This phenomenon can occur in two ways. One way is by the “swamping” of locally adapted genes in a wild population by straying from, for example, a hatchery population. In this case, adaptive gene complexes in wild populations are simply being displaced by the immigration of genes that are adapted to the hatchery environment or to some other locality. For example, selection in one population might produce a large body size, whereas in another population small body size might be more advantageous. Gene flow between these populations may lead to individuals with intermediate body sizes, which may not be adaptive in either population. A second way outbreeding depression can occur is by the breakdown of biochemical or physiological compatibilities between genes in the different populations. Within local, isolated populations, alleles are selected for their positive, overall effects on the local genetic background.
Due to nonadditive gene action, the same genes may have rather different average effects in different genetic backgrounds—hence, the potential evolution of locally coadapted gene complexes. Offspring between parents from two different populations may have phenotypes that are not good for any environment. It is important to keep in mind that these two mechanisms of outbreeding depression can be operating at the same time. However, determining which mechanism is more important in a particular population is very difficult.
beige people, blandifying selection traits
In other words, genetic structure, aka, genetic correlation structure is more than additional ethnic genetic interest—it can be function, hence loss of that structure results in loss of function resulting in outbreeding depression.
Evidence for outbreeding depression is much less extensive than evidence for inbreeding depression, but outbreeding depression is nevertheless a general genetic phenomenon. One problem in studying outbreeding depression is the number of generations that may occur before outbreeding depression reveals itself. The effects of outbreeding enhancement due to the masking of deleterious alleles and outbreeding depression due to hybrid breakdown may cancel each other in the first generation after crossing individuals from two populations. So the effects of outbreeding depression may not be apparent for a few generations.
They just know that inbreeding is more of a problem than outbreeding—and that’s why they’re “justified” in imposing outbreeding on populations with government force and technologically amplified panmixia.
Quotes and sarcasm, deserved.
This paper demonstrates that, in an analysis of Icelandic couples born between 1800 and 1965, there is a “significant positive association” between kinship and fertility; maximal reproductive success was observed for couples with kinship relatedness at the level of third or fourth cousins.
The authors conclude that these differences in reproductive success (i.e. fitness*) have a “biological basis” – that is, a genetic basis.
Strikingly, however, our results show that couples related at the degree of third to fourth cousins exhibited the greatest reproductive success.
In order to maximize fitness, therefore, one doesn’t have to move that far from the endogamous extreme. Just a few rungs upward on the kinship distance ladder produces benefits superior to that of both extremes. It’s totally irresponsible and mendacious to use the fitness costs of obvious incest to argue for reckless hybridization (**) with the most genetically distant organisms with which individuals are cross-fertile.
“It could be argued that in human populations there is a point of balance between the disadvantages associated with inbreeding versus those with outbreeding,” said Alan Bittles, director of the Center for Human Genetics at Edith Cowan University in Western Australia.
Therefore, not only is it unlikely – as has been asserted on this blog previously – that any putative “hybrid vigor” can compensate for lost parental kinship, but it’s also highly unlikely that “hybrid vigor” exists to any significant extent for most human populations past the “second cousin” level. Defining fitness in the proper biological sense, the recent deCODE findings suggest that increased hybridity past an optimal point may in fact reduce reproductive fitness above and beyond the real losses in genetic interests due to foregone parental kinship.
From the Udry study discussed by J. Richards in a previous blog post, to the lack of any evidence of enhanced reproductive success of mixed couples and their offspring, to these latest deCODE findings that reproductive success may be maximized by closer kinship, it would seem that when in doubt, one should err on the side of increased endogamy (to the level of “third cousins” only, of course).
When even deCODE – which decided to sift through James Watson’s ancestry and make public their dubious findings because of a politically correct distaste at what they perceived as Watson’s (presumably “racist”) comments on African intelligence levels – publishes findings that show a biologically based enhanced fitness for mating at high levels of kinship relatedness, then one must wonder how any scientifically objective individual could possibly still peddle the idea that cross-racial mating is somehow a biologically preferable choice.
An important point: it’s really not so important that high kinship actually enhances reproductive fitness, or the mechanisms whereby that occurs. More important is the lack of evidence for the contrary view: that increasing levels of exogamy leads to “hybrid vigor” and enhanced fitness. The findings from this study constitute yet more evidence that “hybrid vigor” is not an important force – if it is one at all – for humans.
It doesn’t exist in humans, we’re not racehorses.
Prized, rare (or unique) traits like genius, maybe, but that’s kin-related, subrace max.
In the absence of such “hybrid vigor,” parental kinship takes “center stage.” The possibility that endogamy may actually raise fitness per se, as suggested by deCODE, is just “icing on the cake,” hammering home the point that mating “between the lines” of genetically distant groups is not required for enhanced fitness.
*Reproductive success and the maintenance/expansion of distinctive genetic information are the reasonable measures of biological fitness, not whether “Tiger Woods smells better on the golf course,” or any other inane commentaries that spew forth from the addled “minds” of certain hysterical proponents of objectively maladaptive inter-racial couplings.
An example of maladaptive inter-racial hybridization is found here. Again, that’s not even considering reproductive fitness or parental kinship, but merely negative health consequences of introducing one race’s genes into another race’s genome.
**Responsible researchers and conservationists are beginning to understand the consequences of reckless hybridization and outbreeding depression. Some quotes, and my comments:
the available data suggest that risks of outbreeding, particularly in the second generation, are on par with the risks of inbreeding.
If there’s no advantage for hybridization in the long run, then what’s the point? Note that this paper is talking about decisions to “intentionally hybridize” animals – we are not concerned with parental kinship when considering animals, only the relative “quality” of the resultant phenotypes. Even with that, hybridization is questionable. However, we are humans, and as such, have concerns above and beyond these considerations – such as kinship issues. So, everything said about hybridization in animals holds true for humans, but, for humans, the underlying cost of hybridization – foregone parental kinship – is something additional that concerns us in dealing with mating choices.
Meanwhile, managers can minimize the risks of both inbreeding and outbreeding by using intentional hybridization only for populations clearly suffering from inbreeding depression…
Yes. This is the conservative approach. While Ashkenazi Jews can be said to “clearly suffer” from “inbreeding depression” the same cannot be said of European ethnic groups, or Europeans as a whole (or, for that matter, Africans, Asians, etc.).
The low IQs of Eastern Europeans are inbreeding depression.
Again – and this cannot be stressed enough – that’s not even considering parental kinship (or genetic interests in general). The Ashkenazim may have preservationist considerations that may lead them to reject hybridization independent of whatever “benefits” genetic mixing may bring, and the cost/benefit ratio may very well favor that rejection. However, given that Europeans are not “clearly suffering” from “inbreeding depression” there is no reason to follow Ziv’s advice and destroy our genetic interests for non-existent “benefits” to “solve” a non-existent “problem.”
Destroy yourself now because you might, at some point, destroy yourself!
….maximizing the genetic and adaptive similarity between populations…
In other words, if, for some reason, hybridization is decided upon, one should pick for the hybridization a population as genetically similar to the original population as possible. One does not pick the most genetically distant populations possible!
…and testing the effects of hybridization for at least two generations whenever possible.
to ensure fertility, not the liger issue
Yes – instead of promoting widespread human panmixia based upon how Tiger Woods might smell on the golf course. Of course, one may look at highly admixed populations throughout the world and use those for “testing the effects.” Even leaving kinship concerns out of the picture, the results with respect to positive traits have not been encouraging.
While the data on outbreeding depression are dwarfed by those on inbreeding depression, the few studies that exist suggest that concerns over outbreeding should be taken seriously, as the effects can in some cases be as damaging as severe inbreeding.
Yes, taken seriously, instead of making juvenile comments about which male celebrity may be better able to “induce orgasm” in which female celebrity. Again, given the costs for humans of foregone kinship, where are the “benefits?”
As a start, managers should strive to do no harm.
What should we think of those who, seemingly, wish to maximize harm?
That is, we should intentionally hybridize populations only when there is hard evidence that a population is suffering from inbreeding depression.
Speculation about how Tiger Woods might smell after a round of golf does not constitute said “hard evidence.” There is no “hard evidence” that European populations (or Africans, Asians, etc.) are “suffering” from inbreeding depression. Other small populations may be “suffering;” in that case, let those groups decide to balance the costs and benefits of hybridization – and a “pro” choice hardly means choosing the most distant groups possible as mates.
…low levels of gene flow are predicted to have disastrous effects on populations vulnerable to outbreeding (Edmands & Timmerman 2003).
As a final postscript, readers may be interested in an alternative viewpoint with respect to the function of sexual reproduction – which stresses species and chromosomal stability over “increased genetic diversity.”
By diversity they mean the healthy range.
Unhealthy is culled by natural selection.
“Well, South Asians are the product of mixing between several Caucasoid and Asiatic people, and problems with their racial classification notwithstanding, the fact remains that European Caucasoids and East Asians clearly belong to different races. In a classic example offered by Arthur Jensen, different bands of a rainbow blend into each other, yet this does not mean that a rainbow doesn’t contain different color bands that are easily distinguished from each other, except at the boundaries. ” marriage post (so not really gene heavy)
Genetic distance studies. Forensic skull analysis. Actually, you can clearly see group and case boundaries.