A reminder: Ethnicity is something you tick on form with a series of boxes ("White, British", "Afro-Caribbean", "British Asian", "African-American", "Deutsch-Türken"). Genetics and genomics is the DNA sequence you were born with. These are *very different* things.

The boxes you tick is very much shaped by the person who made the form; there might be an "Other" but often will be kept as "Other" in statistics. Furthermore people's identity, shaped by society around them, is a deeply cultural and personal aspect.

This is why in the UK the boxes range from the fine grained "White, Irish Traveller" to completely broad "African, other" and distinction on language and culture is as important as visual features.

Your genome is the DNA you were born with; half comes from your father, half from your mother, 1/4 from each grandparent... as you go back in your family tree quite quickly you start to have ancestors who did not provide any DNA to you by chance.

Despite our very rich differences in culture, and obvious differences in individual visual characteristics, such as hair colour and skin colour (which I will come back to), our shared ancestry happens very quickly in our history

Somewhat amazingly sometime between 3,000 BCE to 12,000 BCE the people who lived then either were a genealogical ancestor of either everyone who lived now or none of us. (this I find so counter intuitive I have to read up again each time: https://en.wikipedia.org/wiki/Identical_ancestors_point)

In terms of our genetic history it is a subset of these ancestors, and very rapidly our genetic ancestors become lone individual walks in history back in time until our founding population in Africa.

One part of my genome will meet my wife's equivalent part of her genome in a common ancestor of us both in Africa, just as a different part will meet a common ancestor of my neighbour. I wont tell you which ethnicity boxes they tick, but it really doesn't matter much at all

We are very visual animals, and visual appearance is important to us. Skin colour is around ~30 or so places on our genome, where our genome has something of the order of 300,000 "places" (it is 3 billion letters long, but the mixing between generations happens in chunks).

Skin colour happens to also be a fiendishly complex trait. Most human traits with strong genetics (eg, height) seem to average out; if a bit of genome contributes to height it does so in a consistent way + most of this variation is present in our common, founding African history

Not so for skin colour. Both due to selection by sunlight levels (for making Vitamin D), and probably other bits of selection (choosing partners) skin colour genetics varies far more than the "average" human trait across the globe

You might think this could make skin colour a good tracer of origins, but not really. Firstly there is huge variation in skin colour in neighbours. Secondly the endless migrations and having sex which humans do (we do both *a lot*) means we're endlessly remixing our genetics

We can see this in modern people who are this remixing : 'mixed race' most obviously, but also Afro-Caribbeans, Brazilians, Cape Coloureds, Afrikaaners, Berbers, Pied Noir, Goans.... We can see it increasingly in ancient history

The examples include farmers and other migrations down the Nile and along the east coast of Africa; of Silk Roads from Asia to Europe; of the Beaker people coming in from the Steppes into Europe. All glorious different. All mixing as they travelled and settled, to move again.

All this swirling mix means skin colour genetics is ... complex, and interesting to study, but no better a marker of ancestry than any other bit of genome. It certainly has no "important" role in understanding ancestry.

Do not be fooled by the fact that people are "clearly Black" or "clearly White". Of course their skin colour is consistent and can be seen. Duh. This confident assignment by themselves or others is as useful as saying "this person is definitely short whereas this person is tall"

The elevation - fetishation - of certain traits such as skin colour, facial features at one level is no different from our visual reaction to people's cloth choices, makeup, jewelry and presentation to allow us to display our identity in shorthand ways to each other

Though of course there is a *big* difference: skin colour etc are human traits that are near impossible to change, and as such represent something far less fluid for an individual. But make no mistake- there is nothing profound about skin colour compared to hair colour or height

We could have elevated any of these traits in our endlessly repeating in-group / out-group behaviour when humans meet; we certainly don't need any physical trait differences to create such groups (from the Troubles in NI to Shia/Sunni to ... the endless stories of human conflict)

Ethnicity is *not* about about genetics. Weird but true. It is about culture +identity. Its has some hooks into this complex area of visual features, and thus this tiny bit of genetics, but this doesn't make ethnicity any use for understanding genetics outside of these traits.

The process of ticking ethnic group boxes on forms is not telling anyone key, deep, unchangeable biological truths about people... this is not even true most of the time for "real" genetics; certainly not true for this non-scientific box ticking process.

If you want to understand the genetic influences of human traits, diseases and biology, determine someone's DNA and start from there. If you want to ask about people's identity and ethnicity, design a form for people to tick boxes. Do not confuse these two things.