A recent study on adoption and suicide suggests genetic (biological) rather than environmental factors play a dominant role in risks for suicide.
Researchers used Danish adoption data and compared non-biologically related siblings of orphans (children who had been adopted and biologically related siblings that the orphan did not grow up with. Basically what they looked for were co-occurring pairs of suicide or non-suicide. [See the footnote for a descriptive example.] The researchers found the strongest association of co-occurring suicides in orphans and their (unknown) biologically related siblings.
The authors include some various caveats and methodological qualifiers you can read about for yourself in the cited study above. A most important factor, not mentioned in the study but confirmed in my correspondence with the lead researcher: none of the children studied were transnational orphans. Specifically, I asked, “Are these adoptees all domestic adoptions (meaning only of Danish, or Caucasian, children or not)?” And the reply was, “We looked only at Danish children, so ethnicity were the same for all of them.”
This study accepts as a matter of course an elevated suicide risk for adopted orphans, but defenders of adoption will be glad to hear genetics play the dominant role. This, because it means that the orphan happened already to be prone to suicide—as the suicide of her or his (unknown) biologically related sibling suggests. An analogous anecdote: after I came out to my father, he eventually “got okay with it” when someone told him homosexuality is genetic: that explanation “let him off the hook”; me being gay “wasn’t his fault”. I’d expect the same stuff from parents of adopted orphans who commit suicide—the tragedy “isn’t their fault”.
One may also imagine, with a shudder, what sort of regimens might get implemented by adopting parents to ensure that the suicide time-bomb of their adoption might not go off. Or maybe opponents of adoption could use this result to frighten would-be adopters: “we don’t really know why, Mister and Missus, but orphans who get adopted are far more likely to kill themselves. Caveat emptor!” We might try to imagine what sort of bizarre “screening” process for orphans would be traffickers might develop to eliminate genetically proto-suicidal orphans.
Disregarding the methodological pitfall that insists a genetic/environmental dichotomy actually has useful explanatory power (I doubt it), what other problematic consequences do you see stemming from this finding? What sort of mechanism do you think explains the finding; for me since all of the children are domestic Danish orphans, to talk about “mere physical separation” as evidence of “environmental differentiation” within Denmark seems dubious. The absence of “non-Danish” orphans strikes me as very significant as well.
 To use me as an example: in my adoptive family, I have one sister who was also adopted and one brother who was not; I also have (presumably) biologically related siblings I don’t know. If I commit suicide and one of my adoptive-family siblings does, that argues positively for environmental factors (the study assumes). If I commit suicide and one of my (unknown) biological siblings does, that argues positively for genetic factors (the study assumes). If I do not commit suicide and one of my adoptive siblings does, this argues against environmental factors but does not therefore automatically support a genetic argument. And, finally, if I do not commit suicide, but my (unknown) biological sibling does, this also argues against the genetic explanation, but does not automatically provide evidence for the environmental explanation.
 There remains an ambiguity here. My own question inadvertently permits the conflation of nationality and ethnicity and the researcher’s reply assumes (or states as a fact) that all of the “Danish” children in the study were the same (Scandinavian) ethnicity.