What can we infer about health/nutrition from Evolution?
To truly answer this question, we need to understand what evolution is and how it works. Evolution is the change in allele frequencies over time There are 4 forces that drive evolution:
1. Natural Selection - a trait conveys some positive benefit for survival/reproduction and is 'selected' - aka it helps you reach the age of reproduction, have sex, and pass on that gene. The more individuals with that phenotype will reach the age of reproduction, have sex, and (potentially) pass on that genotype. Phenotypes can be selected against as well - say a specific phenotype is not advantageous in a specific environment , then it is said to be acted on by purifying selection - that genotype is not passed on because those individuals don't reproduce
2. Genetic Drift - For phenotypes that aren't particularly advantageous/detrimental in an environment, those alleles, over time, randomly change frequencies - it's due to chance. This relates to the neutral and nearly neutral theories of evolution, which assert that natural selection did not play the largest role in evolution, and that much of the difference seen between species is due to neutral changes in allele frequencies over time that eventually lead to speciation.
3. Mutation - DNA has 4 bases: A,C,G,T. Anytime there is a mistake in the copying of DNA, say an A is replaced with a C, you get a mutation. There are small mutations, known as point mutations, when one base is changed to another. There are even larger mutations like that of chromosomal inversions. These mutations lead to the creation of new alleles that can be acted on by either of the previous 2 forces of evolution, and ultimately change allele frequencies over time.
4. Migration/Gene Flow - This occurs when two populations meet and exchange genetic information. This can lead to the introduction of new alleles entirely, or offset the current balance between allele frequencies in the previous generation.
So what does all of this tell us about our health? For one, when we're thinking about nutrition and health from an evolutionary standpoint, it's really hard to make generalizable statements about all humans. Humans stem from diverse populations across thousands of years in a number of different environments - what allowed us to proliferate was largely our ability to enter a new environment and manipulate it to our advantage. Not every human is going to have the same traits - some populations have traits that were selected for; some people may have disease susceptibility because of alleles that have been drifting for many generations without ever having the environment select for/against them; virtually every population will have different mutations; and some ancestral populations interbred with other subspecies of the genus Homo and potentially have passed along nutrition/health -affecting genes/variants because of this.
I hope the point that is coming across is that it is purely unscientific to say something to the effect of "humans have not evolved to eat meat" or "humans have not evolved to eat grains", etc etc. I have seen this many times within specific nutrition-minded groups (Paleo, veg, low carb, etc) that make sweeping generalizations about all of humankind. That's not to say foods we've evolved to eat are entirely benign; understanding the impact of long term consumption of evolutionary novel food items, like meat, dairy, grains, legumes, and quite frankly, all domesticated foods, can't be inferred from evolutionary theorizing. Having evolved the ability to utilize and consume specific food products (e.g. lactase persistence, amylase copy number) does not specifically tell us how much dairy or grains are ideal for health. Archaeological evidence of the bones of different water dwelling animals doesn't tell us how much fish consumption is optimal for health over a lifetime. Finding egg shell remains in an archaeological site doesn't tell us whether regular egg consumption is a risk for cardiovascular disease.
It is critical to understand one major concept: what we evolved to do is nothing more than what allowed us to survive and reproduce, in an environment unlike our modern ones. Evolution acts on fertility, not longevity. Much of modern nutritional sciences research is based on increasing longevity, deterring age related disease, and reducing the environmental stresses that potentially drives the former; aka, nutrition is being used to promote life beyond what evolutionary forces act upon. Gene networks that enable someone to live till 100years old or gene networks that cause you to spontaneously die at age 50 would have most likely not been acted upon by evolution forces, unless they also conferred some benefit for /detriment to reaching the age of reproduction and reproducing. There is a lot of debate over average life expectancy throughout human ancestry, and this most likely had a lot of variability depending on geography. However, there is no archaeological evidence that I am aware of to say that individuals were frequently living and reproducing into their 50s+, let alone their 80s, to pass on genes that would confer long life and protection against diseases that are overwhelming seen in advanced years (CVD, Alzheimer's, etc). There is the grandmother'ing hypothesis, which tries to explain human life expectancy's ability to go past the age of senescence (menopause), but, as this is just a theory, and we don't really know how many grandmothers (note, grandmothers, until modernization would've likely been in their 40s, not their 70s) were alive to see grandchildren and potentially care for them in the past, it's hard to say what role this would've played.
The human genome needs to viewed as both a relic and a novelty- we have metabolic processes going back 2 billion years to bacteria but also, we have relatively recent alterations leading to things like lactase persistence. Anatomically modern humans are thought to have arose as far back as 200,000 years ago, and left Africa around 60-70k years ago - the role of evolutionary forces between then and now is unknown. It becomes difficult to say exactly which phenotypic traits we retained along the way from those species with which we had a common ancestor or even directly led to us- Neanderthals are believed to have had a different diet, known morphological differences and immune systems than homo sapiens - does that mean you should eat like a Neanderthal?. Copying the diet of what we think we can infer about our many Paleolithic ancestors' diets may not necessarily be the most advantageous for human health.
What we evolved to do and what is most healthy are not necessarily the same - but they may be. We don't know. That's why there is a field of nutritional sciences. To say that modern nutrition research is trumped by what you think that you can infer from evolution would be difficult. That's not to say that modern nutrition doesn't have it's issues with inference from data, but it's infinitely more reliable than the trying to copy the recreated diets of a population of a past hominid ancestors.
One thing that is also left out in evolutionary approaches to nutrition is the role of culture. The role of processing - everything from fire to farming - has had an effect on what foods we are able to utilize and consume. The entirety of the hominid timeline is marked by its ability to utilize tools to make a vast array of foods fit for consumption, whereas other species have relied on the forces of evolution over long periods of time to become adapted to their specific nutritope. Culture and technology played a large role throughout human evolution - and continues to play a role; the irony seems to be that Paleolithic dieters, in romanticizing past diets, have turned their backs on many of the modern food science technologies that are available.
To truly answer this question, we need to understand what evolution is and how it works. Evolution is the change in allele frequencies over time There are 4 forces that drive evolution:
1. Natural Selection - a trait conveys some positive benefit for survival/reproduction and is 'selected' - aka it helps you reach the age of reproduction, have sex, and pass on that gene. The more individuals with that phenotype will reach the age of reproduction, have sex, and (potentially) pass on that genotype. Phenotypes can be selected against as well - say a specific phenotype is not advantageous in a specific environment , then it is said to be acted on by purifying selection - that genotype is not passed on because those individuals don't reproduce
2. Genetic Drift - For phenotypes that aren't particularly advantageous/detrimental in an environment, those alleles, over time, randomly change frequencies - it's due to chance. This relates to the neutral and nearly neutral theories of evolution, which assert that natural selection did not play the largest role in evolution, and that much of the difference seen between species is due to neutral changes in allele frequencies over time that eventually lead to speciation.
3. Mutation - DNA has 4 bases: A,C,G,T. Anytime there is a mistake in the copying of DNA, say an A is replaced with a C, you get a mutation. There are small mutations, known as point mutations, when one base is changed to another. There are even larger mutations like that of chromosomal inversions. These mutations lead to the creation of new alleles that can be acted on by either of the previous 2 forces of evolution, and ultimately change allele frequencies over time.
4. Migration/Gene Flow - This occurs when two populations meet and exchange genetic information. This can lead to the introduction of new alleles entirely, or offset the current balance between allele frequencies in the previous generation.
So what does all of this tell us about our health? For one, when we're thinking about nutrition and health from an evolutionary standpoint, it's really hard to make generalizable statements about all humans. Humans stem from diverse populations across thousands of years in a number of different environments - what allowed us to proliferate was largely our ability to enter a new environment and manipulate it to our advantage. Not every human is going to have the same traits - some populations have traits that were selected for; some people may have disease susceptibility because of alleles that have been drifting for many generations without ever having the environment select for/against them; virtually every population will have different mutations; and some ancestral populations interbred with other subspecies of the genus Homo and potentially have passed along nutrition/health -affecting genes/variants because of this.
I hope the point that is coming across is that it is purely unscientific to say something to the effect of "humans have not evolved to eat meat" or "humans have not evolved to eat grains", etc etc. I have seen this many times within specific nutrition-minded groups (Paleo, veg, low carb, etc) that make sweeping generalizations about all of humankind. That's not to say foods we've evolved to eat are entirely benign; understanding the impact of long term consumption of evolutionary novel food items, like meat, dairy, grains, legumes, and quite frankly, all domesticated foods, can't be inferred from evolutionary theorizing. Having evolved the ability to utilize and consume specific food products (e.g. lactase persistence, amylase copy number) does not specifically tell us how much dairy or grains are ideal for health. Archaeological evidence of the bones of different water dwelling animals doesn't tell us how much fish consumption is optimal for health over a lifetime. Finding egg shell remains in an archaeological site doesn't tell us whether regular egg consumption is a risk for cardiovascular disease.
It is critical to understand one major concept: what we evolved to do is nothing more than what allowed us to survive and reproduce, in an environment unlike our modern ones. Evolution acts on fertility, not longevity. Much of modern nutritional sciences research is based on increasing longevity, deterring age related disease, and reducing the environmental stresses that potentially drives the former; aka, nutrition is being used to promote life beyond what evolutionary forces act upon. Gene networks that enable someone to live till 100years old or gene networks that cause you to spontaneously die at age 50 would have most likely not been acted upon by evolution forces, unless they also conferred some benefit for /detriment to reaching the age of reproduction and reproducing. There is a lot of debate over average life expectancy throughout human ancestry, and this most likely had a lot of variability depending on geography. However, there is no archaeological evidence that I am aware of to say that individuals were frequently living and reproducing into their 50s+, let alone their 80s, to pass on genes that would confer long life and protection against diseases that are overwhelming seen in advanced years (CVD, Alzheimer's, etc). There is the grandmother'ing hypothesis, which tries to explain human life expectancy's ability to go past the age of senescence (menopause), but, as this is just a theory, and we don't really know how many grandmothers (note, grandmothers, until modernization would've likely been in their 40s, not their 70s) were alive to see grandchildren and potentially care for them in the past, it's hard to say what role this would've played.
The human genome needs to viewed as both a relic and a novelty- we have metabolic processes going back 2 billion years to bacteria but also, we have relatively recent alterations leading to things like lactase persistence. Anatomically modern humans are thought to have arose as far back as 200,000 years ago, and left Africa around 60-70k years ago - the role of evolutionary forces between then and now is unknown. It becomes difficult to say exactly which phenotypic traits we retained along the way from those species with which we had a common ancestor or even directly led to us- Neanderthals are believed to have had a different diet, known morphological differences and immune systems than homo sapiens - does that mean you should eat like a Neanderthal?. Copying the diet of what we think we can infer about our many Paleolithic ancestors' diets may not necessarily be the most advantageous for human health.
What we evolved to do and what is most healthy are not necessarily the same - but they may be. We don't know. That's why there is a field of nutritional sciences. To say that modern nutrition research is trumped by what you think that you can infer from evolution would be difficult. That's not to say that modern nutrition doesn't have it's issues with inference from data, but it's infinitely more reliable than the trying to copy the recreated diets of a population of a past hominid ancestors.
One thing that is also left out in evolutionary approaches to nutrition is the role of culture. The role of processing - everything from fire to farming - has had an effect on what foods we are able to utilize and consume. The entirety of the hominid timeline is marked by its ability to utilize tools to make a vast array of foods fit for consumption, whereas other species have relied on the forces of evolution over long periods of time to become adapted to their specific nutritope. Culture and technology played a large role throughout human evolution - and continues to play a role; the irony seems to be that Paleolithic dieters, in romanticizing past diets, have turned their backs on many of the modern food science technologies that are available.
I found your blog recently (because of the Paleo meta-analysis post) and I'm enjoying it quite a bit.
ReplyDeleteI think you're giving the grandmother hypothesis too little weight. In snakes, parenting and grandparenting don't matter; but in humans, at least parenting certainly does. (Parenting is enough, even without grandparenting, to explain why post-reproductive health would be selected for.)
Also, you are of course correct that evolutionary inferences should not trump modern nutritional science -- but I think many paleo-diet enthusiasts would agree with you about that. I think many would say that evolutionary inferences are good for generating hypotheses about nutrition, but that's all. What ultimately matters is how those hypotheses fare experimentally. (I know I've heard Mat LaLonde say exactly that.)