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For example, personally I'm quite irritable. It's not hard to irritate me and I swear either through an inner voice or whisper very often, but not out-loud. That does not happen very often. This is hardly likely due to some temporal cause.

But at the same time it seems there are people who are less irritable. How much of this is due to nature and how much is due to nurture? Are there any studies?

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  • $\begingroup$ Do I use wrong term? Correct me then, please. $\endgroup$ – rus9384 Sep 27 '18 at 0:09
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    $\begingroup$ How is this opinion-based? I'm asking for studies, for example, for studies no its heretability. Other factors should be here as well. $\endgroup$ – rus9384 Sep 27 '18 at 8:29
  • $\begingroup$ I up-voted, but the issue I see with your question (which you might not be aware of) is that irritability is a pretty broad concept. Various aspects of it have shown various degrees of heritability. $\endgroup$ – Fizz Sep 28 '18 at 2:05
  • $\begingroup$ I accidentally removed the close-vote, but the question is indeed too vaguely defined. $\endgroup$ – AliceD Sep 28 '18 at 8:02
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Irritability is a pretty broad concept. Various aspects/measures of it have shown various degrees of heritability. For example, just in one twin study (Coccaro, 1997):

To determine the degree of genetic and environmental influences on assessments of aggression and irritability in male subjects, the "Motor Aggression" subscales of the Buss-Durkee Hostility Inventory (BDHI) were mailed to 1208 male twins in the Vietnam Era Twin Registry. Data from monozygotic 182 and 118 dizygotic twin pairs were available and were analyzed using model-fitting procedures. Three of the four BDHI subscales demonstrated significant heritability of a nonadditive nature: 40% for Indirect Assault, 37% for Irritability, and 28% for Verbal Assault. Additive genetic variance accounted for 47% of the individual differences for Direct Assault. Nonshared, but not shared, environmental influences contributed to explaining the variance in the model, with estimates ranging from 53% (Direct Assault) to 72% (Verbal Assault). Because some of these BDHI scales have been shown to correlate with indices of central serotonin function, it is possible that impulsive aggression, as reflected by these scales, is heritable in men.

And a study from the genomic era (Riglin, 2017), alas only on irritability in children:

Severe irritability is one of the commonest reasons prompting referral to mental health services. It is frequently seen in neurodevelopmental disorders that manifest early in development, especially attention-deficit/hyperactivity disorder (ADHD). However, irritability can also be conceptualized as a mood problem because of its links with anxiety/depressive disorders; notably DSM-5 currently classifies severe, childhood-onset irritability as a mood disorder. Investigations into the genetic nature of irritability are lacking although twin studies suggest it shares genetic risks with both ADHD and depression. We investigated the genetic underpinnings of irritability using a molecular genetic approach, testing the hypothesis that early irritability (in childhood/adolescence) is associated with genetic risk for ADHD, as indexed by polygenic risk scores (PRS). As a secondary aim we investigated associations between irritability and PRS for major depressive disorder (MDD). Three UK samples were utilized: two longitudinal population-based cohorts with irritability data from childhood (7 years) to adolescence (15–16 years), and one ADHD patient sample (6–18 years). Irritability was defined using parent reports. PRS were derived from large genome-wide association meta-analyses. We observed associations between ADHD PRS and early irritability in our clinical ADHD sample and one of the population samples. This suggests that early irritability traits share genetic risk with ADHD in the general population and are a marker of higher genetic loading in individuals with an ADHD diagnosis. Associations with MDD PRS were not observed. This suggests that early-onset irritability could be conceptualized as a neurodevelopmental difficulty, behaving more like disorders such as ADHD than mood disorders.

Note that since polygenic risk scores currently only cover a small fraction of the heritability found in twin studies (for almost any psychiatric/psychological issue/construct), genomic results are rather tentative. Usually the presence of a gene overlap means something, but the absence of a genetic overlap can simply mean there hasn't been enough data.

And Riglin point out to a recent review Vidal-Ribas (2016) of which they are aware they cannot explain genomically. The latter found/concluded that

irritability forms a distinct dimension with substantial stability across time, and that it is specifically associated with depression and anxiety in longitudinal studies. Evidence from genetic studies reveals that irritability is moderately heritable, and its overlap with depression is explained mainly by genetic factors. [...]

The genetic contribution to the variation of irritability is approximately 30% to 40% in both adults and adolescents. This is close to the heritability estimates for depression and anxiety. Genetic influences on irritability increase slightly over time in males and decrease in females, and unique (as opposed to shared) environmental factors explain most of the remaining (non-genetic) variance in both.

I highly suggest reading this review if you're unfamiliar with the psychiatric approach to irritability because it has a good, detailed background on that (including the substantial changes in DSM-5, which were applied only to children though.) And since the focus on irritability as separate entity is pretty new in psychiatry, the authors of this review note for instance that

Probably the main limitation in the study and treatment of irritability so far is the lack of high-quality measures. Most of the measurement of irritability has been done with instruments created ad hoc, that is, through extracting items from existing scales or interviews that were not intended primarily to measure irritability.

For instance, the heritability data on adults they cited from Coccaro (1997) with which I started this answer, whereas for adolescents (as you probably guessed by now), there are newer studies available; the data cited on the latter in the review is from Stringaris (2012) and there's more specific longitudinal data in Savage (2015).

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  • $\begingroup$ Hm, strange that irritability is said to be linked to anxiety but not impulsivity (they are defined to be orthogonal, right?). I see that irritability requires greater self-control for the same impulsivity. $\endgroup$ – rus9384 Sep 28 '18 at 6:05
  • $\begingroup$ @rus9384: in the DSM approach nothing is defined to be orthogonal to something else. I don't know off the top of my head how correlated impulsivity and irritability would be. But neither have widespread instruments for measuring them; impulsivity is also a pretty broad concept see ncbi.nlm.nih.gov/pmc/articles/PMC4112948 $\endgroup$ – Fizz Sep 28 '18 at 6:20
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You will have to investigate quite a few factors:

  1. There must be a genetic/epigenetic factors to this because we know that personality trait neuroticism has genetic and environmental factors.

  2. You should also investigate into stress - biological and psychological stress.

  3. Investigating theories of psychological development can also come in handy, especially, Freudian theories.

In my personal view, I think a combination of genetic and environmental factors should play role in shaping irritability tolerance, however, additionally environment plays a role of stressor.

In other words, you should have genetics, epigenetics and upbringing as a predictors of general irritability. Immediate state of being can also have influence, but stressor is like a trigger.

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    $\begingroup$ Nice answer to an overly broad question! +1 $\endgroup$ – Steven Jeuris Sep 27 '18 at 8:36
  • $\begingroup$ @StevenJeuris, well, I think this answer is quite universal and applicable to any trait. $\endgroup$ – rus9384 Sep 27 '18 at 8:48
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    $\begingroup$ This answer highlights why a definitive answer would be primarily opinion-based. You can come up with evidence for genetic/epigenetic causes just as much as you can come up with evidence to support environment as a cause. Just like the fact that Freudian theories are considered by some to be pseudoscientific, the nature/nurture debate with many psychological theories still rages on today and may do for a very long time. $\endgroup$ – Chris Rogers Sep 27 '18 at 9:04
  • $\begingroup$ @ChrisRogers, I'm asking to what extent it is caused by nature and to what extent it is caused by nurture. If there are any evidences supporting that it is both nature and nurture or not. $\endgroup$ – rus9384 Sep 27 '18 at 10:12
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    $\begingroup$ @rus9384 - If you want a more extensive rundown on evidence for each, you could ask separate questions on each on reference-request tags. One question asking for both would be very broad as indicated earlier. $\endgroup$ – Chris Rogers Sep 27 '18 at 10:21

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