Ethnic Differences 1
Running head: GENETIC DIFFERENCES BETWEEN ETHNICITIES
Ethnic Differences: The Extent and Significance of Genetics
Michael Mao
Creighton University
Abstract
This paper provides a brief summary over the findings from current studies and research concerning genetic differences between ethnic groups. These findings can be divided up into research pertaining to physical and intellectual disparities associated with different ethnicities. This paper also evaluates the results of these studies, the methodology used, and the respective limitations in an attempt to assess the relative contribution of genetics. A small discussion of future research concerning ethnic differences along with possible societal consequences is included.
Ethnic Differences: The Extent and Significance of Genetics
Throughout history, perceived ethnic differences and inferiority has caused individuals of different ethnicities to constantly fight against persecution for their freedom, civil rights, and equality. Numerous instances of ethnic persecution are seen throughout history, whether it involved Native Americans fighting for their right of land, African-Americans for equality, or Jews struggling to survive during the holocaust. If past historical conflicts resulting from ethnic differences are not an indication of the issue’s importance, then the current debates concerning ethnic equality in all aspects of life including education, work, healthcare, and unconscious prejudices are clearly revealing. Furthermore, increasing research on ethnic differences coupled with the rapidly expanding knowledge of the human genome have provided the availability to pursue research that can produce scientific evidence with concrete support for or against ethnic differences, hence either substantiating the belief of an inferior ethnicity or the belief of ethnic equality despite overt physical appearances. For example, many scientific articles now offer data from studies that support the presence of ethnic differences, such as an increased presence of Tay-Sachs alleles in Ashkenzic Jews, cystic fibrosis in North European populations, and beta-thalassemia in eastern Mediterranean basin populations (Neel, 2001). Although such studies are useful for determining apparent correlations between symptoms and ethnicities, more in-depth studies must be conducted to ascertain the influence of genetic versus environmental factors. Numerous environmental factors such as socioeconomic, cultural, and learned behavior make distinguishing ethnic differences based on genetics uncertain and difficult. Previous research and scientific debates have indeed confirmed the extensive and surprisingly penetrating ways in which environmental influences can contribute to ethnic differences in all aspects of society through the so-called interaction between nature and nurture. However, recent research has increased understanding of ethnic differences by providing evidence clarifying the separate genetic and environmental components of ethnicity. Through the examination of these recent studies, this paper attempts to better understand and clarify the extent of genetic differences between ethnicities as well as discuss the impact this research can have on society.
Ethnicity Term and Background
It is noted that this paper will utilize the term ethnic rather than the term racial. Traditionally, the term race has been used to distinguish biologic and genetic properties of individuals, with skin color being a large determining factor for classification. However, as Flaskerud (2000) notes, the term race is an incorrect term because it has ceased to exist and thus the use of the term is inaccurate and imprecise. Consequently, the term ethnicity will be favored, where ethnicity is generally defined as a shared sense of people hood in a group of individuals based on shared geographic origin, language, religion, customs, kinship patterns, and observable characteristics and phenotypes due to environment and genetics. The five broad ethnic groups commonly identified in the United States consist of “African Americans, Hispanics/Latinos, Asian Americans and Pacific Islanders, American Indians and Alaskan Natives, and White or European Americans” (Flaskerud, 2000). In addition, it is made known that due to the vast majority of research that has focused on ethnic differences between African Americans and Europeans, the topic of this paper may be similarly focused.
Current studies have shown that modern humans evolved in Africa 200,000 years ago, while contemporary human races are estimated to have differentiated at approximately 110,000 and 41,000 years ago through the process of evolution (Rushton, 1995). Rushton further shows that there is indeed a genetic difference between ethnicities, yet these ethnic differences account for only four percent of the entire human genome. The extent of genetic differences between ethnicities is affirmed by Feldman (1997), who notes that less than 15 percent of the distinctions observed in ethnicities are between populations, while the remaining 85 percent are found within populations. Despite the relatively small genomic difference, a wide variety of individual characteristics are attributed to these ethnic differences. Research on ethnic differences tends to fall into two categories: physical differences and intellectual differences. Hence, recent research on physical differences between ethnicities can first be examined followed by an examination of intelligence differences.
Physical Differences between Ethnic Groups
A recent topic that has received a great amount of research concerns differential ethnic susceptibility to a disease. A good model of a verified physical and genetic difference between African Americans and Europeans concerns the genetic polymorphism associated with the sickle cell anemia gene and hemolytic anemia of glucose-6-phosphate dehydrogenase deficiency, G-6-PD (Neel, 2001). Sickle cell anemia is caused by a homozygosity nucleotide substitution in a gene coding for beta hemoglobin found in chromosome 11. The sickle cell gene originated in a tropical environment where Plasmodium falciparum malaria is prevalent and a significant cause of morbidity and mortality. When the sickle cell gene is present in individuals in a homozygous state, it is often fatal. However, when the trait is heterozygous in an individual, it imparts protection to the individual from malaria due to decreased ability of the parasite Plasmodium falciparum to grow. Consequently, natural selection would have selected for this sickle cell gene for African-Americans in tropical climates, thus explaining the ethnic difference resulting in Europeans possessing a greater susceptibility to malaria. Furthermore, this theory gives a potential explanation for the high mutation rates in genes prevalent among African Americans in Africa. In G-6-PD, similar findings have revealed that genetic differences in ethnicities exist as a result of natural selection (Neel 2001).
Mortality and Associated Diseases
In the past 30 years, there has been continuing debate over mortality differences between African-Americans and Europeans, where past studies show that African-Americans seem to have lower mortality rates at older ages, hence a longer life, despite data showing that African-Americans may be receiving less healthcare (Martin, 1997). The mortality rates between ethnic groups was further studied by Elo and Preston (1997), where the two ethnic groups receiving the greatest attention in terms of mortality rates are between African-Americans and Europeans. Data have shown that even though African-Americans have a higher mortality rate at a younger age, they have a lower mortality rate at an older age when compared to Europeans (Elo & Preston, 1997). Elo and Preston suggest that this crossover of mortality of African-Americans surpassing Europeans can be attributed to the theory of survival of the fittest (1997). This study would thus infer that younger and weaker African-American individuals subject to harsher environmental conditions than Europeans would have higher mortality rates at an earlier age, thus leaving the stronger African-Americans to reach an older age and surviving longer than the mix of weak and strong Europeans. Despite these data, one must acknowledge the limitation of this study, where one possible explanation for the observed results is due to misrepresentation of age in African-Americans due to poor vital statistics and census data.
Mortality rates for other ethnic groups are also reported, though there has been less scientific evidence providing explanations for the observed rates. Nonetheless, it is noted that Hispanics generally have a lower mortality rates when compared to Europeans, and this difference increases with age. Asian Americans and Pacific Islanders have the lowest mortality rate of all the groups (Elo & Preston, 1997). These general mortality differences suggest genetic differences between ethnic groups.
Explanations for these differences in mortality rates can be further verified by examining differential ethnic susceptibility to diseases that can lead to earlier mortality. One such disease is congestive heart failure (CHF). This research was conducted at a financially equal-access health care system, which is nationwide and federally funded so that healthcare is provided to all individuals without restrictions due to economic reasons, such as insurance status or inability to pay. Consequently, the research parameter aids by decreasing the environmental variables that may affect the results. The study found that African-Americans on average have a higher prevalence of congestive heart failure than Europeans. Furthermore, evidence demonstrated significant differences between African-Americans and Europeans in regard to short-term and intermediate-term mortality after CHF, where African-Americans possessed a lower mortality. One explanation proposed for this result is that African-American patients may have a greater susceptibility to sodium retention associated with hypertensive heart disease, hence requiring hospitalization at earlier stages of the disease (Deswal, Petersen, Souchek, Ashton, & Wray, 2004). This hypothesis hence suggests that genetic differences in ethnicities leads to increased susceptibility to sodium retention. Further analysis of the data also showed that the African-American ethnicity was an independent predictor of improved survival after hospitalization. Limitations associated with this study are that African-American patients were generally younger and had less comorbidities when compared with European patients, though the researchers attempted to take this factor into account in their analysis (Deswal et al., 2004).
Further evidence related to cardiac diseases that both supports and contrasts the conclusions from the previous study showed that African-Americans are more likely to be diabetic, hypertensive, and possess a higher rate of chronic renal insufficiency. However, they are also less likely to have coronary artery disease or hypercholesterolemia than Europeans. Furthermore, in African-Americans, lesions occurred more often in the left descending coronary artery (Leborgne et al., 2004). Leborgne et al. (2004) state that the deleterious effects of diabetes and hypertension may indirectly cause coronary microcirculation and hence lower left ventricular ejection fractions. Hence, this finding exemplifies the complexity of the role of genetics and the environment, where genetics increases the likelihood of ethnic individuals acquiring diabetes by interacting with an environment that promotes the formation of the disease as well. Consequently, diabetes can increase genetic susceptibility to coronary microcirculation caused by ethnic differences in the prevalence of genes. Contrary to the above study, after controlling for baseline ethnicity differences, ethnicity was found not to be an independent predictor of in-hospital major adverse cardiac events. The limitations involved the use of an older population for African-Americans and that African Americans were less often referred for coronary revascularization than Europeans (Leborgne et al., 2004).
Further Physical Ethnic Differences
In addition to these ethnic differences in disease susceptibility and mortality caused by CHF and cardiac related problems, there are numerous studies that have found different physical aspects that differ between ethnicities. One such study involved preterm birth rates, where significant ethnic differences in the rate of low birth weight and preterm babies were detected (Preterm birth, 2004). African-Americans were associated with the highest percentage of infants born with low birth weight and very low birth rate when compared to Native Americans, Asian-Pacific Islanders, Hispanics, and Europeans. It was noted in the study that this attribution of genetic factors to this phenomenon is limited by environmental factors that might play an indirect role through assisted reproductive technology, which would cause multiple gestations and hence decreased birth weight (Preterm birth, 2004). Another study stated that African Americans get sick faster from smoking (African Americans, 2004). Studies involving advanced chronic obstructive pulmonary disease have found that African American patients who start smoking later in life and smoked less still have the same disease severity at an earlier age when compared to European patients (African Americans, 2004). One other general study involving ethnic differences noted that ethnic differences in the United States showed African-American babies possessed shorter gestation period than European babies, where 51 percent compared to 33 percent are born respectively by week 39 (Phillipe, 1996). Furthermore, standardized tests show that African-American babies mature faster physically in muscular strength, coordination, and locomotion, with Europeans and then Asians following behind. One other difference noted was that African-American college students have a 19 percent higher testosterone rate than their European counterparts (Philippe, 1996).
Intelligence Differences between Ethnic Groups
The second general category of research concerning ethnic differences that has received vast attention concerns intelligence and its correlation to genetics and ethnicity. Previous studies have often attempted to correlate ethnicity, head size, and intelligence to account for the difference in IQ test scores between European and African-American scores. For instance, Rushton (1995) revealed a repeated difference in cognitive ability between ethnicities. However, more recent research has provided many arguments and evidence against such theories. One study conducted by Kamin and Omari (1998) found a number of calculation and other associated errors in previous studies of external head measurements made between African-American and Europeans. These findings would invalidate the conclusions of several studies that purported a correlation between ethnicity, head size, and intelligence. The research further commented that differences in body size, nutrition, and social class would all have effects on head size and IQ. The study concluded that differences in external head dimension, which is small and can be affected by differently shaped heads, are inconsistent and thus its correlation to intelligence is likewise minimal. Hence, data on ethnicity, head size, and intelligence cannot explain the observed ethnic differences in IQ tests between African-American and Europeans (Kamin & Omari, 1998). It follows then that ethnic differences caused by genetics that determine different head sizes would have no influence on intelligence.
Arguments against the connection between ethnicity and intelligence also hold that no formal mechanism has been identified that could explain how the complex attributes associated with intelligence could be connected with the behavior of one ethnic group. For instance, natural selection that testifies to the environment shaping an ethnic group’s intelligence is not a good hypothesis since it is untestable. Furthermore, another argument against attempting to correlate intelligence to ethnicity is the presence of a fundamental difference between a simple trait such as skin color, determined by only a few genes, and a complex attribute such as intelligence, which depends not only on a multitude of unknown genes but by the environment (Olson, 2001).
Discussion and Implications
The implications of these studies are significant and very diverse. Whereas the research pertaining to physical ethnic differences are concerned, it seems that each of the studies gave results that showed no clear superiority or inferiority between ethnic groups. For instance, the study on the prevalence of sickle cell anemia among African-Americans reveal that even though Europeans are more susceptible to malaria, they do not incur the associated disabilities and dangers of sickle cell anemia (Neel, 2001). Furthermore, the studies concerning mortality and associated factors, such as CHF and cardiac problems, reveal that despite variations that can be associated to potential genetic differences between ethnicities, such studies do not disregard the influence of environment. The studies concerning ethnic differences in preterm babies, greater smoking risk, and childhood development and rates of hormone release all reveal deficiencies in providing concrete genetic evidence for the observed ethnic characteristics.
Furthermore, the methodologies of these studies contain many limitations, a few of which were explicitly noted in this paper. One example concerns Philippe’s study that stated that a higher testosterone level was found for certain ethnicities (1996). For a more accurate analysis, it seems that the study should include a greater and more inclusive sample size than college students and United States veterans (Phillipe, 1996). In addition, limitations associated with methodologies used can also be exemplified by Deswal et al. (2004), where it was hypothesized that European patients may have systematically received inferior healthcare. However, a recent study in the Veterans Health Administration has not supported the hypothesis through a study of inpatient treatment and discharge care for CHF, Medicare quality of care, and discharge rates from hospitalization. Nonetheless, it was still noted that certain aspects of the study, such as the small differences concerning the use of outpatient services compared to urgent care emergency room visits between African-Americans and Europeans, could not be addressed adequately by the study. One explanation suggested for the study’s results may be the lack of social support available for African-Americans (Deswal et al, 2004).