r.i.p. blank slate (and what does “the environment” mean anyway?)

so the mother of all meta-analyses of twin studies and the heritability of human traits was published the other day: “Meta-analysis of the heritability of human traits based on fifty years of twin studies” [pdf].

the authors looked at “17,804 traits from 2,748 publications including 14,558,903 partly dependent twin pairs, virtually all published twin studies of complex traits.” 14.5+ MILLION twin pairs! as james thompson said, this study pretty much represents “the mother of ‘F*** Off’ samples.” (~_^) in future, if someone says to you that twin studies were debunked a long time ago, blah, blah, blah, just point them to this paper.

and the upshot is: we are not blank slates. we never were.

from the paper, “[A]cross all traits the reported heritability is 49%.” in other words, these researchers found that pretty much half of the variance in all sorts of physical and behavioral traits in humans — the differences that we see between people — can be accounted for by genetics.

here’s a key table from the paper. i took the liberty of jiggling it around a bit so it would fit better on the blog (h2 is what you should be looking at here — that’s narrow sense heritabilty):

twin studies meta-analysis

the press has picked this up as there being an even split between nature and nurture, genes versus “the environment.” here, for example, from the huffington post*:

“Nature Or Nurture? The Long-Running Debate May Finally Be Settled”

“It’s an age-old debate: do our genes make us who we are, or is it the environment in which we were raised?

“There’s long been agreement that both ‘nature’ and ‘nurture’ play some role in determining many aspects of our physical and mental selves, from our height and weight to our intelligence and disposition. But as to which plays the bigger role in shaping us, scientists have never seemed to agree.

“That debate may now be over, thanks to a sweeping analysis of studies conducted around the world for more than five decades. The analysis — involving more than 14.5 million twin pairs from 39 countries — indicates that nature and nurture are virtually tied.

“Across all of our traits, in other words, genes and environment exert equal influence.”

yeeeessss…but what is “the environment”? on hearing that most people will think of things like reading bedtime stories to kids or playing mozart to your unborn fetus. but those sorts of things are decidedly not what the environment is in this context. from kevin mitchell of wiring the brain:

i’ve blogged this before, but i think we all need to read it again — from steven pinker on “the environment”:

“Even the technical sense of ‘environment’ used in quantitative behavioral genetics is perversely confusing. Now, there is nothing wrong with partitioning phenotypic variance into components that correlate with genetic variation (heritability) and with variation among families (‘shared environment’). The problem comes from the so-called ‘nonshared’ or ‘unique environmental influences.’ This consists of all the variance that is attributable neither to genetic nor familiar variation. In most studies, it’s calculated as 1 – (heritability + shared environment). Practically, you can think of it as the differences between identical twins who grow up in the same home. They share their genes, parents, older and younger siblings, home, school, peers, and neighborhood. So what could make them different? Under the assumption that behavior is a product of genes plus environment, it must be something in the environment of one that is not in the environment of the other.

But this category really should be called ‘miscellaneous/unknown,’ because it has nothing necessarily to do with any measurable aspect of the environment, such as one sibling getting the top bunk bed and the other the bottom, or a parent unpredictably favoring one child, or one sibling getting chased by a dog, coming down with a virus, or being favored by a teacher. These influences are purely conjectural, and studies looking for them have failed to find them. The alternative is that this component actually consists of the effects of chance – new mutations, quirky prenatal effects, noise in brain development, and events in life with unpredictable effects.

“Stochastic effects in development are increasingly being recognized by epidemiologists, frustrated by such recalcitrant phenomena such as nonagenarian pack-a-day smokers and identical twins discordant for schizophrenia, homosexuality, and disease outcomes. They are increasingly forced to acknowledge that God plays dice with our traits. Developmental biologists have come to similar conclusions. The bad habit of assuming that anything not classically genetic must be ‘environmental’ has blinkered behavioral geneticists (and those who interpret their findings) into the fool’s errand of looking for environmental effects for what may be randomness in developmental processes.”

and more from kevin mitchell:

“Just because some trait is not genetic does not mean it is not innate. If we are talking about how the brain gets wired, any number of prenatal environmental factors are known to have large effects. More interestingly, however, and probably a greater source of variance across the population, is intrinsic developmental variation. Wiring the brain is a highly complex procedure, reliant on cellular processes that are, in engineering terms, inherently ‘noisy’. Running the programme from the same starting point (a specific genotype) does not generate exactly the same output (the phenotype) every time. The effects of this noise are readily apparent at the anatomical level, when examining the impact of specific mutations, for example. In many cases, the phenotypic consequences are quite variable between genetically identical organisms, or even on two sides of the same brain. (If you want to see direct evidence of such developmental variation, take a directly face-on photograph of yourself, cut it in half and make mirror-image copies of the left and right sides. You will be amazed how different the two resultant faces are).

If the way the brain is wired is determined, not just by the starting genotype, but, to a large extent by chance events during development, then it is reasonable to expect this variation to be manifest in many psychological traits. Such traits may thus be far more innate than behavioural genetics studies alone would suggest.

in other words, it’s NOT genes + environment (or nature + nurture) — not as most people would think of it anyway. it’s genes + shared environment (which, since it’s shared, i.e. the same for the individuals in question, oughtn’t to make a difference, right?) + nonshared environment (which can include de novo mutations and development noise, which also may be heritable! iow, variation itself might be a genetic trait.). not much room for the effects of nurture here.

so, when you see a figure like 51% for “environmental” causes behind the differences we see in traits between people, remember that that very much includes biological causes like new mutations that are particular to individuals and developmental “noise,” which again may ultimately be regulated by genes.

(and, no, it’s not epigenetics either! see here and here and here.)

h/t once again to jayman for cluing me in on this in the first place! (^_^)
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*to give credit where credit is due, the huff post journalist did mention that part of what’s included in “the environment” is measurement error. that is correct. edit: see comment below about measurement error. so the 49% heritabilty figure should be considered a very conservative figure.

p.s. – there’s even a dedicated website where you can have a look at all the heritability numbers for yourself. enjoy!

see also: Gone with the Wind from dr. james thompson, Nature, nurture and noise from kevin mitchell, and About Developmental Noise and Environmental Hereditarianism from jayman.

previously: it’s not nature and nurture…

(note: comments do not require an email. the blank slate.)

top ten list 2014

here’s a top ten-ish selection of my posts from this year, selected by me (this blog is not a democracy! (~_^) ). they weren’t necessarily the most read or most commented upon posts, but just the ones that i like the best and that i’d like people to read. ymmv!

a BIG thanks to all of you who do read the ol’ blog! and many, many thanks for all the informative and insightful comments. (^_^) …and for some of the crazy comments, too. (~_^)

big summary post on the hajnal line“so, apart from indicating patterns of nuptuality in late medieval and modern europe, hajnal’s line also represents the extent of both manorialism and The Outbreeding Project on the continent. both of these together set up a very new and different sort of social environment for western europeans — a new, and quite unique, social environment which exerted some very different sorts of selection pressures on the populations, particularly on social behaviors, but perhaps on other traits as well.”

medieval manorialism’s selection pressures“medieval society in northern europe (ca. 400-1500 a.d.) produced some quite unique selection pressures which very much shaped the characteristics and personalities of ‘core’ europeans….”

die ostsiedlung“from a sociobiological point-of-view, probably the most underappreciated event in recent western european history. that and the reconquest of spain.”

mating patterns of the medieval franks“by the 800s, second cousin marriages amongst the franks were considered ‘scandalous.’ bishops actively enforced the bans in their dioceses and neighbors willingly squealed on their cousin-marrying neighbors to the bishops. by the 800s-1000s, there is good evidence that both the frankish aristocracy and the lower classes avoided close cousin marriage.” — see also: kindreds, communes, feuds, and mating patterns in medieval france“beginning in the 1000s, there are indications — the rise of lineages and the appearance of communes — that the french kindreds were starting to break apart. however, feuding continued in france into the 1200-1300s, so clannishness did not disappear in france overnight.”

the transition from shame to guilt in anglo-saxon england (and “core” europe)“feelings of guilt were probably selected for over the course of the middle ages in northwestern europe starting in the early part of the period.” — see also: more on the origins of guilt in northwestern european populations“the center of the guilt culture in northwestern europe — the core region which (historically anyway) has been characterized by the least corruption, the highest levels of trust, liberal democracy, free societies, low levels of internal violence, high levels of human accomplishment, the invention of capitalism, the advancement of science, the development of the ideas and ideals of the enlightenment, and pretty much everything else we call western civilization today — is the core where The Outbreeding Project began the earliest in europe.”

sneak preview: violence, punishment, outbreeding, and swashbuckling pirates in medieval england“over the course anglo-saxon period…the death penalty did come to be more widely applied to cases of homicide, but for most of the period there weren’t really very many executions of killers…. more laws demanding the death penalty (or castration) for killings were issued and enforced during the anglo-norman and angevin periods… [but] executions actually remained comparatively low during large parts of the norman period…. as far as i can tell, criminals were executed right and left during the tudor period. the use of capital punishment really ramped up during the 1500s.” — see also: homicide rates in various regions of thirteenth century england“[I]t is possible that every person in England in the thirteenth century, if he did not personally witness a murder, knew or knew of someone who had been killed.”

a study in swiss“my guess is that the swiss are some of western europe’s ‘inbetweeners’ as far as outbreeding goes. i guessed that they probably got involved in The Outbreeding Project later than some other western europeans — the ones in and closer to the center of my ‘core’ europe. and they didn’t experience manorialism either (unless some of them on the swiss plateau did?).”

reverse renaissance?“perhaps the arabized world underwent a *reverse* renaissance process thanks to the introduction by the arabs of the most inbred form of cousin marriage — father’s brother’s daughter (fbd) marriage — to the populations of the middle east/maghreb….” — see also asabiyyah and asabiyyah ii – clannishness and the abbasid caliphate.

fbd cousin marriage and clans and tribes in iraq“i think a long term inbreeding society selects — or *can* select — for what i call clannishness. and iraqis have got that in spades. they’ve got clans and tribes, nepotism, and an obvious inability to handle liberal democracy. not that that’s some sort of goal in and of itself. i’m just sayin’.”

cousin marriage in sub-saharan africa“there is also a wide variety of mating patterns in ss africa. some populations avoid cousin marriage altogether. we’ve already seen this with the bamileke of cameroon and the igbo of nigeria. also the turkana of kenya and quite possibly the amhara of ethiopia (not 100% sure about them — need to double-check). a notable group which apparently avoids cousin marriage is the zulu. but plenty of other ss africa groups do practice cousin marriage like, as you’ll see in the table below, the kongo and luba in the democratic republic of congo, the ashanti in ghana, the sotho-tswana in south africa, and the kpelle of liberia.” — see also: the bamileke of cameroon and fulani, hausa, igbo, and yoruba mating patterns.

the american revolutions“that there were four american revolutions is a result of the fact that four (five?) somewhat different english populations settled in different regions of north america. the cultural and attitudinal differences between these regions persist to this day because, undoubtedly, there are genetic variations between the populations — probably average genetic differences in the frequencies of genes related to behaviors, personality, and even intelligence. these regional differences also persist because, since the very founding of the united states, like-minded people have been self-sorting themselves within the country so that they group together — and that sorting process has *not* been slowing down.”

it’s not nature and nurture…“…it’s nature and…*we dunno*…miscellaneous/unknown/noise?” — this post's actually very important. READ THIS POST! think about it for a while and let it sink in. and make sure to follow the links!

– my "what is hbd" series: what is human biodiversity (hbd)?“human biodiversity (hbd) is very simply the diversity found among and between human populations that has a biological basis.” — see also: what human biodiversity (hbd) is not; examples of human biodiversity (hbd); why human biodiversity (hbd) is true; hbd and racism; and hbd and politics.

– and finally: you and me and hbd“if you accept that humans exhibit biologically based diversity, then you’d better be prepared to accept ALL of it.”

previously: top ten list 2013