
Why are children in the same family so different from one another? (1987) [pdf] - gwern
https://www.gwern.net/docs/genetics/heritable/1987-plomin.pdf
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sbierwagen
(1987)

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gwern
Not that much has changed since then! Non-sharedenvironment remains the
largest source of variance after genes in most human traits, shared-
environment remains largely trivial after childhood, siblings remain quite
different from each other, and the sources of non-sharedenvironment relatively
mysterious aside from more evidence that noise like somatic mutations and
infections are responsible and IMO not so much peer-effects like Harris
hypothesizes in _The Nurture Assumption_.

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onuralp
Shared environment is probably not created equal though. While the family
environment is constant, parents are likely to vary (deliberately and/or not)
in their resource allocation (e.g., attention and care) among their kids. An
interesting recent paper shows that the non-inherited genetic material of the
parents may _still_ have an influence on the kid. [0] What exactly accounts
for that influence remains to be elusive, and it would be quiet astonishing if
the majority of the influence can be explained by well-established (or rather,
exhaustively studied) behavior patterns in psychology. For example: birth
order, number of same-sex siblings etc.

[0]
[https://www.biorxiv.org/content/early/2017/11/14/219261](https://www.biorxiv.org/content/early/2017/11/14/219261)

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gwern
> An interesting recent paper shows that the non-inherited genetic material of
> the parents may _still_ have an influence on the kid. [0]

Yes, but that comes out of the heritability component, not the non-
sharedenvironment component.

> For example: birth order, number of same-sex siblings etc.

Birth order, by definition, can't explain any of the variance in fraternal vs
identical twins, and there's a lot of doubt about whether it exists at all and
for which traits. Likewise, I haven't seen much credible research on sibling
effects - most such sociological research doesn't even bother to try to
control or quantify any of the relevant genetics, and is 100% useless.

