“The Nature-Nurture Debate and Founding of Behavioral Genetics… The Eugenics Movement… What is Behavioral Genetics? … The John/Joan Case… Phenylketonuria (PKU)… Supplemental – Huntington Disease…”
Module A: The Nature-Nurture Debate and Founding of Behavioral Genetics
Module B: The Eugenics Movement
Module C: What is Behavioral Genetics?
Module D: The John/Joan Case
Module E: Phenylketonuria (PKU)
Module F: Supplemental - Huntington Disease
Module A: The Nature-Nurture Debate and Founding of Behavioral Genetics
Place behavioral genetics in historical context.
Plato is probably the first known eugenicist – to design the ideal society, he argued that the best males and best females should be identified, and they should (he developed a marriage quotient).
Shakespeare helped to define the nature-nurture debate: in The Tempest, he describes Caliban as a “A devil, a born devil on whose nature/Nurture can never stick”.
But nature-nurture is most associated with Sir Francis Galton, who is considered the founder of behavioral genetics.
Galton wanted to apply Darwinian principles to the developing discipline of psychology.
Through his studies of eminent men and their relatives, he concluded that that nature prevails greatly over nurture, but he did not completely dismiss the role of nurture.
His students however took the ideas to a logical extreme e.g. our future are determined at the moment a baby is conceived i.e genetic determinism.
At the same time, there was a Eugenics movement i.e. the science devoted to trying to improve the human species by affecting who reproduces (and who does not), and this could tackle social problems.
Genetics determinism and the Eugenics movement undermined the emerging field of behavioral genetics.
Hard to imagine how the Eugenics movement was so popular but it was.
A few possible reasons:
at the end of the Industrial Revolution, as people crowded into cities, many social issues arose as well, and many were worried how to deal with these social issues;
the Industrial Revolution made more affluent, and with affluence, reproduction declined (called a demographic transition).
Some members of the scholarly elite and intellectuals – including some of Francis Galton’s students – hence either advocated (or sympathised) that the solution was to ensure the right people reproduced (and that the wrong did not).
They made cost-benefit analysis, promoted their causes e.g. fitter family contests at State Fairs, influenced public policy, enacted legislation, lobbied for sterilization laws etc.
They were successful in raising the popularity e.g. the name Eugene was very popular then.
The Eugenics movement however was taken up by the Nazis, leading eventually to the Holocaust; when it became known that eugenics had influenced the Nazis, the Eugenics movement quickly became unpopular (and the name Eugene declined in popularity as well).
When this happened, by association, behavioral genetics became an area of research many did not want to be a part of.
Publishing in behavioral genetics mirrored this rise and decline in interest; by the 1940s to 1950s, not many psychologists were doing behavioral genetics research.
This void was filled by an idea that swung to the opposite of genetic determinism: radical behaviorist movement i.e. every one is born a blank slate and we can turn that into anything the person wanted; this dominated psychology discourse for more than a generation.
It was only in the 60s and 70s that there was research in twins and behavioral genetics again.
Definition: area of physiology that involves the use of genetic methodologies to study the nature and origins of individual differences in human behavior.
Three things to note:
use of genetic methodologies (behavioral genetics is a field under psychology, not genetics);
interest in individual differences such as schizophrenia and IQ (as opposed to what is common across humans e.g. how memories work, which are the realm of evolutionary psychology);
use of the methodologies to understand the origins of the individual differences e.g. heritability coefficient.
Even though many people misunderstand that behavioral genetics is about establishing behaviour is heritable, research has yielded very significant insights about the influence of the environment too.
The John/Joan case represents the height of blank slate thinking.
This case involves gender behavior: John Money, from John Hopkins University, developed the theory of gender neutrality, believing that people were born gender neutral and become male and female based upon the interactions with others.
John/Joan case refer to Bruce and Brian Reimer, a pair of monozygotic twins. The twins had to be circumcised but during the circumcision, there was a device malfunction Bruce’s penis was burnt away.
Money thus suggested turning Bruce into a girl, changing his name to Brendan, dressing him as a girl, and keeping the identity secret.
Unfortunately, Brenda did not grow up happy and became suicidal, and the age of 15, Brenda was told about her past. Her immediate reaction was bewilderment, but she was also relieved that there was finally an explanation for how she felt.
She quickly changed back into a boy and took the name David Reimer, and went on to share his story with others.
He married in early 30s, was a good father (to his wife’s kids), but at the age of 38, he committed suicide (we do not really know why).
His struggles illustrate the extent the blank slate mentality dominated psychology.
About the human genetic disorder phenlyketonuria (PKU), and this case study illustrates three basic principles:
gene function i.e. some genes code for behavior, others for biological functions etc;
pleiotropy i.e. genes do not have one effect, but multiple effects;
gene environment interaction i.e. genes don’t work in opposition but together with the environment.
PKU was Discovered in 1934 by a Norwegian pediatrician called AsbjØrn FØlling
Untreated individuals with PKU have these symptoms:
will have IQs below 50;
are irritable, hyperactive and subject to seizures;
have eczema, hypo pigmented skin and musty odor.
PKU is a defect in the enzyme that exists in the liver called phenylalanine hydroxylase:
it is responsible for converting phenylalanine to tyrosine.
it is coded for by a gene, and people with PKU have two deficient forms of that gene (for every gene, humans have two copies i.e. two alleles).
With two deficient forms of this gene, a functioning enzyme cannot be produced.
Since there is a defect in the enzyme phenylalanine hydroxylase, the phenylalanine we consume from our food – which humans have to as phenylalanine is an essential amino acid i.e. our body needs it but doesn’t produce enough of it, so we get it through our diet too – is not converted to tyrosine but channeled into another pathway in the body.
This other pathway turns out to be neurotoxic, resulting in symptoms such as intellectual disability and metabolic products that give the musty order.
PKU thus illustrates
how genotype (the genes inherited) are expressed as phenotypes (the symptoms);
pleiotropy – because there are many symptoms/effects.
PKU also illustrates gene environment interaction because a treatment program exists:
reduce/regulate phenylalanine intake (not all as you need some) very soon from birth (the mother’s system takes care of PKU prenatally);
consume tyrosine supplements;
screen for PKU for newborns through a genetic test.
All these greatly reduce the incidence and effects of PKU – because this intervention has been a big public health success – thus illustrating gene environment interaction – it is every geneticists’ favorite disorder to talk about.
Note: Women who had PKU but are no longer on the PKU diet will produce children with very high level of intellectual disability because the high levels of phenylalanine in their blood system is very toxic to the brain of the fetus.
Lesson ends with a summary of Unit 1’s key topics.
Huntington Disease illustrates three concepts that will be discussed in the course:
In general, genetic disorders are genetic variants and differences in DNA sequences, and these have varying frequencies across different groups and populations;
Inheritance of genes does not actually follow Mendel’s Laws;
Issues related to how humans will respond to the molecular diagnostics of genetic disorder.
What is Huntington Disease?
If a person has 36 or more CAG repeats in this gene on chromosome 4, he or she will develop Huntington disease:
the larger the number of repeats, the earlier the onset age
the number of repeats is more likely to increase if the father is transmitting the gene than if the mother
Neurologically degenerative disorder with symptoms like involuntary motor movements, loss of cognitive functions, and dementia;
It is a progressive illness, and typically a person would die 15 to 20 years after onset;
About 13 to 15% of people with this disease commit suicide;
It is much more common among individuals of European ancestry (from 1 out of 10,000 to 20,000) to East Asia’s 1 out of 200,000;
On average, the age of onset is about 3.5 years earlier if you inherited the mutation from the father than from the mother, and age of onset becomes progressively earlier as you move from the parent generation to the offspring generation.
It was the first classic human genetic disorder to have a pre-morbid diagnostics test; developed in 1993, it raised many questions because it was a death sentence should the test results be positive.
Majority of at-risk individuals would say yes to a test, but only 10% actually do;
How would the individual diagnosed with it cope with it psychologically;
How would the larger family deal with it
All these raises one question: as genetic information becomes more prevalent in future, how will future generations use and respond to it?
