![]() Different cultural factors affect women’s decisions to start their families later in life, but the trend is consistent across many countries and continents over the last century. Twin births are more likely in later pregnancies. For example, 1 in 11 births in Nigeria are twins, but in Japan, the ratio is 1 for every 250 births (Hall, 2003, p. The rate of monozygotic twins is consistent, while dizygotic twins varies across ethnicities (Piontelli, 2002, pp. Dizygotic, or fraternal, twins form at conception by the fertilization of two eggs by two sperm, so their genetic similarity to one another would be like that of any two singleton siblings. We now know that monozygotic, or identical, twins develop by the division of a single zygote over the first several weeks of pregnancy. Newman, that scientists were able to observe polyembryology in mammals-specifically armadillos-and to verify this developmental sequence from the point of conception to multiple fetuses to birth (Newman, 1941, pp. It was not until 1909, when Miguel Fernandez and in a separate study J. Conjoined twins-unfortunately referred to as “double monsters” during that time-were part of the same process, but in those cases, the splitting of the egg was incomplete (Wilder, 1904, p. Identical twins were the result of the egg splitting into two parts fraternal twins were the result of fertilization of two separate eggs. Harris Hawthorne Wilder was the first to speculate that identical, fraternal, and conjoined twins originated at different points in the same process. He coined the terms identical and fraternal to describe the degree of similarity between the twins. In his 1876 article, “The History of Twins, as a Criterion of the Relative Powers of Nature and Nurture,” Galton pointed to the unique potential that twins offered to genetic research: “Their history affords means of distinguishing between the effects of tendencies received at birth, and of those that were imposed by the circumstances of their after lives in other words, between the effects of nature and nurture” (p. Galton argued that because of their observable similarities, twins were a primary source of data. ![]() Deliberately manipulating reproduction was a recognizable and acceptable idea. Breeding in animals and plants had made successful contributions to agriculture using carefully documented bloodlines among the nobility to identify marriage partners was an accepted cultural practice in Europe, the New World, and many other cultures. The reasoning was that if a species adapted through the process of natural selection, then it should be possible to control disease and other undesirable characteristics by intentional selection. By the beginning of the 20th century, eugenics was considered the new liberating science, promising to help control disease and improve the quality of life. While his cousin, Charles Darwin, culminated his theory of natural selection in the 1850s, Galton was beginning to articulate his related theory of eugenics. Sir Francis Galton (1822–1911) was the first to articulate the value of twins to the nature-nurture debate. Sir Francis Galton: The Twin Study Method Though they must be inextricably linked, there is a difference between research on twins and research that uses the twin studies method. Based on the assumption that all twins share their environment and that monozygotic twins also share genomes, phenotypes that vary between monozygotic twins must be the result of environmental factors, while those that are consistently the same must be genetic in origin. How much of who we are is genetically determined and how much is the result of our environment? By comparing the consistency of phenotypes, that is, observable physical and behavioral characteristics, in twins we can hypothesize about their heritability-whether or not a specific characteristic is genetically determined. Studying twins offers a unique opportunity to identify and differentiate physical and behavioral characteristics according to their origin. ![]() We offer high-quality assignments for reasonable rates. This is how your paper can get an A! Feel free to contact our writing service for professional assistance. If you need a thorough research paper written according to all the academic standards, you can always turn to our experienced writers for help. Browse other research paper examples for more inspiration. View sample anthropology research paper on twin studies. ![]()
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