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Thread: How did Homozygous Recessive Genes replace the Homozygous Dominant Genes?

  1. #1
    Noddy
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    Question How did Homozygous Recessive Genes replace the Homozygous Dominant Genes?

    http://www26.brinkster.com/archived/...D=712352931499

    Filed: 11/24/2002, 12:44:19 PM
    Source: Usenet
    Introductory note: this Usenet classic, penned ca. 1997 by a US academic, has come to be regarded as the non-PC (of course) 'Race FAQ'.

    "Question: How is it that in some human populations homozygous recessive genes have replaced the homozygous dominant genes of their ancestors for outward physical appearance?

    As far back as 1950 geneticist William Boyd listed about 20 gene loci for outward appearance traits that are homozygous recessive for typical Asians and/or Europeans but are homozygous dominant for Africans. These recessive genes include the 6 to 8 gene loci for light skin color, the genes for blue eyes, gray eyes, blond hair, red hair, thin lips, straight hair, sacral spot, lack of facial hair (beards), narrow nose shape, and some others.

    Famed academicians J.B.S. Haldane (who published in 1924), R.A. Fisher, and S. Wright all helped to develop the mathematical approaches to population genetics in regard to selection and proved (among many other things) that it would require 1,001,741 generations (i.e. about 25,000,000 years for humans) for a dominant autosomal gene pair to be entirely replaced naturally by a new recessive gene pair in an ideal population (going from a gene frequency of 0.01% to 99.99%) if the improved selective advantage were 1 percent greater per generation (which is a fairly large advantage) for the new recessive genetic trait over the old dominant genetic trait, but the Euro/Asian line of humans split from the African line approximately a mere 100,000 years ago, and we must account for about 20 different recessive gene loci for appearance, not just one.

    The mechanisms of genetic drift (including founder effect), migration, and gene flow have all been invoked to explain the rapid genetic change observed in small populations of early humans, but as an explanation for the observed changes in outward human racial appearance such reasoning is strained. The outward appearances of Euro/Asians seem to have very small, if any, actual advantages in regard to natural selection over that specified by the replaced African genes, but clearly some extraordinarily strong selective mechanism has been at work.

    A partial solution to the problem of how the various races of man came to appear outwardly as they do now was proposed in 1931 by scientist and writer Sir Arthur Keith who pointed out that tribal isolation and the human predisposition for conflict, competition, and warfare against those who appear to be different from our own tribe (i.e. "instinctive prejudice") was most likely the cause, in that driving away or killing people with certain genes very quickly reduces the frequency of those genes in a population, but by the post-war 1950's such thinking had become politically unacceptable, as shown by Boyd's firm rejection of the idea -although he at least took the time to discuss the hypothesis at length in his famous 1950 book "Genetics and the Races of Man", which in many ways the model for L. Luca Cavalli-Sforza's "History and Geography of Human Genes" (1994). We may dislike Robert Ardrey's famous assertion that we are all "killer apes" at heart (African Genesis, 1961), and the solid support for that thesis supplied by Konrad Lorenz and Raymond Dart, but everything in our horrifying history of continual warfare from the Great Wall of China to the Holocaust attests to our inherently xenophobic nature.

    The racial appearance puzzle is avoided in most evolution classes today by invoking Loomis' 1967 hypothesis that light skin color among Europeans and Asians exists because these populations could not get enough sunlight to stimulate sufficient vitamin D production in their skin in those terribly dark Northern continents of Europe and Asia. Although this theory has never been well supported by factual inquiry, it has been repeated so often and it is so politically comfortable that it has become enshrined as an indisputable fact in the minds of many casual students of evolution. In reality numerous valid objections have been raised to the vitamin D theory of light skin color:



    1) It cannot satisfactorily explain the evolution of the many other appearance genes that are also autosomal recessives (such as for blue eyes, and blond hair, and several others) that seemingly have no significant natural selective advantage,

    2) a small patch of the darkest African skin can produce more than the required amount of vitamin D from only a few minutes of exposure to faint sunlight each day (indeed, the Lapps live in arctic latitudes and are rather dark skinned), and in any event most of the vast land mass of Europe and Asia has been found to be quite sunny,

    3) of the 6 to 8 gene pairs for skin color all of the genes for light skin color are recessive to those for dark skin color; for all the dominant genes for dark skin color to be replaced by recessive genes for light skin color would require an intensely strong selection advantage operating for many millions of years, but man left Africa only 100,000 years ago and the natural selective pressure for light skin over dark would be small at best and therefore too slowly acting to fit the time frame,

    4) light skin color is a probably actually natural selective disadvantage at any latitude because sunlight causes skin cancer and may result in severe debilitating sunburn for those with white skin,

    5) `white skin color has a strong peak only in Northern Europe and not in other parts of the world' (this is a quote by Cavalli-Sforza in his book "History and Geography of Human Genes" mentioned above as he discusses the problem with the vitamin D explanation for skin color invoking world pigmentation intensity maps drawn by Carleton Coon in 1954). Cavalli-Sforza also suggests the very light skin color of Northern Europeans may have appeared as recently as 5,000 years ago, a time so recent that no natural selection process could possibly account for it.


    What about "sexual selection"? Often it has been proposed as the reason that racial differences exist, not to mention blue eyed blond women, but such white skinned women are regarded as hideous and repulsive by New Guinea tribesmen. Beauty is a relative concept and it is indeed a racist attitude to assume one type of human is inherently more beautiful than another, rather our individual concepts of human sexual attractiveness appear to be synonymous with people that appear to be similar to our set of internalized norms as imprinted in our childhood years- i.e. we generally find those not of our "tribe" less attractive than those people who more closely resemble us (there are always exceptions of course- some degree outbreeding is surely advantageous at times for a tribe of humans).

    Darwin, in his 1871 book "The Descent of Man, and Selection in Relation to Sex" asserted that racial appearance differentiation in humans was due to what he called "sexual selection", but a close reading of that book shows that for humans he regarded conflict and warfare (including genocide) as part of "sexual selection", a term he actually used for anything other than "natural selection", the other of his two selection mechanisms. Hence Sir Keith's 1931 idea on how the different races came to appear the way they do today really originated with Darwin, and Darwin's intuitive genius has been proven to be correct from what we now know about the genetics controlling human appearance.

    Three other interesting factors affecting human appearance must be considered: 1) climate, 2) neoteny, and 3) intelligence. All of these factors must be considered in conjunction with tribal conflict in order to fully understand how we came to appear the way we do, and it must be understood that these factors are overlayed on a tapestry of genetic drift, founder effect, migration, gene flow, and geographic isolation.




    1. Climate surely has played a factor in the initial development of several appearance traits, although it cannot account for strong selective pressure required for such rapid gene frequency change. For example, a narrow nose, epicanthal eye fold, straight hair, and thin lips are surely advantageous in a cold climate to warm the air we breathe, protect eyes form freezing winds, keep heads warm, and to prevent frozen lips, but blue eyes are a disadvantage in a dazzlingly sunny snow covered terrain, the long ears of Europeans are more prone to frostbite than are the short compact ears of most Africans, and lack of facial hair in the people of frigid Northeast Asia is certainly impractical, hence climate fails to explain neither the origin nor the rapid spread of some human appearance features.

    2. Neoteny has been written about by Kollman (inventor of the term), Bolk, Portmann, and Gould. Louis Bolk best stated the case in 1926 with this famous line: "man is a primate fetus that has become sexually mature". The human fetal growth rate period actually lasts about 22 months - at birth we are simply an extrauterine fetus at the 9 month stage with our brain still growing at the rapid fetal rate, thus did nature solve the birth canal bottleneck problem for producing big brained humans. A series of increasingly neotenic mutations probably account for mechanism of the amazing 4 fold increase in hominid brain size over the past 3 million years, and our outward appearance owes much to this phenomenon (i.e. all adult humans look like a huge primate fetus that can walk). It was once acceptable to point out in textbooks that neoteny related traits in the races of man seem to differ, with Negroids (Africans) being the least neotenic, Mongoloids (Asians) being the most neotenic, and Caucasoids (Europeans) being not quite as neotenic as Asians for several traits, including the important brain to body size ratio and in having less body hair, but more neotenic in regard to pigmentation of hair, skin, and eyes. The empirical support for this distinction is quite compelling, but it has become a somewhat sensitive subject.

    3. Intelligence is surely the most controversial factor that has influenced the different appearance of the human races, but any discussion of the reasons why it has had such an influence is a another very sensitive undertaking. As isolated tribes of humans over the past 200,000 years naturally attempted to expand they inevitably came into conflict with neighboring tribes. For humans and other hominids the most valuable genetic selective trait in such conflicts was probably a higher level of intelligence, for that is what generally determined the winner, although many other factors (such as disease resistance) played a role as well. An advantage in intelligence often allowed an ancient tribe to achieve a higher level of population density, better strategy and tactics for warfare and hunting, and greater levels of altruism and social adhesion within their group. Although, as mentioned above, neoteny related mutations were the genetic mechanism for the amazing 4 fold increase in hominid brain size over the past 3 million years, the value of intelligence for survival and tribal success was the driving evolutionary selection force and continued to be so until the recent advent of civilization.


    Preserving the intellectual advantage of a successfully expanding tribe is a difficult problem however, because interbreeding with a tribe a lesser intelligence dilutes and decreases the genetic advantage of the advantged expanding tribe, thus eventually ending the expansion. The solutions for this problem have always ranged from genocide to ethnic cleansing, but being able to visually identify the genetic heritage of offspring to exclude offspring resulting from intertribal matings was always of great value to a genetically advantaged expanding tribe, allowing for continued expansion until the tribe were to encounter a more genetically advantaged tribe (i.e., generally meaning more intelligent) or some substantial geographical barrier. That is why autosomal recessive genes for outward physical appearance have an advantage over dominant genes in a genetically advantaged tribe: the introduction of a non-tribal dominant gene can be easily visually detected in offspring thus enabling exclusion methods to operate and therefore keeping the tribes' genetic lineage from being diluted.

    Example: for a child to have blue eyes, the recessive genes for blue eyes must be inherited from both parents. A child with darker eyes would immediately be recognized as non-tribal in a blue eyed tribe. The child could possibly be exiled (and in some cases could be killed) by an ancient blue eyed expanding tribe, thus preserving the genetic integrity of the tribe. This example may seem totally absurd in today's civilized world, but human racial evolution goes back at least 200,000 years, long before civilized human behavior developed. If eye color discrimination seem too far fetched however, consider skin color. As recently as 100 years ago the birth of a dark skinned child to a white woman typically resulted in ostracism by her displeased family, and sometimes infanticide was committed. The other recessive appearance traits of present day Europeans and Asians were most likely at one time also used in a similar manner for tribal identification in order to account for their modern day geographic gene frequency distributions.

    Eventually multiple traits (i.e. white skin blue eyed blondes for one example, although there are many others) were used for tribal identification in ever increasing rounds of conflict among tribes. Perhaps the most efficient trait for tribal identification is skin color, in that a polygenic system (6 to 8 gene pairs are involved) of recessive genes for light skin enables the visual identification of mixed tribe offspring having only a small amount of dark skinned dominant genetic racial ancestry - octoroons are thus revealed by the skin color system whereas they would not be detected very often in a single gene system such as eye color. The uniform of skin color was no doubt used by the warriors of conflicting tribes in much the same way as modern day military uniforms are used to distinguish opposing armies - then as now individuals wearing the uniform of the defeated group could be identified and dealt with accordingly by the victors.

    As an overall consequence, tribes or races that have successfully expanded and displaced other tribes or races are likely to be characterized both by 1) genes for appearance that are homozygous recessive to the corresponding genes of the displaced tribe or race and 2) by the trait that gave the successful tribe the winning advantage over the displaced tribe. In the past 200,000 years of tribal conflict among humans (the past 3,000,000 years for all hominids) the trait conferring the winning advantage has most often been a higher level of intelligence, but at times it has also been disease resistance, aggressiveness, numerical advantage, technological superiority, and a variety of other differences. Nevertheless the role of intelligence in this matter should not be underestimated; the fossil record of dramatic hominid cranial capacity increase supports the point quite convincingly, as do differences in the average IQs of present day racial groups.

    Geographical limits eventually stopped the expansions of the Europeans and the Asians (along with overall stalemate at their points of mutual contact), and the Sahara Desert protected the remaining Africans from further encroachment by the Euro/Asians, thus resulting in the distribution of the three major races as found in modern times.

    Lastly, the coming of civilization and the reduction of the significance of geographical barriers have made the world a vast breeding pool into which the entire genetic variance of humanity is supposedly slowly blending - for all 100,000 gene loci, not just those coding for our appearance. All of us are genetic blends to some extent, and our varied appearances demonstrate the point well.

    And that, very briefly and admittedly incompletely, is why the human races look the way they do today."

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    That was a very interesting article. It makes more sense than anything I've ever heard or read about the subject!

    Of course, Nordics are the most "neotenous" so that would also make us the most intelligent. Since all children always have lighter hair and blue eyes. Even kittens have blue eyes at birth......

    Our traits didn't "evolve" because of lack of sunlight, but rather as protection to ensure our people would stay pure. We should follow the guide nature has given us.
    Last edited by GreenHeart; Monday, December 23rd, 2002 at 09:26 AM.

  3. #3
    Noddy
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    I have brown hair, but i had blonde hair till i was about ten, and it is still thick. My dad is Dansih, and my mother English/Celtic. Basically, i am an almost-nordic-if i had blond hair i would be totally nordic. But i do believe that in the name of diversity, like kind should go with like kind-my fiance is the same as me. Got a baby due in feb, wish me luck!

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