Why do Irish people look so different from Scandinavians if they're so close genetically?

[Grace O'Malley]

Possibly:

1 - The Bronze Age/Late Neolithic ancestors of both were so close, basically brothers
2 - There has been very little non-NW influence in both places to shift them apart
3 - Fairly significant Germanic influence in Ireland from the migration era (around 20% according to some figures), and some Insular Celtic influence in Scandinavia too, that draws them back together
4 - The populations were larger and remained relatively outbred, at least compared to the ancestors NE Europeans/Slavs, who must have been a very small isolated group for a long time.

Very good answer.

[Token]

Disregarding some minor gene-flow between them, there is at least 5000 years since their most recent common ancestors. Facial morphology can change drastically in much less time, compare Bell Beaker and Corded Ware skulls for example.

[Grace O'Malley]

Disregarding some minor gene-flow between them, there is at least 5000 years since their most recent common ancestors. Facial morphology can change drastically in much less time, compare Bell Beaker and Corded Ware skulls for example.

But why do they cluster so close then? Any group that has separated even for 1,000 years and shorter don't cluster together. Drift happens quite quickly. Why isn't this evident in a European cluster map? Any group separated that long would form unique genetic clusters. Even look at the Basque?

[Septentrion]

The Irish and Scandinavians are very similar genetically and yet they don't look similar at all, and I'm not only talking about facial features but also pigmentation. There was a study done here by a member (Xenophobic Prussian) on hair colour and he found Scandinavians to be THREE times blonder than Irish people. And in terms of facial features they also look very different, you would just never mistake for Irish someone like Dolph Lundgren for example. Why is it that they're so different in facial features and hair colour despite being so close genetically?

Adaptation to different northern climates made most of the difference as well as geographical location. Ireland is an island, therefore its population is also genetically less diverse than that of Scandinavia. Although both the Irish and Scandinavians are genetically less diverse than continental European populations as a whole especially Southern European ones. The different northern climates gave rise to phenotypes which combines fair skin + blond hair + blue or light eyes to be most common in Denmark, Norway and Sweden, and a gloomier or cloudier climate gave rise to pale or freckled skin + red or brown hair + blue or light eyes in Ireland.

[Token]

But why do they cluster so close then? Any group that has separated even for 1,000 years and shorter don't cluster together. Drift happens quite quickly. Why isn't this evident in a European cluster map? Any group separated that long would form unique genetic clusters. Even look at the Basque?

Genetic drift needs an isolated population with small effective population size marrying between themselves for a long time to take place in any significance. The more geographically isolated and the smaller the size of the effective population, the higher the quantity of genetic drift per time. That means primitive prehistoric populations could suffer genetic drift far more intensely and faster than the Iron Age populations of Ireland, for example. The fact that Ireland is an island never stopped people from invading it and that is why you speak (or spoke until recently) a Central European Celtic tongue to begin with, plus Britain is no small island and its terrain was far more suitable for agriculture at the time than the eastern North European plain, where the would-be Balto-Slavs would undergo a far more intense genetic drift process somewhere between the Bronze and Iron Ages. Even then Irish-specific drift did occur and that's why you can distinguish Irish from Norwegians with more fine-scale analysis such as Davidski's Celtic vs Germanic PCA.

[Jana]

They aren't that close genetically at all except with Icelanders who are part Irish/Scottish (and still distance is above 4)

Distance to: Irish

4.69804215 Icelandic
6.61496788 Norwegian
6.81617195 Danish
10.02400120 Swedish

Distance 6-10 is big in fine scale clustering and populations with such distance won't look that similar at all.
Ethnic groups who look really similar to another population will have distance below 3.

[Peter Parker]

Why do chimpanzees look so different from humans if they're so close genetically?

[Creoda]

They aren't that close genetically at all except with Icelanders who are part Irish/Scottish (and still distance is above 4)

Distance to: Irish

4.69804215 Icelandic
6.61496788 Norwegian
6.81617195 Danish
10.02400120 Swedish

Distance 6-10 is big in fine scale clustering and populations with such distance won't look that similar at all.
Ethnic groups who look really similar to another population will have distance below 3.

It's weird with Ireland on those calculators, there are some people who are extremely drifted, and then some people who are very close to Scandinavians (more so than any English). End result is that the average is not that close by NW Euro standards.

[reboun]

Minor genetic differences can create big differences in phenotype.

[Grace O'Malley]

They aren't that close genetically at all except with Icelanders who are part Irish/Scottish (and still distance is above 4)

Distance to: Irish

4.69804215 Icelandic
6.61496788 Norwegian
6.81617195 Danish
10.02400120 Swedish

Distance 6-10 is big in fine scale clustering and populations with such distance won't look that similar at all.
Ethnic groups who look really similar to another population will have distance below 3.

I don't know why I'm so much closer to Norwegians than the Irish average?

Distance to: Grace
2.07639110 Icelandic
3.67318663 Scottish
3.70654826 Irish_Connacht
3.82745346 Norwegian
3.84933761 Dutch_North
4.10109741 Irish
4.10454626 West_Scottish
4.11882265 Irish_Leinster
4.15441933 Orcadian
4.20343907 Irish_Munster
4.45470538 Denmark
4.51352412 Dutch_Central
4.66038625 Irish_Ulster
4.67193750 English_North
4.68362039 Norway_South_Central
5.03362692 Dutch
5.03711227 Sweden_Götaland
5.04918805 Welsh
5.46866529 English
5.50012727 German_Northwest
5.87728679 English_Midlands
5.93609299 North_German
6.00581385 English_Southeast
6.07132605 English_Southwest
6.61623004 Sweden_Svealand_West

Possibly different areas of Ireland have a closer distance. Even I'm further away than the Irish using K13 makes me wonder why there should be discrepancies like that? I'm above 4 distance to the Irish.