Epigenetic, soft inheritance and intelligence

Paper made by Maria Rydkvist, Stockholm (2017/02/02)

Introduction

Florence Goodenough was an American psychologist and professor at the University of Minnesota who spent a good portion of her intellectual life developing tools for assessing intelligence in young children. Goodenough confronted the most controversy of her career by taking a strong position on the classic nature vs. nurture debate surrounding intelligence. Goodenough maintained that intelligence is a stable entity and challenged the assertion that the environment plays a key role in children’s intelligence scores.

At Columbia she studied under Leta Stetter Hollingsworth best known for her work with exceptional children. At Stanford, Lewis Terman was beginning a study on gifted children and was selecting prospective researchers for his work. Goodenough was noticed by Terman because of her own IQ score.

The heritability or the degree of inheritance of a trait is an important parameter, which shows how much of the trait is caused by genetical effects. Generally it is a fact that the phenotype of an animal is determined by its genotype and its environment. The genotype is the sum total of genes transmitted from parent to offspring. The genotype is the part (DNA sequence) of the genetic makeup of a cell, and therefore of an organism or individual, which determines a specific characteristic (phenotype) of that cell/organism/individual.

The phenotype of an organism is the whole set of characters (or traits) of that organism. Phenotypes are determined mainly by genes and are influenced by environmental factors.

Environmental factors are determined by natural environment and built environment.

By Natural environment means all living and non-living things that are natural. The universe is natural, but often the term “natural environment” only means nature on Earth. Two aspects are usually included:

  • Ecological units which are natural systems without much human interference. These include including all vegetation, microorganism, soil, rocks, atmosphere, and natural events.
  • Universal natural resources and physical phenomena which lack clear-cut boundaries. These include climate, air, water, energy, radiation, electric charge, and magnetism.

In contrast to the natural environment is the “built environment”. There, man has changed landscapes to make urban settings and agricultural land. A simpler human environment largely replaces the complex natural environment as family, education, enriched social environments and peer groups.

Often it is assumed that the phenotype is the sum of the genotype and the environment.

The phenotype can also be seen as the interaction between genetics and environmental factors, some genotypes are better in one environment and others are better in another environment . The three factors that determine phenotype are genotype, inherited epigenetic factors, and non-inherited environmental factors

If a genotype results in a good phenotype in one environment, the same genotype will not necessarily result in a good phenotype in another environment. A particular genotype produces a recognizable phenotype.

What is Epigenetics?

The external environment’s effects upon genes can influence disease, and some of these effects can be inherited in humans. Epigenetics often refers to changes in a chromosome that affect gene activity and expression. Many biologists are skeptical of any form of soft inheritance, Epigenetics should be considered a form of soft inheritance. Epigenetic mechanisms leave DNA sequence unaltered but can affect DNA by preventing the expression of genes thinking that the environment could be pushing the epigenetic information in a direction that is beneficial. These so-called epigenetic modifications are known to be important for “turning genes on and off” during the course of an organism’s life, but their importance in controlling inheritance has been debated. Epigenetically induced beneficial has an epigenetic inheritance.

Lamarck, and more recent neo-Lamarckian researchers, believed that the environment plays a key role in a species acquiring inherited characteristics that drive variation and evolution. Lamarck, for instance, believed that shore birds acquired their long legs by constantly stretching their legs to lift themselves out of the water and that generations later that kind of environment gave rise to birds with long legs. Neo-Lamarckian views of evolutionary change stress the importance of the environment in altering inheritance. The epigenome regulates gene expression in several ways but its source is inheritated.

“When most biologists hear the name Lamarck or the term soft inheritance, the reaction is, ‘Oh my God, here we go again’,”

Unlike the DNA sequence, epigenetic processes are dynamic and not fixed, although some can persist for long periods of time, up to several years or a lifetime. They help a better understanding of human diseases and possibly provide new approaches to curing them further, they are strongly influenced by the environment and by exposure to external factors like diet, living conditions, exercise, stress, chemicals, drugs, and toxins.

Both positive and negative factors can modulate the epigenome. For instance, positive factors such as enriched living conditions, like social interactions, physical activity, and changing surroundings, can promote beneficial epigenetic marks, while severe stress or agricultural chemicals can permanently alter some marks. These modifications can impact various aspects of an organism’s life during any phase of development, and can increase the susceptibility to diseases. For example, traumatic events and severe chronic stress in early life can alter the epigenome in a persistent and sometimes heritable fashion.

For example, Swedish scientists recently conducted investigations examining whether nutrition affected the death rate associated with cardiovascular disease and diabetes and whether these effects were passed from parents to their children and grandchildren (Kaati et al., 2002). These researchers estimated how much access individuals had to food by examining records of annual harvests and food prices in Sweden across three generations of families, starting as far back as the 1890s. These researchers found that if a father did not have enough food available to him during a critical period in his development just before puberty, his sons were less likely to die from cardiovascular disease. Remarkably, death related to diabetes increased for children if food was plentiful during this critical period for the paternal grandfather, but it decreased when excess food was available to the father. These findings suggest that diet can cause changes to genes that are passed down though generations by the males in a family, and that these alterations can affect susceptibility to certain diseases.

How Do Epigenetic Changes Affect Genes?

Epigenetics involves genetic control by factors other than an individual’s DNA sequence. Epigenetic changes can switch genes on or off and determine which proteins are transcribed. While epigenetic changes are required for normal development and health, they can also be responsible for some disease states. Disrupting any of the three systems that contribute to epigenetic alterations can cause abnormal activation or silencing of genes. Such disruptions have been associated with cancer, syndromes involving chromosomal instabilities, and mental retardation.

Epigenetics and Mental Retardation

Fragile X syndrome is the most frequently inherited mental disability, particularly in males. Both sexes can be affected by this condition, but because males only have one X chromosome, one fragile X will impact them more severely. Indeed, fragile X syndrome occurs in approximately 1 in 4,000 males and 1 in 8,000 females. People with this syndrome have severe intellectual disabilities, delayed verbal development, and “autistic-like” behavior (Penagarikano et al., 2007).

People who do not have fragile X syndrome have 6 to 50 repeats of the trinucleotide CGG in their FMR1 gene. Too many CGGs cause the CpG islands at the promoter region of the FMR1 gene to become methylated; normally, they are not. This methylation turns the gene off, stopping the FMR1 gene from producing an important protein called fragile X mental retardation protein. Fragile X syndrome is not the only disorder associated with mental retardation that involves epigenetic changes.

Are intelligence and/or education connected to epigenetics?

Many think about the question if a man with average intelligence genes during his life time educates and studies, and therefore “sharpens” his mind. Is his child is likely to be more intelligent than his father was genetically because his father sharpened his mind during his lifetime up to having his child? Or if the same process can be made to the child in order to sharpen his own intelligence?

There is a research with worms and with mices regardin a genetic defect from the enriched mother to her offspring during embryogenesis (transgenerational transmission) but nothing related to humans and because epigenetic changes. The precise mechanisms for how changes in the epigenenome affect intelligence have not yet been established.

Behavioral epigenetics

The first documented example of epigenetics affecting behavior was provided by Michael Meaney and Moshe Szyf. While working at McGill University in Montréal in 2004, they discovered that the type and amount of nurturing a mother rat provides in the early weeks of the rat’s infancy determines how that rat responds to stress later in life. This stress sensitivity was linked to a down-regulation in the expression of the glucocorticoid receptor in the brain. In turn, this down-regulation was found to be a consequence of the extent of methylation in the promoter region of the glucocorticoid receptor gene. Immediately after birth, Meaney and Szyf found that methyl groups repress the glucocorticoid receptor gene in all rat pups, making the gene unable to unwind from the histone in order to be transcribed, causing a decreased stress response. This pioneering work in rodents has been difficult to replicate in humans because of a general lack of availability human brain tissue for measurement of epigenetic changes.

Regarding stress, studies in rats have shown correlations between maternal care in terms of the parental licking of offspring and epigenetic changes. A high level of licking results in a long-term reduction in stress response as measured behaviorally and biochemically in elements of the hypothalamic-pituitary-adrenal axis (HPA). The opposite is found in offspring that experienced low levels of licking, and when pups are switched, the epigenetic changes are reversed.

In psychopathology and mental health environmental and epigenetic influences seem to work together to increase the risk of addiction. For example, environmental stress has been shown to increase the risk of substance abuse. Similar influences seem to happen in Major depressive disorder, Suicide, Psychopathy, Bipolar disorder, Schizophrenia, Major depressive disorder were much of the work in animal models has focused on the indirect downregulation of brain derived neurotrophic factor (BDNF) by over-activation of the stress axis. Studies in various rodent models of depression, often involving induction of stress, have found direct epigenetic modulation of BDNF as well.

Some researchers note that epigenetic perspectives will likely be incorporated into pharmacological treatments and to reprogram epigenetic changes to help with addiction, mental illness, age related changes, memory decline, and other issues.

This is the kind of soft inheritance related to a previous epigenetic inheritance.

Conclusion

That DNA is not everything it does not mean that DNA can be changed by education or by the environment. The nurture debate of intelligence and that the environment plays a key role in children’s intelligence scores, it can not be supported by epigenetics. It is important to understand the origin and real meaning of nature vs. nurture in Genetics, and to comprehend the meaning of the environment influence once talking within this field of biology. The future research by epigenetics, it could be useful with the next generation of tests and treatments for mental disorders.

References

Does Environment Influence Genes? Researcher Gives Hard Thoughts On Soft Inheritance

https://www.sciencedaily.com/releases/2006/08/060807154715.htm

wikipedia

https://en.wikipedia.org/wiki/Epigenetics

Florence Goodenough (1886-1959), American Psychologist

http://www.indiana.edu/~intell/goodenough.shtml

Article Title: The Pioneering Work of Leta Hollingworth in the Psychology of women

http://www.nebraskahistory.org/publish/publicat/history/full-text/NH1975Hollingworth.pdf

Inherited epigenetic variation — revisiting soft inheritance

http://www.nature.com/nrg/journal/v7/n5/full/nrg1834.html

The behavior of a person’s genes doesn’t just depend on the genes’ DNA sequence – it’s also affected by so-called epigenetic factors. Changes in these factors can play a critical role in disease.

http://www.nature.com/scitable/topicpage/Epigenetic-Influences-and-Disease-895

The transgenerational inheritance of autism-like phenotypes in mice exposed to valproic acid during pregnancy.

https://www.ncbi.nlm.nih.gov/pubmed/27819277

Transgenerational rescue of a genetic defect in long-term potentiation and memory formation by juvenile enrichment.

https://www.ncbi.nlm.nih.gov/pubmed/19193896

Stable inheritance of an acquired behavior in Caenorhabditis elegans

http://www.cell.com/current-biology/abstract/S0960-9822(10)01003-1

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