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CharlesOSmith t1_ivxzaqz wrote

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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rpsls t1_ivya7di wrote

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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Team_Ed t1_ivyfast wrote

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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Aceticon t1_ivyi214 wrote

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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tt1702y t1_ivyy62x wrote

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?

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CharlesOSmith t1_ivz03yb wrote

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.

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tt1702y t1_ivz0kjp wrote

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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