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One thing to note about children's IQ is that, contrary to intuition, environmental factors tend to play a smaller overall role as the child mature into adult.
by gpt5 4y ago
One thing to note about children's IQ is that, contrary to intuition, environmental factors tend to play a smaller overall role as the child mature into adult. Instead, their genetics seem to play a larger role.
As the children mature, the heritability of their IQ grows from roughly 0.45 to 0.8 (similar to height) [1]. The fact that the age of the child at the time of the IQ test is such a large factor is often not accounted for in research, which creates inconsistent results. Ideally, breastfeeding research would compare the IQ at adult age of children that were breastfed for different durations, normalized against their parents IQ.
https://en.wikipedia.org/wiki/Heritability_of_IQ#:~:text=Early%20twin%20studies%20of%20adult,for%20late%20teens%20and%20adults https://en.wikipedia.org/wiki/Heritability_of_IQ#:~:text=Ear....
- Retric 4y ago“Various studies have found the heritability of IQ to be between 0.7 and 0.8 in adults” However, it’s important to realize that environment is generally fairly constrained in these studies. A Twin study is hardly comparing Sierra Leone with Japan, or the Netherlands with North Korea. Extremes like iodine deficiency, disease, or fetal alcohol syndrome are similarly excluded.
- gpt5 4y agoHeritiblity of a trait is not traditionally determined in twins studies but can be done on any random sample of the general population. FWIW, you see the similar trend in adopted children - as they grow older, their IQ trends from being close to their adoptive parents to getting closer to their (completely uninvolved) biological parent.
- Retric 4y agoComparing random members of the general population has both genetics and environmental factors. To isolate the role of either genetics or the environment you need to then control the other factor thus twins for genetics or unrelated people who grow up in similar environments. But both of those comparisons run into problems if these differences don’t represent the full scope of differences with the added issue of similar environments not actually being identical.
- gruez 4y ago>However, it’s important to realize that environment is generally fairly constrained in these studies. A Twin study is hardly comparing Sierra Leone with Japan, or the Netherlands with North Korea. Extremes like iodine deficiency, disease, or fetal alcohol syndrome are similarly exclude. except if you look at the other comparisons made (eg. "Unrelated children—Reared together—Adults "), the correlation factor can go quite a bit lower than 0.7-0.8 (eg. 0.04). The fact the correlation can go this low casts doubt on your theory that the environment is "constrained".
- Retric 4y ago0.04 seems unusually low I have seen studies more in line with this one: “Same person (tested twice) .95 Identical twins—Reared together .86 Fraternal twins—Reared together .55 Biological siblings—Reared together .47 Unrelated children—Reared together .30 Parent-child—Living together .42 Adoptive parent – child – Living together 0.19 Identical twins—Reared apart .76 Fraternal twins—Reared apart .35 Biological siblings—Reared apart .24” So siblings reared apart had less correlation than unrelated children living together.
- gpt5 4y agoUnfortunately, these numbers don't state the age of the child when they were tested, so they are not very useful.
- pyuser583 4y agoThey don’t state lots of other things. Like what “raised separate” means. Was one raised in a Soviet gulag while the other was raised in an Israeli kibbutz?
- deleted 4y ago[deleted]
- cornel_io 4y agoThis is a universal complaint that can apply to almost any heritability study. And I'm not aware of any situations where a further investigation found it to be devastating to the original conclusion (mainly because actually covering all the edge cases you're calling out is somewhere between "cost prohibitive" and "impossible"). That makes me think it's just a generic "I don't like this conclusion so I'll criticize it" Joker card that people play, and not a legitimate debunking.
- Retric 4y agoIQ is unquestionably extremely influenced by genetics. I am simply bringing up the context when people want to toss out specific numbers.
- wisty 4y agoAn adult is less constrained by their home environment, and more constrained by a combination of their genetics and the planet they live on.
- AlchemistCamp 4y ago> A Twin study is hardly comparing Sierra Leone with Japan, or the Netherlands with North Korea. Extremes like iodine deficiency, disease, or fetal alcohol syndrome are similarly excluded. Sure. To take this line of reasoning to its conclusion, an environment that has no oxygen or is otherwise uninhabitable, would prevent any human from living or having any mental abilities whatsoever. In this sense, environmental influences would completely dominate genetics. Similarly, changing 50% of a human's DNA would have them live life as a stalk of wheat. What's your point?
- cm2187 4y agoOn that topic, an interesting discussion in the latest Lex Fridman: https://www.youtube.com/watch?v=hppbxV9C63g https://www.youtube.com/watch?v=hppbxV9C63g
- CrHn3 4y agoDo you consider breastfeeding to be an environmental factor? Breastmilk contains the most microRNA of any body fluid[1] and has the potential to modulate gene expression, so there may be ways breastfeeding affects the genome that we don't understand yet. How long a child is breastfed is associated with epigenetic differences in children.[2] Breastfeeding is negatively associated with the methylation of LEP. Childhood obesity is associated with lower cognitive performance.[3] 1. AAP talk on long term breastfeeding epigenetic effects: https://www.youtube.com/watch?v=-bUeSqPOCTc https://www.youtube.com/watch?v=-bUeSqPOCTc 2. https://pubmed.ncbi.nlm.nih.gov/32443666/ https://pubmed.ncbi.nlm.nih.gov/32443666/ 3. https://onlinelibrary.wiley.com/doi/10.1002/oby.22192 https://onlinelibrary.wiley.com/doi/10.1002/oby.22192