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You are asking about epigenetics.

The general idea is that our exposure to our environment can shape our genomes.

In particular there are some types of environmental exposures that can directly indicate health, and living quality, things like starvation, exposure to chronic stress, habitual use of drugs, or exposure to toxins. On an evolutionary scale the system allows the nourished adult to pass that information on to its gametes which then have information saying "things are good, so let's allow for the best growth for which our genes allow", and the malnourished adult to pass that information on to its gametes which then have information saying "things aren't that good, so let's limit growth to the minimum our genes allow."

Its not fully decoded yet, and the generational influence appears to be more extended than just parent to offspring. Its also a highly tunable and modular modification to the genome so there are lots of gradations to the overall outcome.

So you can think of your final height being a range that is possible given your specific combination of genes. Epigenetic markers on those genes may indicate what height in that range is considered to be the target, and your own environment, and nutrition status will influence where your final height lands relative to the target within your range.

https://pubmed.ncbi.nlm.nih.gov/24963031/#:~:text=Epigenetic%20heredity%20thus%20appears%20to,environmental%20influence%20on%20epigenetic%20traits.

https://www.nature.com/articles/ncomms13490

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I’ve seen no data on malnourished parents affecting the adult height of their offspring, but Swedish administrative data shows that food access of boys during prepuberty predicts the all-cause and specifically cancer mortality of their grandsons.

If you’re a man and your grandpa had good harvests during his slow growth period you have a higher risk of cancer.

Sorry it’s not quite on topic, I just think it’s interesting!

My understanding is that the effect is particularly pronounced on the maternal line— a mothers eggs begin to form in the grandmother’s womb, so direct effects can last 2 generations. But the study I saw talked about “health” and various biological markers, not height… although the two could be linked.

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Is there not a genetic effect re selection and survivor bias?

It wouldn’t necessary apply to any given individual, but a population that experiences one or many large malnourishment event(s) — periodic famines or, say, the holocaust — will end up seeing smaller body types survive at higher rates simply because bigger bodies are harder to feed.

So if you are the descendant of a famine survivor whose body was wrecked by the experience, their personal experience may not directly effect their kids’ genetics regarding body size, but it may nevertheless be true that those kids might be more likely to have their genetics tend that way, regardless.

Obviously wouldn’t apply if we’re talking one-off malnourishment events like individual poverty, but then many people in the west who might have parents with these personal histories or malnutrition are from immigrant populations that may have those selection pressures.

ie: if your parents were malnourished, it’s logically more likely they come from a population where malnourishment is common and small size is genetically selected for — meaning you may be more likely to have small-size genes regardless of whether your parents had been malnourished.

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Genetics works at a much more massive scale (numbers and time wise) unless there's the kind of trully exceptional circumstances where almost all individuals of a tribe perish without leaving any descendands (in which case only the genetical material of the survivours could possibly carry on forward), so most of it is to do with tiny differences in the probability to reproduce which over many generations and across millions of individuals cause a certain characteristic to become preponderant.

So a single generation (or two or three) going through starvation wouldn't do much to the genes themselves unless it was so extreme that the "only handlfull of survivors, no living descendents for the others" situation happenned (and even then it would only affect that tribe and might later dilute itself to non-existence through intermixing with other tribes)

Epigenetics on the other hand has to do with proteins that surround the genome but are not the DNA itself, which can toggle genes ON/OFF or influence their expression, which can change during an individual's life due to environmental factors and which can also be passed from parents to children. It seems to be a far more reactive mechanism but also one which is more temporary.

Whilst epigenetics also has to do with genes, it is something only recently discovered and in it the information is not stored in the DNA.

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• South Koreans are on average much taller than North Koreans. South Korean height really took off from the 90’s once they started experiencing their economic miracle similar to Japan. Likewise the inclusion of more dairy and meat (South Koreans eat more meat than any other Asian country) in their diet makes them the tallest among other Asian countries.
• Japan has had a long history of famine. Post-WWII saw the greatest availability and consistent access to food, and now Japanese people are far taller on average compared to pre-WWII.
• I forgot the source, but I read that a study found that European average heights coincide with periods of famine and prosperity.

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So I would conclude that unless there was extreme severe malnourishment in the population, the malnourished parents will not effect their children’s final height?

That's not accurate. If the parents are malnourished, that is the trigger for epigenetic markings on their gametes. It doesn't have to be population wide.

Yes that’s true but wouldn’t it have to still be starvation for a long period of childhood to cause them to be malnourished. Also what epigenetic’s are you talking about since if you also don’t grow up malnourished, then it wouldn’t cause you to not gain your genetic potential in height. Correct?

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Generally speaking you see a big increase in height between malnourished parents and their children who have plenty of food, so if there is an effect it doesn't dominate the effect of food availability that you have yourself during critical growth periods.

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There are a few comments talking about epigenetics, and there seems to be a bit of error in explanation, so I wanted to try and clarify.

Historically, it has been understood that an organism will not pass on traits that arose as a product of environmental input (you wouldn’t pass along a broken arm to your child, just like you wouldn’t pass down decreased height as a result of malnourishment).

This is where things get interesting though. Epigenetics is the modification of a genome given environmental conditions. Modification of a genome means that offspring will contain the genetic modifications even in the absence of the environmental conditions that brought them about.

For example, an experiment was conducted on rats, in which the first experimental generation (F1) were exposed to jet fuel hydrocarbons (bad toxins). As one might expect, the offspring of these rats was also negatively affected by these toxins. The interesting part though, is that the F3 generation (not exposed to hydrocarbons and not developed in an adult with exposure to hydrocarbons) also showed increased abnormalities -to kidney function, specifically - which was a product of exposure to the toxins. This means that environmental changes to the F1 generation were seen in generations further down the line which had no environmental exposure to these toxins.

If you care about the mechanics of it, the jet fuel hydrocarbons methylated regions of DNA, essentially changing how the script is read by the molecular machinery expressing that DNA and making proteins with the instructions from it. Methylation alters the instructions that the gene is giving to the protein making complex. This methylation (attaching of a methyl group to a nucleic acid) was a direct result of the exposure to harmful chemicals. This methylation is often passed down to offspring, and can have an effect on how the organism grows, develops and responds to external stimulus.

So, the gene itself has not been altered in any way. The organisms DNA is the same. It’s only the amounts of methylation that have changed. The genome now simply contains extra instructions on how to read and express it.

So, it could be possible that one’s height is affected by malnourishment in parents. If a parent experienced high enough environmental stress levels (constant hunger) to lead to modification of how their body responds to food, they could pass that down.

Epigenetics is barely starting to be understood, however, so it is difficult to make accurate claims about whether someone height could be affected by a parents malnutrition (during pregnancy is different obviously).

While it is difficult to make a direct claim, I would be genuinely surprised if there wasn’t some modification to the musculoskeletal development in offspring of malnourished parents.

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This means that if you have adequate food then you are not malnourished like your parents were correct?

Yes

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Also older people shrink and have worse posture and it depends as in your case they were very poor hence that happened. It seems to mostly take one generation from what I’ve seen and read.

The greatest example we have is a Longitudinal Aging Study Amsterdam. At the end of WW2, the Nazis starved the Dutch city of Amsterdam for ~ 2 years.

Women who were starving when pregnant gave birth to children who when they reached adult height were short than expected by ~4.5cm.

Second generation children (grandchildren of the starving pregnant woman) were also shorter than expected, by ~4 cm.

• Females shorter than expected by ~4.5 cm.

• Males shorter than expected by ~3-4 cm.

Since females on average are shorter than males, the % effect is even greater.

Are we talking about extreme starvation like famine and starving for most of childhood?

Am I correct?

Dutch Famine of 1944-45 was starving-to-death starvation. 20,000 people died.

The legacy is historically and scientifically interesting because the Netherlands is a modern, wealthy, highly educated population with excellent health care. The entire famine was extremely well documented, which makes later followups very complete.

So if I was to get adequate nutrition living in a third world country and I lived good, I would reach full potential of height right?

Too difficult to diagnose at a distance. At a minimum, way more complicated.

There is good evidence that about 80% of your adult height is determined by genetics, with the remaining 20% due to environmental factors. Mostly nutrition and disease.

But in poor African countries or other poor areas of the world, only approximately 65% is determined by genetics. There is something different in poor countries besides just genetics or simple environmental factors like nutrition.

The Dutch Famine study is the evidence of something that affects your genetics via something called epigenetics. If your mother was starving while pregnant, you would be shorter than a sibling born before the famine. Plus your children would also be shorter than your nieces and nephews. But then 4th generation is back to normal.

Overall: you need multigenerational optimum nutrition/disease conditions to reach maximum potential based on your genetics.

We are talking about extreme malnutrition am I right? For example starving to death for most of childhood and prenatal growth like the dutch famine where many died from starvation am I right? Therefore having adequate nutrition from parents, you would be good right?

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As a rough rule, it's about averages. Rich people with lots of resources will be taller and reach a plateau within their society, compared to poorer people with fewer resources. But there are always exceptions in each group.

Diseases or childhood illness may prevents you obtaining maximum height.

Nutrition is more than just calories. Ideally you have a varied diet. For instance, you could be really obese from eating sugar but your diet is lacking in protein or a particular vitamin.

The final thing is we can't rule out any effects from your grandparents epigentics, or other random things we cannot predict. Some medications will affect future children.

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