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Several studies are conducted with an aim of establishing how the biological and environmental factors influence the growth, appearance of physical feature and functionality of many organisms (Grohol, 2006). These studies have extended to the study of mankind and the various illnesses and disorders that affect them. Biological factors are mainly studied under the genetic category. Thus these factors are referred to as genetic factors as well. These studies have been extended to complex disorders like schizophrenia.

Schizophrenia is a chronic and severe brain disorder that is characterized by anomalous social behaviors accompanied by a person’s inability to relate well to what is real. The primary symptoms of the disease are confused thinking, withdrawal and reduced social interactions, hallucinations, and false beliefs. Numerous factors are said to be the leading cause of this disorder. However, the main factors can be categorized into two models or theories (Cook, 2012). This discussion aims at establishing the influence of these two models’ factors and their involvement in the cause of the disorder.

Discussion and Analysis

There exist many factors that appear to cause schizophrenia. A study indicates that schizophrenia disorder results from a succession of neural insults from conception of life onward. A significant debate, has been in the society for a long time; the debate is referred to as the nature versus nature debate. Scientists have argued over between genetics or environment, which plays a larger role in psychological and physical health. With no outright winner, as schizophrenia is caused by a conglomeration of these factors, for instance genetic schizophrenia is highly facilitated by environmental factors (Grohol, 2006). Studies have been carried out to establish the contribution of genetics (biological) and environmental factors to the Schizophrenia illness. The contribution of these factors is studied under two principal theories: biological theories of Schizophrenia and environmental theories of Schizophrenia. However, the contributors of Schizophrenia are not limited to biological and environmental factors only, but these two factors carry the considerable influence, and the other factors are sometimes seen as branches of these two contributors.

  1. Biological Theories of Schizophrenia

The biological models indicate that schizophrenia arises as a result of biological faults. For instance, genetic factors dictate that schizophrenia is passed down generation. This means that the individual obtain this abnormally through genetic inheritance from the parents (Cook, 2012). Two major theories arise under this category.

  1. Neurodevelopmental Theory

This theory states that there is an abnormality in the early stages of the brain development. However, this defect takes long to manifest, and is only seen at later stages of life like in adolescence or early adulthood. According to this theory, schizophrenia is a disorder or illness that results from abnormal brain development that starts at very early stages of life, before any symptoms can be noticed (Picker, 2015). The abnormality in brain development is said to be caused by the combination both the genetic and environmental factors.

The neurodevelopmental theory carries more weight among the biological theories as it deals with brain development and the genetic factor. Genetics aspect of schizophrenia is built on a foundation that the illness is passed from parents to their children through genes (Cook, 2012). The genetic aspect can be explained at three different levels, which are family level, twin level, and adoption level (Picker, 2015). The family aspect of genetic studies suggests that the individuals who hail from a family that has a history of this or other mental disorders have a higher risk of developing schizophrenia when compared to the general population. Studies indicate that a person has 1% greater chance of developing schizophrenia if schizophrenia runs in the family (NIMH, 2014). Additionally, this risk increases to 25% if the one of the parent is schizophrenic. If both parents are schizophrenic, the risk rises to 50% (NIMH, 2014).

The twin aspect is explained through various studies, which study both the MZ and DZ twins. In general, MZ twins have higher chances of developing schizophrenia if the other twin is schizophrenic when compared to DZ twins. More specifically, a study conducted by Gottesman and Shields (1972) found that “42% of MZs concordant for schizophrenia, compared to a concordance rate of 9% for DZ twins (NIMH, 2014).” Additionally, a study concluded that, “if one MZ twin was schizophrenic there was a 90% likelihood that the other twin had some mental disorder (NIMH, 2014).” The adoption aspect of the genetic studies offers another perspective of genetic as it encompasses the environmental factor. A study conducted on Danish children concluded that 32% of adoptees detached from a schizophrenic biological parent developed the disorder compared to 18% of the control group (NIMH, 2014). All this aspects indicate that gene play a significant role in development schizophrenia. However no specific gene has been identified for this contribution.

  1. The Dopamine Theory

This theory is slightly different from the previous theory, in that the theory does not deal with the development of the brain. According to this theory, an abnormality arises in the brain due to the change in the dopamine level (Sullivan, 2005). The main causes of change in dopamine levels are the prolonged use of drugs as well as abuse of large quantities of drugs (Chemist, 2012). This theory falls under the biological theories as it deals with the biological change of the brain through a change of the neurochemicals. The principal neurochemicals change is the increase in dopamine levels in the brain, which increases the risk of acquiring the schizophrenia. The dopamine theory is seen as very simplistic in nature for this biological theory is said to be promoted by pharmaceutical with an aim of increasing sales (Picker, 2015).

  1. Environmental Theories of Schizophrenia

These theories are also known as the sociological theories of schizophrenia. The theories explain the external causes of mental disorders. These external elements are based on the environment or an individual social circumstance (Grohol, 2006; Picker, 2015). Three theories fall under the environmental structure, and they are:

  1. Stress Theory

This theory is built on the manner in which people response to different situations or external events (Sullivan, 2005). These responses follow three phases. The first stage is the alarm phase, where the body uses the nervous system to meet the immediate threat. These nervous system responses are adrenaline tense muscles, digestion shutdown, and blood pressure rise (Grohol, 2006). The second phase is the resistance phase, where the body tries to resist or cope with an unavoidable stressor. The two phases utilizes the physiological aspect of stress. The final stage of the stress theory is the exhaustion phase, where the body energy is exhausted by the persistence of the stress. As a consequence, the body becomes vulnerable to physical problems and in turn the body fall ill (Picker, 2015). According to this theory, stress is unavoidable and stress resultants effects can be positive or adverse.

  1. Structural Strain Theory

This theory is built on the economic status of individuals’ foundation. A strain exists among the economically disadvantaged people, which might result in mental breakdown. Strain or stress can be described as structural or individual (Chemist, 2012). The structural stress refers to the processes that define societal level and ranks. Such stress is vital in how individuals view their needs. The individual stress refers to the pains a person experiences as they aim to satisfy their needs.

  1. Labeling Theory

This theory relates to the fact that people tend to classify themselves and others. Studies indicate that the stress arising from labeling is highly negative. The results of labeling stress are the stigmatization, low self-esteem, and withdrawals (Tsuang, Stone & Faraone, 2001). In effect, individual are likely to suffer from social isolation and mental disorders as well as having negative self-concepts (Medoff & Tamminga, 2000).

The environmental theories are broad as they encompass all factors that lead to schizophrenia development except the genetic factor (Tsuang, Stone & Faraone, 2001). Schizophrenia environment includes social, nutritional and hormonal as well as the chemical environment surrounding the fetus in the womb (Boundless, 2014). However, similar to the genetic situation, the exact environmental factors that influence the development of schizophrenia are unknown. The reason for this unfamiliarity is based on the fact that it is challenging to conduct studies that can look at the environmental factors in isolation (Sullivan, 2005).


Interaction of the Biological and Environmental Theories

It is important to note that, the theories discussed under the two categories are highly interlinked. Studies indicate that development of schizophrenia is an outcome of the sum of the influence of both the biological and environmental factors (Chemist, 2012). As a consequence, a hybrid model arises; the model is referred to as the Diathesis-stress model. The model is a theory that looks at both biological factors and environmental factors. According to the model, a combination of genetic predispositions towards diseased conditions and environmental stresses result in abnormal behaviors (Medoff & Tamminga, 2000). The theory suggests that the mental disorders are the consequence of an interaction between nature and nurture, merging biological and psychological approaches for explaining schizophrenia.


Development of schizophrenia can be explained by the environmental and biological theories. This is based on the fact that schizophrenia develops from numerous factors that fall into two categories of the environmental and biological factors. The biological theories narrow, in that the concentrate on the genetic aspect of human development. Genetics dictates that disorders are passed down through genes (Boundless, 2014). The environmental theories are too broad as they encompass all the other factors except the genes. However, difficulty arises on the validity of these theories. There is no any specific gene that has been identified as a cause of the development of schizophrenia. As well, the influence of any environmental factor cannot be critically measured due to the difficulty to isolate the factors (Boundless, 2014). Additionally, development of schizophrenia cannot be attributed to any single factor or model, as studies have proved that the development arises due to the interaction of all these factors. The main limitation regarding these models is the fact that the theories are deterministic. These theories provide clear and comprehensive for the psychosis. The models fail to address the free will aspect; where an individual has a wide platform to determine their actions, behavior, and thoughts (Tsuang, Stone & Faraone, 2001).
















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Medoff, D., & Tamminga, C. (2000). The biology of schizophrenia. Dialogues In Clinical Neuroscience, 2(4), 339. Retrieved from

National Institute of Mental Health (NIMH),. (2014). NIMH · Schizophrenia. Retrieved 11 February 2015, from

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Sullivan, P. (2005). The Genetics of Schizophrenia. Plos Med, 2(7), e212. doi:10.1371/journal.pmed.0020212

Tsuang, M., Stone, W., & Faraone, S. (2001). Genes, environment and schizophrenia. The British Journal Of Psychiatry, 206(2), 18-24.


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