s lifetime. The family is a major support system, a unit to which the individual may turn to for help when in stress or in other types of need. Key to the family system is the value of sharing and cooperation.
Extended kinship ties assume a prominent place within the Mexican American culture. The extended family may include godparents and/or very close friends. Studies show that Mexican families tend to live near relatives and close friends, have frequent interaction with family members, and exchange a wide range of goods and services that include child care, temporary housing, personal advice, nursing during times of illness, and emotional support.
In conclusion, numerous studies (Ramirez 1990 & 1991) demonstrate that family solidarity among Mexicans is not just a stereotypical ideal, but also a real phenomenon. Although expressed differently today because of changing cultural values and socioeconomic pressures, the pattern of strong family orientation continues. It appears that the Mexican Americans continue to have more cohesive family support systems than other groups (Griswold del Castillo, 1994).
Mexican Americans have the highest fertility rates compared with all other groups. Mexican American fertility is significantly higher for every age group:
73% higher than the total population in the 15-24 age group,
43% higher than the total population in the 25-34 age group,
38% higher in the 35-44 age group.
As seen by the table in comparison with blacks and whites in the three age groups, Mexican Americans are 1.5%, 13.3 %, and 14.5 % higher, respectively. Compared with whites, the differences are even more dramatic. In the same three age groups for whites, Mexican Americans have 109%, 52%, and 45% higher fertility rates.
This showing that, Mexican American families tend to be larger. Mexican American families average 4.15 persons, compared with 3.23 for the total population. Furthermore, 71% of all Mexican families have children under the age of eighteen residing in the home, compared with non-Hispanic families, who report only 48.9% have children under age eighteen living in the home. Also, Mexican families are twice as likely to have small children under age six. (Ramirez 1990 & 1991).
Many have questioned what accounts for the high fertility and birth rates among Mexican Americans; it will continue to generate debate over cultural or structural explanations. Or do both play a part in the high rates?
MARRIAGE AND DIVORCE
The marriage pattern among Mexican Americans is similar to those of other groups. According to the U.S. Bureau of Census, individuals over the age of fifteen, 59.6% are married, compared with 59.2 percent for the total United States population. The divorce rate of 5.4%, the lowest rate of all groups, compared with the United States population average of 7.2%.. These percentages are based on the U.S. Bureau of Census.
With respect to family stability among Mexican American families, 75.7% are headed by married couples, 18.6% of Mexican American families are female-headed households and male-headed families 5.8% are likely to take on the single parent role than any other group. These concluding, Mexican families generally appear to be stable, two-parent families with a relatively lower rate of divorce than other ethnic families.
ASSIMILATION and INTERMARRIAGE
Assimilation is defined as a multidimensional process in which ethnic groups begin to blend into a total community. Given this idea, Mexican Americans are only moderately assimilated. They are beginning to be a political strength, a voting bloc sought after, and a strong enough constituency to promote and elect their own politicians. It appears that over the course of several years, this political force will increase. In other areas inequities prevail. Economically, Mexican American family income is still only 73% of the median income for all United States families and Mexican American unemployment rates are much higher. Mexican Americans continue to be concentrated in blue-collar jobs and under represented in white-collar jobs. Educationally, only approximately two out of five Mexican Americans complete high school. Although there has been some progress in these areas, as indicated by the higher proportion represented in colleges, and universities, greater number in white-collar jobs, and increased incomes, the gains are only moderate.
Intermarriage is often considered one major measure of integration, reflective of the degree of other assimilative process (Yinger 1995). Intermarriage in the context usually means marriage between a Mexican American and an Anglo American. Murguia (1992) has compiled one of the most extensive studies on Mexican American intermarriage. The findings indicate that among the three most populous southwestern states, the intermarriage rates range from 9-27% in New Mexico, and from 51-55% in California. Intermarriage rates are greatly influenced by the forces that influence integration. As educational levels increase, residential segregation decreases, and social-class mobility increases with decrease in discrimination, intermarriage should probably increase accordingly. As Mexican American socioeconomic profile moves closer to the socioeconomic profile of the population as a whole, the assimilation process should move accordingly.
CHANGE and ADAPTION
Today’s Mexican American family is a unique culture in American society in that it is fully characterized by neither the Mexican culture nor the American culture, it maintains elements of both. The social and economic pressures of American life have modified the Mexican family, yet the proximity of the Mexican border provides a continual influx of Mexican nationals that serve to maintain the family and emotional ties to Mexico and to enhance the Mexican cultural values.
One key element encouraging change has been the increased movement of families from rural to urban life. Today, more than 85% of all Mexican Americans reside in the urban centers of the southwestern and Midwestern United States. This factor has had a profound impact on the family structure. Although a family orientation remains, Mexican Americans families today are less likely to be composed to extended kin residing in the same household than to be residing nearby, which still facilitates more frequent interaction. The supportive family system is much more characterized by voluntary interaction than by the necessity for economic survival that characterized the rural environment of their forefathers. Due to the various patterns of immigration, there exists much heterogeneity among the Mexican American population. Mexican American families span the continuum of acculturation and assimilation, depending on the conditions of their immigration, length of time in the United States, and their sense of relatedness.
Although there continues to be a disproportionate number of Mexican American families in the lower socioeconomic levels, there has been increasing social and economic mobility, as characterized by a growing number of Mexican American students in college and universities, an increase in Mexican Americans in professional and managerial positions, and a stronger Mexican voice in all aspects of society. As has been true of all women in society, more Mexican American women are entering the force. There are greater numbers entering professions and participating more fully in various walks of life.
These factors come together to continually modify the Mexican American family by changing roles and expectations of all family members. As more opportunities emerge, social forces affect family life, and responses to an economic and political structure occur, the Mexican American family will continue to change and adapt to the forces around them. However, although the traditional Mexican American family has changed and will continue to change, there will continue to be a family form among Mexican Americans that fuses the culture of its roots and that of its American homeland.
Acuna, R. 1991. Occupied America: A History of Chicanos (3rd ed.). New York: Harper and Row.
Baca-Zinn, M. 1993. “Ongoing Questions in the Study of Chicano Families.” The State of Chicano Research on Family, Labor, and Migration. Stanford, CA: Sanford Center for Chicano Research.
Becerra, R. M. 1993. “The Mexican American: Aging in a Charging Culture.” Aging in Minority Groups. Beverly Hills: Sage Publications.
Griswold del Castillo, R. 1994. La Familia: Chicano Families in the Urban Southwest, 1848 to the present. Notre Dame: University of Notre Dame Press.
Hoffman, A. 1994. Unwanted Mexican Americans in the Great Depression. Tucson: University of Arizona Press.
Jaffe, A. J., R.M. Cullen, and T.D. Boswell. 1990. The Changing Demography of Spanish Americans. New York: Academic Press.
McWilliams, C. 1998. North From Mexico. New York: Greenwood Press.
Reisler, M. 1996. By the Sweat of Their Brow: Mexican Immigrant Labor in the United States, 1900-1940. New York: Greenwood Press.
Rothenberg, P. 1998. Race, Class, and Gender in the United States. New York: St. Martin’s Press.
U.S. Bureau of the Census. “The Hispanic Population of the United States: March 1991.” Current Population Reports, P20-455. Washington, D.C.: U.S. Government Printing Office, 1991.
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In the most comprehensive genetic study of the Mexican population to date, researchers from UC San Francisco and Stanford University, along with Mexico’s National Institute of Genomic Medicine (INMEGEN), have identified tremendous genetic diversity, reflecting thousands of years of separation among local populations and shedding light on a range of confounding aspects of Latino health.
The study, which documented nearly 1 million genetic variants among more than 1,000 individuals, unveiled genetic differences as extensive as the variations between some Europeans and Asians, indicating populations that have been isolated for hundreds to thousands of years.
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These differences offer an explanation for the wide variety of health factors among Latinos of Mexican descent, including differing rates of breast cancer and asthma, as well as therapeutic response. Results of the study, on which UCSF and Stanford shared both first and senior authors, appear in the June 13 online edition of the journal Science.
“Over thousands of years, there’s been a tremendous language and cultural diversity across Mexico, with large empires like the Aztec and Maya, as well as small, isolated populations,” said Christopher Gignoux, PhD, who was first author on the study with Andres Moreno-Estrada, MD, PhD, first as a graduate student at UCSF and now as a postdoctoral fellow at Stanford. “Not only were we able to measure this diversity across the country, but we identified tremendous genetic diversity, with real disease implications based on where, precisely, your ancestors are from in Mexico.”
For decades, physicians have based a range of diagnoses on patients’ stated or perceived ethnic heritage, including baseline measurements for lung capacity, which are used to assess whether a patients’ lungs are damaged by disease or environmental factors. In that context, categories such as Latino or African-American, both of which reflect people of diverse combinations of genetic ancestry, can be dangerously misleading and cause both misdiagnoses and incorrect treatment.
Esteban Burchard, MD, MPH
While there have been numerous disease/gene studies since the Human Genome Project, they have primarily focused on European and European-American populations, the researchers said. As a result, there is very little knowledge of the genetic basis for health differences among diverse populations.
“In lung disease such as asthma or emphysema, we know that it matters what ancestry you have at specific locations on your genes,” said Esteban González Burchard, MD, MPH, professor of Bioengineering and Therapeutic Sciences, and of Medicine, in the UCSF schools of Pharmacy and Medicine. Burchard is co-senior author of the paper with Carlos Bustamante, PhD, a professor of genetics at Stanford. “In this study, we realized that for disease classification, it also matters what type of Native American ancestry you have. In terms of genetics, it’s the difference between a neighborhood and a precise street address.”
Three Distinct Genetic Clusters in Mexico
The researchers focused on Mexico as one of the largest sources of pre-Columbian diversity, with a long history of complex civilizations that have had varying contributions to the present-day population. Working collaboratively across the institutions, the team enlisted 40 experts, ranging from bilingual anthropologists to statistical geneticists, computational biologists and clinicians, as well as researchers from multiple institutions in Mexico and others in England, France, Puerto Rico and Spain.
Watch "Genes and Health - Moving Beyond Race," a short documentary produced by the American Museum of Natural History, which features Esteban Burchard along with fellow UCSF researchers.
The study covered most geographic regions in Mexico and represented 511 people from 20 indigenous and 11 mestizo (ethnically mixed) populations. Their information was compared to genetic and lung-measurement data from two previous studies, including roughly 250 Mexican and Mexican-American children in the Genetics of Asthma in Latino Americans (GALA) study, the largest genetic study of Latino children in the United States, which Burchard leads.
Among the results was the discovery of three distinct genetic clusters in different areas of Mexico, as well as clear remnants of ancient empires that cross seemingly remote geographical zones. In particular, the Seri people along the northern mainland coast of the Gulf of California and a Mayan people known as the Lacandon, near the Guatemalan border, are as genetically different from one another as Europeans are from Chinese.
"We were surprised by the fact that this composition was also reflected in people with mixed ancestries from cosmopolitan areas,” said co-first author Moreno-Estrada, a life sciences research associate at Stanford. "Hidden among the European and African ancestry blocks, the indigenous genetic map resembles a geographic map of Mexico.”
Implications for Diagnosing Lung Disease
The study also revealed a dramatic difference in lung capacity between mestizo individuals with western indigenous Mexican ancestry and those with eastern ancestry, to the degree that in a lung test of two equally healthy people of the same age, someone from the west could appear to be a decade younger than a Yucatan counterpart. Burchard said this was clinically significant and could have important implications in diagnosing lung disease.
Significantly, the study found that these genetic origins correlated directly to lung function in modern Mexican-Americans. As a result, the research lays the groundwork for both further research and for developing precise diagnostics and possibly even therapeutics, based on these genetic variations. It also creates a potentially important opportunity for public health policy, especially in Mexico, in allocating resources for both research and care.
“This can shape public health and public policy,” Burchard said. “If you’re testing a group of kids who are at risk for asthma or other health conditions, you want to do it in an area where the frequency of the disease gene is highest. We now have a map of Mexico that will help researchers make those clinical and public health decisions.”
We now have a map of Mexico that will help researchers make those clinical and public health decisions.
Esteban González Burchard, MD, MPH
Burchard, a pulmonologist whose work focuses on the impact of genetic ancestry on children’s risk of asthma and response to asthma medications, has wanted to study the Mexican population since 2003, both as a medical context for Mexican-Americans and as an opportunity to understand Native American genetics. To do so, he reached out to Bustamante, who directs the Stanford Center for Computational, Evolutionary and Human Genomics.
“We were particularly motivated by the fact that the vast majority of genetic studies have focused on populations of European descent,” Bustamante said. “We think there are lots of opportunities for understanding the biology, as well as understanding differences in disease outcome in different parts of the world, by studying the genetics of complex disease in different populations.”
Over the past few years, researchers have begun to understand that genetic variation has a very peculiar structure, Bustamante said. Some common genetic variants reach appreciable frequencies (e.g., 30-50 percent) in many of the world’s populations. Most of these appear to have existed in the human gene pool at the time of the great human diasporas, including the migrations out of Africa. However, Bustamante said a “huge flurry” of other mutations have arisen since then, as human populations grew due to the advent and adoption of agriculture. These are much rarer, occurring in about 1 to 2 percent of the population, and are thought to be both more recent and relevant to health and disease. These rare variants make up the bulk of genetic alterations we see in human populations.
Many of these genetic differences already are known to have a direct impact on our risk for certain diseases, such as the BRCA gene in breast cancer, or our ability to metabolize medications. But before we can develop more precise therapies or prescribe them to the right patients, we need far more knowledge of what those variants are across diverse populations, and how they affect health.
“This is driving the ball down the field toward precision medicine,” Burchard said. “We can’t just clump everyone together and call them European Americans or Mexican Americans. There’s been a lot of resistance to studying racially mixed populations, because they’ve been considered too complex. We think that offers a real scientific advantage.”
A representative chart of a diverse genome, reflecting varied heritage across one individual’s genes, can be found on the Burchard Lab website.
The study was supported by the Federal Government of Mexico, Mexican Health Foundation, Gonzalo Rio Arronte Foundation, George Rosenkranz Prize for Health Care Research in Developing Countries, UCSF Chancellor’s Research Fellowship, Stanford Department of Genetics, National Institutes of Health (grants GM007175, 5R01GM090087, 2R01HG003229, ES015794, GM007546, GM061390, HL004464, HL078885, HL088133, RR000083, P60MD006902 and ZIA ES49019), National Science Foundation, a Robert Wood Johnson Foundation Amos Medical Faculty Development Award, Sandler Foundation, America Asthma Foundation and the National Institute of Environmental Health Sciences.
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