I’m posting this in this general y haplogroup thread instead of the I1 section because I feel that what I’m about to write applies to any subclade branch with many phyloequivalent snps.

I feel that the I1/I2 split to I1 time of most recent common ancestor mystery may never be solved because a lot of ancient dna samples have low testing coverage in terms of the amount of Y chromosome base pair locations covered and the amount of reads per base pair location. I’m not sure if this is due to degradation of the dna over time and/or if it’s just a practicality/cost issue for the scientists testing many samples in their studies?

Over 300 plus SNPs accrued on the Y chromosomes of our forefathers since we diverged apart from I2 around 27,500 years ago up until our common I1 patrilineal ancestor most likely living in Sweden around 4,600 years ago. What happened between 27,500 to 4,600 years ago is a mystery and the only way to get a clearer picture is to test those 300 plus SNPs in ancient dna samples and to compare it to the projected amount of SNPs that should have accrued by the particular time periods that these ancient samples lived in.

For example, let’s say a future hypothetical ancient dna sample is discovered in Austria dated around 12,000 years ago. If 300 plus SNPs occurred from 27,500 to 4,600 years ago we would presume on average an SNP occurred roughly every 75 years. Based on that average our patrilineal ancestors would have accumulated approximately on average around 207/300 plus SNPs by 12,000 years ago (27,500-12,000) / 75 . Let’s say the hypothetical sample in question is positive for 195/300 plus SNPs. I would then predict that it’s quite likely that our forefathers were around the Austria area around 12,000 years ago because 195 SNPs is pretty close to the projected average of 207 SNPs for 12,000 years ago. In theory only approximately 900 years (12 SNPs x 75 years) would have separated the true I1 direct lineage from this closely related at the time but probably currently extinct cousin branch of I1.

Let’s say on the contrary the hypothetical sample is positive for only 50/300 plus SNPs. I would predict then that we would have branched apart from this extinct cousin branch around 23,750 years ago 27,500 - (50 x 75) So even though this hypothetical sample lived 12,000 years ago in this example we branched apart from them 11,750 years prior to that. People can migrate a lot more over 11,750 years compared to 900 years as in the previous scenario so this hypothetical sample extinct branch being from Austria would not be very informative or telling regarding our own direct I1 migration story.

There is a real ancient dna sample from Hungary labeled BAB5 and is dated 5300-4900 BCE. The sample is labeled “I1” because it tested positive for the SNP I-M253. However, I-M253 is just 1/300 plus SNPs associated with the I1 branch. We don’t even know when the I-M253 mutation occurred. If it hypothetically occurred 20,000 years ago would that be informative or telling regarding the I1 Migration story 5,000 years ago? Without knowing how BAB5 would test for the other 299 plus SNPs associated with the I1 branch it’s impossible to know how closely related it is to the modern I1 branch. This sample could have branched apart from the modern I1 branch anytime approximately between 27,500 years ago and 4,600 years ago.

The oldest true I1 ancient dna sample thus far positive for all 300 plus SNPs is sample oll009 from Skane, Sweden dated 1930-1750 BCE. Even though scientists didn’t test all 300 plus SNPs for this sample he is presumed positive for all 300 plus SNPs because he is positive for 2 SNPs on the downstream subclade branch I-DF29. Unfortunately, since the I-DF29 subclade branch arose between 4,000-5,000 years ago testing these particular phyloequivalent SNPs won’t be very useful for ancient dna samples older than that time frame.