An analysis of literature on twin and adoption studies has generated controversy and much debate amongst theorists and scientists throughout the twentieth and twenty-first century. The debate is concerned about how an individual's personality, behaviour and physical characteristics, may or may not be, determined by the individual's upbringing or by their genetics. It is commonly believed that scientists either believe that it is the individual's genetics that determine their characteristics or it is their environment. However, a closer analysis of twin and adoption studies reveals it is a combination of both nature, which is all the inherent characteristics or genetic, biological features regardless of where you were born and raised and nurture, which is all the environmental or learnt and personal experiences that influence an individual's intelligence, behaviour and potential to develop a disease (Ginsburg, 2010). For this reason, evidence will reveal that scientists and theorists cannot say definitively that it is either nature or nurture and epigenetics, a term that illustrates how the environment influences the characteristics of the genetic outcomes in the environment. Epigenetic signatures can be influenced by the environment and change our appearance, types of behaviours and disease susceptibility and how long we live (Tammen, Friso, & Choi, 2013). Besides the recent studies of epigenetics, questions still remain unanswered about research methods to find answers. To illustrate how the nature versus nurture debate has developed and the influence of twin and adoption studies have impacted on this research field. The history of twin and adoption studies, the former is defined as the importance of environment and heritable genetic transmission effects on particular individuals in a sample and the latter is defined as exposing to a different environment than their biological relatives, this demonstrates a more clear definition between the genetic factors and the environment. Studies of twin and adoptive children go back to the English scientist Sir Galton (1822-1911) who did clinical research in 1876 that uses adopted children or adults as their subjects, examining their genetics or environment and how these influenced traits in inheritance of intelligence. His methods involved the use of various types of statistical methods, such as using psychological questionnaires. In his Twins Studies, which is defined as revealing the importance of how environmental and heritable factors influence individuals to given trait or condition (Gillham, 2012; Steves, Spector, & Jackson, 2012). His study led him to believe that success and intelligence was an inherent quality passed down through generations and natural superiority, a concept that asserts that success was due to superior qualities. Following Galton's research, Darwin's (1809 “1882) findings on Natural Selection is a process, in which adapted organisms transfer life genetic traits from stronger offspring best adapted to their environment in succeeding, than to less adaptive generations and are less likely to survive (Brunand