Posted: Wed 24 Aug 2005 16:57 Post subject: Euro admixture in Afro-American population (was "Frank...")
I am trying to consolidate all this data for a more accurate picture.
Wikipedia writes "Further, recent genetic tests on a small population of African Americans revealed their ancestry to be, on average, approximately 19 percent white."
http://en.wikipedia.org/wiki/African_American
Black Americans, on the other hand, have significant European admixture (averaging about 75 percent African and 25 percent European).
http://backintyme.com/Essay040608.htm
Rick Kittles emailed me with even lower amounts of European admixture. In Y-Chromosome DNA tests in the Afro-American population he quoted about 25% of those tested had any markers irrelevant of percentage per person. And of Mitochondrial DNA he said it was about 5%. Even putting that together still only indicates only 30% of Afro-Americans have European admixture according to Kittles' Findings. This kind of clashes with your concept that the average Afro-American has significan European admixture, when his studies seem to indicate only 30% have any european admixture. Have you ever corresponded with him about this? I believe both your sources are genuine so there must be an explanation for these seemingly opposite conclusions.
Posted: Tue 06 Sep 2005 14:18 Post subject: Re: Frank: admixture in Afro-American population
Salsassin wrote:
I believe both your sources are genuine so there must be an explanation for these seemingly opposite conclusions.
I think that the main source of confusion is trying to summarize a complex pattern of genetic admixture into a single number. Let me illustrate with a very simple example. Say that you have a self-labeled "U.S. Black" population of ten individuals with European genetic admixture as follows:
One person has 100 percent European admixture. (100 percent European, zero percent African).
Three people have 20 percent. (20 percent European, 80 percent African)
One person has 5 percent.
One person has 4 percent.
One person has 3 percent.
One person has 2 percent.
One person has 1 percent.
One person has zero percent.
What is the "average" European admixture in the above population? The answer depends on what you mean by "average." There are three equally valid answers:
1. The mean is 17.5 percent. (100+60+5+4+3+2+1+0)/10. This is like saying that a person lying on a block of ice while a torturer applies a blowtorch to his upper surface is perfectly comfortable "on average."
2. The mode is 20 percent. There are more people with this amount than any other fraction. This is like saying that a room with four Europeans and five Africans is totally African "on average."
3. The median is 4.5 percent. This number splits the population into two equal-sized groups, five people with more than this and five with less. This is like taking a vote.
Take your pick. None of the "averages" is any more "right" than any of the others.
Anyone who is seriously interested in this topic should identify which of the three "averages" is being reported in any given study. Failing this, find the raw data (the admixture in each individual sampled). For instance, you can eyeball a typical scatter diagram and make your own estimate.
Here is an example exercise that you can easily do. The second cluster from the left (labeled "264AA") shows the Afro-European admixture ratio of 264 U.S. Blacks. Count the dots. Tabulate the European admixture percent for each dot. Compute each of the three "averages."
Posted: Thu 27 Oct 2005 15:52 Post subject: Re: Frank: admixture in Afro-American population
fwsweet wrote:
Here is an example exercise that you can easily do. The second cluster from the left (labeled "264AA") shows the Afro-European admixture ratio of 264 U.S. Blacks. Count the dots. Tabulate the European admixture percent for each dot. Compute each of the three "averages."
by the weay, what was the sampling for this analysis? Populations sampled I mean.
So forgeting about median admixture in the whole population. What would you say is the percentage of blacks that do not have European admixture?
You are asking how many of the 264 African Americans (the second population from the left) lie along the bottom (zero) axis, as do many of the the 135 Zaireans (third cluster) or the 159 Nigerians (rightmost cluster). The answer, as far as my eyeball can tell, is "zero." I do not see any of the 264 African-American dots lying on the zero axis. Hence, every one of them has at least a trace of European admixture.
Salsassin wrote:
by the way, what was the sampling for this analysis? Populations sampled I mean.
The study from which the scatter diagram was taken is by Heather E. Collins-Schramm, Markers that Discriminate between European and African Ancestry Show Limited Variation within Africa. Click on the title to view the original study. Four populations were sampled in the study. The first was European Americans (147 individuals). The second was African-Americans (264 individuals, as I mentioned). The third was Zaireans (135 individuals). And the fourth was Nigerians (159 individuals).
The number of African American populations sampled (which is what we were talking) about is "one." The number of individuals in this sampled population was, as mentioned originally, 264.
Last edited by fwsweet on Sun 06 Nov 2005 01:06; edited 1 time in total
Hey Frank, have you ever communicated directly with these guys? I think you would ask a lot of questions i wouldn't think about. You do mention both of them in your article, but it sounds like you have only read about them.
So forgeting about median admixture in the whole population. What would you say is the percentage of blacks that do not have European admixture?
You are asking how many of the 264 African Americans (the second population from the left) lie along the bottom (zero) axis, as do many of the the 135 Zaireans (third cluster) or the 159 Nigerians (rightmost cluster). The answer, as far as my eyeball can tell, is "zero." I do not see any of the 264 African-American dots lying on the zero axis. Hence, every one of them has at least a trace of European admixture.
Salsassin wrote:
by the way, what was the sampling for this analysis? Populations sampled I mean.
The study from which the scatter diagram was taken is by Heather E. Collins-Schramm, Markers that Discriminate between European and African Ancestry Show Limited Variation within Africa. Click on the title to view the original study. Four populations were sampled in the study. The first was European Americans (147 individuals). The second was African-Americans (264 individuals, as I mentioned). The third was Zaireans (135 individuals). And the fourth was Nigerians (159 individuals).
The number of African Americans populations sampled (which is what we were talking) about is "one." The number of individuals in this sampled population was, as mentioned originally, 264.
That is bizarre. Rick Kittles is one of the authors of that study that you show says none of those sampled has nno European admixture.
The same one who wrote this:
Quote:
----- Original Message -----
From: "Rick Kittles, Ph.D." <rkittles@africanancestry.com>
To: "'Jaime Pretell'" <jaime_pretell@hotmail.com>
Sent: Thursday, September 23, 2004 10:21 AM
Subject: RE: Quick question about Black population
Less than 5% have European maternal ancestry.
-----Original Message-----
From: Jaime Pretell [mailto:jaime_pretell@hotmail.com]
Sent: Thursday, September 23, 2004 12:02 PM
To: rkittles@africanancestry.com
Subject: Re: Quick question about Black population
In your article
http://www.bioethics.umn.edu/afrgen/html/Geneticsandgenealogy.html
You mention that 30% of African males have paternal European ancestry based on Y chromosome tests.. How many have either paternal or maternal European ancestry?Have you done any mitochondrial tests on women and men?
maybe you understand how that big divergence in both his studies occured. I'm still confused.
Hey Frank, have you ever communicated directly with these guys?
I have personally met and spoken to Shriver. I have corresponded with Kittles. I have no questions that have not already been answered by their published works.
Rick Kittles is one of the authors of that study that you show says none of those sampled has no European admixture. The same one who wrote this, “Less than 5% have European maternal ancestry.” Maybe you understand how that big divergence in both his studies occurred. I'm still confused.
There is no “divergence.” Your confusion may be due to at least two misunderstandings.
First, and most important, you are confusing nuclear autosomal DNA percentages with matrilineal versus patrilineal percentages. They measure different things.
Your autosomal or nuclear DNA is your personal genome. It is what makes you genetically you. You had about 640 ancestors living in the year 1800. Every one of those men and women contributed equally to your DNA. (Of course, you contain only one person’s DNA so, on average, only 1/640 of any one of those people’s genomes survived over the generations to be found in you and 639/640 was discarded, but they are all equally your ancestors.) Imagine, say, that 480 of those ancestors were of pure European admixture and the other 160 were pure subSaharan west Africans. Given this, your autosomal DNA would be of 75 percent European and 25 African admixture, and we would expect your autosomal markers to reflect this. (Marker measurement might not be exact, since some markers might have been among the 639/640 of your ancestors’ DNA that was discarded over the generations, but it will be very close.) And so, the number of ancestry-informative markers in your DNA, which is what we were talking about, tells how much of your ancestry comes from where.
But your matrilineal and patrilineal DNA are something quite different. Among the 320 men of the year 1800 who contributed to your DNA, only one was your patrilineal ancestor. Just one man, and your Y chromosome is precisely his. There may be no other shred of him in you, but his Y chromosome is yours. Similarly, among those 320 women in 1800, only one contributed your mtDNA. Again, there may be nothing else of her in you, but your mtDNA is entirely hers.
It is not unlikely for your Y patrilineal ancestor to have been African, your mtDNA matrilineal ancestor to have been African as well, but all the other 638 men and women who contributed to your DNA to have been European. In this case, your autosomal DNA would show 100 percent European and 0 percent African, even though both your paternal and maternal lineages came from Africa. The two measurements measure different things. Because it is a negligible part of you, patrilineal/matrilineal DNA is irrelevant to your genetic admixture. But because everyone’s autosomal DNA is so mixed, the patrilineal/matrilineal DNA is the only way to track migrations.
In short, every one of the 264 African Americans in Ms. Collins-Schramm’s study (I do not use “Dr.” because she was still a doctoral candidate when she wrote it) had enough Europeans among those 640 men and women of 1800 to show up in autosomal measurements. Collins-Schramm did not report on their mtDNA, to determine the origin of each one’s single maternal ancestor of 1800. If she had, less than 5 percent of those 147 women might have been European, as Kittles implied. Or they might all have been African. Or, for that matter, 95 percent of them might have been European. We were talking about admixture. We were not talking patrilineage or matrilineage.
Your second misunderstanding may be to assume that all regions of the country are the same. Kittles’s “5 percent” of European matrilineage (NOT admixture) may have been a national average. It is higher than that in the northeast and along the gulf coast. It is lower than that in the Sea Islands. Either way, it is irrelevant to overall admixture.
Last edited by fwsweet on Thu 27 Oct 2005 20:58; edited 1 time in total
Yeah, I got a similar response from Dr. Kittles.
----- Original Message -----
From: Rick Kittles, Ph.D.
To: 'Jaime Pretell'
Sent: Thursday, October 27, 2005 1:40 PM
Subject: RE: Question on admixture. Correlating two studies.
Jaime,
You are confusing the two different genetic systems. The Collins-Schramm paper analyzed autosomal markers which refelect both maternal AND paternal DNA contributions. The study I responded to you before via email was about maternal and paternal lineages (Y chromosome and mtDNA). Those lineages are not inherited and mixed like autosomal DNA. A person, for instance a woman may have a black mother and a white father (50% of her genes are European) but since she has no Y chromosome we cannot detect that 50% if we just looked at her mtDNA. In fact her mtDNA would be African.
So bottom line, in your estimation, what is the percentage of the Afro-American population that has any type of admixture with Europeans? With native Americans? Virtually all or a lesser number?
And do you think Steve Sailer was being disengenious or misunderstood the studies?
Sailer wrote:
studies, done before direct genetic testing was feasible, suggested that African-Americans were 25 or even 30 percent white. Shriver's project is not complete, but with data from 25 sites already in, he is coming up with 17-18 percent white ancestry among African-Americans.
I have no way of knowing. Most non-scientists are imprecise in what they write. (Eg.: when someone writes "average" do they intend median, mode, arithmetic mean, or geometric mean?) Consider the words, "17-18 percent white ancestry among African-Americans." Do those words mean that only 6 million African Americans have even the tiniest detectable trace of European ancestry? Or do they mean that the total gene pool of the U.S. Black community contains 17-18 percent European DNA? The first would be inaccurate. The second is within the ball park.
So bottom line, in your estimation, what is the percentage of the Afro-American population that has any type of admixture with Europeans? With native Americans? Virtually all or a lesser number?
The short answer is virtually all of them. But this is in the same sense that virtually all U.S. Whites have a trace of Native American in them and one-third of U.S. Whites have Black in them. As girlfromthenc pointed out recently, faint traces of this or that do not mean anything in a social sense.
The more socially meaningful question is how effective has the endogamous color line been in preventing Black-to-White genetic leakage. It has been very effective indeed. Conversely, White-to-Black gene flow has been much larger.
Some time ago, I posted in this discussion group links to several studies (including Shriver's, but many later ones also) that address this question. But rather than re-post them, I plan to include them in the article index that William is assembling.
Last edited by fwsweet on Fri 28 Oct 2005 19:26; edited 1 time in total
So bottom line, in your estimation, what is the percentage of the Afro-American population that has any type of admixture with Europeans? With native Americans? Virtually all or a lesser number?
The short answer is virtually all of them. But this is in the same sense that virtually all U.S. Whites have a trace of Native American in them and one-third of U.S. Whites have Black in them. As girlfromthenc poited out recently, faint traces of this or that do not mean anything in a social sense.
The more socially meaningful question is how effective has the endogamous color line been in preventing Black-to-White genetic leakage. It has been very effective indeed. Conversely, White-to-Black gene flow has been much larger.
Some time ago, I posted in this discussion group links to several studies (including Shriver's, but many later ones also) that address this question. But rather than re-post them, I plan to include them in the article index that William is assembling.
Cool look forward to it. Yeah, noticeable admixture would be a more pertinent measure, but how do you measure that.
Joined: 10 Oct 2005 {Posts: 11 } Location: Gulf Coast
Posted: Thu 27 Oct 2005 19:32 Post subject:
fwsweet wrote:
The more socially meaningful question is how effective has the endogamous color line been in preventing Black-to-White genetic leakage. It has been very effective indeed. Conversely, White-to-Black gene flow has been much larger.
Has White-to-Black gene flow truly been that much greater than Black-to-White? Or could that be a manifestation of the endogamous color line itself? If the line were drawn using fixed (non-subjective) ratios rather than by self-associating, what then would the admixing percentages be?
An example might be a man who identifies as "white" today, with a first cousin who is "black". If these two individuals share similar admixtures, then the results are purely subjective, aren't they?
I suspect I'm being convoluted. I guess I'm trying to say that the gene flow is perhaps more bi-directional than the results indicate because of how the color line is drawn, as opposed to the color line being the cause of admixing percentages. It doesn't prevent the admixing so much as it defines it. (Did that make any sense?)
Has White-to-Black gene flow truly been that much greater than Black-to-White? Or could that be a manifestation of the endogamous color line itself? If the line were drawn using fixed (non-subjective) ratios rather than by self-associating, what then would the admixing percentages be?
Outstanding! That is the most thought-provoking technical question that we have had around here in a long time. As I understand it, it deals with the very definitions of “White” and “Black.” In other words, imagine that we apply the “racial” perceptions of Puerto Ricans or of late 19th-century Ohio judges: folks who are 51 percent European are White, and those who are 51 percent African are Black. Such a redefinition would reclassify as White many Americans who now identify as Black. If we then looked at the bidirectional gene flow across this new (50-50) color line, would we see it as more balanced? Is the current imbalance merely an artifact of our drawing the line via hypodescent?
I do not have an answer, but I can suggest two ways of approaching it. First is with Collins-Schramm’s scatter diagram, second is with unnatural selection.
Ignore the rightmost two sections of the above diagram; just consider the plots of European-Americans and African-Americans. The two groups were plotted separately (apart from each other along the horizontal) merely because the members of one group see themselves as White and the others consider themselves Black. But what if Collins-Schramm had never asked her subjects how they self-identified? What if she had just plotted them all in one scatter diagram? You can imagine the result by cutting the A-A section out of the graph and laying it down over the E-A section. If you did this, you have just one scatter diagram, but you would still see two distinct clusters of dots: one cluster tightly jammed against the top, the other cluster loosely smeared upwards from the bottom. Even without knowing how they self-identify (or indeed that they self-identify differently), you could demonstrate two phenomena. First, the fact that there are two distinct clusters (Puerto Rico has only one) shows that you have captured two endogamous populations. Second, the fact that one cluster is tight and the other is spread out shows that the former has fewer “wrong” genes than does the latter.
A second approach goes back to something that girlfromthenc asked several months ago suggesting that the actual absolute gene flow is bidirectional and balanced. As I recall, she suggested that just as many genes slip through the color line one way as the other, and that the reason European admixture in Blacks is higher than African admixture in Whites is merely because there are eight times as many Whites as Blacks. “X” number of Black genes flowing into the White community are dispersed and diluted among a much larger population. But the same “X” number of White genes flowing into the Black population has an eight-times greater impact on percentage admixture because the Black population is one-eighth the size of the White.
At the time she mentioned this, I agreed with her since all my training in genetics suggested that gene flow between adjacent breeding populations is always bidirectional and balanced. But now I have my doubts for two reasons. First, this would predict that “wrong” admixture would differ by a factor of 8 (the population ratios). If Whites have 0.7 percent African admixture, then Blacks should have 5.6 percent European admixture. But Blacks have around 17 percent European. But if that number is right, then Whites should have over 2 percent African, and they have less than 1 percent. Something does not compute. Second, I see evidence (presented in Afro-European Genetic Admixture in the United States) that there has been unidirectional selection in the U.S. population. That people of in-between genetic admixture who “look White” to most Anglo-Americans are allowed to choose their ethnicity, but those of identical admixture who happen to “look Black” are not given the choice.
In short, I do not have an answer to the question, but those are the two ways that I would attack it.
Last edited by fwsweet on Fri 28 Oct 2005 00:03; edited 2 times in total
Joined: 10 Oct 2005 {Posts: 11 } Location: Gulf Coast
Posted: Thu 27 Oct 2005 22:43 Post subject:
fwsweet wrote:
In other words, imagine that we apply the “racial” perceptions of Puerto Ricans or of late 19th-century Ohio judges: folks who are 51 percent European are White, and those who are 51 percent African are Black. Such a redefinition would reclassify as White many Americans who now identify as Black. If we then looked at the bidirectional gene flow across this new (50-50) color line, would we see it as more balanced? Is the current imbalance merely an artifact of our drawing the line via hypodescent?
Yes! Exactly what I was trying to say - thank you!
Quote:
A second approach goes back to something that girlfromthenc asked several months ago suggesting that the actual absolute gene flow is bidirectional and balanced. As I recall, she suggested that just as many genes slip through the color line one way as the other, and that the reason European admixture in Blacks is higher than African admixture in Whites is merely because there are eight times as many Whites as Blacks. “X” number of Black genes flowing into the White community are dispersed and diluted among a much larger population. But the same “X” number of White genes flowing into the Black population has an eight-times greater impact on percentage admixture because the Black population is one-eighth the size of the White.
At the time she mentioned this, I agreed with her since all my training in genetics suggested that gene flow between adjacent breeding populations is always bidirectional and balanced. But now I have my doubts for two reasons. First, this would predict that “wrong” admixture would differ by a factor of 8 (the population ratios). If Whites have 0.7 percent African admixture, then Blacks should have 5.6 percent European admixture. But Blacks have around 17 percent European. But if that number is right, then Whites should have over 2 percent African, and they have less than 1 percent. Something does not compute.
Fascinating line of reasoning. Just to stick with this "dilution" into the larger White population thought for a second - I wonder if part of the answer to this non-congruity might not be answered historically? (Note: I can't really tell whether this thought supports girlfromthenc's theory or not - we're moving beyond my technical capabilities quickly...lol...)
Charles Byrd introduced me to your ODR forums when he posted a query I'd sent to IV a few weeks ago. I had remembered (some years ago) reading that the percentage of admixture in families who were established in the US prior to the Civil War was higher than commonly understood - perhaps over 60%. Presumably, Collins-Schramm’s scatter diagram, had it been done in 1870, would have differed quite a lot from today's.
Immigration to the US didn't really kick fully into gear until near the end of the 19th Century, at which time there was an enormous European influx. Sheer numbers would have immediately begun to affect any measures of "white".
So attempts to gauge admixture between these two endogamous groups would necessarily be skewed without historical base-lines, wouldn't it?
Posted: Fri 28 Oct 2005 18:17 Post subject: Re: Frank: admixture in Afro-American population
fwsweet wrote:
I think that the main source of confusion is trying to summarize a complex pattern of genetic admixture into a single number.
Its commonly said that "race" has no genetic basis, and is a completely fabricated social construct. If so, how are researchers able to find how much "white" or "black" genetic admixture a person has???
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