# Outbreeding Depression in Humans?

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outbreeding depression refers to cases where offspring from crosses between two different different populations have a lower level of fitness than offspring from crosses between individuals from the same population.

One of the ways that outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different breeding populations. Within local, isolated breeding populations, alleles are selected for their positive, overall effects in complementary combination with other specific alleles. Due to nonadditive gene action, the same genes may have rather different effects in different genetic backgrounds--hence, the potential evolution of locally coadapted gene complexes.

Examples in Switchgrass

These effects can be observed in switchgrass (Panicum virgatum). While actually a single species, switchgrass comes in many different varieties, with striking differences between the different types. This genetic diversity reflects the divergent evolution and adaptation to a wide range of different environments. The different varieties of switchgrass can generally be grouped into two distinct forms: the lowland cultivars and the upland cultivars.

The lowland variety tends to produce more biomass, and grow up to 2.7 meters high in favorable environments. The upland variety is generally of more northern origin, and is more cold-tolerant. Upland switchgrass types are generally shorter, less than 2.4 meters in height, and less coarse than lowland types. The upland types tend to have more vigorous rhizomes so they tend to be more sod-forming, whereas the the lowland cultivars may appear to have a bunchgrass habit. Lowland cultivars appear more plastic in their morphology, produce larger plants if stands become thin or when planted in wide rows, and they seem to be more sensitive to moisture stress than upland cultivars.

One study mentions potential negetive effects on native varieties on switchgrass caused by outbreeding depression, which could be a cause for concern.

"Gene flow matters in switchgrass, a potential widespread biofuel feedstock", Charles Kwit, C. Neal Stewart. Department of Plant Sciences, University of Tennessee, Knoxville, Tennessee; and BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee

"The potential for genetic pollution has been investigated in switchgrass..."

"Appropriate Use of Genetic Manipulation for the Development of Restoration Plant Materials", T. A. Jones, J. G. Robins, Progress in Botany, Volume 72, Part 5, p 249-264, 2011

Examples in Humans?

Different groups of humans have been separately evolving for tens of thousands of years. There has been plenty of genetic divergence over this long period of time. Could it be possible that each of these separate groups of people have achieved, through natural selection, a fine-tuned balance of hormones and subtle gene expression, which could become upset by sudden change?

Herbert Spencer and the Harvard geneticist Edward East, a pioneer in hybrid corn research, proposed that genetic crossing would disrupt the smooth operation of the physical and mental qualities which have been established in each race over hundreds of generations by natural selection.

Carleton Coon, former professor at Harvard and president of the American Association of Physical Anthropologists, wrote: "Genes that form part of a cell nucleus possess an internal equilibrium as a group, just as do the members of social institutions. Genes in a population are in equilibrium if the population is living a healthy life as a corporate entity. Racial intermixture can upset the genetic as well as the social equilibrium of a group."

An analysis of more than 3 million respondents revealed the average pay was $15.74 per hour for people of mixed race,$17.39 for black people and \$22.04 for white people. This was despite the fact that 18 per cent of mixed-race people had college degrees, compared with 11 per cent of black people and 28 per cent of white people.

"Can the 'one-drop rule' tell us anything about racial discrimination? New evidence from the multiple race question on the 2000 Census", Robert W. Fairlie

University of California, Santa Cruz

A study by J. Richard Udry’s National Longitudinal Study of Adolescent Health, which sampled a random, nationally representative school-based sample of U.S. adolescents in grades 7 through 12, during 1994-1995, showed an increase in behavioral problems amongst mixed-race children, as well as significantly higher rates of asthma, and generally poorer health. Another interesting finding was that mixed children that had a black parent were significantly more likely (63% more) to have skin problems.

J. Richard Udry, Janet Hendrickson-Smith, Carolina Population Center, University of North Carolina at Chapel Hill, 2003

Anita Patel,M.D., transplant nephrologist at Henry Ford Hospitalfound that kidney transplants between individuals of the same race had statistically betteroutcomes than transplant across different races.

http://www.time.com/time/health/article/0,8599,1993074,00.html

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It may seem an ad hominem argument against them but it was usual in that time that rather than science hypothesis were driven by racism... That is why phrenology was so popular in those times... I think it is illogical to think outbreeding depression is possible when human populations are not so different from each other and when survival for humans is so similiar throughout most of human populations... I had say indeed that rather than outbreeding depression we should enjoy hybrid vigour from racial mixing and that racial purity is more of a disease (when it is real) than anything else... furthermore, it is very unusual.

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There are a lot of misconceptions in this post, also misquotation. Let me just point this out.

"Genes that form part of a cell nucleus possess an internal equilibrium as a group, just as do the members of social institutions. Genes in a population are in equilibrium if the population is living a healthy life as a corporate entity. Racial intermixture can upset the genetic as well as the social equilibrium of a group."

The original quote is a bit longer (also note that this is from the 60s):

The above is the behavioral aspect of race relations. The genetic aspect operates in a comparable way. Genes that form part of a cell nucleus possess an internal equilibrium as a group, just as do the members of social institutions. Genes in a population are in equilibrium if the population is living a healthy life as a corporate entity. Racial intermixture can upset the genetic as well as the social equilibrium of a group, and so, newly introduced genes tend to disappear or be reduced to a minimum percentage unless they possess a selective advantage over their local counterparts.

I am making these statements not for any political or social prupose but merely to show that, were it not for the mechanisms cited above, men would not be black, white, yellow, or brown. We would all be light khaki, for there has been enough gene flow over the clinal regions of the world during the last half million years to have homogenized us all had that been the evolutionary scheme of things, and had it not been advantageous to each of the geographical races for it to retain, for the most part, the adaptive elements in its genetic status quo.

The latter part bluntly refutes

Different groups of humans have been separately evolving for tens of thousands of years. There has been plenty of genetic divergence over this long period of time.

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The latter part bluntly refutes..

A significant proportion of fine scale genetic structure in humans is clinal

http://www.sciencedi...002929709001578

" Table 2 summarizes the results of this test and demonstrates that significant evidence of clinal variation is observed for all continents"

Genetic studies also indicate significant inter-population migration since at least the Pleistocene.

http://mbe.oxfordjournals.org/content/26/8/1823.full

"We find evidence for this ancient admixture in European, East Asian, and West African samples, suggesting that admixture between diverged hominin groups may be a general feature of recent human evolution."

There is no genetic evidence to suggest long term isolation of human races, and significant evidence to suggest that gene flow between races is characteristically high throughout human evolutionary timescales.

Edited by Arete
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• 1 year later...

It may seem an ad hominem argument against them but it was usual in that time that rather than science hypothesis were driven by racism... That is why phrenology was so popular in those times... I think it is illogical to think outbreeding depression is possible when human populations are not so different from each other and when survival for humans is so similiar throughout most of human populations... I had say indeed that rather than outbreeding depression we should enjoy hybrid vigour from racial mixing and that racial purity is more of a disease (when it is real) than anything else... furthermore, it is very unusual.

That does seem very much like an ad hominem argument. You have left yourself open to many questions:

1. Are human populations really not so different from each other? Against what standard can we claim that? (it needs clarification and support)

2. Is survival for humans, and has it historically been, so similar for different populations in different environments as to render this field of study negligible?

3. Certainly we should enjoy hybrid vigour from racial mixing when it exists, but can you prove its significance and also that it outweighs outbreeding depression in all cases?

4. Can you define what you mean by "racial purity" and what evidence do you have that it is a "disease" and also very unusual?

Your answer seems well intentioned but unfortunately it may suffer from the same kind of ideological distortion as previous science that was influenced by racism, in your case it seems to be tainted by political correctness and a mild politically progressive orthodoxy. I will grant you that the effect is relatively mild in your case; there have been extremists who have called for an outright ban on entire fields of research which could have anything to do with racism, with all the dark historical resonance of the Church stifling progress in ages past:

http://blogs.scientificamerican.com/cross-check/2013/05/16/should-research-on-race-and-iq-be-banned/

I think this is an area of research which has been severely stifled, ignored and viewed with outright horror. I place the blame to a large extent on the shoulders of none other than Hitler. It simply happened too recently to repoen this stuff with neutrality and objectivity. The few brave souls who ventured back into these dark areas have received very little support, funding or recognition. I think above all, everything in science must be approached with pure, cold, detached, rational objectivity and scientific curiosity. Nothing is sacred and nothing is beyond questioning.

Edited by anonymouswanderer
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Shit, why stop at depression.....

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Let's outbreed every unfavourable trait, never heard of that one.

Edited by DevilSolution
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Shit, why stop at depression.....

......

...............

.........................

Let's outbreed every unfavourable trait, never heard of that one.

Sorry DevilSolution, I think you have misread the OP's intent. But I assumed the same thing by the title until I read the post.

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I can't take any of this seriously for the following reasons.

1) Human domestication leads to greater inactivity.

2) We aren't slaves to our genes.

3) Physical activity upregulates epigenes, the good genes that make us feel strong.

4) Natural vitamin and mineral deficiencies in the general public should be of major concern since these vitamins and minerals regulate our biochemistry, and not how we "should" manipulate genes. Humility, not arrogance.

Lazyness is a brutal disease.

Edited by turionx2
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• 1 month later...

Not much research is done on politically sensitive areas like this. Because honest research can produce politically inconvenient results that can end careers no mater how factually correct.

But I did find one study on the Health statistics of mixed race children

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448064/

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Not much research is done on politically sensitive areas like this. Because honest research can produce politically inconvenient results that can end careers no mater how factually correct.

But I did find one study on the Health statistics of mixed race children

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1448064/

A) I would argue the opposite - there is an exceptionally extensive body of research on genetic variation in humans, some of which is cited previously. This research has demonstrated that, by and large, the major "races" of humans represent cultural groups, which have undergone a considerable level of admixture throughout time, such that they do not reflect distinct genetic clusters. As a result, it is not possible for one to speculate about "outbreeding depression" between races, as to do so requires that races are distinct genetic entities - which they aren't.

B) The study you cite investigates the psychological impact of identifying as mixed race. It makes no explicit or implicit link to any sort of heritable causation at all - in fact the opposite - citing environmental factors to do with identity crises as the most likely (albeit speculative) explanation for their observations.

C) The (now banned) OP was trying to evidence some rather absurdly flawed notions regarding the validity of draconian eugenics and compulsory sterilization, so this was never really a good faith discussion.

Ultimately, if your aim is to look at humans through the lens of population genetics (rather than try and push a controversial political agenda) starting with traditional "races" as your a priori grouping is not sensible.

e.g.

http://www.nature.com/nrg/journal/v10/n4/full/nrg2554.html

etc

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as with studies of endangered species, a low population of animals gets more unhealthy as the offspring become more inbred with fewer adults. I have heard that bi-racial children are happier, more intelligent and more emotionally stable than an average child born of ethnically similar parents. The president of the united states, one particular example of a biracial marriage, seems healthy, intelligent, and emotionally stable enough to handle arguably the most demanding job on the planet....

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