Charles Darwin first proposed the theory of evolution in his book “On the Origin of Species” that gave a better understanding of how animal species evolved over time. Gregor Mendel’s work laid the foundation for genetics, which was formerly considered as an alternative to Darwin’s theories. Nevertheless, particular combinations of both Charles Darwin’s ideas on evolution, and Gregor Mendel’s lifework on the patterns of inheritance have fused to form the basis of modern biology. Genetic and environmental factors both have played a critical role in the behavioral development within animal species through adaptation and other methods of survival inside an ecosystem. Instinctive responses actually developed over a long period of time in nature that allowed animals to adapt to various circumstances within an ecosystem. Survival of the fittest, and generations of natural selection within an environment eventually caused gene-to-gene interactions, as well as gene-to-environment interactions. Eventually, an organism’s genetic material is modified to the point at which a trait needed for survival becomes phenotypically expressed. A modification to the genetic material of an organism does not only adjust the appearance and function, but also contributes to the alteration of specific patterns of behavior as well. Altered patterns of behavior could increase an organism’s ability to survive any threat presented within an ecosystem. This enables better chances for passing down the organism’s genetic material through reproduction, ultimately to permit the preservation of its own species.
The phrase “Nature versus Nurture” has continually been debated between peers since Darwin’s theories on evolution, and especially amongst scientists of all branches and fields across the board. Nature is normally perceived as a naturally occurring event like certain patterns of inheritance in genetics; whereas, nurture is characterized as the structure and foundation for which an individual developed. This includes the perception developed overtime based on how you were either taught, or raised from infancy to adulthood. Our genetic composition immediately interacts with our environment from the instant of conception. Natural gene-to-gene interactions can cause genetic variation along with factors from the surrounding environment. The concept of nature versus nurture should actually be perceived as a contribution from both, where both genes and the environment manipulate the methods of adaptation within the developing organism. Incorporated into a psychological standpoint, the probability of whether a neurological or psychological disorder will develop over time is decided from various factors that affect the interactions between our genome and our surrounding environment. “Developmental theory suggests that environmental influences interact with biological risk factors throughout the course of development” (Lee, Li, Sonuga-Barke & Halperin, 2012)
The limbic system within the brain is responsible for emotional behavior and is connected to the impulsivity and hyperactivity symptoms commonly associated with both ADHD and bipolar disorder. The molecular description has been proposed as a dysfunctional pathway between the frontal cortex and limbic system. This means that it is possible for the brain to have a weakened frontal cortical system, making it have little effect on the transfer of information to the limbic system, thus, leading to the onset of this neurological disorder. Another affected part of the brain is called the cingulate gyrus within the limbic system, and is critical to understanding various psychological disorders, specifically ADHD. The cingulate gyrus functions to create chemical pathways in the brain that transfers information in-and-out of the limbic system. The neurological dysfunction that occurs in patients with ADHD could be due to either a malfunctioning cingulate gyrus, or malfunctioning frontal cortex, both of which would disrupt communication between the critical systems in the brain.
ADHD has noticeable patterns of inheritance, but to what extent? The first research to thoroughly examine a single genetic interaction responsible for the onset of these particular symptoms associated with ADHD discovered a link with the X-linked-fragile-X-mental-retardation-gene or FMR-1. They used a linear “mixed-model” approach for statistical analysis called “Imekin-Function” to better understand the variations between multiple alleles that lead to the onset of ADHD. The result from this study concludes that the FMR1-gene is a rare mutation that can increase the susceptibility to inheriting and developing ADHD. (Hunter & Epstein, 2012) Research and scientific advancements in the various fields of genetics has allowed new insight on the pathology of psychological disorders, which in turn has furthered our understanding of the respective patterns of inheritance. “Although ADHD is highly heritable (Thapar, Harrington, Ross, & McGuffin, 2000), genetic studies are complicated by environmental influences on ADHD and by the fact that genetic influences on psychopathology are likely to depend on the experience of varying environmental conditions. (G x E; Waldman, 2007).” Scientists have targeted 27 possible genes that correlate with particular levels of dopamine, norepinephrine, and serotonin. These neurotransmitters within the brain and their possible dysfunction have been linked to many psychological disorders, which in turn has the possibility to play a major role in the overall development of ADHD regarding genetic variation.
Functional Magnetic Resonance Imaging (MRI) machines are used to analyze brain activity, and has been utilized throughout neurological research. Neurologists have studied differences between normal brain scans brain scans of individuals afflicted with psychological disease appear. Some noticeable differences that a patient with bipolar disorder exhibits include smaller prefrontal cortexes when compared to that of a normal individual. The prefrontal cortex is responsible for the brain’s ability to process information, make decisions, and solve problems.
New research conducted in molecular psychology has uncovered patterns of inheritance of multiple psychological disorders; however, no one gene has been positively correlated to the onset of these disorders. Studies on bipolar disorder show that specific genetic variations and environmental adversity increases susceptibility to this psychological disorder. These top susceptibility genes correlated to bipolar disorder belong to precursors within various biochemical pathways, such as the ion-channel proteins, which involves the transfer of such chemicals in the brain associated to the development of psychosis. “Genes are not the only risk factor for bipolar disorder. Studies of identical twins have shown that the twin of a person with bipolar illness does not always develop the disorder, despite the fact that identical twins share all of the same genes.” (National Institute of Mental Health)
Research from organizations like the “Genome-Wide Association Studies” and the “Bipolar Disorder Phenome Database” has enabled advancements in the identification of the patterns of inheritance by comparing an individual’s genome with various environmental influences while studying the specific interactions and chemical changes within the brain. “The overlap in heritability attributable to common genetic variation was about 15% between schizophrenia and bipolar disorder, about 10% between bipolar disorder and depression, about 9% between schizophrenia and depression, and about 3% between schizophrenia and autism.” (Wray & PGC, 2013)
Schizophrenia is another very interesting example of neurological dysfunction that also shows patterns of inheritance. The term schizophrenic means, “split-mind” and is commonly associated with split or multiple personalities disorder; however, the disorder is actually when the brain’s processing and rationalizing systems malfunction. The brain’s ability to correctly interpret reality diminishes rapidly. Patients with schizophrenia typically exhibit dysfunctional thought processes and varying degrees of hallucinations that lead to overall paranoia that can leave the patient withdrawn and reclusive. About 1% of Americans are afflicted with this neurological disorder.
There is evidence suggesting that some genes are correlated to an increased risk of having schizophrenia; however, there is no specific gene solely related to the onset of this neurological disorder. Like most patterns of inheritance, there are several variables that must be taken into account, such as environmental interactions and genetic predispositions. “Scientists think interactions between genes and the environment are necessary for schizophrenia to develop. Many environmental factors may be involved, such as exposure to viruses or malnutrition before birth, problems during birth, and other not yet known psychosocial factors.” (National Institute of Mental Health) Genes known to contribute to the synthesis of specific chemicals in the brain have the potential to malfunction and cause problems leading to the onset of the disorder. More specifically, the particular dysfunction of chemicals in the brain associated with schizophrenia and other psychological disorders can give important clues to identifying the origins of where the problem initially occurs.
Based on the information presented, my opinion for future research would be to “reverse engineer” the events including the interactions between chemicals in the brain and other major phenomena that lead to the dysfunctional development associated. We can trace the direct origins of which these chemicals are synthesized, and follow the entire process leading up to the biochemical dysfunction correlated to the development of psychological disorders. The point at which the malfunction occurs, whether it be discovering the chemicals produced and disrupted, or even further identifying the specific genetic interactions of which created precursors associated with the pathological event. “Many possible susceptibility genes for bipolar disorder overlap with top candidates for schizophrenia, including CACNA1C, DISC1, COMT, DTNBP1, NRG1, DAOA and more. Bipolar disorder overlaps with major depression as well. Especially gene-variants of the serotonergic system, for example the well-studied insertion/deletion serotonin transporter polymorphism, are shared between both affective disorders.” (Bengesser, 2013)
Bipolar disorder, schizophrenia, and A.D.H.D. all show obvious patterns of inheritance and genetic linkage. All have similar genetic phenomena like mutations, and translocations (etc.) that lead to the onset; however, external stimuli are considered to be the most significant factor in the overall development of psychological diseases. “For example, common genetic variation accounted for 23% of schizophrenia, but evidence from twin and family studies estimate its total heritability at 81%. Similarly, the gaps are 25% vs. 75% for bipolar disorder, 28% vs. 75% for A.D.H.D., 14 percent vs. 80% for autism, and 21% vs. 37% for depression.” (Psychiatric Genomics Consortium, 2013)
Therefore, nurture does play a critical role in the pathology of psychological disease within an individual, but nature can increase the susceptibility. One side of the debate is as strong or as weak as the other, because both genetic variation and the environment contribute at varying degrees to the onset. The accurate explanation of how psychological disorders develop are derived from a combination of both genetic patterns of inheritance, as well as environmental variables applied to the overall development of an individual.