A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal Survey of Youth

Abstract

In this study we attempt to determine whether dysgenic fertility is associated with the Jensen effect. This is investigated with respect to a US population representative sample of 8110 individuals from the National Longitudinal Survey of Youth for whom there exists complete data on IQ and fertility. In addition to the general sample, the sample was also broken out by race and sex so as to examine whether or not the Jensen effect manifested amongst different sub-populations. The method of correlated vectors revealed significant Jensen effects in five of the seven samples, and in all cases the effect was in a direction indicating that subtests with higher g-loadings were associated with larger dysgenic fertility gradients. The magnitude of the difference between Spearman’s ρ and Pearson’s r was non-significant in all cases, suggesting that biasing factors were minimally influencing the result. This finding suggests that dysgenesis occurs on the ‘genetic g’ at the heart of the Jensen effect nexus, unlike the Flynn effect, which is ‘hollow’ with respect to g. Finally, the finding is discussed in the context of two converging lines of evidence indicating that genotypic IQ or ‘genetic g’ really has been declining over the last century.

Full text

A Jensen effect on dysgenic fertility: An analysis involving the National
Longitudinal Survey of Youth
Michael A. Woodley
a,
⇑
, Gerhard Meisenberg
b
a
Independent researcher, UK
b
Ross University School of Medicine, Picard Estate, Portsmouth, Dominica, West Indies
article info
Article history:
Available online xxxx
Keywords:
Dysgenic fertility
g-Loading
Jensen effect
Method of correlated vectors
NLSY
abstract
In this study we attempt to determine whether dysgenic fertility is associated with the Jensen effect. This
is investigated with respect to a US population representative sample of 8110 individuals from the
National Longitudinal Survey of Youth for whom there exists complete data on IQ and fertility. In addition
to the general sample, the sample was also broken out by race and sex so as to examine whether or not
the Jensen effect manifested amongst different sub-populations. The method of correlated vectors
revealed significant Jensen effects in five of the seven samples, and in all cases the effect was in a direc-
tion indicating that subtests with higher g-loadings were associated with larger dysgenic fertility gradi-
ents. The magnitude of the difference between Spearman’s
q
and Pearson’s rwas non-significant in all
cases, suggesting that biasing factors were minimally influencing the result. This finding suggests that
dysgenesis occurs on the ‘genetic g’ at the heart of the Jensen effect nexus, unlike the Flynn effect, which
is ‘hollow’ with respect to g. Finally, the finding is discussed in the context of two converging lines of evi-
dence indicating that genotypic IQ or ‘genetic g’ really has been declining over the last century.
Ó2012 Elsevier Ltd. All rights reserved.
1. Introduction
1.1. The Jensen effect
The Jensen effect is a term first coined by Rushton (1998) to de-
scribe Arthur Jensen’s finding that the vector (rank of the effect
magnitude) of many biologically significant variables typically cor-
relates both positively and significantly with the vector of subtest
g-loadings. In other words the Jensen effect results from the ten-
dency for subtests exhibiting the highest g-loadings to be best at
discriminating amongst individual differences in biological vari-
ables. Jensen’s (1998) method of correlated vectors has its origins
in the work of Spearman (1927), who proposed what became
known as Spearman’s hypothesis, namely that Black–White differ-
ences would be most pronounced on tests that are the strongest
measures of g. Recently Spearman’s hypothesis has been rebranded
as the Spearman–Jensen hypothesis, owing to Jensen’s develop-
ment of the method of correlated vectors (Rushton, 1998). Consis-
tent with the hypothesis, a number of studies have found large and
significant Jensen effects on Black–White differences (see Rushton
& Jensen, 2010 for an overview). The nomological net of biological
variables for which Jensen effects are known to exist is very broad,
and includes inbreeding depression scores, evoked potentials,
brain pH, reaction times, test heritabilities (Jensen, 1998; van Blo-
ois, Geutjes, te Nijenhuis, & de Pater, 2009), fluctuating asymmetry
(Prokosch, Yeo, & Miller, 2005), brain size (Rushton & Ankney,
2009), and sex differences (Nyborg, 2005) amongst others.
Even though it is not without its detractors (e.g. Ashton & Lee,
2005), the existence of the Jensen effect would appear to have sig-
nificant ramifications. Firstly it effectively falsifies Thomsonite
models of the development of intelligence (e.g. Bartholomew,
Deary, & Lawn, 2009; Thomson, 1916; van der Maas et al., 2006),
which argue that garises chiefly from random sampling or mutu-
alistic reinforcement amongst distinct ‘neural elements’ or bonds,
rather than from the existence of a special quality or ‘mental en-
ergy’, as was first posited by Spearman (1927). This is because
the Jensen effect reveals the existence of an apparent nexus
amongst diverse biological variables and g, which suggests that
the factor corresponds to something very fundamental to brain
neurophysiology and genetics, rather than being a mere statistical
regularity (Eysenck, 1987; Rushton & Jensen, 2010). Secondly, it
permits the ‘hollowness’ (i.e. the degree to which differences are
most pronounced on non-gvariance rather than gvariance) of
important phenomena like the Flynn effect to be determined. De-
bate has raged about whether or not the Flynn effect occurs on g
(see Wicherts et al., 2004 and Woodley, 2011a for summaries).
The most comprehensive study to date is that of te Nijenhuis (in
press), who has determined, based on a comparison of studies from
the Netherlands and the US, that the Flynn effect is ‘hollow’, as its
0191-8869/$ - see front matter Ó2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.paid.2012.05.024
⇑
Corresponding author.
E-mail address: M.A.WoodleyPhD@gmail.com (M.A. Woodley).
Personality and Individual Differences xxx (2013) xxx–xxx
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journal homepage: www.elsevier.com/locate/paid
Please cite this article in press as: Woodley, M. A., & Meisenberg, G. A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal
Survey of Youth. Personality and Individual Differences (2013), http://dx.doi.org/10.1016/j.paid.2012.05.024

effect magnitude is typically slightly negatively correlated with
subtest g-loadedness. Other apparently ‘hollow’ effects include,
Spearman’s Law of Diminishing Returns (Jensen, 2003) and IQ
gains due to the effects of retesting (te Nijenhuis, van Vianen, &
van der Flier, 2007).
1.2. Dysgenic fertility
The correlation of IQ and its proxies with fertility has been con-
sistently negative since testing began (Lynn, 2011; van Court &
Bean, 1985). The existence of this negative correlation had been
intuited by Galton (1869) in the 1860’s. Furthermore in the mod-
ern world, the negative correlation appears to be global in extent,
existing both within (Meisenberg, 2008) and between countries
(Lynn, 2011; Lynn & Harvey, 2008; Meisenberg, 2009; Reeve,
2009). This dysgenic effect, as it became known, has been a consid-
erable source of debate, not least of all because of the existence of
the countervailing Flynn effect, which confounded even the earliest
attempts to directly quantify it (Lynn, 2011). Even though there
has been much speculation about the likely impact of dysgenics
on populations (e.g. Cattell, 1936, 1937, 1991; Itzkoff, 2003; Ny-
borg, 2012), until recently there has been no concrete evidence
of such an impact. The first substantive evidence has been found
using temporal correlation analysis (Woodley, 2012a), in which
Western genotypic IQ means were reconstructed from 1455 to
2005 based on the assumption that they trended in the same direc-
tion as the status-fertility correlation, i.e. positively until the mid
1800’s and then negatively afterwards (Skirbekk, 2008). This
reconstructed genotypic IQ measure was found to be the strongest
predictor of technological and scientific innovation rates, which
trend in a similar manner, with peak per capita innovation rates
having occurred in the 1870’s, followed by a sharp decline (Hueb-
ner, 2005). In the study the Flynn effect was reconstructed for pre-
vious centuries based on the idea that its rise was relatively
shallow up until the beginning of the 20th century, at which point
it rose very sharply (three points per decade) and then stagnated
after 2000 (Meisenberg, Lawless, Lambert, & Newton, 2005). The
Flynn effect estimates correlated very strongly with historical esti-
mates of the growth in GDP (PPP) per capita, and in regression a
composite measure of these had a strongly inverse relationship
with a combined measure of illiteracy and homicide. These find-
ings were interpreted on the basis that genotypic IQ most strongly
corresponds with the ‘genetic g’ at the heart of the nomological net
of the Jensen effect. As the Flynn effect gains are ‘hollow’ with re-
spect to g, it is argued that these occur on subfactor specific sources
of variance, which are free to vary independently of g. The negative
impact of homicide and illiteracy on the Flynn effect was taken to
indicate a contribution from improved environmental conditions,
consistent with the life history model proposed in Woodley
(2011a, b; 2012b).
Thus far no study has attempted to directly determine if there is
a Jensen effect on dysgenic fertility differentials, however the stud-
ies of Meisenberg (2010) and Meisenberg and Kaul (2010) have
both found evidence that dysgenic fertility differentials might be
associated with the effect. In both studies, dysgenics was investi-
gated with respect to fertility differentials on the various subtests
of the Armed Services Vocational Aptitude Battery (ASVAB), which
is the principal cognitive ability battery used in the National Lon-
gitudinal Survey of Youth (NLSY). The ASVAB has good criterion
validity, and formed the backbone of Herrnstein and Murray’s
(1994) comprehensive analysis of the social correlates of g.InMei-
senberg (2010) a sample-wide dysgenesis rate of .8 of a point of
genotypic IQ per generation was inferred based on the assumption
that regression to the mean was to the sample mean. Meisenberg
and Kaul (2010) stratified the NLSY based on race and sex and used
race-specific means instead of the sample mean. They found a dys-
genesis rate of about .4 points per generation for the White cohort,
.8 points for the Black cohort and 1.2 points for the Hispanic cohort.
In both studies and across racial groups the gradient of dysgenic
fertility was found to be most pronounced amongst females and
also on grather than the individual subtests. This finding strongly
hints at a Jensen effect on dysgenic fertility, which would be signif-
icant as it implies that dysgenics is part of the genetic nexus of the
Jensen effect, and (in line with the suggestion made in Woodley
(2011a, 2012a, b) occurs on ‘genetic g’. For the first time, the
hypothesis that dysgenic fertility is associated with the Jensen ef-
fect will be explicitly tested.
2. Methods
Following the protocol in Meisenberg (2010) data were col-
lected from the NLSY79 for all 8110 cases which had information
on fertility and intelligence. The subjects were aged 14–22 at the
inception of the study in 1979.
2.1. Cognitive ability measures
The ASVAB was administered in 1980. The ASVAB includes five
academic tests (science, arithmetic, word knowledge, paragraph
comprehension, mathematics knowledge), three vocational tests
(auto & shop info, mechanical comprehension, electronics info),
and two speeded tests (numerical operations, coding speed). The
scores of each subtest were age-adjusted separately for race and
sex. The g-factor was extracted from these age-adjusted test scores
as the unrotated first factor of a maximum-likelihood factor
analysis.
2.2. Dysgenic fertility gradient
For 7439 subjects the self-reported number of children was
known for 2008. For those who were not interviewed in 2008, re-
sponses from the 2006, 2004, or 2002 interviews were used in-
stead. Thus the sample has completed or nearly completed
fertility. To calculate the gradient of dysgenic fertility each subtest
was correlated with the total number of children.
2.3. Vector correlations
Spearman’s rank correlation and Pearson’s product moment
correlation were both used (in SPSS) to determine the correlated
vector correlation between the magnitude of test g-loading and
the magnitude of the dysgenic fertility gradient. The Nequals
the number of ASVAB subtests (10). Fisher’s r-to-ztransforma-
tion was used to determine whether the two methods produced
significantly different magnitude results which would indicate
the existence of biasing factors (Nyborg, 2005). The NLSY data
were also broken out along race and sex lines, following the pro-
tocol of Meisenberg and Kaul (2010) so as to determine whether
the Jensen effect exists within these categories. The sample sizes
for each of the sub-populations are as follows: White males
N= 2039, White females N= 2102, Black males N= 1224, Black
females N= 1258, Hispanic males N= 617 and Hispanic females
N= 648.
3. Results
Table 1 reveals significant Jensen effects (where the Pvalue for
Spearman’s
q
is <.05) on dysgenic fertility for White males, White
females, Black females and Hispanic males, but not for Black males
and Hispanic females. Despite this in all instances the vector corre-
lation trends in the expected positive direction.
2M.A. Woodley, G. Meisenberg / Personality and Individual Differences xxx (2013) xxx–xxx
Please cite this article in press as: Woodley, M. A., & Meisenberg, G. A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal
Survey of Youth. Personality and Individual Differences (2013), http://dx.doi.org/10.1016/j.paid.2012.05.024

A difference in the magnitude of Spearman’s
q
(the generally
preferred indicator of a Jensen effect) and Pearson’s rfavoring
the latter suggests that outliers or peculiarities associated with
either the subtest g-loadings or the dysgenic fertility magnitudes
might be biasing the results (Nyborg, 2005). The differences are
generally small however (with the biggest being .221 in the case
of Hispanic females and the smallest being .016 in the case of His-
panic males), and are non-significant in all cases, which suggests
that bias is minimal.
4. Discussion
It appears that dysgenic fertility is indeed a Jensen effect. Not
only is the effect significant in the majority of cases (five out of
the seven analyses – in all cases the effect trends in the expected
positive direction) but its effect magnitude is relatively large and
is on a par with other variables for which Jensen effects have been
recorded (e.g. Jensen, 1998; Rushton & Jensen, 2010). This finding
using a large and representative sample of the US population, along
with subpopulations and a well validated measure of intelligence,
therefore allows us to place dysgenic fertility into the genetic
nexus of the Jensen effect.
The White males exhibit the least dysgenic fertility of all groups
examined, with fertility differentials being positive in most cases.
It must be noted however that the abilities with respect to which
the White males are apparently in ‘eugenic’ fertility are the ones
exhibiting lower g-loadings. Hence, even for this group the ten-
dency is for fertility to be depressed on highly g-loaded abilities.
The results of this study help to contextualize other findings in
the literature, which have thus far not been discussed in relation to
dysgenesis. Silverman (2010), for example, has found that visual
reaction time has increased substantially since Galton first started
measuring it between 1884 and 1893. In Galton’s measures, reac-
tion time means were .183 s for men (N= 2522) and .187 for
women (N= 302). Silverman demonstrates that Galton’s measures
were typical of his era with reference to reviews of reaction time
studies from 1911 (which did not include Galton’s studies), in
which reaction times ranged from .151 to .200 s, with a median
of .192.
Silverman’s review of twelve modern (post 1941) reaction time
studies reveals a substantially longer mean for both men (.250 s)
and women (.277 s), with a combined sample size of 3836. Silver-
man concludes that in 11 of the 12 studies and in 19 of the 20 com-
parisons, as well as in his meta-analysis, the differences in reaction
time means between Galton’s estimates and modern estimates are
statistically significant. Silverman speculates that these findings
might result from increased exposure to neurotoxins. An alterna-
tive hypothesis is that because dysgenic fertility and reaction times
are both part of the genetic nexus of ‘genetic g’, dysgenic fertility is
prolonging reaction time in addition to reducing g. This would
make Silverman’s finding strong evidence that genotypic IQ
(‘genetic g’) really has been in decline since the last decades of
the 19th century.
Another issue that our finding may shed light upon is the appar-
ent anti-Flynn effect on measures of crystallized intelligence (in
particular crystallized knowledge), which has been observed in a
number of countries, sometimes spanning multiple decades (e.g.
Khaleefa, Sulman, & Lynn, 2008; Lynn, 2009; te Nijenhuis, in press;
Wicherts et al., 2004). Declines in measures of crystallized intelli-
gence typically solicit little commentary in the literature, as gains
in measures of fluid intelligence usually swamp these losses (e.g.
Khaleefa et al., 2008; Lynn, 2009; te Nijenhuis, in press; Wicherts
et al., 2004). A handful of researchers have proposed that measures
of crystallized intelligence might be superior measures of grelative
to measures of fluid intelligence (Gignac, 2006; Gregory, 1999;
Table 1
ASVAB subtests along with their respective g-loadings and dysgenic fertility gradients for the whole of the NLSY sample (N= 8110), White males (N= 2039), White females (N= 2102), Black males (N= 1224), Black females (N= 1258),
Hispanic males (N= 617) and Hispanic females (N= 648).
ASVAB
subtests
Subtest
g-loading
(whole
sample)
Dysgenic
fertility
(whole
sample)
Subtest
g-loading
(White
males)
Dysgenic
fertility
(White
males)
Subtest
g-loading
(White
females
Dysgenic
fertility
(White
females)
Subtest
g-loading
(Black
males)
Dysgenic
fertility
(Black
males)
Subtest
g-loading
(Black
females)
Dysgenic
fertility
(Black
females)
Subtest
g-loading
(Hispanic
males)
Dysgenic
fertility
(Hispanic
males
Subtest
g-loading
(Hispanic
females)
Dysgenic
fertility
(Hispanic
females)
Science .918 -.147 .895 .000 .860 -.062 .879 -.015 .854 -.194 .906 -.165 .893 -.302
Arithmetic .857 -.103 .845 .036 .850 -.038 .781 -.008 .737 -.16 .804 -.124 .814 -.195
Word knowledge .916 -.152 .899 -.005 .877 -.094 .912 -.012 .912 -.202 .912 -.172 .910 -.322
Paragraph
comprehension
.853 -.131 .850 .012 .799 -.050 .851 -.031 .852 -.173 .869 -.167 .871 -.292
Numerical
operations
.733 -.086 .700 .500 .647 -.036 .700 .055 .696 -.175 .721 -.072 .702 -.211
Coding speed .665 -.074 .641 .510 .548 .004 .639 .036 .613 -.162 .682 -.070 .669 -.231
Auto-shop
information
.737 -.105 .645 .480 .616 -.042 .715 .045 .561 -.130 .760 -.106 .718 -.202
Math knowledge .844 -.130 .833 .005 .834 -.057 .766 -.052 .793 -.222 .808 -.171 .811 -.241
Mechanical
comprehension
.809 -.097 .780 .460 .740 -.039 .732 .056 .531 -.062 .807 -.140 .720 -.195
Electronic
information
.848 -.127 .823 .170 .750 -.056 .797 -.015 .668 -.102 .862 -.210 .783 -.189
Pearson’s r.899
*
.914
*
.783
*
.665
*
.786
*
.871
*
.768
*
Spearman’s
q
.830
*
.939
*
.758
*
.614
(ns)
.806
*
.855
*
.547
(ns)
nb: The signs on the dysgenic effects are negative, and ‘eugenic’ effects are positive, hence these are reversed when comparing the magnitude of dysgenesis with the magnitude of the subtest g-loadings yielding positive vector
correlations.
*
P<.05.
M.A. Woodley, G. Meisenberg / Personality and Individual Differences xxx (2013) xxx–xxx 3
Please cite this article in press as: Woodley, M. A., & Meisenberg, G. A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal
Survey of Youth. Personality and Individual Differences (2013), http://dx.doi.org/10.1016/j.paid.2012.05.024

Matarazzo, 1972; Robinson, 1999). Consistent with this is the find-
ing that in head-to-head comparisons using a sufficiently broad ar-
ray of intelligence measures, measures of fluid intelligence (such as
Ravens matrices) have been found to be substantively less g-loaded
than measures of crystallized knowledge (such as vocabulary, see
Johnson, Bouchard, Krueger, McGue, & Gottesman, 2004). Further-
more Miller (2000a) has argued that crystallized knowledge (such
as vocabulary) is likely to have been (and still is) a very significant
indicator of general fitness (underlying genetic quality), which
might therefore account for its relatively high g-loading, as Miller
has also argued that the positive manifold results from the effects
of pleiotropic mutations which in abundance would lower both g
and general fitness (Miller, 2000b, c). The observations of multi-
decadal declines in crystallized knowledge might therefore relate
to dysgenic fertility via the genetic nexus as both anti-Flynn effects
and dysgenic fertility concern subtests exhibiting high g-loadings.
The finding of a Jensen effect on dysgenic fertility is significant
to future research, as in light of the aforementioned findings it
strongly suggests that ‘genetic g’ really has been in decline since
the end of the 19th century. This reinforces the significance of
the idea that changing genotypic IQ has had real world impacts
on important factors such as the rates of scientific and technolog-
ical innovation amongst Western populations (Woodley, 2012a).
Acknowledgments
We would like to thank two anonymous reviewers and also
Bruce G. Charlton for comments that improved this manuscript.
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Please cite this article in press as: Woodley, M. A., & Meisenberg, G. A Jensen effect on dysgenic fertility: An analysis involving the National Longitudinal
Survey of Youth. Personality and Individual Differences (2013), http://dx.doi.org/10.1016/j.paid.2012.05.024