Shared environmental sources of the variation in nonverbal intelligence are largely twin-specific: the study of twin and sibling pairs from Russia,статья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 17 ноября 2018 г.
Аннотация:Our previous research on Russian adolescent twins revealed a substantial
shared environmental variation in the individual differences in
the non-verbal ability (65%, Malykh et al. 2016), unlike the other
behavior genetic research of cognitive abilities (30%, Polderman et al.
2015). The current study aimed to estimate the role of twin-specific
shared environmental effects by comparing twin and sibling pairs.
The sample included 730 twin pairs (305 MZ, 425 DZ, mean age 13
years, SD = 2.9 years) and 154 sibling pairs (139 full sibling, 15 half
sibling, mean age 11 years, SD = 3.2 years). The mean age difference
in sibling pairs was 4.4 years. The non-verbal ability was assessed by
means of Raven’s Progressive Matrices. The twin-sibling model
included the age variable to filter out the age-related variation. The
MZ and DZ twins showed substantially higher similarity in cognitive
ability than full and half siblings (r = 0.78 and 0.67 versus 0.20 and
0.23) which indexes the twin-specific shared environment. The total
estimate of the shared environmental effects was 73%, the rest of the
phenotypic variance accounted for non-shared environment (27%).
Half of the shared environmental variance was twin-specific (34% of
the total variance). The age had statistically significant effect in the
twin-sibling model (b = 1.36, p\0.05). Our results suggest that the
large part of the shared environmental effects of the non-verbal
intelligence is twin-specific. This matches the twin-sibling research
on the child twins (Koeppen-Schomerus et al. 2003). We suggest that
the twin-specific environmental effects observed in our study stem
from the school environment. Unlike siblings, twins undergo the
school program synchronically and often attend the same class.
Therefore the twins share more environmental variation than siblings.
As an additional analysis we computed the similarity in the two
groups of full siblings divided by the median age difference 4 years.
The siblings with closer age exhibited higher similarity in the level of
cognitive ability than the siblings of dissimilar age (r = 0.44 and
- 0.07)