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This question already has an answer here:

Is there any evidence of outbreeding depression in human beings?

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marked as duplicate by theforestecologist, fileunderwater, James, kmm, another 'Homo sapien' Mar 24 '17 at 4:06

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • $\begingroup$ @Remi.b - why would this be a dupe? This question has nothing to do with the definition of species, but with the possibility to eliminate the genetic component of depression. I actually like this question a lot. +1 $\endgroup$ – AliceD Mar 23 '17 at 20:29
  • $\begingroup$ @AliceD The currently most upvoted answer provided in Does it make sense to classify all humans in a single species? specifically target the this question. $\endgroup$ – Remi.b Mar 23 '17 at 20:32
  • $\begingroup$ @Remi.b and is the convention then to close this one? I have seen many (still open) questions that are answered by answers to other questions. $\endgroup$ – AliceD Mar 23 '17 at 20:35
  • $\begingroup$ @AliceD Ok. So, do you think I could just copy-paste the section 'Do we have documented cases of outbreeding depression?' of my answer at the other post to make the answer here? Keeping this post open eventually allow others to target more specifically this issue here while they can't on the other post that is a little bit broader in sense, right? $\endgroup$ – Remi.b Mar 23 '17 at 20:39
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    $\begingroup$ Ok, I removed my close vote. I copy-pasted my answer. I did not add any info (or reference) though as the whole point of the question is to try to find more references and I already tried and failed to find other references of interest. Thanks Alice $\endgroup$ – Remi.b Mar 23 '17 at 20:55
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Answer below is copy-pasted from the section Do we have documented cases of outbreeding depression? of my answer here.

Many cases of inbreeding depression have been documented in humans (McQuillan et al. 2012, Strauss et al. 2013, Lettic et al. 2008, Gellera et al. 1990) but cases of outbreeding depression seem much rarer if any!

I spent some time screening through the literature searching for potential evidence of outbreeding depression. The only paper I found is Udry et al. 2003.

Udry et al. 2003:

  • First, note that they do not place their results in the context of our present discussion and do not talk about outbreeding depression.

  • They report that children of "mixed-race" in US colleges report having more behavioural troubles. One would obviously note that there could well be true that "mixed-race" children experience a different environment (incl. social environment) than "non-mixed-race" children. Such results therefore does not suggest the existence of any outbreeding depression.

  • They also reports more skin problem in mixed-race children. Unfortunately, 1) their p.value is only slightly significant and 2) they track tens of variables without correcting for multiple comparisons and only one came out significant suggesting it is likely to be a false positive.

So, in short: No, there is little to no evidence of outbreeding depression in humans

It is not impossible that there is a publication bias in which researchers looked for inbreeding depression more than for outbreeding depression but I doubt it would be the case. Such bias seems possible only if the outbreeding depression, should it exist, would be very slight and hard to detect outside a rigorous scientific study. In essence, such potential publication are impossible to detect.

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  • $\begingroup$ Great! +1 I am a huge fan of digging up old questions and with another vote you'll get your well-deserved revival badge. I love this :) $\endgroup$ – AliceD Mar 23 '17 at 21:14