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> Environmental factors can cause genes to be turned off or on The principle here is straight forward, but it's not clear to me that anybody has actually demon

> Environmental factors can cause genes to be turned off or on The principle here is straight forward, but it's not clear to me that anybody has actually demonstrated a clear 'signal' in the process. In other words there is evidence that stress caused by fire trauma can change the way genes are expressed in an individual, and I believe there is evidence that stress from trauma can impact gene expression at the process of genetic recombination. However I've not seen any evidence that, for instance, stress caused by fire will induce any sort of specifically fire related gene expression in offspring. Would an orphan who never knew their parents have an elevated fear of fire if both their parents had survived a severely traumatic experience with fire? To my knowledge, that's still purely speculative. The closest I've seen is the suggestion that offspring of famine survivors may have an epigentic change that makes them gain weight: >The field of epigenetics gained momentum about a decade ago, when scientists reported that children who were exposed in the womb to the Dutch Hunger Winter, a period of famine toward the end of World War II, carried a particular chemical mark, or epigenetic signature, on one of their genes. The researchers later linked that finding to differences in the children’s health later in life, including higher-than-average body mass. But that leaves open many questions. What other epigentic changes did these people have that seem unrelated to food/weight? And how many people who suffered from trauma unrelated to food availability have changes that effect weight gain?

iguy 8y ago
The Dutch children are an odd example here, because they themselves experienced hunger in the womb. That their bodies remember this isn't surprising at all. The markers through which this is remembered are sometimes called epigenetic, the word seems to be a little fuzzy... I guess there is a small step between individual cells having persistent changes, and daughter cells in the same individual inheriting such changes. (But again unsurprising: the embryo needs to mark some cells as future-leg-material when it's only a few hundred cells, and their millions of actual-leg-cell descendants remember.) The big and controversial step is to writing such changes into the germ-line, so that offspring of the individual cary such a memory. And my understanding is like yours, that there's some evidence for crude things (like massively stressed / starved mice having offspring who are calibrated a bit differently) but not really anything solid for the sort of finer changes we like to speculate about in humans. It's not impossible, and it need not be un-Darwinian: your genes care more about how many grandkids you have than how many kids, and if pre-adjusting your kids to the environment is advantageous, then they certainly have the motive to do it. And there are corners of biology in which you could hide a mechanism to do this (just a little bit) where we would not yet have seen it. But a lot of the tantalising studies seem to underplay ordinary inheritance. For example, lots of abused children, sadly, have a 1st-degree relative who abuses children. Some of whatever is wrong with the abuser may also be wrong with the victim (through no fault of anyone's!) and this may show up on all sorts of measures. Removing such things from your data is going to be super-hard, and if you succeed, you are more likely to get a boring paper.
- darkpuma 8y ago
  >"The Dutch children are an odd example here, because they themselves experienced hunger in the womb. That their bodies remember this isn't surprising at all." Good point, there's an ocean of difference between experiencing hunger in the womb, and being well nourished in a womb belonging to a woman who was once malnourished. I don't have that study available to me at the moment to check, but I wonder what they say about children born from those same mothers years after the famine was over. Surely they looked at that too, since if the same signal was present that would certainly enhance their findings. If the study doesn't mention those later children at all, that would suggest to me they're guilty of p-hacking.
  - DoreenMichele 8y ago
    I think it is kind of a stretch to call it epigenetics when the mother was traumatized while pregnant with the child in question. I think we need a different concept for that. But I can well imagine that, in most cases, trauma leaves a body permanently altered in some manner and that this can potentially impact later children. With no real scientific basis to back it up, I will suggest that if trauma is passed on to the children biologically, the degree and manner of the inheritance may vary depending upon whether the traumatized parent was the father or the mother. Logically, the fact that the biological mother (in "old fashioned" pregnancies) both contributes DNA and also serves as the incubator for the fist nine months of life, whereas the father only contributes DNA, should make a difference in how heritable such a thing is.
    - darkpuma 8y ago
      That makes sense, if there is any measurable effect on children who's fathers but not mothers have suffered trauma such as starvation, that would be a compelling result.
- nanomonkey 8y ago
  I wonder how much of the change could be explained by a change in the gut flora/fauna that was passed on to the Dutch children due to their parents' starvation.

iguy 8y ago

The Dutch children are an odd example here, because they themselves experienced hunger in the womb. That their bodies remember this isn't surprising at all. The markers through which this is remembered are sometimes called epigenetic, the word seems to be a little fuzzy... I guess there is a small step between individual cells having persistent changes, and daughter cells in the same individual inheriting such changes. (But again unsurprising: the embryo needs to mark some cells as future-leg-material when it's only a few hundred cells, and their millions of actual-leg-cell descendants remember.) The big and controversial step is to writing such changes into the germ-line, so that offspring of the individual cary such a memory. And my understanding is like yours, that there's some evidence for crude things (like massively stressed / starved mice having offspring who are calibrated a bit differently) but not really anything solid for the sort of finer changes we like to speculate about in humans. It's not impossible, and it need not be un-Darwinian: your genes care more about how many grandkids you have than how many kids, and if pre-adjusting your kids to the environment is advantageous, then they certainly have the motive to do it. And there are corners of biology in which you could hide a mechanism to do this (just a little bit) where we would not yet have seen it. But a lot of the tantalising studies seem to underplay ordinary inheritance. For example, lots of abused children, sadly, have a 1st-degree relative who abuses children. Some of whatever is wrong with the abuser may also be wrong with the victim (through no fault of anyone's!) and this may show up on all sorts of measures. Removing such things from your data is going to be super-hard, and if you succeed, you are more likely to get a boring paper.

darkpuma 8y ago
>"The Dutch children are an odd example here, because they themselves experienced hunger in the womb. That their bodies remember this isn't surprising at all." Good point, there's an ocean of difference between experiencing hunger in the womb, and being well nourished in a womb belonging to a woman who was once malnourished. I don't have that study available to me at the moment to check, but I wonder what they say about children born from those same mothers years after the famine was over. Surely they looked at that too, since if the same signal was present that would certainly enhance their findings. If the study doesn't mention those later children at all, that would suggest to me they're guilty of p-hacking.
- DoreenMichele 8y ago
  I think it is kind of a stretch to call it epigenetics when the mother was traumatized while pregnant with the child in question. I think we need a different concept for that. But I can well imagine that, in most cases, trauma leaves a body permanently altered in some manner and that this can potentially impact later children. With no real scientific basis to back it up, I will suggest that if trauma is passed on to the children biologically, the degree and manner of the inheritance may vary depending upon whether the traumatized parent was the father or the mother. Logically, the fact that the biological mother (in "old fashioned" pregnancies) both contributes DNA and also serves as the incubator for the fist nine months of life, whereas the father only contributes DNA, should make a difference in how heritable such a thing is.
  - darkpuma 8y ago
    That makes sense, if there is any measurable effect on children who's fathers but not mothers have suffered trauma such as starvation, that would be a compelling result.
nanomonkey 8y ago
I wonder how much of the change could be explained by a change in the gut flora/fauna that was passed on to the Dutch children due to their parents' starvation.