More evidence of genetic discontinuity between Neolithic and modern Europeans

[Taranis]

Not sure if it's what you are asking for?
Son, man can never give mitochondrial DNA to his kids, therefore it stops there. That's the part of DNA called Maternal, mtDNA. Not the X chromosome.

Well, my point is that when a woman only has sons, these won't be able to give their mother's mitochondrial DNA towards their kids. In that case, a mitochondrial lineage could disappear (or 'son out'). It's basically exactly the opposite of what I described as 'to daughter out', when Y-chromosomal lineages disappear because the only offspring are daughters. I must admit however that this is probably less likely with mitochondrial lineages than with Y-chromosomal lineages due to the different selection pressures involved.

 

[Maciamo]

I agree on all acounts, Maciamo. What I do wonder though is this: is it possible for mitochondrial Haplogroups to "son out" just like it's possible for Y-Haplogroups to "daughter out"?

I absolutely think that some mt-haplogroups can son out. I read an article a few years back that said that mtDNA haplogroups had an effect on brain acidity/alkalinity. It's easy to imagine that mtDNA can therefore also influence the pH of a woman's uterus, which is to this day the main factor influencing the gender ratio in babies. Concretely an acidic environment kills off male sperm and consequently favours baby girls.

The article found a correlation between brain acidity and haplogroup H, therefore favouring girls. It's hardly a surprise that this is the most common haplogroup in Europe nowadays. This is why it is dangerous to link the frequency of an mtDNA haplogroup with the percentage of actual (autosomal) ancestry associated with that haplogroup. 50% of hg H in a country doesn't necessarily means that 50% of the ancestors 5,000 or 10,000 years ago belonged to this haplogroup. There was probably a progressive natural selection in favour of this haplogroup over the centuries simply because it favours girls and therefore automatically increases in frequency compared to other haplogroups. I believe that some of the rarer haplogroups (I, W, X, N1a, N9, C, etc.) could have had their frequency dramatically cut over time just because they favoured boys. I would need more data to confirm this, but looking at my genealogy I could clearly see some matrilineal branches having a much higher ratio or girls, and others of boys, constantly over several centuries.

Y-DNA influences the sperm count of his carrier. A higher sperm count increasing the chances of producing boys, there is probably a natural balance taking place between Y-DNA and mtDNA. In other words, every time a new mutation on the Y-chromosome causes an excess of boys in the population, mtDNA lineages linked to a low pH (more boys) decrease in frequency and are replaced by mtDNA lineages boosting the female population. I am now seriously considering this phenomenon as a major explanation to the quick replacement of both mtDNA and Y-DNA lineages since the Neolithic.

Studies so far have confirmed what I expected, namely that men belonging to haplogroup R1b1b2 have the highest sperm count (apparently followed by R1a1a). It would make sense that countries with the highest percentages of R1b1b2 (strong boy bias) also have the highest percentages of mtDNA H (strong girls bias). Is that the case ? Apparently yes. Northeast Spain justly happen to have the highest percentage of R1b1b2 (85% among the Basques and 83% in Catalonia) and H (61% in the Basques) in Europe. The few European countries that have less than 40% of hg H are Romania, Greece, South Italy and Central Italy (but not North Italy, where H reaches 47%), all regions with a relatively lower frequencies of R1b1b2.

Back to our North/East Asian mtDNA from the Neolithic, I would expect that if the paternal lineages that accompanied them had a considerably lower sperm count that R1b1b2 and R1a1a (for example hg Q or C), these mtDNA lineages would have quickly disappeared after the arrival of hg R1 by "sonning out". This is simply because the natural balanced established between the male and female Asian lineages had a higher pH due to the lower sperm count generated by the Y-chromosomes. Once a high sperm count lineage entered the equation, most women would have ended up giving birth to a much higher ratio of boys than girls, resulting in the inevitable sharp decline of these mt-haplogroups' frequencies.

I would expect haplogroup G2a to have a substantially lower sperm count too, since it was apparently quite common all over Europe in the Neolithic but has become minor nowadays. I have suggested before that the Indo-Europeans, armed with Bronze weapons and riding horses killed most of the men of Europe's Neolithic/Chalcolithic cultures. However that does not explain why Paleolithic lineages like H, V and U5 survived and prospered, why Neolithic lineages like N1a and X2 suffered an apparently significant reduction. The best explanation is that N1a and X2 were originally linked to a Y-haplogroup with a relatively low sperm count (G2a), which made them more vulnerable to the introduction of a high-sperm-count haplogroup like R1b1b2. H and V on the other hand, seemed to have thrived, benefiting from the demise of high pH mt-haplogroups.

Once again, it's something that mathematics could not have predicted. It's pure biochemistry.

 

[MOESAN]

These mt dna results are indeed unusual for Europe today, but in general terms, as the title of the thread itself indicates, this is just the latest in a line of scholarly articles showing the discontinuity between modern populations and ancient ones. Paleolithic mt dna seems to be quite different from Neolithic mtdna, which is again different from modern mt dna. The same was found to be true for Etruscan and modern Tuscan populations as the overall distributions were very different. (although there was continuity between early medieval results and modern Tuscan results).

The extinction rate for mtdna is high (see Oetzi's results for example) and certain lineages can, even in a very short time, become highly under or over represented, as this study done on Icelandic mt dna makes clear, and this is true even absent any significant migration.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1180299/pdf/AJHGv72p1370.pdf

The same is true for y-dna, although perhaps not to as great an extent. One member of the amateur community recently did a mathematical analysis to illustrate just that.

A population of 1000 males undergoes 4 percent per generation growth for past 150 generations, resulting in 370,000 males today. With sufficient dna tags (STRs, SNPs, etc) one could imagine each of those 1000 original males representing a distinctive genetic y line.

What do we see today among those 370,000 descendants in the way of distinct original lines? 87 percent of those 1000 lines went extinct; they are gone from today’s population. The most populous represented original line accounts for 4.4 percent of today’s population. The 10 most populous lines represented today account for 24.1 percent of the 370,000. And the 20 most populous lines represent 40.6 percent of the 370,000.

The above results indicate the very strong creation of demographic “winners” and “losers” of y lines based solely on statistical flucuations --- before any other factors are brought into consideration. This source of demographic winners versus losers must be understood before speculations about connnections of populous y haplogroups today to migrating, militarily advanced, technically advanced, culturally advanced......... etc. tribes of the distant past can be even tried intelligently.

I couldn't agree more.

it's "bizarre" - it seams based on HTs variations more than on HGs variations because today iceland SNP big HGs seam very closed yet to the western norvegian ones... lineages die but almost with the same rate in every big group of HG... it seams me that a lot fo the lost lineages are the 'orphan' ones, rare unique HTs (in HGs) carried by immigrated foreigners at a very very low scale... an arithmetic and biasing interpretation I think

 

[Savant]

Yeah, I think the Paleolithic Continuity Paradigm advocates, once ridiculed, are becoming more and more validated with time.

 

[Taranis]

Yeah, I think the Paleolithic Continuity Paradigm advocates, once ridiculed, are becoming more and more validated with time.

I hope you're meaning that statement ironical, because rather the opposite is the case.