"My assertion stands: IQ or intelligence does not exist at birth, just capability"

Your assertion does not stand. It withers under nearly a century of research where we've been verifying via testing that infants have intelligence. We currently have two primary test methods: visual and sensorimotor. Of the two the visual based has been shown to be more accurate. We've had it reliable be shown a strong predictor of not just performance later in life but actual IQ test performance. And I'm not referring to general statistics here, but multi-decade longitudinal study where the tests were given to infants as young as 5 months old and those exact infants were tracked throughout their scholastic life and into their early twenties and IQ tests administered.

The visual based tests are quite predictive but due to mechanics and our own limitations more difficult to do at earlier ages. At earlier ages we hav to use the slightly less consistent but still "moderately" predictive sensorimotor based tests we've had since at least the 1920s. While,less consistent and predictive, they are still predictive. This means they predict accurately more often than they do not.

If your assertion were true then we would not be able to have predictive tests at all for infants. Sensorimotor based intelligence testing has been shown to be predictive to inside of three months. While it may be hypothetically possible that infants somehow develop an intelligence between birth and three months of age, there is no evidence to suggest that is the case. Instead what we have in actual science, and scientific history, is a trend of creating better tests that reveal the intelligence at earlier and earlier ages.

You assertion is the article of faith here, not that we have an innate intelligence. We also have decades of research that indicates we have a genetic base of an upper bounds on an individual's IQ that is lowered, but not increased, by environmental factors such as cultural and nutritional. A key thing to note about this research is that there is no disagreement among the researchers that there is an innate maximum intelligence level determined by genetics - the questions are around how to more accurately measure it and what stunts it, then how to use that information to prevent that stunting.

It is difficult to overstate how strong our actual IQ testing is - though many completely fail to understand what IQ actually is. Having a high IQ is never something I’ve accepted as a compliment because I didn’t do it. I find the idea to have no more merit than complimenting someone on their height, eye color, or the color of their skin. Which is, to say, no merit. Despite nearly a century of trying we’ve found no means by which you can increase your IQ. None. On the other hand, let us look at IQ. To keep the math simple lets look at the original formulation:

IQ = 100 x (mental age/chronological age)

Mental age is determined by testing problem solving. The typical example is that you take a ten year old and have them solve problems. If they solve problems at a twelve year old level their mental age is 12. Plug that into the formula and they’d have an IQ of 120. However, IQ is - as one can clearly see - relative. Even under the newer, more accurate, formula it is relative to your age range. This is another reason that IQ testing in youth isn’t a standalone. Take that ten year old in the example. He or she may simply be ahead of the curve at that point, but that doesn’t mean he or she continues to be. In two years if you repeat the test that kid may be average because they are still solving problems at the twelve year old level. However, that doesn’t mean there isn’t something more important in IQ. Let us take your example of Einstein. True, we have no actual test records for him. However, we can reasonably estimate it based on the combination of his work and the fact that we do have tests for "modern peers”.

We can do so because no eminent physicist, chemist, astrophysicist, etc. has produced even a tenth of Einstein’s output with an IQ of, say, 80. None. Dr. Feynman, one of the preeminent scientists of our time (some may recall the Challenger O-ring problem - that was him doing the demo for Congress) had an IQ of 125 - and no I’m not joking this is the figure he himself gave. The lower bounds on physicists of note in the modern era with known test results is slightly above 115, and for minor noteworthiness 110. There are none below 110. None. The sad thing about general discussion about Feynman’s IQ is that people try to claim, ignorantly and wishfully, that 125 is “average” when it is not. Then again, once you reach a certain age your IQ becomes more difficult to measure because IQ tests were developed specifically for children. There is far more agreement on our ability to measure general intelligence in children than in adults. If you remember and understand what an IQ test does and that it is _by design* a relative measure, that makes sense. This is exacerbated by the effects of low IQ. Someone with a low IQ, such as 80 or less, isn’t winning Nobel prizes (the separate “Peace Prize” notwithstanding). Their IQ is low enough that it has meaningful impact on the rest of their lives. The more technological our basic society becomes the more this will matter.

However, above a general level of around 85 or above (on any of the various actual IQ tests) it becomes less meaningful, and the higher up the scale one is the less meaningful it is. This is because IQ is not, and can not be, designed for that end of the scale but for identifying those at the bottom - or at risk for being there when used longitudinally.

By contrast, consider height in the NBA. The average player is 6’7” and it is a tight range. Height is obviously a significant factor in playing basketball at the higher competitive levels. Sure, shorter people such as 6’2” can be successful and I’m sure we’d agree that a 5’3” person can play the game. But can they rise to the ranks of notable in the real of professional basketball? Yes. The shortest player to have achieved that level of success was 5’3”. Curiously, 5’3” is 80% of 6’7”. Interestingly, 100 is 80% of 125. Anyway, if I gave you stats on an NBA player and asked you to estimate height, and we had an “HQ”, or Height Quotient, you’d be able to roughly estimate their height based on that ratios and testing and you would conclude with a high degree of certainty that the player was not 4’7”. But even then you’d be less accurate than doing the same with IQ. Why? Because a 6’ human can improve their basketball skills, but even a human with 130 IQ can’t improve their intelligence. We can improve our knowledge, but not our intelligence.

And as to this being a discussion about “faith”, no. You don’t get to spend the entire post talking about intelligence and making baseless assertions about it, then mention faith in, literally, the last three words of the post and claim it is about faith rather than intelligence and expect that to withstand scrutiny. To that end, any decently trained psychologist could test your mythical wild-born child and argue he or she was intelligent. We can test infants, but not some “wild born” child? We can test and measure the IQ of people born deaf and the lacking auditory understanding, but not a “wild” born child because he or she has had no formal education? Preposterous. Education isn’t intelligence, but rather something requiring intelligence. To claim that infants don’t have intelligence, and that “nobody" would argue a wild, uneducated child has no intelligence despite a century of research indicating quite clearly the opposite is an expression of faith at best. Too claim that you can’t test an uneducated child for IQ, a test designed specifically to test the uneducated, is absurd. To then also claim you don’t need to back such a claim up in any way only further removes it from the realm of reasoning.

edit: ugh markdown reformatting