You assume that first, there are a significant number of people who don’t mind degrading, menial labor (instead of putting up with it because they have no choice), and that people performing manual labor are stupid. I see no reason to buy either; those are class warfare propaganda points, not reality.
There is a classic urban legend about the physical height of French men. The story goes that Napoleon picked only the tallest men for his Guard…and that the Guard had such high casualties, that the average height of French men was reduced by some measurable amount.
The problem is that height is hugely polygenetic. I have seen studies that show, to reduce the average height by two inches, the Napoleonic wars would have had to have killed off over 99.9% of everyone above average height, and not just once, but for several generations. Just killing off a few per cent of the tall guys, just once, won’t do the job.
The same with intelligence. It isn’t like blue eyes! (Controlled by a single gene.) We all know smart people with dumb kids…and dumb people with smart kids. For dumb people to degrade the average human intelligence would require them to have 99.9% of all the kids, for many generations. This simply isn’t happening.
The difference in height between North and South Korean pretty much disabuses this notion. It’s much easier/faster to get the same effect by simply starving people. If you catch them early enough, you’ll see results within a generation, too.
You run into some problems really fast when you assume most traits aren’t influenced by any extrinsic factors.
Worse yet, we know intelligence isn’t purely genetic and trying to separate that part out of the mix is a mug’s game with the existing data (though some of our resident racists have certainly tried to make that exact case).
Making it worse for the “race realists” is that recently even more environmental factors that influence intelligence were noticed recently.
Just from memory: I remember recent studies that report that a few IQ points are lost if you live in a violent environment (particularly hits to the head), more reports of poverty also reducing IQ and things like the diet of the parents (lack of folic acid for example) also not only leading to problems with the spine, but also affecting brain development.
But it isn’t genetic. Provide healthy nutrition to the infant babies of these people who have been shortened by starvation, and the babies will grow up just as tall as their South Korean counterparts. If you suggest that the babies won’t grow up as tall, you would seem to be invoking Lamarckism.
Yeah, bad edit. I was supporting your point and it came bad out. English fail, Antibob smash.
Grin! Hardly the first time I’ve disagreed with someone who was agreeing with me! We’ll blame it on the English language. This would never have happened if we were still speaking classical Latin or Greek! 
There is no tendency for the average I.Q. to be decreasing over time. In fact, it’s slowly increasing. This is apparently because the environment for improved I.Q. is slowly improving. There’s no evidence that the I.Q. is changing for genetic reasons at all:
For those who brought up idiocracy, I think it’s worth pointing out this comic. The movie, while funny and insightful, has no basis in reality or any real understanding of evolution. Not only are the dumb not “out-breeding” the smart, but the very concept makes no sense. Intelligence is very heavily influenced by environment, and IQ is hardly a measure of value to society - hence why you can end up with MENSA members with IQs off the chart who happen to be complete morons. Looking at you, Ian Juby. And all the brainpower in the world is utterly wasted if you don’t direct it well, if you don’t get a good education, if you starve half the time, if you take too many knocks to the head… Need I go on? The entire basic premise of this thread is wrong, wrong, wrong. And that the OP references George Carlin (political satire; while often very funny, kind of a crank and conspiracy theorist), Idiocracy (political satire; not based in reality), and a New Yorker cartoon that he fundamentally failed to understand (newsflash: it’s riffing on you) is pretty much par for the course.
You know, I think I use the word “insightful” incorrectly in the above post.
For what it’s worth, the OP referred only to educational levels, not intelligence.
Aloha
That’s actually worse.
You could maybe come up with a justification involving intelligence that made some sense if you didn’t look too closely at the data.
But educational attainment is not highly correlated with genetics. And while educational attainment tends to be correlated (though not absolutely and not particularly strongly) with fewer children, to suggest it influences anything on an evolutionary scale is akin to Lamarckism.
And, furthermore, it’s more obvious that the average educational attainment is increasing than that the average intelligence is increasing. After all, one can argue forever about whether increasing scores on I.Q. tests shows anything or if it’s just an artifice of how tests work. There’s really no question though that a higher percentage of people are graduating from high school, college, grad school, or professional school.
Ironically, Professor James Flynn, who identified a rise in IQ scores through the 20th century (“the Flynn Effect”), has now expressed concerns about this trend(which is seen in most Western countries).
“…unless women with higher education started producing more babies…” Wow! Lamarckism at its finest! Women with higher education will produce babies…with higher education!
The social effects of educating women are well documented. But the genetic effects? As close to nil as makes no significance.
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Behavioural traits, including intelligence are heritable (see Pinker ‘My Genome, My Self’ 2009).
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Higher intelligence makes it easier for people to do well academically. So intelligence tends to be associated to some extent with education level. See for instance, Deary et al Intelligence and Educational Achievement
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If the most educated women tend to have fewer children then over time you’d expect the population average to shift.
It makes perfect sense.
I don’t think that’s what Flynn means. Flynn’s comment is based on the assumption that those with higher education also tend to have higher average intelligence in the first place. Which is a reasonable assumption - see the Deary paper above for example.
No, because how much education you get is overwhelmingly about social class and how much money you have, not intelligence. You can be an idiot, and if you’re rich and connected you’ll be given a “Gentleman’s C” at worst; while you can be a genius and if you are poor you’ll be lucky if you finish high school.
And humans are so long lived and reproduce so slowly that a transient thing like that gets lost in the noise. The family that’s rich and powerful now may well be penniless refugees in a few generations.
The 1950s called. They want their cliche back.