By Michelle Li
Published 4:09 EST, Mon November 15th, 2021
“Nature or nurture” is a long standing question in the sciences; are people more influenced by biological or environmental factors when maturing? Twin studies attempt to answer that question, and although it has not been fully answered, these studies begin to provide an understanding of which aspects of human beings can be attributed to specific factors, whether those are genes or the environment in which people have grown up. Twin studies were first introduced to the scientific world in the 1870s by Sir Francis Galton. Galton attempted to answer this question of “nature or nurture” (Twin studies, 2007). In a number of published articles, he ultimately argued that nature was the more influential factor after studying the results of a questionnaire that focused on how similar or different twins turned out to be after aging, regardless of growing up together or separately. Although Galton’s conclusion was an early argument to a question that has still not been fully answered, it revealed the potential of studying twins in terms of gaining knowledge of the different genetic and environmental influences in human lives, and, eventually, how that knowledge relates to biomedical research relating to diseases.
Twins studies are valuable to biomedical research in that the unique cases of twins allow researchers to separate genetic and environmental influences. Twin cases are separated into two types: Dizygotic and Monozygotic. Dizygotic, or fraternal, twins are not genetically identical but are raised in the same settings from birth. These twins are conceived through two separate, fertilized eggs. They develop in the womb and are born at the same time, but they do not share the same genetics. Monozygotic, or identical, twins—on the other hand—do have the same genetic predispositions, as they have developed from the same fertilized egg. The single fertilized egg splits into two, allowing for two embryos to develop and explaining the identical genetic material (Brogan, 2020). Twin studies also offer the opportunity to control for the factors of age and gender, but the genetic similarity between identical twins is ultimately key to twin research.
When raised in separate environments, identical twins are not influenced by environmental factors, allowing for researchers to study only the biological influences. Similarities in behavior or predispositions to diseases that both twins possess would indicate a biological basis, as environmental influences have been controlled (Brogan, 2020). Conversely, studying identical twins raised in the same environments also have the potential to identify environmental triggers that are connected to diseases. When the genetics and environment of identical twins are the same, similar reactions or onsets to diseases after exposures from the environment can be identified, possibly linking environmental triggers to different conditions.
One twin study conducted by Chirag Lakhani that utilizes insurance claims data from the insurance company Aetna analyzed more than 56,000 twins. The insurance records allowed researchers to study the health of the twins while looking for a connection with some of the 560 diseases that the study focused on. Diseases that occur more often in identical twins in the study were believed to have a genetic influence, and the diseases that occurred in siblings regardless of their twin status were believed to have an environmental influence. Ultimately, the study found that of the 560 diseases that researchers focused on, 40% had a genetic component, while 25% had an environmental component (“Nature or nurture twins study”).
Twin registries are collections of data on twins that are used for future studies. Many countries have established their own twin registries, and they may be overseen by universities or other nongovernmental organizations. Twin registries allow researchers to analyze existing twin data that has been archived, study data related to the development of twins, and pursue twins overtime for longitudinal data for studies completed over longer time frames (Brogan, 2020).
Advantages and Disadvantages
The major advantage of twin studies is that the unique situation of twins allows researchers to begin to calculate and separate the genetic and environmental influences on characteristics of people. Factors, specifically genetics or environment as well as age and gender, can be controlled in order to focus on the impact of a specific factor (Brogan, 2020).
In addition, there are also disadvantages and limitations. Separated, identical twins can still have (and often do still have) similar living environments (although they will not be the same). Twins that become orphans are commonly raised by relatives that share similar socioeconomic situations, influencing housing, living conditions, and financial stability. Adopted twins may also be sent to similar families to avoid favoritism (Brogan, 2020). These situations lessen the ability to effectively separate genetic and environmental influences, which is what makes twin studies valuable.
Twin studies are valuable opportunities to study the genetic and environmental factors that influence a person’s characteristics. Looking through the scope of medicine, twin studies can be used to identify genetic and environmental components of diseases or conditions. While these components are still yet to be fully understood, twin studies have offered partial answers and have the potential to return more significant research that relates to disease onset or other areas of medicine.
Michelle Li, Youth Medical Journal 2021
Brogan, R. F. (2020). Twin studies. In Gale Science Online Collection. Gale. Retrieved September 20, 2021, fromhttps://link.gale.com/apps/doc/KEIGGJ810319895/SCIC?u=mlin_m_newtnsh&sid=bookmark-SCIC&xid=2c42af4e
“Nature or nurture twins study helps sort out genes role in disease.” (2019, January 14). Community Healthcare System. Retrieved September 24, 2021, from https://www.comhs.org/about-us/newsroom/health-library/2019/01/14/nature-or-nurture-twins-study-helps-sort-out-genes-role-in-disease
Twin studies. (2007). In World of Genetics. Gale. Retrieved September 20, 2021, fromhttps://link.gale.com/apps/doc/CV2433500512/SCIC?u=mlin_m_newtnsh&sid=bookmark-SCIC&xid=fa0ee4c8