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Will Intelligent Latter-day Saints and Smart Conservatives Inherit the Earth? Differential Selection for Intelligence in the USA Based on Religiosity and Conservatism

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  • Ulster Institute for Social Research

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There is solid evidence that human populations have been selecting against intelligence-related genetic variants since the mid to late 1800s. The selection is generally weak, but varies by ethnic group and sex. Since religious teachings usually include strong pro-natalist components, we investigated whether this might also affect the selection for intelligence among different religious groups. We found that Latter-day Saints in the USA show slightly positive selection for intelligence, whereas all other religious groups examined did not robustly differ from the average. We similarly found that conservatives, in general, show a weaker selection against intelligence than do liberals.
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Evolutionary Psychological Science
https://doi.org/10.1007/s40806-022-00327-y
RESEARCH ARTICLE
Will Intelligent Latter‑day Saints andSmart Conservatives Inherit
theEarth? Differential Selection forIntelligence intheUSA Based
onReligiosity andConservatism
EmilKirkegaard1· EdwardDutton2
Received: 21 February 2022 / Revised: 25 May 2022 / Accepted: 26 May 2022
© The Author(s), under exclusive licence to Springer Nature Switzerland AG 2022
Abstract
There is solid evidence that human populations have been selecting against intelligence-related genetic variants since the mid
to late 1800s. The selection is generally weak, but varies by ethnic group and sex. Since religious teachings usually include
strong pro-natalist components, we investigated whether this might also affect the selection for intelligence among different
religious groups. We found that Latter-day Saints in the USA show slightly positive selection for intelligence, whereas all
other religious groups examined did not robustly differ from the average. We similarly found that conservatives, in general,
show a weaker selection against intelligence than do liberals.
Keywords Mormons· Religion· Pro-natalism· Fertility· Conservatism
Introduction
There is a substantial body of evidence that human popula-
tions, in particular in the West, have been selecting against
genetic variants related to intelligence since at least the late-
nineteenth century. A recent review (Dutton & Woodley of
Menie, 2018) has demonstrated that Western populations
are declining in terms of the prevalence of alleles indi-
rectly associated with high intelligence (Beauchamp, 2016;
Kong etal., 2017; Hugh-Jones & Abdellaoui, 2021) that
their reaction times (a robust negative correlate of IQ) are
becoming longer (Woodley etal., 2013; Madison & Sänger,
2016) and that various other proxies for intelligence are
changing in such a way as to indicate that intelligence is in
decline, including colour discrimination (Woodley of Menie
& Fernandes, 2015), and per capita major innovation across
time (Woodley, 2012).
More recently, IQ scores themselves have been found to
be in decline in many Western countries. This fall had been
cloaked by the Flynn effect — the secular rise in IQ scores
across the twentieth century — whereby, seemingly, an
increasingly science-oriented society had pushed the highly
environmentally sensitive subtests relating to ‘similarities’ to
their phenotypic maximum, resulting in a rise in IQ scores
even though the more heritable components of intelligence
were declining (Flynn, 2012). By the late 1990s, this pheno-
typic maximum had been reached, resulting in the underlying
intelligence decline being noticed on IQ tests and, indeed,
specifically on general intelligence, which is highly heritable
(Dutton etal., 2016). Empirically, the selection against intel-
ligence has been found to be about r = − 0.10 (Reeve etal.,
2018), although there are certain exceptions at the national
level, such as in Sweden where, among males, there is a posi-
tive IQ-fertility gradient based on army conscription data,
partly due to very low IQ males having no children at all
(Gardner etal., 2022; Kolk & Barclay, 2019). This seems to
be partly because low IQ males have less access to marriage
(Kolk & Barclay, 2021). However, these studies are only on
males, so there could be a negative IQ-fertility nexus overall,
when females are also analysed. Moreover, it has been argued
that Swedish conscription data is unrepresentative. A Swed-
ish cohort study, published in 1988, found that IQ and fertil-
ity correlated in Swedish men born up to 1924, after which
there was no relationship (Vining etal., 1988).
Furthermore, the negative correlation between fertility
and IQ has been found to be a Jensen effect, meaning that
* Edward Dutton
e.c.dutton@dunelm.org.uk
Emil Kirkegaard
emil@emilkirkegaard.com
1 Ulster Institute forSocial Research, London, UK
2 Asbiro University, Lodz, Poland
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Evolutionary Psychological Science
1 3
it is on general intelligence, not some other non-g ability
that weakly correlates with g (Peach etal., 2014; Woodley
& Meisenberg, 2013). Various explanations have been sug-
gested for this negative relationship, including intelligence
predicting the impulse control to use contraception and the
ability to employ it correctly and more intelligent women
delaying and then limiting child-bearing in order to pursue
education and a career in a social context in which this is
possible and even encouraged (Dutton & Woodley of Menie,
2018).
Congruous with this decline, since at least 1900, there has
been evidence of a negative relationship between fertility and
assorted proxies for intelligence such as education, income
and socioeconomic status, though the extent of this relation-
ship varies by country (Lynn, 2011). Recent research from
the UK has found that only families where both parents are
on welfare and where police and social worker intervention
is also required have above replacement fertility (Perkins,
2015). Criminality is a robust correlate of low IQ as is being
on welfare (Frisell etal., 2012; Hegelund etal., 2019). The
problem with these measures is that they are only proxies for
intelligence. Intelligence has been found to be up to 0.8 herit-
able in adulthood (Lynn, 2011, p.101) but its expression in
proxies such as education or earnings will be partly culturally
contingent and may subtly shift over time, as may the rela-
tionship between these traits and fertility. For example, edu-
cation level is likely to be a better proxy for intelligence in a
more meritocratic society and localized cultural factors, such
as male susceptibility to alcoholism and alcoholism repelling
females, may contribute to national level differences in these
relationships. In Sweden, for example, being a middle-aged
childless man is correlated with alcoholism but the precise
direction of the relationship is unclear (Hadley, 2019, p.53).
Alcoholism is negatively correlated with IQ (Jensen, 1998).
These broad causes have been explored in detail else-
where (Sarraf etal., 2019; Dutton & Woodley of Menie,
2018; Lynn, 2011). We are concerned here, however,
with inter-group differences in the extent of this negative
fertility-intelligence nexus. For example, one study found
that in the USA, the correlation between fertility and IQ
is 0.162 among white women but 0.271 among black
women. Black-white female differences in the correlation
between education and fertility and income and fertility
are in the same direction (Meisenberg, 2010). Another
US study, which included Hispanics, found that the nega-
tive correlation was most pronounced among Hispanic
women. It was 0.27, compared to − 0.24 for black women
and − 0.074 for white women. The negative correlations for
males were weaker, but the same racial differences were
found (Meisenberg & Kaul, 2010). That said, there is some
evidence that certain socioeconomically useful personality
traits are under positive selection, such as Agreeableness
(Jokela etal., 2017).
Many traditional religions tend to be strongly pro-natalist
and there is a robust relationship between religiosity and
fertility in the USA (Hayford & Morgan, 2008; Kaufman,
2010; Vogl & Freese, 2020). In addition, Pew Research
has found that 78% of ‘conservatives’ are certain that they
believe in God (Pew Research Center, 2022a) compared
to 45% of liberals (Pew Research Center, 2022b), so con-
servatism clearly significantly crosses over with religiosity.
Moreover, it has been found that conservatism, independent
of religiosity, predicts fertility in Western countries (e.g.
Fieder & Huber, 2018) and that when intelligence is con-
trolled for religiosity and conservatism are key predictors
of fertility (Dutton & Rayner-Hilles, In Press). It has also
been found that among members of The Church of Jesus
Christ of Latter-day Saints1 there is a positive association
between income (a robust IQ proxy) and fertility (Stanford
& Smith, 2013) as well as between broader socioeconomic
status and fertility (Heaton, 1986).
However, it should be emphasized that religiosity is a
cultural trait with its heritability ranging from 0.4 for cer-
tainty of religious belief to 0.66 for being ‘born again’ and
0.71 for fundamentalist religiosity (Bradshaw & Ellison,
2008). Kaufmann (2010) has found that the retention rate
for the Amish, who are extremely counter-cultural, is 85%
and that this is increasing across time. Two centuries ago,
when almost everybody was ‘religious’, then it may have
been that genetics and childhood environment played a less
significant role in religiosity than is the case today. But in
that, there is proxy evidence that certain religious groups do
not follow the negative IQ-fertility nexus, we might expect
to find that the negative fertility-IQ nexus would be weaker
among the religious and the conservative, or even that it
would not exist or actually was reversed. This is the hypoth-
esis which this study will test.
Method
Data
We used data from the US General Social Survey (GSS)
(https:// gss. norc. org/), 2018, release 3 (GSS7218_R3.sav).
The GSS is a long running, recurrent representative sample
of adult Americans. The sample is mainly cross-sectional
but with some longitudinal sub-samples. This dataset was
1 This is the church’s full official name. In accordance with rec-
ommended usage, we will refer to it elsewhere in this article as “the
Church” and its members as “Latter-day Saints.” Colloquially, this
group is often known as “Mormons,” but this historic terminology is
not preferred. See https:// newsr oom. churc hoe susch rist. org/ style- guide
for details.
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Evolutionary Psychological Science
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chosen due to the availability of an intelligence measure
and detailed religious self-identification.
Intelligence was only measured with the Wordsum
10-item vocabulary test (variables worda to wordh). This
test has been widely used in prior research and is valid
and reliable enough for practical use. We scored both the
Wordsum as a sum score (total correct answers) as well
as using item response theory. The latter method is theo-
retically slightly superior as this weighs items by their
informativeness instead of assuming equal weights. The
scores are highly correlated in practice (r = 0.87 in this
study). We used the mirt package to extract a single factor
from the 10 items, which we took as a proxy for general
intelligence (the g factor; Jensen, 1998). All loadings were
positive, see R notebook output for details. We standard-
ized the scores within wave using the White subset (i.e.
0 = White mean, 1 = White standard deviation). This pro-
vided us with scores for 31,970 subjects.
Fertility was assessed with self-report, as was age, sex,
and race/ethnicity (social race). We additionally computed
a cohort, sex, and age controlled version using a natural
spline model (R formula fertility ~ rcs(age) * sex, within
each survey wave).
There are multiple variables available for religious
groups and subgroups (denominations, schools, sects,
etc.). As the earlier study had reported positive findings for
Latter-day Saints, we wanted to include membership in the
Church in our study so as to analytically verify the finding.
Furthermore, we wanted a broad selection of groups with
sufficient sample size for testing an interaction term with
intelligence. This represents a test for differential selection
by religious group. The variable other contains a detailed
breakdown of Protestant groups, though it also includes
Latter-day Saint groups, despite Latter-day Saints not
regarding themselves as Protestant. We coded a dummy
variable as whether a person belonged to this group or not.
There were a total of 786 Latter-day Saints, and 64,028
non-Latter-day Saints in the dataset. For the main analy-
sis, we used the variable relig which contains 13 broader
groups. Both variables were asked in all years, so offered
the largest amount of data possible, for a maximum of
68,470 subjects.
For politics, we used the self-placement scale (polviews).
We additionally coded a 0–1 version of this, so that
extremely liberal = 0 and extremely conservative = 1. While
this is not the best way to operationalize political ideology,
it provides a convenient and commonly used starting point
(Carmines etal., 2012; Swedlow, 2008).
Race was coded as White, Black, or other, since only
one variable is available for the entire time period (race).
We additionally created a near-completed fertility subgroup
defined as males aged 45 or more, and females aged 40 or
more.
We set the p value threshold at 0.01, though this should
still only be considered suggestive considering the number
of tests conducted across the entire study.
We were interested in possible confounds, so we used
a series of regression models with increasingly stringent
controls:
1. No controls
2. Sex (gender)
3. Sex and its nonlinear interaction with age
4. Sex and its nonlinear interaction with age, survey year
5. Sex and its nonlinear interaction with age and with sur-
vey year (3-way)
6. Sex and its nonlinear interaction with age and with sur-
vey year (3-way), race
7. Sex and its nonlinear interaction with age and with sur-
vey year (3-way), race, and the interaction between the
indicator term and an age nonlinear
All nonlinear terms were modelled using natural splines
(rcs() in rms package). For the cohort standardized fertility
outcome, the controls for these terms were dropped, leaving
3 models.
Results
As the model output is very long, we only show the most
important terms in the summary tables below (Tables1, 2,
and 3), the full model summary output can be found in the
R notebook.
The first set of models show that despite the increasing
set of controls, the interaction for Latter-day Saint self-
identification and intelligence (g) has a consistent low p
value, (though the final model only has p = 0.01), and a
positive estimate. Thus, American Latter-day Saints are
not subject to the same level of selection as American
non-Latter-day Saints. The interaction value for Latter-
day Saints is in fact larger than the overall negative value
for intelligence, showing that American Latter-day Saints
are subject to positive selection while others are subject to
negative selection.
The second set of models are limited to the completed
fertility cohort, which halves our sample size but removes
any remaining worries about age effects. The interaction
term in these models still has a low p value, but it is in the
‘critical’ zone with an average value of about 0.04. The final
sets of models show results using the alternative fertility
outcome variable, with cohort effects removed beforehand.
These p values are also low, again with p = 0.01 for the
final model. Overall, though, the consistently low p values
would be extremely unlikely given no differential selection
for American Latter-day Saint individuals compared with
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Evolutionary Psychological Science
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Table 1 Model results for Latter-day Saints
Raw fertility as outcome
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
1234567
G − 0.11 (0.010, < 0.001***) − 0.11 (0.010, < 0.001***) − 0.25 (0.009, < 0.001***) − 0.25 (0.009, < 0.001***) − 0.26 (0.009, < 0.001***) − 0.22 (0.009, < 0.001***) − 0.22 (0.009, < 0.001***)
LDS 0.78 (0.088, < 0.001***) 0.77 (0.088, < 0.001***) 0.89 (0.079, < 0.001***) 0.90 (0.078, < 0.001***) 0.89 (0.077, < 0.001***) 0.95 (0.077, < 0.001***) − 1.03 (0.802, 0.201)
g * LDS 0.36 (0.096, < 0.001***) 0.36 (0.095, < 0.001***) 0.30 (0.085, < 0.001***) 0.32 (0.085, < 0.001***) 0.31 (0.084, < 0.001***) 0.30 (0.083, < 0.001***) 0.21 (0.085, 0.014)
Sex Yes Yes Ye s Yes Ye s Yes
Age Yes Ye s Yes Ye s Yes
Survey year Yes Ye s Yes Ye s
Survey year
* age
Yes Ye s Yes
Race Yes Ye s
LDS * age Yes
R2 adj 0.006 0.013 0.207 0.216 0.241 0.247 0.248
N31890 31890 31815 31815 31815 31815 31815
Table 2 Model results for Latter-day Saints
Raw fertility as outcome
Completed fertility subset
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
1234567
G − 0.25 (0.014, < 0.001***) − 0.25 (0.014, < 0.001***) − 0.25 (0.014, < 0.001***) − 0.25 (0.014, < 0.001***) − 0.26 (0.013, < 0.001***) − 0.22 (0.014, < 0.001***) − 0.22 (0.014, < 0.001***)
LDS 1.17 (0.134, < 0.001***) 1.17 (0.134, < 0.001***) 1.16 (0.133, < 0.001***) 1.15 (0.133, < 0.001***) 1.14 (0.130, < 0.001***) 1.20 (0.130, < 0.001***) − 2.97 (3.496, 0.395)
g * LDS 0.27 (0.140, 0.054) 0.27 (0.140, 0.053) 0.28 (0.139, 0.044) 0.28 (0.138, 0.042) 0.28 (0.136, 0.037) 0.27 (0.135, 0.047) 0.27 (0.136, 0.044)
Sex Yes Yes Yes Ye s Yes Ye s
Age Yes Ye s Yes Ye s Yes
Survey
year
Yes Ye s Yes Ye s
Survey
year *
age
Yes Ye s Yes
Race Yes Ye s
LDS * age Yes
R2 adj 0.023 0.025 0.032 0.041 0.08 0.087 0.087
N16845 16845 16845 16845 16845 16845 16845
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Evolutionary Psychological Science
1 3
American non-Latter-day Saint respondents, though we can-
not be entirely sure.
Next, one might wonder whether this is a general reli-
giousness effect. To examine this, we ran the same models
but using any religion as the test term. The results are shown
in Tables4, 5, and 6.
In contrast to the earlier results, ‘any religion’ does not
show a consistent interaction pattern with intelligence in
the first set of models (Table4). Curiously, it reaches a low
p value only in the middle models (3–6), but even here the
effect size is about 33% of that for Latter-day Saints (0.07
vs. 0.31). For the second set of models based on completed
fertility (Table5), there is no interaction detectable at all.
The final set (Table6) shows a weak interaction in the first
two models, but not in the third (p = 0.19), and in those, the
effect sizes are about 80% smaller than for Latter-day Saints
(0.04 vs. 0.20). Thus, overall, the results are not convinc-
ing that religion is associated with differential selection for
intelligence, but it might be slightly so. Since ‘any religion
includes Latter-day Saints, our earlier results of course imply
that it has to be so, at least very slightly so.
To check for whether the other specific religions show a
pattern like that seen in Latter-day Saints, we checked the
8 groups we had coded earlier. The model outputs are too
long to show here, but none of the tested religions show a
consistent pattern like the one observed in Latter-day Saints.
Some groups show some low p values in some models, e.g.
Catholicism shows signals of an interaction in a few models,
such as models 3–5 for raw fertility (p’s < 0.01), but not in
the others. Catholicism shows no signal in the models with
completed fertility. As before, the effect sizes are small com-
pared to the models for Latter-day Saints. In general, despite
the many tests, we found not much to support other religions
having the same differential selection pattern for intelligence
as American Latter-day Saints have.
Finally, we tested political ideology. We tested models
using both a dummy coding and a linear numerical coding.
The first would reveal any nonlinear patterns, but the results
were mostly linear, so we show those for the linear coding,
shown in Tables7, 8, and 9.
The results for political ideology mirror those for Latter-
day Saints in America, except they are more consistent. In
fact, every model across the three model sets show p < 0.01
except for one with p = 0.02. This is probably due to the
much higher statistical precision using a numerical vari-
able for the entire sample compared to a binary indicator
as for religion, which includes small subsets of the sample.
Across the models, the interaction is about half the size of
the overall selection for lower intelligence. Thus, conserva-
tives show consistently weaker selection for lower intel-
ligence, with a few models indicating selection for higher
intelligence (e.g. Table7, model 2). Quantitatively, the value
for the conservative term shown is the implied compari-
son between extremely liberal and extremely conservative
extremes. Thus, if we use results from the final model using
cohort standardized fertility, extreme conservatives have an
estimated 0.08 selection against intelligence compared
to − 0.20 among extreme liberals.
We also fitted a model that included the proposed interaction
terms simultaneously, as well as religious attendance (attend, as
with politics views, we recoded this on 0–1 scale for interpreta-
tion and improved statistical precision). The model showed that
each of the predicted moderators of the intelligence-fertility
relation held up when jointly analysed. The overall effect of
g on fertility is 0.34. The interaction with Latter-day Saint
identity is 0.20 (0.087, p = 0.019), with political ideology 0.14
(0.036, p < 0.001***), and religious attendance 0.10 (0.027,
p < 0.001***). Thus, a Latter-day Saint who attends church
often and who is politically extremely conservative is expected
to achieve a fertility-intelligence slope of − 0.34 + 0.20 + 0.14 +
0.10 = 0.10, i.e., each standard deviation of intelligence would
predict an additional 0.10 lifetime fertility. This estimate is,
however, very uncertain. At the request of a reviewer, we also
tested for the interaction between political ideology and the
two measures of religiousness (self-identification as a Latter-
day Saint, and religious attendance), but neither showed an
Table 3 Model results for
Latter-day Saints
Cohort standardized fertility as outcome
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
123
G − 0.16 (0.005, < 0.001***) − 0.14 (0.006, < 0.001***) − 0.14 (0.006, < 0.001***)
LDS 0.57 (0.049, < 0.001***) 0.60 (0.049, < 0.001***) − 0.66 (0.511, 0.194)
g * LDS 0.20 (0.053, < 0.001***) 0.19 (0.053, < 0.001***) 0.13 (0.054, 0.013)
Race Yes Ye s
LDS * age Yes
R2 adj 0.029 0.037 0.038
N31815 31815 31815
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Evolutionary Psychological Science
1 3
Table 4 Model results for any religion
Raw fertility as outcome
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
1234567
G − 0.08 (0.026, 0.003**) − 0.08 (0.026, 0.002**) − 0.29 (0.024, < 0.001***) − 0.30 (0.023, < 0.001***) − 0.30 (0.023, < 0.001***) − 0.27 (0.023, < 0.001***) − 0.24 (0.024, < 0.001***)
any religion 0.74 (0.029, < 0.001***) 0.71 (0.029, < 0.001***) 0.39 (0.027, < 0.001***) 0.32 (0.027, < 0.001***) 0.31 (0.027, < 0.001***) 0.30 (0.027, < 0.001***) − 0.85 (0.277, 0.002**)
g * any religion − 0.02 (0.028, 0.526) − 0.02 (0.028, 0.482) 0.07 (0.025, 0.01*) 0.07 (0.025, 0.003**) 0.06 (0.025, 0.015) 0.06 (0.025, 0.009*) 0.03 (0.026, 0.274)
Sex Yes Yes Ye s Yes Ye s Yes
Age Yes Ye s Yes Ye s Yes
Survey year Yes Ye s Yes Ye s
Survey year
* age
Yes Ye s Yes
Race Yes Ye s
Any religion
* age
Yes
R2 adj 0.024 0.028 0.209 0.216 0.241 0.247 0.247
N31770 31770 31698 31698 31698 31698 31698
Table 5 Model results for any religion
Raw fertility as outcome
Completed fertility subset
* p < 0.00; ** p < 0.005; *** p < 0.001
Ter m Model
1 2 3 4 5 6 7
G − 0.21 (0.044, < 0.001***) − 0.22 (0.044, < 0.001***) − 0.23 (0.044, < 0.001***) − 0.24 (0.044, < 0.001***) − 0.25 (0.043, < 0.001***) − 0.22 (0.043, < 0.001***) − 0.22 (0.043, < 0.001***)
Any religion 0.62 (0.052, < 0.001***) 0.60 (0.052, < 0.001***) 0.56 (0.052, < 0.001***) 0.47 (0.053, < 0.001***) 0.42 (0.052, < 0.001***) 0.41 (0.052, < 0.001***) − 0.53 (1.387, 0.702)
g * any religion − 0.02 (0.047, 0.728) − 0.02 (0.047, 0.738) 0.00 (0.047, 0.917) 0.01 (0.046, 0.868) 0.01 (0.045, 0.867) 0.02 (0.045, 0.703) 0.01 (0.045, 0.746)
Sex Yes Ye s Yes Yes Yes Yes
Age Yes Yes Ye s Yes Ye s
Survey year Yes Ye s Yes Ye s
Survey year
* age
Yes Yes Ye s
Race Yes Ye s
Any religion
* age
Yes
R2 adj 0.027 0.028 0.034 0.041 0.079 0.086 0.086
N16780 16780 16780 16780 16780 16780 16780
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Evolutionary Psychological Science
1 3
interaction (p’s = 0.06 and 0.94). This result is probably low
power, so cannot be interpreted as strong evidence for a lack
of an interaction. The full model output is given in the supple-
mentary materials.
Discussion
It appears to be the case that religiosity, specifically Ameri-
can Latter-day Saints, and conservatism moderate and even
reverse the negative relationship between fertility and intel-
ligence in the American population. In other words, certain
cultural practices, as long as they are maintained, exert an
influence on the genetics of the population. American Latter-
day Saints are not genetically distinct from other populations
in the area (Merrill & Salazar, 2002), and they were never
subject to a genetic bottleneck, as with isolated groups such
as the Ashkenazi Jews (Plomin, 2018) or the Amish (Wood
Klinger, 1983). They have simply maintained a form of con-
servative religiosity that highly prizes children as blessings.
One possibility is that a person who has genuinely
absorbed beliefs of the Church will have a strong desire to
sacrifice their own interests for those of the community and,
thus, not be a financial burden on the community. Accord-
ingly, we would expect poorer and on average less intelli-
gent American Latter-day Saints — in a religion that accepts
the use of contraception — to limit their fertility in a way
that wealthier and on average more intelligent American
Latter-day Saints would not. It might be argued that a cer-
tain IQ is necessary to successfully use contraception, so
less intelligent Latter-day Saints would be unable to do this.
But it can be countered that a component of negative IQ-
fertility nexus — as mediated by contraception — is being
too impulsive and present-oriented to use contraception at
all (see Lynn, 2011). This impulsivity could potentially be
overwhelmed by, or weakened by, a strong sense of com-
munity orientation.
Furthermore, there is evidence that high intelligence
within the normal range — as distinct from outlier high
intelligence, which may be associated with non-conformity
via crossover with autistic traits (Dutton & Charlton, 2016;
Karpinski etal., 2018) — is associated with conformity to
the dominant set of values in a community, something known
as the cultural mediation hypothesis (Woodley of Menie &
Dunkel, 2015). This relationship appears to exist because
intelligent people are better able to discern the dominant set
of values, better able to realize the socioeconomic benefits of
conforming to them, and possess the effortful control neces-
sary to convince themselves of the veracity of these values.
Once they have done this, they will competitively signal
their conformity to these values in order to achieve even
higher social status (see Dutton & Rayner-Hilles, In Press).
Accordingly, it may be that intelligent American Latter-day
Saints signal their commitment to the Church’s community
values by having the largest family that they could afford.
Congruous with this suggestion, historian Anne Braude has
averred that: ‘Mormons believed an infinite number of dis-
embodied souls were waiting to be born as Mormons, hop-
ing one day to advance to heaven. The quickest way to usher
in the most souls to heaven was for righteous men to have
many wives and father many children, all of whom would
spend eternity in heaven together’ (Braude, 2007, pp.23–24).
Another possibility is that the Church strongly promotes
pro-social behaviour (or ‘Agreeableness’), which itself cor-
relates with fertility (Jokela, 2012), due to the nurture and
self-sacrifice involved in having children. More intelligent
Latter-day Saints might better absorb this, indirectly result-
ing in higher fertility among them.
However, there are other possible explanations. Wealth cor-
relates with intelligence so, in an extremely family-oriented
religion, we might expect the wealthy to spend their money on
having children. Devout Latter-day Saints tend to have more
stable marriages (though the direction of causality is unclear)
which would militate in favour of more children. Certainly, the
divorce rate is much lower among Latter-day Saints than non-
Latter-day Saints, at least with regard to temple marriages in
the Church (Chadwick etal., 2010). Thus, it may be that more
intelligent Latter-day Saints tend to be able to keep marriages
Table 6 Model results for any
religion
Cohort standardized fertility as outcome
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
123
G − 0.19 (0.015, < 0.001***) − 0.17 (0.015, < 0.001***) − 0.15 (0.015, < 0.001***)
Any religion 0.20 (0.016, < 0.001***) 0.20 (0.016, < 0.001***) − 0.53 (0.173, 0.002**)
g * any religion 0.04 (0.016, 0.01) 0.04 (0.016, 0.007*) 0.02 (0.016, 0.194)
Race Yes Ye s
Any religion * age Yes
R2 adj 0.03 0.037 0.038
N31698 31698 31698
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Evolutionary Psychological Science
1 3
Table 7 Model results for political ideology as coded numerically (0–1, where 0 = extreme liberal and 1 = extreme right)
Raw fertility as outcome
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
1 2 3 4 5 6 7
G − 0.23 (0.023, < 0.001***) − 0.24 (0.023, < 0.001***) − 0.36 (0.021, < 0.001***) − 0.35 (0.021, < 0.001***) − 0.35 (0.020, < 0.001***) − 0.32 (0.020, < 0.001***) − 0.32 (0.020, < 0.001***)
Political ideology 0.75 (0.044, < 0.001***) 0.77 (0.044, < 0.001***) 0.40 (0.040, < 0.001***) 0.40 (0.039, < 0.001***) 0.38 (0.039, < 0.001***) 0.44 (0.039, < 0.001***) − 1.05 (0.486, 0.03)
g * political
ideology
0.26 (0.041, < 0.001***) 0.27 (0.041, < 0.001***) 0.23 (0.037, < 0.001***) 0.22 (0.037, < 0.001***) 0.20 (0.036, < 0.001***) 0.20 (0.036, < 0.001***) 0.20 (0.036, < 0.001***)
Sex Yes Yes Yes Ye s Yes Ye s
Age Yes Yes Ye s Yes Ye s
Survey year Yes Ye s Yes Ye s
Survey year
* age
Yes Ye s Yes
Race Yes Ye s
Political ideology
* age
Yes
R2 adj 0.015 0.022 0.209 0.218 0.244 0.25 0.251
N29247 29247 29182 29182 29182 29182 29182
Table 8 Model results for political ideology as coded numerically (0–1, where 0 = extreme liberal and 1 = extreme right)
Raw fertility as outcome
Completed fertility subset
* p < 0.01; ** p < 0.005; *** p < 0.001
Ter m Model
1 2 3 4 5 6 7
G − 0.36 (0.033, < 0.001***) − 0.36 (0.033, < 0.001***) − 0.37 (0.033, < 0.001***) − 0.35 (0.033, < 0.001***) − 0.35 (0.032, < 0.001***) − 0.31 (0.032, < 0.001***) − 0.31 (0.032, < 0.001***)
Political ideology 0.37 (0.063, < 0.001***) 0.38 (0.063, < 0.001***) 0.35 (0.062, < 0.001***) 0.35 (0.062, < 0.001***) 0.30 (0.061, < 0.001***) 0.37 (0.061, < 0.001***) 3.95 (1.852, 0.033)
g * political
ideology
0.21 (0.057, < 0.001***) 0.22 (0.057, < 0.001***) 0.22 (0.057, < 0.001***) 0.20 (0.056, < 0.001***) 0.18 (0.055, 0.001**) 0.17 (0.055, 0.002**) 0.17 (0.055, 0.002**)
Sex Yes Yes Ye s Yes Ye s Yes
Age Yes Yes Ye s Yes Ye s
Survey year Yes Ye s Yes Ye s
Survey year * age Yes Ye s Yes
Race Yes Ye s
Political ideology
* age
Yes
R2 adj 0.023 0.024 0.03 0.039 0.079 0.087 0.087
N15398 15398 15398 15398 15398 15398 15398
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Evolutionary Psychological Science
1 3
together longer and therefore have more childbearing years in
a culture in which giving birth out of wedlock is still not an
option for many women as it is so socially unacceptable. The
State of Utah, for example, has enacted a specific program
to promote the importance of marriage (Maldonado, 2011,
p.383). Another possibility may be that some smart Latter-
day Saints who are less interested in family life may self-select
out of an extremely family-oriented church (i.e., apostatize),
and the bright people remaining within it are more likely to
have intrinsic motivation to have more children. Congruous
with this possibility, it has been found that those who leave
the Church have lower educational, socioeconomic status, and
fewer children than they those who remain (Cranney, 2019).
However, we should be careful in discussing even the
mainline Latter-day Saints as though they are somehow a
homogenous organization. Most obviously, there is a clear
distinction between practicing American Latter-day Saints
(who tithe, keep to all the rules and are allowed to enter
the Church’s temples) and ‘Jack Mormons’ (see Coates,
1992). The latter have cultural, personal, or family ties to
the Church. They have been vaguely raised as in the Church
but are not especially devout and do not tithe. Practicing
Latter-day Saints are expected not only to tithe but to devote
an enormous amount of their free time to aiding their church.
This would, in effect, act to select out less intelligent Latter-
day Saints via the associations between intelligence and
future-orientation, altruism, community-orientation, and
depth of interests (Eisenberg-Berg, 1979; Jensen, 1998;
Jones, 2008).
Beyond American Latter-day Saints, we have found some
evidence that religiosity itself reverses the negative fertility-
intelligence nexus. However, as discussed, our measure was
sub-optimal here. Studies indicate that it is specifically religi-
osity that involves collective worship — not merely belief —
that is associated not just with fertility but also genetic mental
and physical health (Dutton etal., 2018; Sarraf etal., 2019).
Our study is on firmer ground, however, with conservatism
which, as we have discussed, appears to strongly cross over
with religiosity. This reduces the negative fertility-intelligence
nexus. How would conservatism do this?
Most obviously, there is evidence that contemporary
extreme liberalism, currently, literally promotes anti-natalism,
encouraging people to not have children for the good of the
environment (e.g. Extinction Rebellion) via a process of a
runaway individualism where a person must signal their lib-
eralism to a greater extent than the next liberal (see Dutton
& Rayner-Hilles, In Press). Thus, competitive signalling in a
liberal context could lead to the choice of infertility. By con-
trast, conservatism tends to promote traditional ways of think-
ing, including traditional religiosity (which is pro-natalist) and
putting the good of the nation or family above the self, which
is also implicitly pro-natalist as these need to survive (Graham
etal., 2009).
In addition, liberalism has been found to be associated
with mental instability and depression while conservatism
has been found to be associated mental stability and feeling
that life has meaning (Schlenker etal., 2012; Kirkegaard,
2020; Bernardi, 2021; Kwon, 2022). This may be because if
a person feels negative feelings strongly — in particular a
sense of unfairness and envy — they will agitate for radical
change. Similarly, if a person fears those around them, they
will desire power over others and so desire a strongly con-
trolled society rather than a free-market one. These negative
feelings will be comorbid with other negative feelings, such
as a propensity towards depression and this feeling that life
is meaningless may make you not want to have children.
Congruous with this, depression mediates the relationship
between anti-natalism and Machiavellianism (Schönegger,
2021), Machiavellianism is strongly associated with being
high on liberalism though not on conservatism (Moss &
O’Connor, 2020). Furthermore, having children, unless to
use them for socioeconomic gain such as higher welfare
payments (see Perkins, 2015), can be regarded as selfless
and, indeed, Agreeableness is a predictor of fertility (Jokela,
2012). It would thus follow that individualists would be dis-
inclined to have children.
Table 9 Model results for political ideology as coded numerically (0–1, where 0 = extreme liberal and 1 = extreme right)
Cohort standardized fertility as outcome
* p < 0.01; ** p < 0.005; *** = p < 0.001
Ter m Model
123
G − 0.22 (0.013, < 0.001***) − 0.20 (0.013, < 0.001***) − 0.20 (0.013, < 0.001***)
Political ideology 0.26 (0.024, < 0.001***) 0.30 (0.024, < 0.001***) − 0.71 (0.308, 0.022)
g * political ideology 0.13 (0.023, < 0.001***) 0.13 (0.023, < 0.001***) 0.12 (0.023, < 0.001***)
Race Yes Ye s
Political ideology * age Yes
R2 adj 0.03 0.038 0.039
N29182 29182 29182
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Evolutionary Psychological Science
1 3
Taken together, these studies allow us to understand why
liberalism would render the negative intelligence-fertility
nexus more pronounced — by promoting anti-natalism and
critiquing natalist organizations such as traditional churches
— while conservatism would render it less pronounced. In
addition, in a liberal context, IQ is associated with leftism
(Dutton & Rayner-Hilles, In Press) meaning that intelligent
people are more likely to go to university and absorb left-
wing ideas, including anti-natalism. And, indeed, in extreme
cases, conservatism would be sufficient to overwhelm the
negative IQ-fertility nexus, resulting in a positive associa-
tion between fertility and intelligence. Accordingly, religion
(among American Latter-day Saints in particular) and con-
servatism appear to be the shell, the protective outer coating,
by which intelligence is safeguarded, and, indeed, promoted.
Future research should build on our findings by exploring
other anomalies in data on the fertility-intelligence nexus.
For example, in most Western countries, there is a negative
correlation between fertility and education, among women
and, more weakly, men (Göttmark & Andersson, 2020). In
Finland, male education level is positively associated with
fertility (Nisén, 2016). Could this also be true of male IQ?
We saw earlier that in Sweden the IQ-fertility nexus ceased
to exist by the time of the cohort born after 1924. Could
Finland, which industrialized relatively late (see Dutton,
2019), be lagging slightly, helping to explain this positive
relationship? What are the cultural factors that cause this and
how do they relate to conservatism and American Latter-day
Saints’ cultural idiosyncrasies?
Limitations
Our study has a variety of limitations. First, the measures
were suboptimal. General intelligence cannot be measured
with high reliability using only 10 vocabulary items. This
implies that our results are most likely weaker (closer
to 0) than they really are. Despite this issue, we were in
general able to find patterns for intelligence, including
interactions with other variables. The same point applies
to our measures of religious belonging, which are simple
either or measures. In reality, someone can be more or
less extreme or dedicated in their beliefs in the doctrines
of the Church (or Catholic doctrines, etc.), and a perfect
study would allow for this (see Kirkegaard & Lasker,
2020). As mentioned earlier, though it the norm to meas-
ure political ideology using a self-placement question,
this approach has been found to be suboptimal since the
political ideology of many people cannot be accurately
summarized only in one dimension (Carmines etal., 2012;
Swedlow, 2008). Ideally, then, one would employ a more
fine-grained measure. We might speculate that in the two
dimensional model, it is the social conservatism aspect
that relates to the relationship between intelligence and
fertility, not economic conservatism. The present dataset
allows for a more fine-grained analysis of ideology than
we employed here. However, we wanted to keep the analy-
sis simple, so we opted for the one-dimensional approach.
Second, some of our models included younger persons
and attempted to deal with age confounds by including
it as a covariate. This enables a much larger sample size,
but at the cost of potential bias. This can arise despite the
included covariate term if age relates differentially to the
variables of interest, for example, that conservatives with
high intelligence reproduce earlier in life than liberals.
We tried accounting for this using an interaction term for
age as well, but this might not be enough. We opted for
the use of the full dataset since the effect sizes we are
investigating are fairly small, so we need all the statistical
power we can get. In general, our use of cohort and age
standardized analyses, as well as completed fertility analy-
ses should alleviate some of this concern. Third, our data-
set used only data from the USA. While it is known that
intelligence is negatively associated with fertility exists
across the western and some non-western countries, it is
not known whether this interaction might exist elsewhere
too. It would be preferable if the next study concerned a
country in Europe.
Acknowledgements We would like to thank peer reviewer Dr Russell
Warne for his comments on earlier drafts of this manuscript.
Author Contribution Emil Kirkegaard: method and results. Edward
Dutton: introduction and discussion.
Availability of Data and Material The data is not available.
Code Availability Not applicable.
Declarations
Ethics Approval Not applicable.
Consent to Participate Not applicable.
Consent for Publication Not applicable.
Conflict of Interest The authors declare no competing interests.
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