Is there any evidence of outbreeding depression in human beings?
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.
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.