Heritability and why Parents (but not Parenting) Matter



To be blunt, most of what you think you know regarding why
parents matter is very likely wrong.

This article is written by Brian
Boutwell and Razib Khan

“…Who in the world am I? Ah, that’s the great

— Alice from Alice’s Adventures in
 by Lewis Carroll

Like Alice, we’ve all pondered the question: “who am I?”
 Moreover, we often couple it with the reasonable
companion query: “how did I get to be this way.”  Not all
of us are rich and famous, we can’t all bend guitar strings
like Hendrix, and most of us will never have supermodel looks
or the physical prowess of a professional athlete.  There
is fascinating unity in all of us, though, concerning how we
answer the question of “why am I this way” as opposed to some
other possible version of myself.  Whether we credit them
for our successes, or point at them as a hurdle that we had to
clear, most of us implicate our parents when constructing a
narrative about why we are the way that we are.  It’s not
an unreasonable intuition.  But how we intuit about the
world can mislead us; sometimes that “light at the end of your
tunnel” is, in reality, “just a freight train coming your
way.”*1 To be blunt, most of what you think you
know regarding why parents matter is very likely wrong.

You are the product of precisely two biological parents (even
the so-called, “three-parent babies” are somewhat of a
misnomer).  Whether you know them or not, whether you like
them or not, the fact that you have parents (and were, in fact,
not cloned from a prior version of yourself) carries with it
great consequences.  Yet, family socialization effects on
personality are not large, not prominent, and not pronounced
(and for many traits, they are absent).¹ What
parents do to their children (in particular,
their style of parenting and efforts at socialization) does not
leave permanent marks and does not differentiate individuals
within the population for outcomes like intelligence,
antisocial behavior, and a host of other
outcomes.1,2,3 So why then, are parents
consequential (beyond the obvious role that they play in
providing safety, shelter, etc.)?  How do we rectify the
apparent contradiction?

Let’s first discuss a term that has appeared frequently in our
discussions: heritability. Heritability represents the
proportion of variance in a particular trait that is explained
by genetic variance within the population. As we’ve described
before, heritability captures the role that genetic differences
play in making some people (relative to others) taller or
shorter, heavier or lighter, more intelligent or less
intelligent, so on and so
forth.1,2  Virtually every measurable
trait (which varies within the population), we now know, is
heritable. This reality has become
remarkably unimpressive to many behavioral geneticists, though
it continues to blindside some scientists who have managed not
to pay attention for the last several
decades.1,2,3  The shift among journal
reviewers has been remarkable to witness, really, moving from:
“there’s no way that trait X is heritable” to “of course trait
X is heritable, who cares?” or even the more dubious (and
disingenuous) “heritability is pointless, let’s talk about
epigenetics [or gene-environment
interaction]!”2,3 Changing sentiments aside,
heritability continues to be an extremely relevant point for
behavioral scientists to wrangle with.  Understanding why
it is important, moreover, will take us a long way to
understanding why parents (but not their parenting styles) are
of such monumental importance in explaining variation in

To complicate things just a bit, you should know that there are
two types of heritability: narrow and broad
sense.If you’ve ever heard the expression
(perhaps from a plant or animal breeder) that a trait “breeds
true” then you’re already informally acquainted with
narrow-sense heritability.*2  Heritability
in the narrow-sense captures variation that results from
additive genetic influence.Heritability in
the broad-sense includes other genetic effects which are
non-additive (i.e., also in a technical sense, they can be
non-linear).Imagine taking the effect of
every gene that influences a trait—most of which would be very
small—and adding them up; thus the term, “additive.”
 Additive traits tend to breed true—meaning that variable
characteristics manifest in the offspring in a similar (i.e.,
correlated) fashion to parents who possess such characteristics
(at the population level and individual level).

Non-additive effects don’t breed true with the same degree of
fidelity—in fact, these effects bust up the clean transmission
of traits from parents to children (to use a sports analogy,
it’s a bit like a cornerback in football deflecting the
quarterback’s perfect spiral aimed at the receiver).  Two
brown-eyed parents can give rise to blue-eyed children, for
instance.  Prior to Brother
 (just in case you weren’t aware, he was a monk)
ever fiddling with his first pea pod (peas; the bane of all
childhood existences), breeders were keenly interested in
whether they could breed for certain traits.  Could you
make the pigs fatter, or could you make the crops more disease
resistant or drought tolerant?  If the answer was yes,
then wealth and fame was surely in your future.  Knowing
something about the narrow-sense heritability of a trait was
important in that day and time, and it remains that way today.

We’re treading on delicate ground here because any time you
start to talk about breeding, genetics, and (gasp) humans, it
conjures up demonic specters.2,3 As if summoned
from some regrettable Ouija board session, the ghastly ghoul of
state-sponsored breeding programs comes barging into the room.
 We’ll assume that we’re all in agreement regarding the
moral repugnance of coercive eugenics, thus stipulating that
such programs should never (ever, ever, ad infinitum) return.
 The thing is, humans already have their own breeding
initiative, and they have for some time now.  If you don’t
believe us, consider for yourself how you picked a mate.
 Did it happen to be at random? No?  What possibly
could have gone wrong with that approach?  Think about it
another way; say that you signed up for a high dollar dating
service.  After several dud dates, and a subsequent phone
call with customer service, would you be pleased to find out
that your dates were being picked by the complex matching
algorithm known as flinging darts against a wall with photos
tapped on it?  If your answer is yes, then please stop
reading and let’s get you signed up for: www.Boutwell-KhanDatingServices.com;
our motto is: We throw darts as randomly as anyone, and we
offer coupons!

Individuals discriminate on a range of qualities when searching
for a mate.5,6  Even arranged marriages
can’t get around this reality.  The difference with an
arranged marriage, of course, is that it is often a more
“collective process”, with parents exhibiting increased control
and discernment (perhaps more than the newly betrothed would
like).  Regardless of who does the choosing (parents or
children), it isn’t done haphazardly.  The qualities of
emphasis might vary in some situations (for instance, whether
the goal is short term liaison versus long term partnership, it
might dictate what one is willing to tolerate in a
partner)5 but the process is still far from
random.  The qualities that humans prefer in their mates
(what men look for in women and vice versa), moreover, are
remarkably consistent across cultures.  There has been
some excellent work on this topic carried out by evolutionary
psychologists.5,6  Why does any of this
matter?  Remember the issue of “breeding true”; well it
applies to humans just like it applies to pea plants.
 First, though, we need to talk more about sexual (and
artificial) selection and foxes.

Famed biologist Richard Dawkins noted in his enjoyable (and
important) book “The Greatest Show on
7 that sexual (and artificial)
selection offers powerful evidence in favor of Darwin’s
arguments about natural selection.  It certainly does, and
conveniently for our purposes, it also provides a very useful
bit of insight.  Consider the landmark and very famous
work (highlighted by Dawkins) carried out on the selective
breeding of foxes
.8 The goal of the work,
in large part, was to better understand the processes of animal
domestication. Foxes displaying high levels of tameness (when
around a human) were bred with each other.  As it turns
out, if you continually cross one tame fox with another, what
you eventually get is an animal that starts to act (and even
look) more like a dog than a
fox.7,8  “Humans are not foxes!” objects
the incredulous critic. True, but we don’t get to play by
different rules (apologies to our creationist friends [and
sadly, to many sociologists*3]).  The same
evolutionary processes that apply to the fox and the hound (and
every other organism on the planet), apply to us.7,8

Now we are getting more to the meat of the issue.  Only a
few pieces of information are needed to know something about
what is likely to happen to a quantitative trait over time that
is selectively bred for in a population.9 All
that you need is the narrow-sense heritability of the trait
(h2), the mean for trait (or the average value of the
trait in the population), and the values possessed by the
parents on a certain trait, and you are in
business.9 Positive assortment for an extreme
value in a trait that is highly heritable  (e.g., tall
people pairing up with other tall people) is a mechanism for
altering the distribution of values for that trait in the
population.  You obtain a greater number of very tall
people (thus, shifting the mean for height upwards)!  This
is largely why parents matter, and this is also why knowing
something about the heritability of a trait remains important
Boutwell’s first essay
 on the topic of parenting for a
more methodological treatment of why h2 is

Consider an example that dovetails with the previous point.
 Criminologists (and psychologists) have been aware for
some time that criminal involvement runs in
families*4 and is also heritable (a good
portion of that heritability seems to be narrow-sense, though
not all; see quillette.com/#comments).
 The psychologist Robert Krueger and
colleagues10 some years back, provided evidence
that humans mate assortatively for antisocial and criminogenic
behaviors (put differently, highly antisocial individuals tend
to pair off with each other in a non-random fashion).
 Does this completely explain the concentration of crime
in certain families?  No.  Can it be safely ignored
and assumed to be irrelevant?  No.  Just as
narrow-sense heritability is a puzzle piece that can tell you
something about where the distribution of a trait could be
headed in a population, it also helps inform the question of
why certain traits cluster in families.9

An observant reader will argue that heritability is not a fixed
quantity; it is subject to change over time.  The finding
that the narrow-sense heritability of most personality traits
is about .50 (or slightly lower), for instance, does not mean
that it has always been that way, or that it will always be
that way.While true, this point doesn’t serve
as the ammunition for refuting the relevance of narrow-sense
heritability that some might think.  At any point in
history, the environment might explain more (or less) of the
variance in some trait.  Nonetheless, if that fact somehow
negated the import of h2 then plant scientists
and animal breeders should search for other ways to spend their
time—breeding programs would be impossible (and they are not).
 Now, if you listen even more closely, you can hear the
murmur of critics ready to hurl the objection of “epigenetics”
in our direction.  We knew it would come up; it inevitably
does these days.  But you must never forget that
epigenetics is not a “get out of jail free” card that grants us
immunity or exemption from evolutionary processes.  It
certainly does not make heritability obsolete.

If epigenetic effects are highly variable across generations,
given that the statistical methods used by behavioral
geneticists subdivide “environmental” effects from heritable
effects, then epigenetics will be included into that parameter
(i.e., one of the environmental parameters). Alternatively, if
epigenetic effects are highly transmissible across generations,
then they are to a large
extent heritable (an important point in its
own right that so many sideline enthusiasts gloss over).
 This comes, of course, with the necessary caveat that
strong environmental shocks can induce
epigenetic changes.  Importantly, extant empirical
research does not suggest (yet) that these sorts of heritable
epigenetic dynamics are pervasive enough to be problematic for
heritability estimates.  They likely exist, but
they are the exceptions
, not the rule.11


Over the course of two essays, I (Boutwell) have tried to walk
you through a series of topics that I see as incredibly
important in modern social science.
The first 
dealt with problems in social science
research (genetic confounding).  The largest takeaway
point was simply that you cannot trust most research because
most of it does not control for genetic influences on the
outcomes they study (and we know that these effects are
 The second
 essay dealt with the complexity of
ferreting out a parenting effect among the bewildering
complexity of gene-environment correlation and interactions.
 I also introduced you to the idea that epigenetics is
unlikely to be the savior that many thought it was guaranteed
to be.  For the third installment, Razib and I have tried
to illustrate a fundamental evolutionary point: heritability
matters.  Once again using parents as an exemplar.

Parents pass genes to their children.  In a Darwinian
sense, this is of incredible importance.  Darwin, the
brilliant scientist, prescient about so much, was nonetheless
unaware that genes were the “packets of inheritance”
responsible for making parents and progeny similar to one
another.  It took the “religious” devotion of a monk
(Mendel) to drive that point home.  Regarding those genes,
Richard Dawkins poetically pointed out that (p.20):

They are in you and in me; they created us, body and mind;
and their preservation is the ultimate rationale for our
existence. They have come a long way, those replicators. Now
they go by the name of genes, and we are their survival

Granted, this is probably not the defense of parents that you
wanted, but then again, we never promised to deliver
(necessarily) what you wanted.  We did intend to provide a
“big-picture” rationale for why parents matter and why
heritability does too.  In that regard, there is no better
way to make the point then evolutionarily.  Parents matter
because they pass genes from their generation to the next;
that’s a pretty big deal in our estimation.

If what you were looking for is an impassioned crusade for why
a certain approach to parenting is essential to civilized
society, you won’t find that here.  There are times when
it is best to let go of the feelings that you have regarding
how the world works. In many cases, your self-assurance
regarding your knowledge on some topic affords you little
protection from science (anyone joining up for
the Flat Earth Society these days?).
 Famed biologist Robert Trivers strained our intuitions
about the nature of parenting years ago by pointing out that
the interests of mom and dad are not always the same as their
filial creation (their child*5).  Behavior
genetic studies were the flood that further obliterated the dam
(for some context as to how parenting effects can be
reconsidered, see my previous essay How
to Find a Parenting Effect
).  Parenting styles in
the normal range of variation simply do not shed much insight
into why people differ.

So that you don’t depart this parenting trilogy feeling too
upset, though, consider a final point.  Your parents are
important to you.  Do you really need to
tack on the qualifier that they molded you like a ball of clay?
 In order for you to appreciate your parents, must it be
the case that they injected your personality directly into your
head?  They didn’t, they injected it into your DNA (lovely
image, right).  Your environment outside the home, as well
as pure luck and happenstance shaped it from there.  You
can still love and appreciate your parents, though.  Not
one thing must change.  So as not to break with tradition
from our first two parenting discussions, we leave you with the
insights of someone else.  This time, Paul Simon has the
last word.

“Still, a man hears what he wants to hear and disregards the


This article was originally published in


Razib Khan is
a writer and doctoral candidate in genomics at the University
of California. Follow him on Twitter: @razibkhan

Brian Boutwell is an Associate Professor of Criminology
and Criminal Justice at Saint Louis University. Follow him on
Twitter: @fsnole1



  1. Find us two other academics that can work Lewis Carroll and
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  4. For a striking example, see: Frisell, T., Lichtenstein, P.,
    & Långström, N. (2011). Violent crime runs in families: a
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    individuals. Psychological medicine, 41(01),
  5. Trivers, R. L. (1974). Parent-offspring
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  6. Simon and Garfunkel; The Boxer


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Tags: brian
, epigenetic
, genetics, heritability, parenting effects, razib khan

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