Nature Vs. Nurture

Twin Study Overview - Dealing With Schizophrenia



What Is Schizophrenia

Understanding the Debate of Nature Vs. Nurture





I am a Pennsylvania State University student who has been asked to do a web site on a topic that relates to Biological Anthropology. I have examined the factors of genetics and the environmental influences that will shape a person's make-up. I have used the relationship of twins, raised together and those raised separately. I have also examined the disorder of schizophrenia and its relationship to this subject.

For decades scientists have quarreled over the stereotypical question of "nature vs. nurture". Scientists have used twin studies to understand heredity and environmental influences on behavioral development. Twin and adoption studies can tell the extent to which family resemblance is due to shared genes and the extent of shared environment. Because of the identical genes carried by monozygotic twins (identical) they have an appeal to scientist. With the website, it discusses that there is a strong genetic link to the development of psychological disturbances and drug dependencies. These findings have added the studies of the relative importance between heredity and environment in an individual's development. In the case of the human brain development, some researchers are convinced that genetic predispositions are what lead people to what they are. On the other hand, there are many others that promote the factor of the environment, stating that outside forces are what impact the lives of humans and shape them as they grow. Both genetics and the environment alter the synaptic organization of the brain. By using the nature vs. nurture debate, many studies have been done on twins, including ones that were raised together and raised separately, to try to come to an outcome. This topic has been studied intensely, and many scientists try to use schizophrenia disorder as a means to try to understand why one twin might have the disease and the other might not.



Before we can discuss schizophrenia relating to the "nature vs. nurture" debate, we must understand exactly what schizophrenia entails. Symptoms of any type of schizophrenia must be present for at least six months before it can be diagnosed. There are many types of schizophrenia. The most prevalent form is called paranoid schizophrenia which is found in 40% of .5 - 1% of the people diagnosed with the disorder. Paranoid schizophrenia is characterized by delusions and hallucinations surrounding persecution, and by feelings of jealousy and grandiosity. The second form of schizophrenia is called catatonic. This type of schizophrenia is characterized by a person retaining a fixed and bizarre position for an extended period of time. At times catatonics also suffer from periods of restless movement. The third form is disorganized or hebephrenic schizophrenia. With this type of schizophrenia, the patient is incoherent and experiences flat or inappropriate emotions, with disorganized behavior and bizarre stereotyped movements and grimaces. In explaining the disorder of schizophrenia as it pertains, is a good tool in explaining nature's contribution to this disorder. They give the different types of schizophrenia, the causes, and treatments. Each category is nature related, meaning that they feel that it is a genetic disorder. Each treatment that is given is a type of medicine that is taken orally. Another treatment is elecoconclusive therapy that relieves some symptoms of catatonia and depression in schizophrenics. They do mention psychotherapy, but only if it is combined with some type of medication. Another useful website is which explains major breakthroughs for the treatment of mental illnesses. Scientists are hoping to identify the genes which might cause mental health disorders. They believe that after they identify these genes, new drugs can be used to help sustain the disorder.



At the beginning of the twentieth century, most people viewed "nature" as the most important determinant of behavior. Simple genetic traits are those that are not affected by the environment's influences in one's life and are seen to support "nature". During the period of the 1930's to 1960's, the belief shifted. During that time many people believed that "nurture", or environmental factors, was the main determinant of behavior. Complex traits, or those traits that are affected by growth and the environment stands out here. It is clear that identical twins are neither physically nor behaviorally identical to one another. If they do not have identical diets and nutrition, then they will not be the same height or weight. Or they may surer dissimilar injuries, or wear their hair different lengths. Isn't it true that identical twins will wear different clothes, have different types of friends, choose different kinds of mates and like different social activities? They usually choose different occupations and have different life-long ambitions. Identical twins will often not share the exact same values or beliefs. If genetically identical twins, were raised in different environments then their physical and behavioral characteristics would differ accordingly. Let us think about identical twins that are separated from their parents at birth. An upper middle class family living in Korea raises one twin, while a tribe in Saudi Arabia has raised the other twin. Being raised in such different environments, how identical could these twins end up looking and acting? With such different value systems will they have the same beliefs? Will they have the same needs, desires, and ambitions? Living in such different areas could they possibly like the same kinds of people, enjoy the same foods, have the same sense of style in their clothes? By living such different lives, obviously the answer is no! Danielle Cappelletti, of Marshall, University, feels that there is minimal evidence that exists to prove that schizophrenia is genetic. In her website, she refers to psychiatrist Peter R. Breggin, who believes that the twin studies that have been done to prove that schizophrenia is genetic is wrong. Breggin says that there are so few cases of identical twins that are reared apart, that it is almost impossible to make a conclusive argument about the genetic influences of a mental disorder, such as schizophrenia. Breggin discusses a study that was done on people with schizophrenia. He says that while the percentages of twins that both are schizophrenic are high, they are not the usual 100% or 50% that are normally seen among people with genetically transmitted disorders. Breggin refers to a study that was done that proved many percentages for people with schizophrenia. The study shows that the average population has a 10% chance of being schizophrenic. In the case of identical twins, with one who has the disorder, the other has a 48% chance of also acquiring the disorder. In the case of fraternal twins there is a 17% chance of a schizophrenic disorder. If a person's genes solely cause schizophrenia, than if one identical twin has the disease, than the other should also. In the website titled "Nature, Nurture: Not Mutually Exclusive," Beth Azar discusses that human behaviors are not influenced by nature or nature, but nature and nurture. Robert Plomin, PHD. Explains that the genetic influence on traits such as personality, intelligence, and behavioral disorders, such as schizophrenia account for half of the variance. This proves that the environment influences the rest of the variance. When there is talk about the environment, there are two influences:

1.    Shared environmental factors which are common to children reared together and cause similarities in their behavior; and
2.    Non-shared environmental factors which are factors such as school, different social activities, and the different interactions that the children have with their parents. The different encounters that the children have can influence them differently.

Davis Reiss, M.D., as well as his collegues, including Plomin, began the Non-shared Environment and Adolescent Development project. This project included twins. Within this website, this project is discussed to a great extent and talks about many of their findings. Throughout their study, they found that parental behavior (genetics) is influenced by genetics and now called "The Nature of Nurture". Their research provided three examples.

1.    Parents who transmit a gene to a child like being musically gifted will most likely have parents who not only are also musically talented, but also provide an environment that helps to promote the musical ability.
2.    Children who have musical ability will most likely be selected by a teacher for a special event. This gives that child a better chance then somebody who might not possess the genetic talent, but might be able to provide the same work. But because of the known ability from the one child, they are given special opportunities.
3.    Musically gifted children might seek out friend who also have a musical talent, once again giving them different environmental influences.

The following website, explains the facts in the book, "Schizophrenia and Manic-Depressive Disorders". E. Fuller Torrey and his colleagues describe their research by studying 66 pairs of identical twins, one of whom has schizophrenia, and one whom does not. Throughout their research they examined brain wave patterns, blood flow patterns, medical records, the twins position in the womb, and even the whorls of the fingerprints. In the end, Torrey and his colleagues admit to the uncertainty of what exactly causes schizophrenia. They also mention that genes do play a role, but like stated by so many others, the role of genes determining schizophrenia is not as much believed as once thought. In reality, most studies done on identical twins, show that it is very unusual to find that both twins are affected by the disease. Relatives, and especially relatives who are more genetically linked, of somebody with schizophrenia, are more likely to also develop the disease as seen in the below chart. Below is a chart taken from

Source: Reprinted by permission of the author. From Gottesman, I.I., Schizophrenia Genesis: The Origins of Madness, New York: W.H. Freeman, 1991, p.96 (c) 1991 Irving I.



Our lives - are thy pre-chosen? Do we live with the script that is written in our genes.

If we could decipher every gene and the functions of each gene, could we understand who would acquire schizophrenia, heart disease, or become a violent person? Within the website, , there is a discussion on not only does a gene need to exist, but the type of environment one grows up in, has just as high a percentage on influencing a person to acquire a type of disorder. Dr. Sue Meyer said, "Gathering knowledge and understanding is a good thing, but we need a bit of humility. We are not just a collection of genes." For many decades, the question of "nature vs. nurture" has existed, and there is still not one right answer. Still unable to decide if one is more important, twin studies have been a constant experiment to find the truth. This website,,1510,3945,00.htm explains how the very complex interaction of the environment and genetic makeup between the two is what the real answer is. This website also explains how siblings who grow up in the same family, still grow up in very "different" families. They might have a close genetic make-up, but the difference in the household between the first-born and the second born is very different. As explained in this website, "The child's development is a complex dance in which nature and nurture both lead and are led." So which is it, "Nature vs. Nurture"? In website,, Adam Methany and his colleagues push towards the genetically linked side. If somebody were to ask, lets say a Penn State college student, what they might think, their answer might be siding towards the environment (nurture). Doesn't each experience that somebody goes through, change that person and make them somebody that they weren't 10 minutes before. Throughout this website, as well as all the others that were refereed to, nobody is exactly sure which influence is stronger. Although it is known that both factors have a very strong influence. So in the end, I am going to have to jump on the bandwagon and say the title should no longer be "nature vs. nurture", but "nature and nurture". Biology and environment are both very important. Each plays a role in shaping who we all are in the past, present, and future.