Birth Order and Siblings: What the Research Actually Shows

Birth order is one of the most popular
topics in popular psychology — and one
of the most misrepresented. The idea
that firstborns are responsible and
achievement-oriented, middle children
are overlooked and people-pleasing,
and youngest children are charming
and rebellious has become so embedded
in popular culture that many people
accept it as established fact.

The research tells a more complicated
and more honest story. This article
covers what the evidence actually
shows about birth order and personality,
what the real effects of birth order
are, and what parents need to know
to raise each of their children well.

The Popular Theory — and Its Origins

The birth order theory most familiar
to popular audiences was developed
by Austrian psychiatrist Alfred Adler
in the early twentieth century.
Adler proposed that the order in
which children are born into a
family significantly shapes their
personality, their approach to
relationships, and their life
trajectory — through the different
experiences, roles, and family
dynamics that each birth position creates.

Adler’s ideas were compelling and
intuitive — and they captured
something real about the different
experiences of children in different
birth positions. They were also
developed before the era of
rigorous empirical testing and
have not fared well under that testing.

What the Research Actually Shows

The most rigorous examination of
birth order and personality was
conducted by researcher Julia
Rohrer and colleagues at the
University of Leipzig, published
in 2015 in the Proceedings of
the National Academy of Sciences.
This study — using large national
datasets from the United States,
the United Kingdom, and Germany,
with sample sizes in the thousands —
examined the relationship between
birth order and the Big Five
personality traits: openness,
conscientiousness, extraversion,
agreeableness, and neuroticism.

The findings were striking in
their consistency: birth order
had no significant effect on
any of the Big Five personality
traits. Firstborns were not
more conscientious. Lastborns
were not more agreeable.
Middle children were not
more neurotic. The personality
differences that popular
psychology attributes to
birth order were simply
not there in the data.

Research by Tomas Chamorro-Premuzic
at University College London
on birth order and personality
reaches similar conclusions —
the effects of birth order
on personality, when studied
with appropriate controls
for family size, socioeconomic
status, and other confounds,
are minimal to nonexistent.

What Birth Order Does Affect

The absence of personality
effects does not mean birth
order has no effects at all.
Research identifies several
domains where birth order
does show consistent,
if modest, effects:

Intelligence and academic achievement.
Research by Petter Kristensen
and Tor Bjerkedal in Norway —
using a large sample of
military conscripts — found
a small but consistent firstborn
advantage in measured IQ.
Research by V. Joseph Hotz
and Juan Pantano on birth
order and educational outcomes
similarly finds a small firstborn
advantage in academic achievement.

The proposed mechanism —
the “tutoring hypothesis” —
suggests that firstborns
benefit from teaching younger
siblings, which consolidates
their own learning; and from
a period of exclusive parental
attention before siblings arrive,
which may support early cognitive development.

However the effect sizes are
small — a few IQ points on
average — and the practical
significance for individual
children is limited.

Parental investment and attention.
Research on parental behavior
toward different birth-order
children finds real differences
in the amount and type of
parental attention each child
receives — firstborns typically
receive more direct parental
teaching and more parental
attention overall, while
laterborns receive less
direct parental attention
but more sibling interaction.

These differences in parental
investment are real — they
reflect the genuine reality
that parents have more time
and energy for one child
than for several, and that
parental anxiety and attention
to developmental milestones
typically decreases with
subsequent children.

Risk-taking and novelty-seeking.
Research by Frank Sulloway at
UC Berkeley on birth order
and openness to experience
finds that laterborns show
somewhat more openness to
novel experience and risk-taking
than firstborns — a finding
he attributes to the evolutionary
logic of niche differentiation,
the tendency for siblings
to develop distinct identities
to compete for parental resources.
However Sulloway’s findings
have been contested by
subsequent researchers
and should be treated
with caution.

Why the Popular Theory Persists

If the research does not
support the strong birth
order personality effects
that popular psychology
describes, why does the
theory persist so strongly?

Confirmation bias. People
who know their birth position
notice and remember instances
that confirm the stereotype —
the responsible firstborn,
the rebellious youngest —
and discount or forget
the many instances that
do not fit.

Within-family versus
between-family comparisons.
Research by Judith Rich
Harris suggests that birth
order effects observed
within families — where
siblings genuinely do
occupy different roles —
largely disappear when
comparing people across
different families.
A firstborn child may
be more responsible
than their own younger
siblings while being
no more responsible
than firstborns in general.

The genuine reality
of different family experiences.
Birth order does create
genuinely different family
experiences — firstborns
do have a period of
exclusive parental attention,
laterborns do grow up
with siblings already
present, youngest children
do experience a different
family dynamic than oldest ones.
These different experiences
are real. Their effects
on personality are more
modest than the popular
theory suggests.

What This Means for Parents

The research on birth order
has several practical implications
for parents of multiple children:

Avoid birth order stereotyping.
Labeling children according
to birth order stereotypes —
“you’re the responsible one,”
“you’re the free spirit,”
“you’re the peacemaker” —
can become self-fulfilling
prophecies that constrain
children’s development
rather than describing it.

Be aware of differential
parental investment. The
research finding that
firstborns typically receive
more direct parental teaching
and attention is worth
being aware of — not
as a guilt-inducing fact,
but as something parents
can consciously work
to balance through
one-on-one time with
each child.

Recognize each child as
an individual. The most
important practical conclusion
from the birth order research
is that birth position
is a weak predictor
of who a child will be.
Temperament, individual
experience, and the
specific parent-child
relationship are far
stronger determinants
of personality and
development than
birth order.

Support sibling deidentification
positively. Research on
sibling relationships
finds that siblings
naturally differentiate
themselves from each other —
developing distinct interests,
strengths, and identities.
Supporting this differentiation
positively — celebrating
what is unique about
each child without
comparison — is more
beneficial than either
enforcing similarity
or allowing birth order
stereotypes to define difference.

Try This This Week

Practice 1 — The Individual Spotlight
What it is: A weekly
practice of deliberately
celebrating something
specific and unique
about each child —
independent of birth
order, independent
of comparison with siblings.

How to do it: Once a week,
find a moment with each
child individually and
share one specific,
genuine observation
about something you
noticed about them:
“I noticed this week
that you are really
patient when things
are difficult.”
“I love the way you
get completely absorbed
in the things you care about.”
“I noticed how kind
you were to your friend
when they were upset.”

The observation should
be specific, genuine,
and not comparative —
not “you’re more patient
than your brother”
but simply “you are patient.”

Why it works: Research
on parental differential
treatment and sibling
relationships finds that
children who feel
individually seen and
valued by their parents —
independent of comparison
with siblings — show
stronger self-esteem
and better sibling
relationship quality
than those who feel
their identity is
defined primarily
by their position
in the family.

Practice 2 — The One-on-One Date
What it is: A regular,
predictable one-on-one
time with each child —
protected from sibling
interruption — that
communicates individual
value and provides
the individual parental
attention that research
finds beneficial for
all birth positions.

How to do it: Schedule
a brief — even thirty minutes —
regular one-on-one time
with each child. Let
the child choose the activity.
Give your complete,
undivided attention
for that time —
phone away, siblings
elsewhere.

The activity matters
less than the consistency
and the quality of attention.

Why it works: Research
on parental one-on-one
time and child outcomes
finds consistent benefits
across birth positions —
all children benefit
from individual parental
attention, and the
research finding that
laterborns receive
less of it suggests
that deliberate scheduling
can correct an imbalance
that develops naturally.

The Bottom Line

Birth order is real —
children in different
birth positions genuinely
have different family
experiences. Its effects
on personality are
much more modest than
popular psychology suggests —
and the strong birth
order personality stereotypes
are not supported by
the best available research.

What matters far more
than birth order is
the quality of the
individual parent-child
relationship — the
warmth, attention,
and genuine seeing
of each child as
the specific, irreplaceable
person they are.

Your firstborn is not
destined to be responsible.
Your youngest is not
destined to be the
baby forever. Your
middle child is not
doomed to feel overlooked.

They are who they are —
shaped far more by
temperament, experience,
and your relationship
with them than by
the order in which
they arrived.

Sources

Rohrer, J. M., Egloff, B., &
Schmukle, S. C. (2015).
Examining the effects of
birth order on personality.
Proceedings of the National
Academy of Sciences,
112(46), 14224–14229.

Sulloway, F. J. (1996).
Born to Rebel. Pantheon Books.

Kristensen, P., & Bjerkedal, T.
(2007). Explaining the
relation between birth order
and intelligence. Science,
316(5832), 1717.

Harris, J. R. (1998).
The Nurture Assumption.
Free Press.