Mice can inherit learned sensitivity to a smell (2013) | Hacker News Reader

Mice can inherit learned sensitivity to a smell (2013)

sciencedaily.com

67 pointsmarojejian21 comments

I've read the paper. We don't know the exact mechanism by which this works, but I would bet that it's related to the chemical exposure (as the authors suggest in the Discussion section), i.e. exposure to the scent causes ingestion of the chemical which then affects the genetic contents of the gametes. That's really really interesting, but isn't the same as "learned behavior can be inherited". In this case, it looks like it's sensitivity to the scent that is inherited, which was confirmed not just via behavioral methods but by looking at the neurons devoted to it.

https://www.nature.com/articles/nn.3594.epdf?referrer_access...

Genetic memory is likely a reality, how it works and through which mechanisms is an open question.

Without genetic memory a lot of the complex inherited behavior we see in animals which emerges even outside of groups wouldn’t be possible.

It’s also clear that some mechanism would have evolved to allow you to update these behavior patterns on some level across generations.

A crazy theory of mine is that perhaps there learning at the lower levels of reality that drives evolution. If evolution can meta-program its genetic code and learn, it could account for the cambrian explosion.

It doesn't need to be that sophisticated.

If we take the "trauma/PTSD" example based on some studies e.g. the Holocaust survivors one [1] it seems that some genetic or epigenetic changes do occur the outcome of those changes is still debated.

My own personal view of this is that genetic memory is basically a way of an organism to signal to the next generation how to better utilize it's current genetic toolkit to better survive.

And we have other examples of it, obesity for example has clear influence on the genetics of male sperm and these changes disappear after weight loss is maintained and would reappear if there is a major weight gain.

To me the reason for this is pretty clear your body assumes that if you are collecting fat there is a good reason for it, and transferring that knowledge to an offspring would increase their survival rate.

Another good example is predators anyone who's been around one knows the feeling you get even when you can't see them (on an anecdotal level I'm one of the last ones to get the goosebumps from something like a wolf or a mountain lion and I have a horrible sense of smell, I've known some people with effectively a super nose that would get the hibbie jibbies much more often in the woods or during trekking and I'm pretty sure that it's still because of predators we can't see but still pickup via smell even if it's unconscious) and it's quite different than the feeling you get around other dangerous animals like big bovines big deer (including elk/moose) that can be pretty darn dangerous in some situation it's not even the same scare/feeling that you get from big dogs.

To me that idea that we (or I am) a descendant of people that happened not to be eaten by wolfs and lynx because we somehow were sensing them due to random mutation seems to be highly unlikely especially since I've known people that get the same sense from animals that cannot really harm us today like the Bobcat which is while a Lynx is more the size of a very large house cat or a medium dog than a big cat.

To me it's much more reasonable that some ancestors encountered a predator, deemed it as an extreme threat and that experience was in some way or another encoded into our genes that would allow us to identify them better.

Now I'm not saying that experience can alter the orienting or defensive responses/reflexes but they can fine tune them to specific scenarios, even only as this seems to be the most efficient way of doing this.

[1] http://www.pbs.org/newshour/extra/daily-videos/can-trauma-be...

I'm going to throw out an off-the-cuff hypothesis. What about microchimerism as an inheritance process? Microchimerism is the presence of of cells that originate from another individual and are distinct from the cells of the host. Transmission between mother fetus has been observed. Moreover, olfactory bulbs are one area with continued adult neurogenesis. Thinking on that, I reasoned that if so, there might be increased neurogenesis in the olfactory bulbs during pregnancy in mice. A quick lit search came up with: https://www.ncbi.nlm.nih.gov/m/pubmed/12511652/ Yes, increased neurogenesis during pregnancy in response to particular hormone. Pretty out there hypothesis, I know...

In the wrong direction (male fetus to mother, not sure they tested the other direction), but... http://onlinelibrary.wiley.com/doi/10.1634/stemcells.2004-01... "The male cells were found almost exclusively in Block 1, corresponding largely to the olfactory bulb."

Now this is starting to be interesting!

Note that the “inheritance” can come from the father, and also happens with in vitro fertilization.

Wow. Good point.

Well it's also true that you can pick up cells from people you are genetically similar too and live in close proximity to. This might play a part in group cohesion?

It makes more sense that learned behavior and can be inherited by offspring rather than random mutations producing complex advantageous behavior but exciting to hear that it's been replicated.

I wonder if offspring of older parents possess an advantage of possibly having more learned behavior passed down.

Final vindication of Lamarck.

The Darwinism/Lamarckism thing is wrapped up in politics. Darwinism is used as a justification of the social order. Might is right. The strong survive. Lamarckism has a more touchy feely feel to it. Not that Darwinism is fundamentally wrong! Its just that the nuances are ignored because of the politics.

I thinks that's a misinterpretation of Darwinism. The strong don't survive. The surviving ones survive. That's the whole point. Darwinism isn't an optimisation algorithm. A set of circumstances that were favourable for survival with a particular trait may not necessarily be favourable in the future. At any given point, though, the ones that survived are the ones that you can see, so it appears as though they were "selected". This theory is nicer than Lamarckism because it literally needs no mechanism. In order to accept Lamarckism you need to show that species change due to environmental pressures. That's more difficult.

To be fair, I think that's memebox3v's exact point. They say: 'Darwinism is used as a justification of the social order... the nuances are ignored because of the politics.' One such nuance is the point that you make.

> Darwinism isn't an optimisation algorithm. A set of circumstances that were favourable for survival with a particular trait may not necessarily be favourable in the future.

While agreeing with the thrust of your post, personally I think that Darwinism is a form of optimization, but the mild confusion around Darwinism that you're describing is a confusion about what that system optimizes for.

Darwinism optimizes for survival in the specific environment and circumstance, and plays out over time. Darwinism does not optimize for "best" or "strongest" or the "mightiest".

I think this also blows apart some nascent theories regarding toxoplasmosis.

This isn't particularly rigorous. Like all of these studies that claim to support epigenetic memory in mice, they've started with mixed genetic background mice, so that none of the offspring are genetically identical to the parents. You can't rule out the possibility that genetic differences are responsible for this result.

This is publication bias in action. Studies that don't show epigenetic inheritance don't get published. Where are all the properly controlled experiments using inbred strains?

Surely there are ways of studying this without clones. That's what statistics are for.

I am far from a geneticist (or in fact any form of scientist), but why do normal experimental controls not work in the case of this experiment?

You perform the odor exposure to half of your group and not the other half (the control group). Then you compare the results (measurement of the offspring) between control group and non-control group.

Assuming that your group size is large enough that the measured difference can be considered statistically significant, then it doesn't matter what other variances there are - you have controlled for them.

There are strains of mice which have very little genetic variability, thus excluding (or at least diminishing) other variations than the studied effect. This study apparently didn't use one of such strains, so many genes could interfere. Large enough is otherwise really large.

Sometimes I wonder what the epigenetic effects of porn will be on the long run. The illusion of living in a plentiful environment could have unforeseen consequences over the brain of our children.

Reply on news.ycombinator.com