Our inability to identify the genes responsible for intelligence doesn’t equate to them not existing. Our understanding of genetics is still extremely nascent.
I'll tell you what genes are responsible for intelligence if you can tell me which machine code instructions are responsible for Mario. ;-)
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I might need to expand on that a little:
I predict that "the genes responsible for intelligence" are not a thing. I think that genes tend to work together to make a living organism similar to how machine code instructions work together to make a program run.
So for example: I'm pretty sure that looking at the design of eg. a 6502 can't directly predict the existence of Mario:
If you can't easily predict what neurons will do based on their layout, what chance do you have to predict the exact outcome of the genes which specify that layout?
You're going to need more data than just the genes alone.
The analogy doesn't work as we have indeed identified genes for many biological traits. For example, whether someone is vulnerable to certain diseases. So if iq is a biological trait, like eye color or height, it is odd that we haven't yet found any iq genes.
This isn't a strong 1:1 mapping. Genes are not horoscopes!
No gene works in a vacuum. Genes code for proteins that work together to perform diverse functions. Sure: in some situations you can indeed directly identify that a gene knock out or substitution might affect certain functions, but this is rather misleading!
Genetics is actually very much Turing complete and Genes might best be looked at as a kind of software (this might be considered an understatement).
For comparison: I'm sure we agree that a single machine code instruction by itself is meaningless. However, if you knock out or add a JSR (Jump to SubRoutine aka function call) at the right spot: sure you can claim that the JSR codes for a particular functionality. But: JSR is 3 bytes on a 6502, would you really believe someone who told you that 3 bytes is what it takes to "make Mario jump"?
In reality there's a lot more instructions behind it (with perhaps calls to further subroutines, and more subroutines past that). Genes are not quite 6502 code of course, if anything they're rather more sophisticated.
To look at some of your examples:
You mention eye color which is determined by quite a number of genes working together (eg. location, color select, pigment) .
Height is affected by ... almost everything all at once over a longer period of time (eating, sleeping, age, eating at a particular age, metabolic rate : which itself is fairly sophisticated... there's wall charts that span an entire room). This to the point where some people give up and say "height is actually mostly environmentally determined". (Of course in reality it's an interaction between Genes and environment)
Vulnerability and immunity to diseases is very interesting indeed, if you eg. look at the role of somatic hypermutation in acquired immunity.
And all of these would obviously not work without working cells with DNA transcription, metabolism, membranes, replication, etc. ;-)
In short: be a little bit careful with claims in newspapers that say people have found a "Gene for X".
I bet one could change one or more of several different sets of bits in several different parts of the program that would change the color of mario's hat.
(Perhaps thinking of it in terms of "what bits you should change" is asking the wrong question, instead it might be handier to look for the sprite definition, or to look for the sprite plotting subroutine)
These studies are highly powered statistically. One conclusion you can definitely draw is that common variation in intelligence is not primarily caused by common genetic variation.
Evidently, our genes determine our brain, and are what makes us more intelligent than other animals. But between individual humans, genetic variation contributes to only a few percent of variation.
Yeah, sfblah is right. We will be able to predict based on our knowledge of the little molecules inside you at some point, we just can't do it now.
The 70-80% is heritable and not via parenting. It is contingent on an environment that provides things like food and air, and the basic idea is that we control for the environment in some simplistic way via twin studies.
To illustrate, there is almost no difference between the genetics of humans 20,000 years ago compared to today. Yet there is a vast difference in what people understand and how they interact with the world, i.e. there has been an increase in "intelligence" in the past 20k years without there being any alteration to genetics.
It is also shown by the so-called "Flynn effect" [0], which is a substantial rise in measured IQ by over 1 SD in numerous populations during the 20th Century alone. This is comparable to the mean difference in intelligence between individuals, and absolutely cannot be accounted for by changes to genetics.
> To illustrate, there is almost no difference between the genetics of humans 20,000 years ago compared to today.
There is also almost no difference between genetics of humans and chimpanzees. No difference, except in a few areas that happen to matter a lot.
As it turns out, 20 000 years is plenty enough for natural selection to make dramatic change in the genetic makeup of the population. For a most obvious example, look at the spread of lactase persistence mutation, which occurred and started spreading less than 20 000 years ago.
> It is also shown by the so-called "Flynn effect" [0], which is a substantial rise in measured IQ by over 1 SD in numerous populations during the 20th Century alone. This is comparable to the mean difference in intelligence between individuals, and absolutely cannot be accounted for by changes to genetics.
The Flynn gains are hollow, though. They are not on g factor, and it’s the g factor that’s responsible for the predictive validity of IQ.
Imagine a society where people use human foot length to measure distances. After a century or two, they observe that everything is getting shorter, a sort of anti-Hubble effect. Nobody noticed, however, that people have become taller on average, and so their feet became longer, so the actual change is only in the used metric, not the latent variable they are trying to measure. Flynn effect is like that.
