Is there any evidence for that, or is it pure speculation on your part?
No.
The DNA in one cell, stretched out, would be over 2 metres (6+ feet). Since you have trillions of cells, the length of your DNA is something like twice the diameter of the solar system.
When comparing people to other animals, what they mean is that chimpanzees and humans use DNA to encode mostly similar proteins. The term “junk DNA” was long used to describe DNA that did not encode proteins or seem to do much. However, it turns out this “junk DNA”, accounting for 98% of the genome, is very important in regulating which proteins are made. The junk DNA between humans and chimps is much more different than the protein encoding parts. “98% similarity” tends to ignore the junk DBA.
Intelligence and personality traits (openness, conscientiousness, extroversion, agreeable, neurosis) , in twin human studies, tend to have correlations between 0.2-0.6, far from absolute.
And since intelligence depends on nature (DNA in a complex multi factorial way), nurture (environment and early imprinting) and ^epigenetics* (DNA and protein expression is affected in the short term by environmental and emotional factors not yet well understood), it is hard to put numbers to intellectual differences between species. With epigenetics, nature IS nurture.
Easily; they could evolve without hands, or be on a world without the resources for a high population or advanced technology.
Human biology? That’s just what being raised with a serious nutrition deficiency does to people, and they’ve been starved to the point that male NK defectors are noticeably shorter than SK women. Unless they are biologically unique then they’ll have suffered damage to their intelligence.
It’s a fair hypothesis. Is there any evidence to support it?
Yes? It’s been known for a long time.
The trouble with some idea of a metric of DNA difference is that it is impossible to create one that is meaningful with current understanding of biochemistry.
A single mutation in one location can yield anything on a spectrum from a non-viable embryo to absolutely no change in function whatsoever. As noted above, we only really have some handle on the protein encoding parts of DNA, and very sketchy understanding of the rest. Junk DNA doesn’t turn out to be entirely junk in, so far, very poorly understood ways. A clue is how well some parts of junk DNA is preserved. But most of the junk DNA is very hard to consider as anything but actual junk, or at least containing even a tiny fraction of information. We seem to preserve about 11% of our DNA as a species. That is a still a great deal more than is needed to code for the proteins.
How we measure intelligence isn’t exactly clear either. If we are constrained to a metric defined on humans, which is likely about as much as we can sensibly do (as much as we like to paint ourselves as the smartest critters on the planet) we still end up with some very diverse ideas about what constitutes intelligence.
However all we have is the usual pair - nature and nurture. Nature is basically your DNA.
We can throw in some element of random luck. How the brain develops is murkily understood at best. The manner in which the early brain is flooded with cells, followed by a huge culling of cells bringing about the basic morphology is very poorly understood. Somewhere in just this step must lie some very fundamental aspects that define intelligence. About which we really have no clue. I have a lingering feeling that this is more chaotic than controlled, and may account for a huge fraction of differences in personality, and ability. Such a process might reasonably be selected for. So arguably partly DNA anyway. But if the DNA codes for throws of the dice, does it code for the outcome? Probably not.
We throw up geniuses and prodigies with no understanding about how they come to be.
So I’m going to posit that there is a significant fraction of just plain luck in an individual human’s intelligence than just what can be explained with DNA/nature and nurture.
Yeah. DNA is a recipe, not a plan; a list of instructions rather than a model. So the effects of a change can be all out of proportion to the genetic difference. To continue with the recipe analogy, “300 degrees” and “301 degrees” is a one word change, but so is “add salt” and “add beef”. Not only that it’s iterative, one step occurring after the other and affected by what comes before so it’s very easy for a shift early in development to have large later effects; that’s a major reason why a fetus is so much more vulnerable than a child, much less an adult.
Worth noting here is that certain diseases, like Down syndrome, are caused by having extra copies of a chromosome (a third, properly known as a “trisomy”). Most human trisomies aren’t survivable past early pregnancy.
Humans are supposed to have 23 chromosomes, marijuana has 20, hermit crabs have 254. Bacteria only have 1. So the raw chromosome count isn’t super meaningful in telling you the abilities of a certain species.
A better (and more well-worn) question is whether one’s genetics, the information coded in their DNA, accounts for intelligence. The answer is that most likely it does, to an extent, with some qualifications. At a broad level, some skills and abilities seem to be genetically encoded… for example language, toolmaking, the symbol recognition for reading, social abilities that help us use other humans as part of a “brain”, some metabolic abilities that help a human build and feed a bigger brain. But those things are prerequisites for intelligence, not intelligence itself.
Except, as you say, deleterious mutations are selected out. You can’t just sum the mutation rate in this way. It’s also pointless when we can just directly compare the DNA.
There is ample evidence of physical stunting of North Koreans vs. South Koreans. Although mental/intelligence stunting can also be a consequence of malnutrition the degree of impairment will vary considerable, just as the degree of physical stunting does.
I’m not aware of any actual studies, and mental stunting is not as obvious as the physical variety. There probably has been some effect but I’d be cautious about quantifying it without actual data.
The simple answer is - intelligence is a combination of nature and nurture (inheritance and environment). To some extent, it seems to be a matter of “mix and match”. Intelligent people seem to have fairly intelligent kids, but plenty of geniuses come from nondescript parents, and plenty of geniuses have unnotable offspring - the randomness of genetics. In the discussion, also note that while people many have 2 copies of a gene, it also may be that only one is expressed or active.
We learn as much by seeing as by talking (or reading). There are examples of flint tools several hundred thousand years old, presumably before we had coherent complex speech. Somebody learned to do it, and someone else watched and was guided to do the same. “Monkey see, monkey do”. Speech just made the process faster and more precise.
And like strength, intelligence is many things. Who’s stronger - the guy who can bench press several hundred pounds, or the 98-lb woman who can run a marathon? We have language abilities, mathematical abilities, pattern recognition and 3D visualization, problem-solving, memory, and understanding other humans and their behaviour.
The problem with dissecting nature from nurture is that we really don’t have a good measure of one without the other. We don’t test on smarts, we test on what we’ve learned.
I’ll also point out what I would call the “Asimov problem”. A very smart man has a very smart daughter and a son on the autism spectrum, something I’ve seen in several families I know. To what extent could there be “too much” of any smart gene(s)? IIRC partly this may be mosaic expression of genes with XX, if some attributes are linked to the X chromosome.
It’s not quite random; it’s the tendancy of extremes in genetics to move towards the average. “Regression toward the mean” is the term for that. Unusually smart people tend to have children that are smarter than average but less intelligent than them; unusually stupid people tend to have less intelligent children than average but who are smarter than them. The extremes aren’t stable.
I skimmed (will read in depth later if necessary). That article supports the idea that poor nutrition affects IQ. It doesn’t say anything about Koreans.
I’m not trying to be pedantic just for fun. I just don’t want anyone to walk away from the Factual Questions forum with any confusion about what’s an established fact vs. a reasonable sounding hypothesis, because those things are not the same.
I’m not aware of any actual studies, and mental stunting is not as obvious as the physical variety. There probably has been some effect but I’d be cautious about quantifying it without actual data.
Thanks. I think it’s pretty likely, but human intelligence is a such a charged topic that it behooves us all to be cautions about our assumptions.
Which is also a combination of nature and nurture, because intelligent parents are likely to work towards their children’s education and intellectual enrichment.
You can get some handle on things like this by studying twins, adopted children, and so on, but that often leaves you with comparatively small data sets, and intelligence is difficult to study to begin with.
Post-WWII Japanese gained several inches over their pre-war compatriots. The studies I’ve seen attribute it to improved nutrition, not genetics. I suspect the same is true for North vs. South Korea.
This is particularly true. I had a blue-collar job for a while when I took a break (dropped out) of university. I once went to visit a co-worker. He had 3 kids, the total reading material in their house was the Saturday newspaper and 2 or 3 Golden Books for the kids. I suspected those kids were not going to be deep thinkers when they got older. (Don’t know, lost touch. But he was a borderline alcoholic too…)
OTOH, my dad was a university professor who did sabbaticals all over the world. Whereas, as my step-mother delighted in reminding me, my uncle was a pig famer.
There’s also a caution that the basis of the primary study of identical twins’ intelligence (by Cyril Burt) was in fact mainly fabricated. (one basic critique was “where did he find all these twins separated at birth?”) Nevertheless, like misinformation nowadays on the internet, it had spread and been repeated as fact so many times based on third-hand references before being discredited that the concept is hard to root out of the field of study. (Hint - surprisingly, he “found” that yes, intelligence was 100% hereditary. All those lowly working class grunts were destined to stay that way, and all those hoity-toity upper class deserved to stay that way because - genetics)
My personal, non-scientific take has long been that genetics set the limits of your intelligence (your highest potential, your most likely actual IQ or whatever measurement you care to use) but environment has a lot to do with where you actually wind up. An ideal environment will let you get closer to your ultimate potential. A very poor environment can leave you lower down on the scale.
This is why you can have a person brought up in an “ideal” environment (however you define it) who is “only” average, or even less so. And some people in horrible environments are nonetheless average or above average intelligence - they might have genetics that set their potential higher than average that can (to some degree) compensate for a bad environment.
It’s not all genetics nor all environment - they interact with each other in each and every one of us.
I would add there are 3 factors - genetics, physical development, and learning environment.
It’s a fact that issues like fetal alcohol syndrome, poor nutrition in gestation or early years, etc. can affect physical brain development - which is a separate aspect from how stimulating one’s environment is intellectually.
This swiftly gets us into the whole field of epigenetics.
The entire question of how gene expression and proteins are regulated. This can affect the next generation as quite a bit of maternal and a bit of paternal regulating state is included in a new zygote.
A developing organism’s growth is highly controlled by more epigenetic processes, and early life conditions can lead to changes to epigenetic state that runs for the rest of its life. Cell differentiation is largely controlled by epigenetic mechanisms. Otherwise you would grow up to be a homogeneous blob.
It isn’t impossible that good maternal nutrition sets the controlling parameters for maturing into a tall muscular adult. Not a change in DNA, but a change in the regulation of DNA. Intelligence might get some bias as well, but the usefulness of this is less obvious. There is probably a good argument to evolve heritable epigenetic controls that tweak characteristics to fit the environment, particularity setting the controls for smaller, less hungry adults in environments where food is not plentiful.
This is still down to your DNA, but you are not defined by just your DNA, the specifics on how significant parts of your DNA are modulated are set before birth, and it appears a lot is set before conception.
There is more to ancestry than just the wiggly molecules.
Are you saying photons or sound waves affect epigenetics? I’m not sure what other non-chemical mechanisms could have an impact.