I'm not so sure that it's genes where speech and grammar is concerned, that's down to whoever it was who taught those people to speak in the first place.
You do, however, have a point about the grooming, or lack of it, and it does appear to follow a pattern. I'd best not say any more but there is a section of society who all seem to look alike, greasy hair scraped back into a thin ponytail, overweight and wearing tight leggings with a short top that emphasises the rolls of Michelin Man fat.
The education system probably carries a lot of the responsibility. Children might not have had prospects of going to university with lots of worthless qualifications but I bet they got a better education than has happened for many years.
Then years of Labour politicians telling people of their "right" to live off benefits.