explain this

Sure. There will almost certainly be, as always, many factors. IQ is probably one of them. IQ is also heritable. This would give rise to the suspicion that there may be a genetic cause. However, IQ is not wholly heritable. IQ is also not going to be the only factor. In short, there's no simple explanation.

However, as I have often said in other places, the cause is irrelevant. If niggers commit 50% of the crime then you can eliminate 50% of crime by eliminating the niggers. That, at least, is simple. But 'we' ('society') don't just optimise for low crime rates. If we did we could just get rid of laws - no laws, no crime. We have other material goals. We also have values that we aspire to live up to. There is, again, no simple prescription that perfectly balances our values and our goals to the satisfaction of all. Everyone in society is going to be unhappy about something. Thus, I don't consider the mere existence of complaints a problem.

It's not about who's right or wrong on the final solution to the nigger question. Niggers aren't a question, they're just a thing that exists, and there are multiple possible reactions to the existence of niggers that intersect with our goals and values. There's no "solution" because there's no "problem." Would we live in a society with less crime if we started rounding up the niggers? Probably. The most important question - and the one that you're not asking - is if it would be a better society. And that's a question that you will have to answer for yourself, with reference to what you value.

I have a relatively paternalistic attitude towards niggers - I consider them like a dog, which must be cared for and nurtured as a matter of duty - so I'm not in favour of genocide.

Which, I suppose, answers your apple question.