Editing Heritability (section)

==Overview==

Heritability measures the fraction of phenotype variability that can be attributed to [[genetic variation]]. This is not the same as saying that this fraction of an individual phenotype is caused by genetics. For example, it is incorrect to say that since the heritability of personality traits is about 0.6, that means that 60% of your personality is inherited from your parents and 40% comes from the environment. In addition, heritability can change without any genetic change occurring, such as when the environment starts contributing to more variation. As a case in point, consider that both [[gene]]s and environment have the potential to influence intelligence. Heritability could increase if genetic variation increases, causing individuals to show more phenotypic variation, like showing different levels of intelligence. On the other hand, heritability might also increase if the environmental variation decreases, causing individuals to show less phenotypic variation, like showing more similar levels of intelligence. Heritability increases when genetics are contributing more variation or because non-genetic factors are contributing less variation; what matters is the relative contribution. Heritability is specific to a particular population in a particular environment. High heritability of a trait, consequently, does not necessarily mean that the trait is not very susceptible to environmental influences.<ref>{{cite journal | vauthors = Maccoby EE | title = Parenting and its effects on children: on reading and misreading behavior genetics | journal = Annual Review of Psychology | volume = 51 | issue = 1 | pages = 1–27 | date = February 2000 | pmid = 10751963 | doi = 10.1146/annurev.psych.51.1.1 | s2cid = 43435035 }}</ref> Heritability can also change as a result of changes in the environment, migration, [[inbreeding]], or how heritability itself is measured in the population under study.<ref name=VisscherHillWray/> The heritability of a trait should not be interpreted as a measure of the extent to which said trait is genetically determined in an individual.<ref>{{cite journal | vauthors = Sauce B, Matzel LD | title = The paradox of intelligence: Heritability and malleability coexist in hidden gene-environment interplay | journal = Psychological Bulletin | volume = 144 | issue = 1 | pages = 26–47 | date = January 2018 | pmid = 29083200 | pmc = 5754247 | doi = 10.1037/bul0000131 }}</ref><ref>{{cite journal | vauthors = Block N | title = How heritability misleads about race | journal = Cognition | volume = 56 | issue = 2 | pages = 99–128 | date = August 1995 | pmid = 7554794 | doi = 10.1016/0010-0277(95)00678-r | s2cid = 204981536 }}</ref>

The extent of dependence of phenotype on environment can also be a function of the genes involved. Matters of heritability are complicated because genes may [[canalization (genetics)|canalize]] a phenotype, making its expression almost inevitable in all occurring environments. Individuals with the same genotype can also exhibit different phenotypes through a mechanism called [[phenotypic plasticity]], which makes heritability difficult to measure in some cases. Recent insights in molecular biology have identified changes in [[transcription (genetics)|transcriptional]] activity of individual genes associated with environmental changes. However, there are a large number of genes whose transcription is not affected by the environment.<ref>{{Cite journal | vauthors = Wills C | title = Principles of Population Genetics, 4th edition | doi = 10.1093/jhered/esm035 | journal = [[Journal of Heredity]] | volume = 98 | issue = 4 | pages = 382 | year = 2007 | type = Book Review | doi-access = free }}
* ''review of'': {{cite book | first1 = Daniel L. | last1 = Hartl | first2 = Andrew G. | last2 = Clark | name-list-style = vanc | title = Principles of Population Genetics | publisher = Sinauer and Associates | location = Sunderland, MA | year = 2007 | pages = xv + 652 | isbn = 978-0-87893-308-2 }}</ref>

Estimates of heritability use [[statistical analyses]] to help to identify the causes of differences between individuals. Since heritability is concerned with variance, it is necessarily an account of the differences between individuals in a population. Heritability can be [[univariate]] – examining a single trait – or multivariate – examining the genetic and environmental associations between multiple traits at once. This allows a test of the genetic overlap between different phenotypes: for instance [[hair color]] and [[eye color]]. Environment and genetics may also interact, and heritability analyses can test for and examine these interactions (GxE models).

A prerequisite for heritability analyses is that there is some population variation to account for. This last point highlights the fact that heritability cannot take into account the effect of factors which are invariant in the population. Factors may be invariant if they are absent and do not exist in the population, such as no one having access to a particular [[antibiotic]], or because they are omnipresent, like if everyone is drinking [[coffee]]. In practice, all human behavioral traits vary and almost all traits show some heritability.<ref>{{cite journal |last1=Turkheimer |first1=Eric |name-list-style=vanc |title=Three Laws of Behavior Genetics and What They Mean |url=http://people.virginia.edu/~ent3c/papers2/three_laws.pdf |access-date=29 October 2013 |journal=Current Directions in Psychological Science |volume=9 |issue=5 |date=October 2000 |pages=160–164 |issn=0963-7214 |doi=10.1111/1467-8721.00084 |s2cid=2861437 |archive-date=19 October 2013 |archive-url=https://web.archive.org/web/20131019043842/http://people.virginia.edu/~ent3c/papers2/three_laws.pdf |url-status=live }}</ref>