Optimal nutrition brings up the issue of human biodiversity, though in other contexts social justice warriors call this “racism” and “pseudoscience.” If you have a fairly uniform ancestry, like my relatedness to British and Irish populations as a white Southerner, at least according to what 23andMe tells me, then I have the advantage of studying ethnically similar people for some ideas about optimal diets.
But what should you do if your parents or grandparents come from remote branches of the human species which didn’t have the opportunity to interbreed until fairly recently? Seems like you might have conflicting genetics for your diet based on the fact that people in different places evolved to survive on the radically foods available in their local ecosystems.
Optimal nutrition brings up the issue of human biodiversity, though in other contexts social justice warriors call this “racism” and “pseudoscience.”
Metacomment: You keep throwing these highly controversial statements into posts. It comes across as using tribal cheering, or worse, tribal booing. People are downvoting your posts not only for poor thinking but the fact that you seem to try to connect almost every single post you can to your politics. The comments might be better received if you focused on facts and evidence rather than remarks like the above.
Further, at least in this case the statement is transformed from “highly controversial” to “straightforwardly wrong” by its insertion into this context. The idea that people with different ancestry might benefit from different diets is not, so far as I am aware, a thing that “social justice warriors” call racism or pseudoscience. (Though I expect some of them do. For any reasonably large group, you can find some members who do pretty much any crazy thing.)
But what should you do if your parents or grandparents come from remote branches of the human species which didn’t have the opportunity to interbreed until fairly recently?
Go with the diet of the majority ancestral group, I think.
Some quick informal arguments: imagine health response to diet is set by many genes of small additive effect. (This is often true for any complex trait; behavioral psychology, and a lot of the heritability of common diseases is being identified in GWASes as that.) Imagine there are population-level differences; this is trivially obvious (lactose and alcohol), but that there’s a lot more than this (probable, since crops differ so much from region to region). Say, 1000. And you inherit genes from 1 of 2 ancestral groups, Red or Green. Each ancestral gene is +1 for that group, 0 otherwise.
Now, if you have 2/3s Red ancestry and you eat a Red diet, what’s your diet score? Well, 666 of your genes are Red, and so you get 1*666=666; 333 of your genes are Green and you get 0*333=0, total 666. If you ate Green, then it’s the other way around, 0*666 and 1*333, total 333. Clearly you want to eat Red. What if you’re 3⁄3 Red? Then 1*1000 vs 0*1000, obviously you still want to eat Red. What if you have a bare majority Red, 501/1000? Well, 501 (Red diet) > 409 (Blue diet). No matter what fraction, you always do better by going with your plurality descent.
Q: what if there’s uncertainty about the fraction of ancestry? A: the binomial around your estimated fraction is going to be pretty tight; randomness means if your family tree is 2⁄3 Red, you’re going to be close to 2⁄3 of your diet genes being Red if there’s more than a few dozen diet genes. And a quick $100 at 23andMe will fix any uncertainty about ancestry anyway.
Q: what if there’s more than one relevant ancestral group and/or diet? A: the reasoning still works even if it’s maximizing the gain from a split of genes like 10%/1%/1%.../1%.
Q: why not ‘match’ fractions of diet with fractions of ancestry, eg. if 1⁄3 Red and 2⁄3 Green, eat Red breakfasts but Green lunches & dinners? A: For the same reason “probability matching” doesn’t maximize your expected-value when the probabilities are known (as they will be in this case); it might work if your genes were changing or there was a lot of uncertainty, but that’s not the case and so ‘pulling the suboptimal arm’ is just suboptimal.
Q: what if I know that I am lactose-intolerant through self-experiment, should I really eat as much cheese as my Dutch ancestors? A: No.
Q: what if I know that I am lactose-intolerant because my 23andMe report shows I didn’t get the relevant SNPs, should I really eat as much cheese as my Dutch ancestors? A: No.
Q: what if there are genes of differing effect sizes, where some seem to have large effects on how diet affects health? A: Well, if you don’t know about them, then you’d expect all ancestral groups to have the same expected-value; and if you do know about specific ones, you can add them to the calculation based on their effect and different prevalences between groups.
Q: what if genes’ effects aren’t additive, but are crazy wild-ass interacting nonlinear networks and stuff like that? Nonlinear nonlinear nonlinear whoooo! A: lots of stuff seems to be additive, and anyway, if your genes are really that hard to predict, why would that make your minority genes outperform your plurality genes? It’s wild stuff either way.
I find it credible that people with different genes could have different optimal diets. How much of those difference would be between different ethnic groups, and how much would be between individuals within the same group, I have no idea. I also have no idea how much “what my ancestors ate” is close to “what would be optimal for me to eat”. Also, I have no idea whether a diet optimized for a specific human would be significantly better than a diet optimized for an average human, compared with the improvement we would get by switching from an average first-world diet today.
I would like to see this question answered, preferably by someone who already doesn’t have their bottom line written either way.
(A few random thoughts: Food allergies suggest that at least some individuals need wildly different diets than their neighbors. I would expect ethnic group differences in eating dairy products, and in vitamin D requirements. If Soylent becomes popular among people from different ethnic groups, we could get some nice data.)
Food allergies are basically immune issues, and what I’ve read of them suggests that they’re more likely to come from environment (the immune system gets antsy and starts attacking random harmless compounds when it doesn’t have enough actual pathogens to shoot at) than genetics as such, so I think they’re probably a non-starter here.
There’s plenty of non-allergic variation in what different populations can handle food-wise, though; lactose intolerance and the alcohol flush reaction caused by differences in aldehyde dehydrogenase expression are the first two I can think of. These are often uncontroversially linked to ethnicity: lactose intolerance for example is very common outside North or Central European, North Indian, and certain African populations, and the alcohol flush reaction is a mainly East Asian phenomenon.
If you’d said “Neolithic”, I would’ve been right there with you—but not paleo-. Documented forager diets are hugely varied: even if we throw out the Arctic Circle populations as obvious outliers, they range from mostly plant to mostly animal; the animal component can be mostly aquatic or mostly terrestrial; and the plant component is even more idiosyncratic. I have no reason to believe this wouldn’t have been true in the ancestral environment.
There are some unifying factors: most of the forager diets I’ve read about have more fish and fruit than modern Western diets, to name an exceedingly obvious example. But there’s a far cry between that and saying that they can meaningfully be treated as a unit in this context.
Apparently fish is by far the healthiest form of meat
That is not self-evident to me.
Red meat is considered harmful mostly because it’s usually high in saturated fat which has been demonized for the past few decades. If you think saturated fat is fine, I don’t see why you’d consider red meat unhealthy.
Fish, on the other hand, is considered healthy largely because of omega-3 fatty acids and the reason that contemporary Western humans need them is that the usual diets have massively skewed omega-3/omega-6 ratios. And the reason for that is all the seed oils (soybean, sunflower, etc) that we consume. I don’t know if eating fish would be especially “healthy” for someone with a normal o-3/o-6 ratio.
A 1999 meta-analysis of five studies comparing vegetarian and non-vegetarian mortality rates in Western countries found that in comparison with regular meat-eaters, mortality from ischemic heart disease was 34% lower in pescetarians, 34% lower in ovo-lacto vegetarians, 26% lower in vegans and 20% lower in occasional meat-eaters.[9]
Now it’s possible that this correlation does not imply causation. Its also possible that the meat-eaters are eating low-quality processed meat, or are overcooking their meat.
Fish does pose worries about mercury. I have been considering going pescetarian at some point in the future, but if I can get the same benefit by using olive oil instead of sunflower oil then I won’t bother.
I am aware of observational studies. But if you want to quote some, please find ones which examine total mortality and at least discuss the confounding factors.
E.g. this is a better example, but note that in this case they lump fish and chicken together under “white meat”.
Er, what percentage of the ancestry of a modern Irishman do you think comes from the people living in Ireland in the stone age? It seems reasonable to consider the staple Irish diet over the last few centuries as being a good starting place for a modern Irish diet (or, at least, to assume it fits a modern Irishman’s genes better than the traditional Japanese diet).
This depends how fast evolution happens, and I’m not an evolutionary biologist. But paleo diet people at least think that humans are mostly adapted to eat what we ate during the stone age. I also don’t know what percentage of Irish DNA comes from stone-age Ireland, or more to the point from areas with similar food sources during the stone age.
But regardless, many aspects of a modern diet (e.g. food additives) are very new, and not present in anyone’s ancestory.
I’m not saying that different ethnic groups don’t respond to food in different ways, but I haven’t heard much about this, and with the possible exception of Eskimos who might be adapted to eat a pure meat diet, I doubt it’s of much importance when planning diet.
I’m not saying that different ethnic groups don’t respond to food in different ways, but I haven’t heard much about this
One obvious example is lactose tolerance. It’s a fairly new adaptation and it seems to have started in Northern Europe. If your ancestors come from there, you’re much more likely to tolerate milk as an adult—compared to, say, most of Asia where lactose tolerance is rare.
This is, in fact, the only example I have heard of of different food preferences across ethnic groups. But in this case there is only one change to be made—removing milk from the diet—and regardless, some europeans are lactose intolerant too. So rather than reasoning based on ethnic group which corrlates with lactose intolerance, you might as well just reason based on lactose intolerance, since it is something which can be diagnosed.
This depends how fast evolution happens, and I’m not an evolutionary biologist.
It seems reasonable to think meaningful evolution happens over the course of centuries (especially because there was rapid population growth over the time period in question). It’s not obvious to me what the impact of gut flora is, though- I would expect their generations to be much faster (thus it would be reasonable to imagine there are potato-optimized bacteria even if there aren’t potato-optimized humans yet) but it seems that the more your microbiome matters the less your evolutionary heritage matters.
But regardless, many aspects of a modern diet (e.g. food additives) are very new, and not present in anyone’s ancestory.
Agreed, with the observation that the ‘traditional’ diet doesn’t include those either. My claim is that I’d expect an Irishman to be better off eating 10 pounds of potatoes a day than eating at McDonald’s every day or eating an all-meat Paleo diet.
Rapid population growth decreases the efficiency of purifying selection.
Doesn’t that depend on how uniform the growth is? If a third of women have 0, 2, and 4 children respectively, then I would expect the genes that put you in the most fertile group to spread more slowly (in both relative and absolute terms) than under conditions where a third of women have 0, 3, and 9 children respectively.
Rapid population growth decreases the efficiency of purifying selection.
I don’t think that’s true, unless we’re thinking about “efficiency” in different ways.
In general we think of selection in terms of gene frequencies, not raw abundance. Which means that all that is relevant is relative fitness, and if your fitness advantage remains the same, doubling everyone’s reproduction rate doesn’t change the force of selection.
Unless you’re talking about the time until a deleterious, entirely recessive allele goes extinct? Since in that case drift is the only force that will push it from “very rare” to “non-existent”, increasing population size will decrease time to extinction of the deleterious recessive allele (drift is faster/stronger in smaller populations).
I don’t think that’s true, unless we’re thinking about “efficiency” in different ways.
I think what the OP means is that conditions which allow rapid population growth are conditions which reduce the natural selection pressure.
An extreme version of this is the observation that if everyone survives and breeds, there is no fitness advantage to any gene and the gene frequencies do not change.
I’m probably being overly anal here, but this something I work with on a professional basis.
Preface: when I’m talking about ‘fitness’, I mean the (slightly simplified) biological definition of the term, which means “number of offspring you have before you die”
I think what the OP means is that conditions which allow rapid population growth are conditions which reduce the >natural selection pressure.
This doesn’t need to be true at all—see below.
An extreme version of this is the observation that if everyone survives and breeds, there is no fitness advantage to >any gene and the gene frequencies do not change.
Also not necessarily true (because “everyone survives and breeds” is very different from “everyone survives and has an identical number of offspring).
Selection occurs due to differences in relative fitness, which can be calculated as (personal fitness)/(average fitness of everyone). If everyone has 2 offspring, everyone has a relative fitness of 1. If we have a good year, and everyone has 3 offspring, we have the same relative fitness.
You and OP seem to be thinking about situations in which some sort of environmental limits on fitness have disappeared, and now everyone is limited by some trait for which there is less/no variation. That’s actually a really special situation. Certainly the statement “Some events reduce variation in relative fitness while also increasing average fitness” is true. But so is the statement “Some events increase variation in relative fitness while also increasing average fitness”. Any time conditions increase the fitness of above-average fitness individuals, average population growth increases and selection becomes STRONGER. This is something you would definitely expect in organisms for which individuals actively compete for patchy resources—in a good year, the alpha/owner/whatever of a given territory will get most of the increased value of said patch, and individuals who were without territory may not gain anything at all. (it really depends on the situation, though)
Anyways, average fitness and variation in fitness are two largely independent things. “Rapid population growth”, or even “nobody dies before breeding” doesn’t inherently mean less selection/slower evolution. Sometimes just the opposite (see http://en.wikipedia.org/wiki/Adaptive_radiation)
This is what I get for replying shortly after waking up while thinking not all that clearly in terms of the rate of extinction of new variants over the rate of appearance of new variants.
My claim is that I’d expect an Irishman to be better off eating 10 pounds of potatoes a day than eating at McDonald’s every day or eating an all-meat Paleo diet.
Do you mean just potatoes? Doesn’t seem to be a very balanced diet. And paleo diets are not all meat—humans are naturally omnivores.
Do you mean just potatoes? Doesn’t seem to be a very balanced diet. And paleo diets are not all meat—humans are naturally omnivores.
Agreed that there are more balanced paleo diets- I brought up the all-meat one in the hopes of making it clear I was comparing over-simplified diets to each other. You can be okay on an all-meat diet so long as you avoid rabbit starvation, and similarly I’m under the impression that you can be okay with just potatoes, but an actual diet would look more like 80-90% of calories from potatoes, 10-20% of calories from whatever (vegetables, animals, etc.).
Optimal nutrition brings up the issue of human biodiversity, though in other contexts social justice warriors call this “racism” and “pseudoscience.” If you have a fairly uniform ancestry, like my relatedness to British and Irish populations as a white Southerner, at least according to what 23andMe tells me, then I have the advantage of studying ethnically similar people for some ideas about optimal diets.
But what should you do if your parents or grandparents come from remote branches of the human species which didn’t have the opportunity to interbreed until fairly recently? Seems like you might have conflicting genetics for your diet based on the fact that people in different places evolved to survive on the radically foods available in their local ecosystems.
Metacomment: You keep throwing these highly controversial statements into posts. It comes across as using tribal cheering, or worse, tribal booing. People are downvoting your posts not only for poor thinking but the fact that you seem to try to connect almost every single post you can to your politics. The comments might be better received if you focused on facts and evidence rather than remarks like the above.
Further, at least in this case the statement is transformed from “highly controversial” to “straightforwardly wrong” by its insertion into this context. The idea that people with different ancestry might benefit from different diets is not, so far as I am aware, a thing that “social justice warriors” call racism or pseudoscience. (Though I expect some of them do. For any reasonably large group, you can find some members who do pretty much any crazy thing.)
Go with the diet of the majority ancestral group, I think.
Some quick informal arguments: imagine health response to diet is set by many genes of small additive effect. (This is often true for any complex trait; behavioral psychology, and a lot of the heritability of common diseases is being identified in GWASes as that.) Imagine there are population-level differences; this is trivially obvious (lactose and alcohol), but that there’s a lot more than this (probable, since crops differ so much from region to region). Say, 1000. And you inherit genes from 1 of 2 ancestral groups, Red or Green. Each ancestral gene is +1 for that group, 0 otherwise.
Now, if you have 2/3s Red ancestry and you eat a Red diet, what’s your diet score? Well, 666 of your genes are Red, and so you get 1*666=666; 333 of your genes are Green and you get 0*333=0, total 666. If you ate Green, then it’s the other way around, 0*666 and 1*333, total 333. Clearly you want to eat Red. What if you’re 3⁄3 Red? Then 1*1000 vs 0*1000, obviously you still want to eat Red. What if you have a bare majority Red, 501/1000? Well, 501 (Red diet) > 409 (Blue diet). No matter what fraction, you always do better by going with your plurality descent.
Q: what if there’s uncertainty about the fraction of ancestry? A: the binomial around your estimated fraction is going to be pretty tight; randomness means if your family tree is 2⁄3 Red, you’re going to be close to 2⁄3 of your diet genes being Red if there’s more than a few dozen diet genes. And a quick $100 at 23andMe will fix any uncertainty about ancestry anyway.
Q: what if there’s more than one relevant ancestral group and/or diet? A: the reasoning still works even if it’s maximizing the gain from a split of genes like 10%/1%/1%.../1%.
Q: why not ‘match’ fractions of diet with fractions of ancestry, eg. if 1⁄3 Red and 2⁄3 Green, eat Red breakfasts but Green lunches & dinners? A: For the same reason “probability matching” doesn’t maximize your expected-value when the probabilities are known (as they will be in this case); it might work if your genes were changing or there was a lot of uncertainty, but that’s not the case and so ‘pulling the suboptimal arm’ is just suboptimal.
Q: what if I know that I am lactose-intolerant through self-experiment, should I really eat as much cheese as my Dutch ancestors? A: No.
Q: what if I know that I am lactose-intolerant because my 23andMe report shows I didn’t get the relevant SNPs, should I really eat as much cheese as my Dutch ancestors? A: No.
Q: what if there are genes of differing effect sizes, where some seem to have large effects on how diet affects health? A: Well, if you don’t know about them, then you’d expect all ancestral groups to have the same expected-value; and if you do know about specific ones, you can add them to the calculation based on their effect and different prevalences between groups.
Q: what if genes’ effects aren’t additive, but are crazy wild-ass interacting nonlinear networks and stuff like that? Nonlinear nonlinear nonlinear whoooo! A: lots of stuff seems to be additive, and anyway, if your genes are really that hard to predict, why would that make your minority genes outperform your plurality genes? It’s wild stuff either way.
An interesting point, but a bad way of saying it.
I find it credible that people with different genes could have different optimal diets. How much of those difference would be between different ethnic groups, and how much would be between individuals within the same group, I have no idea. I also have no idea how much “what my ancestors ate” is close to “what would be optimal for me to eat”. Also, I have no idea whether a diet optimized for a specific human would be significantly better than a diet optimized for an average human, compared with the improvement we would get by switching from an average first-world diet today.
I would like to see this question answered, preferably by someone who already doesn’t have their bottom line written either way.
(A few random thoughts: Food allergies suggest that at least some individuals need wildly different diets than their neighbors. I would expect ethnic group differences in eating dairy products, and in vitamin D requirements. If Soylent becomes popular among people from different ethnic groups, we could get some nice data.)
Also, I’m curious if hybrid vigor might give people of mixed descent some advantages, as well.
Food allergies are basically immune issues, and what I’ve read of them suggests that they’re more likely to come from environment (the immune system gets antsy and starts attacking random harmless compounds when it doesn’t have enough actual pathogens to shoot at) than genetics as such, so I think they’re probably a non-starter here.
There’s plenty of non-allergic variation in what different populations can handle food-wise, though; lactose intolerance and the alcohol flush reaction caused by differences in aldehyde dehydrogenase expression are the first two I can think of. These are often uncontroversially linked to ethnicity: lactose intolerance for example is very common outside North or Central European, North Indian, and certain African populations, and the alcohol flush reaction is a mainly East Asian phenomenon.
I’d guess that the diets of a paleolithic Irishman and a paleolithic African are far more similar to each other than to a modern American diet.
If you’d said “Neolithic”, I would’ve been right there with you—but not paleo-. Documented forager diets are hugely varied: even if we throw out the Arctic Circle populations as obvious outliers, they range from mostly plant to mostly animal; the animal component can be mostly aquatic or mostly terrestrial; and the plant component is even more idiosyncratic. I have no reason to believe this wouldn’t have been true in the ancestral environment.
There are some unifying factors: most of the forager diets I’ve read about have more fish and fruit than modern Western diets, to name an exceedingly obvious example. But there’s a far cry between that and saying that they can meaningfully be treated as a unit in this context.
An interesting point. Apparently fish is by far the healthiest form of meat, but does this depend upon whether your ancestors lived near the sea?
That is not self-evident to me.
Red meat is considered harmful mostly because it’s usually high in saturated fat which has been demonized for the past few decades. If you think saturated fat is fine, I don’t see why you’d consider red meat unhealthy.
Fish, on the other hand, is considered healthy largely because of omega-3 fatty acids and the reason that contemporary Western humans need them is that the usual diets have massively skewed omega-3/omega-6 ratios. And the reason for that is all the seed oils (soybean, sunflower, etc) that we consume. I don’t know if eating fish would be especially “healthy” for someone with a normal o-3/o-6 ratio.
Wikipedia says:
Now it’s possible that this correlation does not imply causation. Its also possible that the meat-eaters are eating low-quality processed meat, or are overcooking their meat.
Fish does pose worries about mercury. I have been considering going pescetarian at some point in the future, but if I can get the same benefit by using olive oil instead of sunflower oil then I won’t bother.
[Standard disclaimer about confounding in these types of studies being even harder than normal.]
I am aware of observational studies. But if you want to quote some, please find ones which examine total mortality and at least discuss the confounding factors.
E.g. this is a better example, but note that in this case they lump fish and chicken together under “white meat”.
Er, what percentage of the ancestry of a modern Irishman do you think comes from the people living in Ireland in the stone age? It seems reasonable to consider the staple Irish diet over the last few centuries as being a good starting place for a modern Irish diet (or, at least, to assume it fits a modern Irishman’s genes better than the traditional Japanese diet).
This depends how fast evolution happens, and I’m not an evolutionary biologist. But paleo diet people at least think that humans are mostly adapted to eat what we ate during the stone age. I also don’t know what percentage of Irish DNA comes from stone-age Ireland, or more to the point from areas with similar food sources during the stone age.
But regardless, many aspects of a modern diet (e.g. food additives) are very new, and not present in anyone’s ancestory.
I’m not saying that different ethnic groups don’t respond to food in different ways, but I haven’t heard much about this, and with the possible exception of Eskimos who might be adapted to eat a pure meat diet, I doubt it’s of much importance when planning diet.
One obvious example is lactose tolerance. It’s a fairly new adaptation and it seems to have started in Northern Europe. If your ancestors come from there, you’re much more likely to tolerate milk as an adult—compared to, say, most of Asia where lactose tolerance is rare.
This is, in fact, the only example I have heard of of different food preferences across ethnic groups. But in this case there is only one change to be made—removing milk from the diet—and regardless, some europeans are lactose intolerant too. So rather than reasoning based on ethnic group which corrlates with lactose intolerance, you might as well just reason based on lactose intolerance, since it is something which can be diagnosed.
I’m not sure it exactly counts as food, but there are substantial geographical variations in genes related to alcohol metabolism.
It seems reasonable to think meaningful evolution happens over the course of centuries (especially because there was rapid population growth over the time period in question). It’s not obvious to me what the impact of gut flora is, though- I would expect their generations to be much faster (thus it would be reasonable to imagine there are potato-optimized bacteria even if there aren’t potato-optimized humans yet) but it seems that the more your microbiome matters the less your evolutionary heritage matters.
Agreed, with the observation that the ‘traditional’ diet doesn’t include those either. My claim is that I’d expect an Irishman to be better off eating 10 pounds of potatoes a day than eating at McDonald’s every day or eating an all-meat Paleo diet.
Rapid population growth decreases the efficiency of purifying selection.
EDIT See below for corrections. Only vaguely true under certain circumstances. Mostly wrong. Was tired and thinking of the wrong metrics.
Doesn’t that depend on how uniform the growth is? If a third of women have 0, 2, and 4 children respectively, then I would expect the genes that put you in the most fertile group to spread more slowly (in both relative and absolute terms) than under conditions where a third of women have 0, 3, and 9 children respectively.
I don’t think that’s true, unless we’re thinking about “efficiency” in different ways.
In general we think of selection in terms of gene frequencies, not raw abundance. Which means that all that is relevant is relative fitness, and if your fitness advantage remains the same, doubling everyone’s reproduction rate doesn’t change the force of selection.
Unless you’re talking about the time until a deleterious, entirely recessive allele goes extinct? Since in that case drift is the only force that will push it from “very rare” to “non-existent”, increasing population size will decrease time to extinction of the deleterious recessive allele (drift is faster/stronger in smaller populations).
I think what the OP means is that conditions which allow rapid population growth are conditions which reduce the natural selection pressure.
An extreme version of this is the observation that if everyone survives and breeds, there is no fitness advantage to any gene and the gene frequencies do not change.
I’m probably being overly anal here, but this something I work with on a professional basis. Preface: when I’m talking about ‘fitness’, I mean the (slightly simplified) biological definition of the term, which means “number of offspring you have before you die”
This doesn’t need to be true at all—see below.
Also not necessarily true (because “everyone survives and breeds” is very different from “everyone survives and has an identical number of offspring).
Selection occurs due to differences in relative fitness, which can be calculated as (personal fitness)/(average fitness of everyone). If everyone has 2 offspring, everyone has a relative fitness of 1. If we have a good year, and everyone has 3 offspring, we have the same relative fitness.
You and OP seem to be thinking about situations in which some sort of environmental limits on fitness have disappeared, and now everyone is limited by some trait for which there is less/no variation. That’s actually a really special situation. Certainly the statement “Some events reduce variation in relative fitness while also increasing average fitness” is true. But so is the statement “Some events increase variation in relative fitness while also increasing average fitness”. Any time conditions increase the fitness of above-average fitness individuals, average population growth increases and selection becomes STRONGER. This is something you would definitely expect in organisms for which individuals actively compete for patchy resources—in a good year, the alpha/owner/whatever of a given territory will get most of the increased value of said patch, and individuals who were without territory may not gain anything at all. (it really depends on the situation, though)
Anyways, average fitness and variation in fitness are two largely independent things. “Rapid population growth”, or even “nobody dies before breeding” doesn’t inherently mean less selection/slower evolution. Sometimes just the opposite (see http://en.wikipedia.org/wiki/Adaptive_radiation)
This is what I get for replying shortly after waking up while thinking not all that clearly in terms of the rate of extinction of new variants over the rate of appearance of new variants.
I’ve definitely made the same mistake before. More than once. Which is why I felt confident enough on this to offer a correction.
Do you mean just potatoes? Doesn’t seem to be a very balanced diet. And paleo diets are not all meat—humans are naturally omnivores.
Agreed that there are more balanced paleo diets- I brought up the all-meat one in the hopes of making it clear I was comparing over-simplified diets to each other. You can be okay on an all-meat diet so long as you avoid rabbit starvation, and similarly I’m under the impression that you can be okay with just potatoes, but an actual diet would look more like 80-90% of calories from potatoes, 10-20% of calories from whatever (vegetables, animals, etc.).