Plomin argues that the medical model for psychological disorders is flawed
Common psychological disorders are not caused by a single gene but rather by the cumulative effect of many genetic differences. There are no qualitative disorders, but only quantitative dimensions and people differ in how much of a particular trait or disorder they exhibit. The author suggests a shift in vocabulary from "disorders" to "dimensions" to reflect this understanding. For example, schizophrenia is now referred to as schizophrenia spectrum disorder, and autism is referred to as an autistic spectrum disorder.
The author argues that behavioral symptoms used to diagnose severe disorders such as schizophrenia and autism are strong but can still be quantitatively assessed and are part of the normal distribution. People with these disorders exhibit bizarre behavior, but everyone has experienced some of these symptoms at some point. The author suggests that we need to stop being obsessed with diagnosing whether people "have" the disorder and instead focus on quantifying the symptoms and dimensions.
In the field of behavioral genetics, two prominent findings have been made. The first is that the environment is not just passively influencing us but instead we actively select and create environments based on our genetic propensities. The second is that despite growing up in the same family, children can be vastly different. This was previously a mystery but has been explained by the realization that children resemble their parents because of their genetic similarity, not because of shared environmental experiences. Research shows that some traits, such as altruism, are moderately heritable and have no shared environmental effect. Intelligence and school achievement are exceptions where a shared environment can have an impact during childhood, but this effect decreases as children grow into adolescence. Non-shared environments, such as different experiences and events, are the leading explanation for differences between individuals. To study non-shared environmental influences, a ten-year study of 700 families with adolescent siblings was conducted and showed that parents' negativity was a response to their children's depression and antisocial behavio.
"Equal opportunity and Meritocracy"
Plomin examines the implications of genetic research on these two concepts. The author argues that equal opportunities do not mean equal outcomes, as genetic differences still play a role in outcomes despite equal environmental opportunities. The concept of gene-environment correlation is introduced, which suggests that our experiences are correlated with our genetic propensities and thus affect outcomes. The research presented in the chapter focuses on the effect of equal opportunities on educational achievement in Europe and the US in the 20th century and suggests that heritability is expected to increase as access to education expands and the shared environment decreases.
In terms of meritocracy, the author argues that the selection process in schools, for example, is often not based on merit but on factors such as family wealth or power. The research found that the type of school in the UK only explains 1% of the variance in General Certificate of Secondary Education (GCSE) scores. The author also points out that genetic research should not lead to the classification of people into castes based on their genes and restrict them from changing their socioeconomic situations. Instead, Plomin suggests adopting a new value system that replaces meritocracy with a just society where all jobs, even those
requiring less intelligence or education, are valued, and everyone is given a chance to lead a happy and fulfilling life.
The Human genome
The Human genome is made up of DNA, which is a sequence of four nitrogenous bases - adenine (A), cytosine (C), guanine (G), and thymine (T). These bases pair up to form a double helix structure, and the sequence of these base pairs determines the genetic information. The DNA sequence codes for the production of proteins responsible for the structural and functional aspects of cells and tissues. Proteins comprise a sequence of 20 different amino acids, and the specific sequence of amino acids determines the protein's structure and function.
Mutations in the DNA sequence can occur due to various reasons, such as environmental factors, errors during replication, and spontaneous changes. A mutation can change the meaning of a three-letter code, leading to a change in the sequence of amino acids in a protein. This change in the amino-acid sequence can alter the protein's function and potentially lead to genetic disorders.
The recent development of gene-editing techniques such as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) has made it possible to cut and replace DNA mutations precisely. The technique is being explored to treat several single-gene diseases in somatic cells that are not passed on to future generations. However, editing DNA in many cells in the body to bring about a therapeutic effect is challenging and requires more research.
Unlike physical traits, psychological traits are not determined by a single gene mutation. The heritability of psychological traits results from thousands of genes, each having a small effect. Most DNA associations with psychological traits involve SNPs (single nucleotide polymorphisms) in non-coding regions of DNA, which regulate the transcription of other genes. The exact mechanism of how these SNPs affect psychological traits is complex and involves several pathways between genes and complex traits. Biologists tend to approach the question of how DNA affects behavior at the biochemical level, while psychologists take a top-down approach and try to find answers at the level of behavior.
Overall, the relationship between DNA and psychological traits is complex and multi-faceted, involving a complex interplay between genes, biochemistry, physiology, neurology, and psychology. The discovery of the role of DNA in psychological traits is an exciting area of research, but the exact mechanisms are still being explored and understood.
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