I want to respond to a number of issues with the aim of helping to shut them down, although I don't think the main issue has been resolved - we must wait for better evidence.
(1) It's not appropriate to suggest that Muazzam is a racist - he's talking his own race down, and that's the opposite of what racists do. It's still something we want to talk him out of, but no condemnation is required.
(2) Race is a real thing and the current fashion in science for denying it is a mistake, although counterintuitively it could become correct in the future, so they've merely jumped the gun [if you're not a native English speaker, that's an idiomatic expression meaning they've done something too soon]. The differences between different races are generally trivial and superficial, but they are none the less real: those trivial, superficial differences are what race is mostly about, but crucially you also have to have large groups of people who share the same codings in order for it to be classed as a race. If we were to mix all the world's people together such that nothing distinguishes different populations from each other any more and extreme differences have practically disappeared (we'd likely have to arrange random marriages for them all for many generations to get there), a white or black person could still emerge from time to time by chance with DNA which could not distinguish them from the black or white people of today, and yet it would no longer be correct to label them as being of a different race due to the lack of numbers of other people with the same codings existing as a community - they would merely be isolated oddities.
(3) Let's get back to today though with race still being a reality. The differences are caused by tiny coding differences, but the differences can be significant, such as radical colour differences, bone density differences (black people tend to have heavier bones which make them less competitive when swimming, but that doesn't mean there can't be a black person at the top in swimming - it merely makes it less likely), muscle tissue differences (some races of black people have exceptionally high levels of fast-twitch muscle which make them dominate sprints), oxygen-carrying capacity differences (Tibetans are better able to survive life at high altitude - we can match part of that ability by taking EPO, but at the risk of circulation shut-down and death during sleep, as happened with dozens of racing cyclists, and that doesn't happen to Tibetans), etc.
We generally accept that there are such differences between races, but don't like it when anyone tries to extend it to intelligence, just as people don't get particularly upset at being called slow in relation to their athletic performance but become angry if someone calls them dim - one is not regarded as an insult, but the other most certainly is, even though both may be statements of fact. Fortunately though, we haven't managed to measure any definite differences in overall intelligence between races.
(4) Are there any intelligence differences between races at all? The best evidence I've heard of is with Australian Aborigines where they outperform other races at a task which I can't quite remember the details of, but it was something to do with looking at a set of objects and remembering them all. This difference seemed to exist even when Aborigine children had been brought up in a different cultural setting from the natural communities they would have been living in if my tribe hadn't invaded their land to abuse them and destroy their way of life. That is just one particular mental skill, and it's not one that most of us care about being inferior at, but it's possible that many other such differences occur between races. It is unlikely in the extreme though that any such differences would add up to the point where any one race could be measured as being more intelligent than another.
(5) IQ tests are often highly flawed with a significant number of the questions depending on knowledge rather than intelligence, but there can be bigger factors in play than that: a large part of the improvement in IQ test scores over time in some countries has now been identified as being caused by older generations not liking to guess an answer when they don't know it (because that was considered to be a bad thing to do in the culture of that time), so they left many questions unanswered. Later generations were advised to guess whenever they didn't know the answer, and that automatically led to improved scores, not just by random chance giving them a fifth or quarter of right answers to the questions they couldn't solve, but better than that because many of the wrong answers can be eliminated easily, pushing the odds further in their favour. It is also possible to train people to do better in IQ tests by exposing them to the kind of questions that are used in IQ tests and showing them how to solve them - this can easily make a difference of 20 points. A lot of education can accidentally train children to do better in IQ tests.
(6) IQ tests only measure a narrow range of shallow skills, and they normally do so as a race against the clock, which means that a slow thinker who could score higher than most people if there's no time limit could look like one of the worst performers when forced to rush. The tests do have a real value though as they relate fairly well to people's performance in actual jobs. However, there is much more to intelligence, and people with IQs approaching 200 aren't always the best problem solvers (although some of them are right up there) because the skills involved are not all measured by IQ tests - IQ tests fail to measure deep logical thinking, and that appears to be something that no one is even trying to measure.
(7) Most importantly for this discussion though, when we look at the performance of people of different races where they've been brought up together in the same culture, it's hard to see any difference in intelligence between them, although it is difficult to remove cultural differences. In Britain, black children tend to perform less well than white ones, although there are communities in which white children perform just as badly for the same social reasons (deprivation). Asians, including people of Muazzam's race, generally perform better than whites because they are driven harder - their parents push them because they know that they'll have to overcome racism when they apply for jobs, so they need to be better than the rest. The culture with black people hasn't caught up with this and we don't know how well they would do if they were systematically pushed as hard.
We also see top thinkers coming out of all races, but if there are fewer of them from some races than others, it is most likely that there are cultural reasons behind this with some kinds of academic learning being disliked for religious reasons. There was a time when Religions seemed compatible with science, so scientific knowledge was pursued vigorously in an attempt to understand God's creation, but there are now problems where scientific findings don't fit so well with what people wanted to find, and that's put the brakes on in some cultures which were previously leaders.
There are vast numbers of dim people about in all societies, so it's easy to look around you and imagine the whole population is thick. You can see that reflected in the people they vote into power to run everything, but it's hard to point at any country and say that the people there appear to be more intelligent than the people of another country when both countries are run by monkeys. Some governments may appear to be substantially more intelligent for a time, but then they can do startlingly stupid things which suddenly reveal the truth about them. I don't know what the reality of it is, but I suspect the differences are almost entirely cultural ones where established wisdoms can either hold back a society or propel it forwards - some cultures have better sets of established wisdom in them than others which leads to better performance, but it would be a mistake to think that those people are more intelligent as it really comes down to luck. But I'm having to fall back on a lot of guesses because we simply don't have sufficient evidence to go on to give absolute answers.
In conclusion, it would be a mistake to rule out the possibility that some races are on average less intelligent than others when we don't have enough evidence to prove it, but it would also be a mistake to assume that some races are less intelligent without sufficient evidence. It is, so far as I can see, an unresolved issue, though the odds are that any significant differences that we can measure are caused overwhelmingly by culture, and that intelligence differences may well have no role whatsoever, but the science is incomplete and we cannot resolve the argument yet.
When AGI takes over the world, every house with ivory or rhino horn in it will be burned to the ground.
MSB-OS: http://www.magicschoolbook.com/computing/os-project - direct machine code programming