"no matter the relative number of individuals in relation to the whole"
Precisely. Funny thing is that this relative number is highly relative itself. I mean, being purposely exaggerated for the sake of illustration, T is in fact just a subgroup of K, which accounts for most of European individuals. Of course, they splitted very early. Point is that Y-DNAs change permanently, no matter the labels.
If you allow me some mental exercises, without intending to be really surgical, but trying to think out of the box, I was just thinking (as someone interested in Y-DNA)...
Strictly, if by "success", an elastic term, we mean relative growth/expansion (not just absolute numbers, since forces/correlations change over time, and since in fact most of macro-hgs must have experienced growth in the last thousands of years when it comes to absolute numbers) and by non-success we mean relative retraction, which also implies some sort of virtual competition, then place and timeframe is again important. We usually talk on macro-haplogroups. In fact, we "personified" them, which may be misleading. But in each period and each area, under different forces, there will be other virtual actors (subclades) "competing" with one another, so to speak, even when they belong to the same macro-haplogroup (mind you, first of all, they are letters and numbers that represent a set of specific shared mutations, but their subclades may be somewhat distant from each other in time and then in number of shared mutations too; rigorously, every individual is unique, and the actual competition happens between people - in the past strongly correlated to certain hgs, but not that much anymore -; so people may be more "objectivelly" successful in some manner). And hgs won't "thrive" everywhere and everytime. In this sense, again, success would be more linked with expansion than to absolute frequency, be it over space, be it over time in a specific area, a thing that depends, again, on the context discussed, and we know it always changes. (But as suggested, victory may mean surviving to certain "accidents", or casualities. I.e., just surviving, even with all adversities imposed, may be also a kind of victory sometimes. So, it's not always a matter of suplanting competitors, but also of overcoming "circumstances". We're used to think that a lineage is only "successful" if it's frequent "everywhere" or very frequent somewhere. Well, in certain way, perhaps, but "success" must be then properly defined. I don't want to be relativistic, btw, but this complex subject itself seems to be highly "relative"; binary reasoning may led us to a wrong way.)
Back to the initial point. For example, due to some sort of correlation, you may have a certain set of closely related ascendant/descendant clades which experienced a comparative high expansion in number and frequency between 5000-4000 years ago, causing a very high frequency of these clades even thousands of years later, but hypothetically you can have younger related subclades - then in a different context - that experienced a retraction even if compared to subclades from different and now "absorbed" macro-haplogroups. There must be practical examples in each context, such 35% of Serbs belonging to I-Y3120 (only ~2000 years old) according to Serbian Project, while, additionally, ~2/3 of these 35% would belong to I-PH908 (just ~1800 years old). Impressive! It also surprises me haplogroups such R-Y10827, which apparently grew well from 1600 ybp, even belonging to a "minor" R-P312 clade. R-M222 under R-L21 is also very interesting (great expansion of subclades from 2000 ybp). And on and on. YFull recently released a different view that makes all these huge variations more evident. Example: https://yfull.com/sc/tree/R-P312/ . Of course, there must be sampling bias sometimes (R-L21 vs. R-U152, for instance); still... Point is, were they all comparatively super-fertile? Don't think so. I-PH908 and others also exemplifies as "lucky" in broad sense (one more elastic term) may play a role, and phenomena such founder effects are just an example of that. But mind you, this "lucky" would include also what I'd call "inertia", especially when there is continuity, but not only (it could happen as well after invasions/replacements in relation to newly introduced hgs and their new interactions in the new place). I mean, relative growth may continue to happen for some random reasons in each context, even in the more recent ones, however, importantly, they'll tend to correlate with some already frequent older hg. Let's say, a 75% hg would have more chances to "win the lottery" over some 15% different hg in a given place and in a given situation of expansion. So it'd work like a wave. But "improbabilities" may also happen, of course, and in some manner that's the history of Y-DNA.
Theoretically, certain mutations that define (sub-)haplogroups could also play some role, but I see no evidence that they are that important, at least not to the point to largely justify modern frequencies (see articles in my first comment on this subject). I really doubt, for instance, that haplogroups such R1a would from now on suplants over time other haplogroups such J2a in, let's say, Turkey, in the fashion of Bronze Age Europe, even if this country suffered some kind of foreign "intervention", je je. Or J2a in Eastern Europe in relation to R1a. Other times, other circumstances. Huge variations in frequency of the same clade in different places, including those where they have an ancient presence, are per se evidences of how lucky matters.
Too many variables in the game anyway, and it's hard to "exhaust" it in ("poor english") summarized texts like this one, and possibly even in deep professional works.
So that's the point. What if we compare younger clades, whatever the haplogroup? We could name them with whatever letters, in order to not being distracted by ancestor clades that previously experienced important expansions. Of course, even so - even talking in different timeframes -, modern Y-DNA frequencies/distributions are the most important reference in hand. Some old haplogroups are still "successful" in general and simple sense, not just because they expanded in frequency sometime in the past, but also because they keep being frequent (haven't retracted significantly in the last times). Also, belonging to certain subclade still implies belonging to certain clade (in the example in a previous comment, R1b-A8039 - rare - is still R1b-L151 - very common. So ok. All of this may be confusing because haplogroups are not people. This is highly complex, and I think some simplifications I've seen are just fun. I mean, 2/3 of European pop descending in male line from three BA kings? Were they coincidently affected at the same time by different super-SNPs? I mean, the three SNPs that define R1b-L151 worked for R1b-P312 and R1b-U106 but not to R1b-A8039? The same for others below, in each level. je je Come on! Really not about fertility. Anyway, if some mutations that help define certain frequent haplogroups are that important in some way, then we should know soon, as we know mtDNA hgs must have slight implications in health etc.
As a last example which applies to our time, I could mention Middle Eastern and North African subclades such as J1's, which must be growing in frequency in Europe and will keep growing in the next years, due to immigration (numbers don't distinguish it from invasion, lol), birth rate among ethnic groups etc. Under the perspective we're discussing here, it means these virtual entities are being "successful" at this time. Of course, the variables in the game are not the same, but they have never been the same and they never will be.
Conclusion is that, at this moment, given all complexity involved, modern haplogroup distribution/frequencies in general are hardly explained by significant physiological (dis)advantages, as far as I can see.
Sorry for the long text. I'm done now. It's completely off-topic. Just thought about it reading your post and decided to share.
Thank you Regio. It was an authentic lesson of an expert on how the “lineages” of certain haplogroups may or may not thrive. In the dynamics of evolution there are variables that we cannot count on such as wars, plagues, climate change, successful or unsuccessful migrations, etc. In fact, mutations are always happening, and the great clades sometimes lose their meaning in face the mutations that, quickly, create new subclades, sometimes so far from the original clade. The clinical eye of an analyst like you can see the implications far downstream. Already a layman like me need something more aimed at beginners, as something more upstream, such as the good old clades of two letters and a number. LOL. Big Hug and thanks once again for invest in all those explanations that certainly are useful for all of us.
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