Electronic Supplementary Material Intralocus sexual conflict over height
Table S1. Descriptive statistics (mean ± s.d.) of the respondents and siblings from the
Wisconsin Longitudinal Study (only sibling pairs where the age difference was less than ten
years were included).
Respondent
Male
Female
(N=1,665)
(N=1,857)
Height (cm) 179.2 ± 6.5
164.2 ± 6.1
Birth year
1938.8 ± 0.5
1938.9 ± 0.4
Number of 2.5 ± 1.5
2.8 ± 1.7
children
Selected Sibling
Male
Female
(N=1,669)
(N=1,853)
179.0 ± 6.3
164.0 ± 6.1
1939.6 ± 5.2
1939.7 ± 5.2
2.5 ± 1.6
2.7 ± 1.7
Table S2. Pearson correlation coefficients describing the association between sibling heights.
(all p < .0001)
Pearson r
.475
.406
.449
Heritability (h2)a
0.950
0.812
0.898
Brothers (N=808)
Sisters (N=996)
Opposite-sex
siblings (N=1,718)
a
To obtain h2, the correlation coefficient r between heights of full siblings is multiplied by 2.
This calculation, however, includes the effect of the shared environment and thus
overestimates h2. These correlation coefficients are reasonably close to what is expected on
the basis of the h2 range reported for height in Western populations [11, see main text].
Table S3. Poisson regression parameter estimates (± s.e.) and p-values (based on Z-value) for
the effect of height, height2, birth year (centered) and birth year2 on reproductive success for
the male (N = 1,669) and female (N = 1,853) siblings of the main respondents.
Male siblings
Female siblings
Parameter estimate (± s.e.) p-value Parameter estimate (± s.e.)
Intercept -18.48 (± 8.94)
.039
2.25 (± 0.38)
Birth year -0.030 (± 0.003)
<.001
-0.039 (± 0.003)
a
Birth
-1.32*10-3 (± 5.25*10-4)
year2
Height
0.22 (± 0.10)
.028
-7.63*10-3 (± 2.33*10-3)
b
Height 2
-6.20*10-4 (± 2.80*10-4)
.027
a
Squared term of birth year not significant for males (p =.604)
b
Squared term of height not significant for females (p = .563)
p-value
.013
<.001
.012
.001
Figure S1. The effect of the (a) male and (b) female height (in bins of 2.5 cm) on the number
of children ever born for the selected siblings of the main respondents (see main text). For
men, bins below 165 cm and above 192.5 cm, and for women bins below 150 cm and above
177.5 cm were collapsed. A significant curvilinear effect was found for men (with the
optimum at a height of 177 cm) and a negative effect for women (Table S3).
Table S4. Mixed model Poisson parameter estimates (± s.e.) and p-values (based on Z-value)
for the effect of the average height (standardized) and height2 of the sibling pair, sex of the
individual and their interactions on the number of children (N = 7,044). A random intercept
was included for sibling pair.
Intercept
Sex (ref. cat=male)
Pair height
Pair height 2
Sex * Pair height
Sex * Pair height2
Parameter estimates (± s.e.)
0.93 (± 0.014)
0.054 (± 0.019)
-0.025 (± 0.014)
-0.035 (± 0.011)
-0.035 (± 0.018)
0.046 (± 0.015)
Random effect
Sibling pair
Parameter estimates (± s.d.)
0.025 (± 0.16)
p-value
<.001
.004
.066
.002
.052
.003
Figure S2. The effect of the average height of the sibling pair (average over heights
standardised per sex) on (a) the number of children (mean ± s.e.) through the brother (closed
circle and solid line) and the sister (open circle and dashed line; predictions based on
estimates Table S4) and (b) the difference in reproductive success (pooled s.e. from (a))
between sisters and brothers (minus the overall average difference in number of children
between the sexes – see text). Height was divided in bins of 0.5. Bins ≤-2 and ≥2 were
pooled.
Table S5. Mixed model Poisson parameter estimates (± s.e.) and p-values (based on Z-value)
for the effect of the average height (standardized) and height2 of the sibling pair, sex of the
individual and their interactions on the number of children in opposite-sexa sibling pairs (N =
3,346). A random intercept was included for sibling pair.
Intercept
Sex (ref. cat=male)
Pair height
Pair height 2
Sex * Pair height
Sex * Pair height2
Parameter estimates (± s.e.)
0.95 (± 0.019)
0.023 (± 0.026)
-0.029 (± 0.019)
-0.048 (± 0.016)
-0.021 (± 0.025)
0.061 (± 0.021)
p-value
<.001
.37
.13
.003
.41
.004
Random effect
Parameter estimates (± s.d.)
Sibling pair
0.024 (± 0.15)
a
Estimates were very similar when including same-sex sibling pairs (see main text, Table 1,
and Table S4). No significant three-way interaction was found between sex and type of
sibling pair (same-sex versus opposite sex) and the average height of the sibling pair (p = .41)
nor the squared average height (p = .31). Thus, the effect of height was not specific to
opposite-sex sibling pairs, nor could they be attributed to the inclusion of same-sex sibling
pairs.
Table S6. Mixed model Poisson parameter estimates (± s.e.) and p-values (based on Z-value)
for the effect of the height (standardized) and height2 of both individuals from the sibling
pair, sex of the individual and their interactions on the number of children (N = 7,044). A
random intercept was included for sibling pair.
Intercept
Sex (ref. cat=male)
Height
Height 2
Sex * Height
Sex * Height2
Parameter estimates (± s.e.)
0.94 (± 0.014)
0.045 (± 0.018)
-0.019 (± 0.012)
-0.037 (± 0.008)
-0.035 (± 0.016)
0.043 (± 0.011)
Random effect
Sibling pair
Parameter estimates (± s.d.)
0.024 (± 0.16)
p-value
<.001
.014
.105
<.001
.023
<.001
Table S7. Mixed model Poisson parameter estimates (± s.e.) and p-values (based on Z-value)
for the effect of an individual’s height (standardized) and height2, sibling sex, and their
interactions on the number of children by the siblinga, while controlling for the sex of the
individual (N = 7,044). Because we had data available from 3,522 pairs of siblings, a random
intercept was included for sibling pair (see main text).
Intercept
Sex (ref. cat=male)
Sibling sex (ref. cat=male)
Height
Height 2
Sex sibling * Height
Sex sibling * Height2
Parameter estimates (± s.e.)
0.82 (± 0.039)
0.021 (± 0.015)
0.064 (± 0.018)
-0.0067 (± 0.025)
-0.012 (± 0.017)
-0.012 (± 0.015)
0.024 (± 0.010)
p-value
<.001
.160
<.001
.791
.019
.454
.017
Random effect
Parameter estimates (± s.d.)
Sibling pair
0.025 (± 0.16)
a
Rather than analysing the effect of height on reproductive success within sibling pairs, a
different approach to examine intralocus sexual conflict over height would be to examine
what the effect of an individual’s height is on the reproductive success of the sibling of that
individual. This approach is more similar to that of [7, see main text], who showed that
physically and hormonally masculine men and women rated their brothers as more attractive
than their sisters. In line with this study, we predict that the height of an individual predicts
the reproductive success of a sister differently than the reproductive success of a brother.
Thus, a significant effect of an interaction between an individual’s height and the sex of the
sibling on the reproductive of that sibling is expected.
Acknowledgements
This research used data from the Wisconsin Longitudinal Study (WLS) of the University of
Wisconsin-Madison. Since 1991, the WLS has been supported principally by the National
Institute on Aging (AG-9775 and AG-21079), with additional support from the Vilas Estate
Trust, the National Science Foundation, the Spencer Foundation and the Graduate School of
the University of Wisconsin-Madison. A public-use file of data from the Wisconsin
Longitudinal Study is available from the Wisconsin Longitudinal Study, University of
Wisconsin-Madison, 1180 Observatory Drive, Madison, Wisconsin 53706 and at
http://www.ssc.wisc.edu/wlsresearch/data/. The opinions expressed herein are those of the
authors.