> if the trait is genetic as you hypothesize

Oh, no, to the contrary. I was merely saying it felt as if YOU implied this. If you want to know my position, no, I completely reject the notion that e.g. Somalians carry genes that make them more prone to violence, murder, theft, rape etc. There are barely any studies that support it, the few that do are from notorious researchers that pretty much everyone regard as blatant racists (e.g. look up Rushton). While there is evidence to suggest the contrary. (e.g. when comparing an adopted child from a minority background into a majority family shows the impact of socioeconomic status rather than DNA.)

> The data suggests there is some trait which is correlated with ethnicity and also with crime

Anyway, back to my point... You still don't seem to be at all open to the notion that there may be no 'traits' or that their influence aren't very great.

That is, where traits describe (usually genetic) characteristics of a person, which could explain a person's behavior in his environment, have you considered the opposite? That the environment's characteristics affect the behavior of the individual? That's overwhelmingly what sociologists have concluded (studied sociology in undergrad, my gf in grad). Fact is, a lot of immigrants in Europe came for menial labor in the 60s and 70s, were put in housing next to the factories they worked in, besides having barely been educated (overwhelmingly illiterate) as children, receive no form of education after their arrival in Europe (e.g. language or cultural education). Hundreds of thousands grew up isolated from any natives, worked daily in the factories, and at some point after 10-20 years moved to the cities when the industry shifted away from menial labor in Europe and the jobs dried up. So now you have people with absolutely no skills fit for the modern economy, no ability to read or write, no affiliation with local culture etc. That creates unemployment, poverty, it creates tensions, it creates conflicts. These people had zero political representation in government, zero representation in the media, no voice, and absolutely no competitive position in the marketplace. People with a gigantic social, financial and human capital disadvantages, and anyone from this minority who tries to escape from situation is met with stigma, with the stereotype views, which often leads to discrimination in the workplace even for highly educated individuals with that ethnic background. Indeed to the extent that there are lots of people walking around with an unsubstantiated notion that immigrants are genetically less able, less intelligent, less moral, the very definition of the nazi untermensch doctrine, which feeds into the discrimination, isolation and ostracizing of members of this minority, in school, work, politics, media. And this is what perpetuates the problems. The next generation of kids are born to illiterate unemployed parents with very limited financial means for education, self-exploration, extra-curricular activities, creative materials (toys, computers), no books or newspapers in the house, a language deficit etc etc. These kids don't have a fair shot and by age 6 they already are behind in school, and if you know one thing about education is that when you are behind on this week's homework, then understanding next week's becomes more difficult, and the deficit becomes greater and greater, to the point a kid isn't learning anymore, doesn't feel comfortable in school, loses confidence. That's when you see the dropout rate spike. Now you have kids 14 years old who barely go to school, aren't able to land a job a few years later.

THAT is what causes so many issues. Bad policies for people of the lowest socioeconomic class that starts a cascading effect and perpetuates throughout multiple generations. This isn't controversial among the sociologists that research it. What is extremely controversial is the notion of the untermensch, that some ethnicities are genetically lesser than others, and some ethnicities are superior. It's inherently racist, and time and time again we see these things come out of the mouths of extreme right-wing political leaders of various parties in Europe.

Now given the above, it's clear that of COURSE there's an explanation for the obvious correlation between the average immigrant and crime. And the data shows it's rooted in things like financial, social and human capital. Not genes. And guess what, policies are THE instrument to improving that. e.g. providing language and networking opportunities for illiterate immigrants helps. Providing extra language classes and reading sessions for kids with illiterate parents, helps. Removing the financial barriers to education for financially disadvantaged kids, helps. All of these things are pretty elementary, right? So yes, countries with better policies to crime get less crime than they otherwise would, and that has nothing to do with that country having less people from an ethnicity that has a genetic disposition to violence, rape, theft, murder. Why is this even a debate?