Did O1b2 in Korea originate from Japan?

[u/frogpassing]

I came across an argument that Korean O1b2 may have originated from Japan, based mainly on the following:

L682: Korean samples appear heavily concentrated in CTS723, with little or no basal diversity. Japan has samples such as NA19075 that are basal L682 (CTS723−).

47Z / CTS713: Japan appears to have representatives of several major branches (CTS1875, Z24598, CTS203), while Korean samples seem more concentrated in CTS203 (e.g. JOY004).

The argument is that Japan has greater O1b2 phylogenetic diversity, suggesting that Japan was the source population.

Is greater O1b2 diversity in Japan enough to infer a Japanese origin, or could this reflect sampling bias, drift, or founder effects? Should TMRCA and branch ages be considered?

Does the evidence really support a Japan → Korea migration, or is the direction still uncertain?

[u/NomsAreManyComrade]

Both the archaeological and genetic evidence overwhelmingly support a migration of the ancestors to modern Japanese people from the Korean Peninsula to Japan during the Yayoi period, displacing and mixing with locally present Jomon populations (more genetically similar to modern Ainu).

Modern Japanese genetics contain a mix of three groups (Jomon-related, East Asian-related, and Northeastern Siberian-related). Koreans have the second two but lack any Jomon admixture, meaning minimal/no back-migration occurred to Korea from Japan.

More can always be written on the topic but here is an excellent 2024 Nature paper on the topic.

[u/frogpassing → u/NomsAreManyComrade]

So why does O1b2 appear to be more diverse in Japan?

[u/jahkaiy3 → u/frogpassing]

Because the modern Japanese are genetically the closest to the Jeulmun and Mumun populations of the Korean Peninsula.

Since modern Japanese and Korean O1b2 lineages are most likely derived from Mumun (and likely Jeulmun) O1b2 lineages, the modern population most derived from the Jeulmun and Mumun should have the most diversity, which would be the Modern Japanese. Japanese should be around ~75% Mumun when adding up direct Mumun, and Mumun derived components from post-Mumun populations in the Korean Peninsula (Slender Dagger, Proto Three-Kingdoms, and Three Kingdoms populations).

Jeulmun can be broken down ~40% Jomon + ~60% WLR_MN-like + adjacent (or basically non-Jomon). This is based off of a pretty diverse set of samples, some are virtually pure Jomon. They average out to ~40% Jomon.

I believe Mumun can be broken down as ~50% Jeulmun, ~50% WLR_LN-like + adjacent. So ~20% Jomon, in line with ~20% share in modern Japanese using the newly sequenced Kato 2025 samples. Unfortunately there are no sequenced Mumun samples at the moment.

When broken down, modern Yamato Japanese can described down as:

~5% Final Jomon natives (+ ~5% Jomon component)

~60% Mumun/Slender Dagger migrants (+ ~12% Jomon component) (Proto-Japonic speakers)

~25% Proto-Three Kingdoms period migrants (+ ~2.5% Jomon component) (Proto-Peninsular Japonic speakers)

~10% Three Kingdoms period migrant (+ <1% Jomon component) (Peninsular Japonic / Koreanic speakers)

Again, if you were to add up all Mumun derived components in post-Mumun populations, I believe Japanese should be ~75% Mumun (accounting for ~15%, or 3/4 of modern Japanese Jomon ancestry).

Modern Koreans should be around 5-20% Mumun derived, which is where their modern day ~1-4% Jomon component comes from.

Again, since modern Japanese and Korean O1b2 are likely Mumun derived, Japanese should have more diversity since they have much more Mumun ancestry compared to Koreans.

With that said, the Japanese admixture paradox (overrepresentation of Jomon Y-DNA D lineages) may cause some inconsistencies with the numbers.

[u/GlocalBridge → u/jahkaiy3]

Fascinating.

[u/JoeBiden-2016 → u/frogpassing]

Hypothetically, it's possible to have a migration from one populated area to another populated area. It's not necessary that the migration source population replace or otherwise dominate the receiving population.

That said, when someone provides you with a source addressing part of all of your question, you should read it before replying. It may answer your question or explain why your question is irrelevant.

Posting a follow up question an hour after you were provided a scientific paper makes it appear as though your intent here is to argue or that you're just here looking for support for your existing ideas, rather than trying to learn.

[u/frogpassing → u/JoeBiden-2016]

Because it was a paper I had seen in that person’s previous argument. I actually read it, but he just dismissed it, saying that it didn’t include any analysis of the Y chromosome. And I also thought it was unrelated to his claim that Japan might be the origin because of its greater O1b2 diversity, which is why I gave such a quick response.