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I received a free copy of this to review through the Amazon Vine programme. It's a lengthy textbook and I won't be finished anytime soon. But reading the introduction and initial chapters is enough to discern a profession transitioning through intellectual crisis.
Here are my notes so far.
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"We do have a scientific paradigm for psychology. We know that genes and environment construct brains, brains produce behaviour. Individual differences in genome plus environmental divergences result in non-identical brains, differences which have a measurable effect on neuroanatomy .. and thence on behaviour.
From behavioural genetics we know that the heritability of psychological traits is generally more than 50%. Nurturing differences are often really the consequence of genetic correlations: disturbed parents tend to have disturbed children. Heritability in action. Non-shared environmental effects (eg not family) typically have random and transient effects on psychological traits such as personality and intelligence. Real abuse and damage always excepted.
Psychology sort of knows this and sort of doesn't. There are researchers who know what a GWAS is, who know their way round a brain scan. And then there is the long legacy of pure nurturism: behaviourism, psychoanalysis, attachment theory, sociomoral reasoning, social information-processing theory and so on.
These one-sided plausible-sounding abstractions of commonplace observations have sadly produced neither real insight, reproducible results nor consistently-effective interventions. In many cases large scale experiments using twin studies and GWAS have shown that their conclusions are simply false. Perhaps though this will change, now we're beginning to really understand the etiology of normal and abnormal psychology. Robert Plomin's "Blueprint" is a readable review covering all these points.
All this has additional force in the case of forensic psychology. But who would wish to be in the position of the textbook editor in 2018, forced to straddle competing and incompatible paradigms while maintaining that forensic psychology is a mature discipline on firm foundations, whose professionals can be relied upon in the investigation process, in court and during the follow-on treatment of prisoners.
Forensic psychology has two main aspects: the legal aspect deals with evidence, witnesses and the courts while the criminological aspect deals with crime and criminals. Our textbook starts by reviewing theories addressing the causes of crime: why do criminals offend and what is the effect on their victims? As mentioned above there are many kinds of theory, and they tell very different kinds of story.
Here is an illustrative quote (p. 58, section 2.2.1 - LCPs are life-course persistent offenders).
“The main factors that encourage offending by the LCPs are cognitive deficits, an under-controlled temperament, hyperactivity, poor parenting, disrupted families, teenage parents, poverty and low socioeconomic status (SES).
Genetic and biological factors, such as a low heart rate, are also important (see Chapter 4).”
Of course all of the so-called main factors on the first list are strongly heritable, and therefore have substantial genetic causation which would be captured by a polygenic score (not mentioned in the copious index).
Amazing to read this in a 2018 textbook."
Full review here.
Two comments:
ReplyDelete1. From the point of view of criminology, it is not incorrect to say that someone is a persistent offender because they have trouble controlling their temper, even if ultimately, this is largely a result of their genetic makeup. The information that someone has a short temper is both easier to obtain, and more informative than a polygenic score indicating a high likelihood of a short temper.
2. While Plomin's book is remarkable, and his scientific work even more so, I feel he goes a little too far in his complete dismissal of environmental effects. Surely, this is partly a natural response to decades of bias in the opposite direction in the social sciences (what you call "nurturism").
Consider for example drugs affecting the endocrine system or more simply, hormonal supplements. These very clearly have measurable, biologic effects, which can be cumulative over years, quite literally transforming one person into another, both physically and behaviorally. Of course, the effects are still constrained by genes and will vary across different individuals (which is what Plomin means by "random": not systematic, due to different genotypes interacting differently with the same environment). But the effects are undeniable, and certainly qualify more as nurture than nature.
Plomin's treating "abuse" as an entirely different category is also somewhat suspect to me. Abuse comes in degrees, just like everything else, and Plomin himself insists that "abnormal is normal". If abuse can have measurable effects, it stands to reason that milder forms of abuse have milder effects. Discontinuities are quite rare in nature, and I don't think Plomin explains what property of abuse makes it special as far as having an effect goes, and why that property is lacking in milder but still severe of types of environmental interactions.
To be clear, I fully accept the statistically robust results presented in Plomin's book. I am just wondering how much environmental variation there really was in his samples. Concretely: what counts as a normal childhood in Uganda or even Russia might well be considered "abuse" in England.
1. If you want to gauge a phenotype and you have a test for that and additionally a well-validated polygenic score, then with heritability < 1 and an accurate test, the test is better. Sometimes you don't have an available/adequate test, though.
Delete2. I see existing estimates of the genetic contribution to phenotypical variance as a floor, a lower bound (due to small sample sizes, PGS noise, test imprecision, additive only, etc) but plainly for many phenotypical outcomes the heritability ceiling will always be less than 1. MZ twin studies provide a good indication of the real strength of genetic constraints (how often do we see really qualitative life-course differences between identical twins?).
I agree that Plomin's treatment of (non-shared) environment is one-sided and somewhat superficial, probably to make his message less nuanced and to counteract the dominant paradigm of nurturism as you indicate.