The role of diet in human evolution

  • Thread starter Ken Natton
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I have kept the title of this thread quite general because, depending on how it goes, there are a few different points that I’d like to discuss, and that’s really the general theme, as it were. I know the format preferred on this website is for those of us with less expertise to ask questions of the experts. Having once again, with my clumsiness, contributed to getting someone else’s evolution discussion closed, I’d like to have a go at getting what I see as a more interesting and worthwhile evolution discussion going and I would be pleased to draw some contributions from those with the real knowledge on these points. Anyway, let’s see how it goes.

So. I have heard tell before of a gene called Amy1, and it is another one that generates a useful comparison between humans and chimps. It isn’t that chimps don’t have Amy1, they do, but they have very few copies of it. Humans have lots of copies of it. It is shown to be used in a process called ‘starch hydrolysis’ and the fact that we have many more copies of it than do chimps means that we are much better at processing starchy food than are chimps. That, according to the account I read, in turn means that we are much better at resisting the kinds of disease that cause diarrhea. When you know that diarrhea remains the second biggest killer of children under the age of 5 (after malaria of course), the selective advantage of an ability to resist such illness is fairly obvious.

Apologies if it is another obvious point, but foods listed as ‘staples’ the world over are all essentially starchy foods – potato, rice, maize, wheat and so forth. Historical accounts tell us that the domestication of certain strains of wheat that could be planted and harvested in the same fields on a regular cycle were what enabled our ancestors to give up the nomadic lifestyle, settle and establish civilisations. That last event is, of course, far too recent to be an evolutionary change, it is more of a cultural change. Nonetheless, it does seem to loom large and obvious that starchy foods have played an extremely important role in the story of how we got to here.

So I suppose the place I would like to start the discussion is on this point: This ability to process starchy foods so well, is this something that is completely unique to humans? Are there any other higher level, complex species that can do it as well as us? Of course, everyone feeds bread to ducks, but just because they eat it, does it necessarily mean that they can process it that well? There are certainly some smaller bird species that it is advised you should not give bread to because they will eat it, but it expands in their bellies and can even kill them. I don’t know, if you gave a piece of bread to a chimp would it simply turn its nose up at it? Or would it eat it but just not process it so well, and thus generally not prefer such food?

If there are other species that do process starchy foods well, then that might lead me to different questions about the comparisons. But if it is the case that humans are the only species that use starchy food so well, is it a reasonable conclusion that starchy foods are, at the very least, one extremely important factor in exactly what it is that distinguishes us from all other species? I don’t know. Thoughts please?
 

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  • #2
I know the format preferred on this website is for those of us with less expertise to ask questions of the experts.
well I am not an expert(still a student) but I hope that doesn't bar me from contributing.

Having once again, with my clumsiness, contributed to getting someone else’s evolution discussion closed...
Thanks for reminding me of the nightmare.

I’d like to have a go at getting what I see as a more interesting and worthwhile evolution discussion going.
This sure will be interesting.


That last event is, of course, far too recent to be an evolutionary change, it is more of a cultural change. Nonetheless, it does seem to loom large and obvious that starchy foods have played an extremely important role in the story of how we got to here.
I know that the discussion is not supposed to start just yet. However I would like to say that culture can have noticeable impacts on genetic composition.

Large-scale scans using patterns of linkage disequilibrium to detect recent selection suggest that many more genes evolved in response to agriculture. Genetic change in response to the novel social environment of contemporary modern societies is also likely to be occurring.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3024025/

So I suppose the place I would like to start the discussion is on this point: This ability to process starchy foods so well, is this something that is completely unique to humans? Are there any other higher level, complex species that can do it as well as us?
Considering the huge selective advantage starchy foods offer, it wouldn't be surprising if animals other than humans have evolved the means to digest them. I am sure of some wild boars digging up tubers for a meal (cheers to Nat Geo) but not sure if they form their staple diet.
 
  • #3
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Student or otherwise, mishrashubham, you are considerably more expert than me. And if it came across that I was seeking to proscribe what people should contribute then that is absolutely not what I intended. I’m grateful for your input, and for whatever input you think might feed the discussion.

Here’s the basis of what is in my mind. I have encountered several contributors on various forums who seem to get quite angry at what they perceive as an arrogance in the suggestion that humans are special. Of course, I quite accept that we have no more right to survival or to access the earth’s resources than any other species. And believe me, no-one needs to convince me that we do our most profound wrong when we destroy another species with our carelessness. But that there is a hugely significant difference between humans and all other species, including ‘intelligent’ species like elephants and dolphins and chimpanzees, seems to be the most glaringly obvious truth to me. And it seems a hugely significant question to me to ask exactly what happened, why did we emerge from the crowd to dominate in the way we have?

And of course, I am not for a moment suggesting that question is new. It is one that we have been asking for a long time and there have been any number of theories – our inherent curiosity being fed by our opposable thumbs is one that springs to mind – that have had varying degrees of currency at different times. But in my recent engagements with forums like this one, and in various things that I have read, I have started to grasp that diet has been, at the very least, one very important strand in that story.

I suppose that the other problem is that this website guards the rigour of what is here asserted very closely and the truth is that this is a story about which there is still relatively little known with any certainty. But there are some theories that are much more likely than others. At the very least there are pieces of evidence that point in this direction or that. And it seems to me that there might be some clues and some degree of fascination in what some of the contributors here might be able to offer. At some level, all I really wanted was to see an evolution discussion that went beyond evolution is true / evolution is false. It seems a pity to me that the latter seems to be the one that draws the most contributions from both sides.
 
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  • #4
Pythagorean
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Ken Natton said:
Here’s the basis of what is in my mind. I have encountered several contributors on various forums who seem to get quite angry at what they perceive as an arrogance in the suggestion that humans are special. Of course, I quite accept that we have no more right to survival or to access the earth’s resources than any other species. And believe me, no-one needs to convince me that we do our most profound wrong when we destroy another species with our carelessness. But that there is a hugely significant difference between humans and all other species, including ‘intelligent’ species like elephants and dolphins and chimpanzees, seems to be the most glaringly obvious truth to me. And it seems a hugely significant question to me to ask exactly what happened, why did we emerge from the crowd to dominate in the way we have?
Why must the question be narrowed to nutrition?

One hypothesis that has nothing to do with nutrition, except perhaps that it made getting food easier: inbreeding led to greater cooperation, which led to territorial domination, which gives access to a larger diversity (and more constant supply) of nutritional resources and eventually, boredom...

another hypothesis: drugs

a finding that could finally shed light on such evolutionary conundrums, researchers from Indiana University Bloomington (IUB) have found that a gene thought to influence perception and susceptibility to drug dependence is expressed more readily in human beings than in other primates. This difference coincides with "evolutionary bursts" that are evident in our lineage, say the researchers in the journal PLOS Biology.
http://www.scienceagogo.com/news/20051015003117data_trunc_sys.shtml
 
  • #5
Student or otherwise, mishrashubham, you are considerably more expert than me.
By PF standards I am really an ignoramus.

And it seems a hugely significant question to me to ask exactly what happened, why did we emerge from the crowd to dominate in the way we have?
NOTICE: What I am about to mention is just one of the several factors that contributed to the evolutionary success of our species.

I tend to think that what set us apart was our ability to learn quickly and actively teach it to future generations. The chimpanzees are also quick learners but young chimps learn by passively observing their parents. They are not taught to do things. We on the other hand try to pass all our knowledge to our children. Also significant is that humans have long term memory, so information is kept in the brain for a long period of time. Chimps on the other hand have extremely good short term memory (several times better than ours).

And may be the most important factor is that after the split, human were exposed to a variety of natural environments and tested them to their limits (due some river in Africa the name of which I cannot remember). Thus selective pressure (don't click this link, leads to N/m^2) was greatly increased leading to better counter measures (in form of increased intelligence).



First of all Pythagorean, your former avatar was way better.
Why must the question be narrowed to nutrition?

inbreeding led to greater cooperation, which led to territorial domination, which gives access to a larger diversity (and more constant supply) of nutritional resources...
Could you please elaborate? As far as I know inbreeding is actually detrimental to reproductive success as it increases chances of recessive diseases.
Also I really didn't get the drug part of it.
 
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  • #6
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By PF standards I am really an ignoramus.

I tend to think that what set us apart was our ability to learn quickly and actively teach it to future generations. The chimpanzees are also quick learners but young chimps learn by passively observing their parents. They are not taught to do things. We on the other hand try to pass all our knowledge to our children. Also significant is that humans have long term memory, so information is kept in the brain for a long period of time. Chimps on the other hand have extremely good short term memory (several times better than ours).
well IMO its our ability to speak that allowed to pass on ideas and knowledge that set us apart from other primates. And with speech and language all other complex structures (and this only my opinion) such as society, structure , invention, changing our environmental etc would have evolved.

@ken
agriculture definitely gave rise to civilization. I would think that we already had the ability to metabolize our sugar, but was agriculture able to put such pressure on genome that it increase the no. of copies of our gene?.Is it a case of environment putting pressure on us or we already had the ability, so agriculture was a natural outcome ?
 
  • #7
well IMO its our ability to speak that allowed to pass on ideas and knowledge that set us apart from other primates.
Very true. The ability to convey information accurately and efficiently using speech and language has probably made the biggest impact on human survivability.
 
  • #8
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Well okay, I suppose that diet was the broad theme that I was choosing to discuss in this thread. I suppose that if I am saying that is the theme and I’m identifying ‘how we came to dominate’ as what I’m interested in investigating, then I have to allow the possibility that the conclusion of the discussion will be that diet wasn’t all that significant. But my sense is that it was. And this, as I understand it, is why. Yes language, culture, the ability to learn from our elders and many other similar features are all deeply significant, but I would suggest that they are all symptoms rather than cause. It seems reasonably clear that the heart and soul of it is our big brain. And the key thing to grasp about that big brain is that it is a very energy hungry organ. The ability to support that big brain required the necessary infrastructure, and a suitable fuel supply.

There is an old evolution story about how our distant ancestors had a much heavier lower jaw that required a huge muscle to control it that in turn, limited the size of the brain. When we learned to control fire and to cook food, the need for the heavy lower jaw was removed and the muscle shrunk allowing capacity for the larger brain. But allowing capacity for it, and actually developing it are two different things. And certainly, diet was not why we developed the big brain, but diet certainly was a primary facilitator. Or so it seems to me.

And yes, agriculture, the domestication and harvesting of crops was the key technological development that led to civilisation, but I still say that is history – ancient history certainly, but still history, not evolution. We are talking only five to ten thousand years ago. By that time, we had already long since evolved our ability to process starchy food. Agriculture, as I said, just removed the need to keep moving on to find fresh food sources.

Now if there are other species that are as good at processing starchy food as we are, that presumably also have many copies of that Amy1 gene, then there has to be more to it than just starchy food. If, as seems possible to me, it is only humans that have that ability, then that would constitute fairly strong evidence in support of the belief in the importance of starchy foods. I accept, I might be overplaying the significance of starchy food and I might be overplaying the importance of diet. That is what I was looking to discuss and interested in what others had to say.
 
  • #9
Ygggdrasil
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One hypothesis that has been floating around is that the invention of cooking was key to the evolution of modern humans. The main thrust of the argument is that the ability to cook food helped provide early hominids with more calories in their diet, and this surplus of calories was essential for the evolution energy-intensive structures such as larger brains. First, cooking breaks the food down chemically, making it easier to digest and more nutritious to humans. For example, cooked eggs release 91-94% of their protein to be used as fuel by humans, whereas raw eggs release only 51-65% (although eggs were probably not a part of early hominid diets, the general principle applies to other foods). Therefore, cooking food can nearly double the energy obtained from foods otherwise eaten raw. A species that eats primarily raw foods must also have a larger amount of energy diverted to the digestive system in order to help break down the foods and extract nutrition from them. A shift toward a diet consisting of cooked foods, however, removes this selective pressure, allowing early hominids to devote energy and resources away from the digestive system and toward the development of other structures such as the brain. Finally, cooking foods also gave early hominids access to more food sources as cooking can detoxify many plant-based foods, thus making it easier for them to obtain calories and nutrition.

These ideas are explained more fully in a book by anthropologist Richard Wrangham, Catching Fire: How Cooking Made Us Human (NY Times book review) and in the following paper from the journal Current Anthropology (paper freely available at http://scienceblogs.com/gregladen/WranghamEtAl.pdf [Broken], paper summarized here).

It's important to note that these changes would have taken place during the hunter-gatherer stages of human evolution and would have preceded the shift of the human diet toward starch-rich foods. Indeed, many of the starch-rich staples are inventions of humans (via selective breeding) and would have required an agrarian society. Therefore, it is likely that the expanded copy numbers of the amylase genes and other such adaptations were selected for only after humans took up agriculture.
 
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  • #10
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Wow Ygggdrasil, way to turn my whole argument on its head! Thanks for the references, it is obviously going to take me some time to read and absorb that paper and clearly the book is one I need to get. What you are telling me about the selection for amylase genes coming after the take up of agriculture does astonish me. My source for what I thought I knew is really just a 1970s TV series shown here in the UK called The Ascent of Man, written and presented by Jacob Bronowski. He tells the story of a particular strain of wheat, I think, that original consisted of 14 chromosomes. By an extraordinary series of the kind of coincidences that make anti-evolutionists scoff, it formed a hybrid first with one other species and then with another to make a species that consisted of 42 chromosomes. The next coincidence was a mutation that was required to make the hybrid fertile. And the final one was that such a thing coincided with the needs of mankind, because, as Bronowski tells the story, the problem for this hybrid species was that its ears were far too heavy to be carried by the wind. Left to nature it is a species that would have quickly disappeared, but manual sewing and harvesting meant that it survived. And its key advantage was much higher yields than the strains with just 14 chromosomes. It produced harvests that meant that tribes could feed not only themselves and their families, but significant numbers of domesticated animals. And the key point is that these events occurred only something like ten thousand years ago, and in the middle east, not in Africa. My understanding of evolution is that that is far too recent, and that the species to whom these events occurred was clearly homo sapiens, not some ancestor species.
 
  • #11
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If there are other species that do process starchy foods well, then that might lead me to different questions about the comparisons. But if it is the case that humans are the only species that use starchy food so well, is it a reasonable conclusion that starchy foods are, at the very least, one extremely important factor in exactly what it is that distinguishes us from all other species? I don’t know. Thoughts please?
Correct me if I'm wrong but aren't grasses "starchy foods". I know you speak of breads which are processed grasses which interested me. Horses, cattle, bovine...et al thrive on grasses. Is this too obvious? Does this just apply to domesticated livestock for the most part and say wild horses and javalinas have a more diverse diet?

It almost seems the humans inability to deal with unprocessed starches that initiated some change. Cattle has multiple stomachs and has a process to deal with this. Horses I'm unsure of but have lived near ranches and see a strict diet of some sort of grain.

Sounds silly but I wonder what the history of baking is?! Breads are mentioned in ancient texts but I have seen in health food stores things like "essene bread" that are essentially raw or fermented grains not nessesarilly baked... Perhaps these were the intermediate steps to processing? Could even pre-date fire and cooking as we imagine.

There are factions of raw food people. The vegan brand I have met tends to have a pallor, the ones who eat raw meat and in fact spurn grains such as maize tend to appear more robust. Very unscientific and just and observation.

Interesting topic. I worked for a few years in a vegetarian health food restaurant and some of the ideas were strange upon reflection but as with the essene bread perhaps have a kernal of truth (no pun intended but that's a good one huh/?!<G!>)

W
 
  • #12
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Correct me if I'm wrong but aren't grasses "starchy foods". I know you speak of breads which are processed grasses which interested me. Horses, cattle, bovine...et al thrive on grasses. Is this too obvious? Does this just apply to domesticated livestock for the most part and say wild horses and javalinas have a more diverse diet?
Most of the carbohydrates in grasses are in the form of cellulose (dietary fiber), not starch. Like cellulose, starch is a polymer of glucose, except the glucose monomers are connected by a different type of covalent bond. Whereas humans posses the enzymes to break starch into glucose, we lack the enzymes required to break cellulose into glucose and thus cellulose passes through our bodies undigested. Horses, cattle, and other ruminants are able to digest cellulose because their stomachs contain bacteria capable of breaking cellulose into glucose.

Cellulose plays key structural roles in plants and is very abundant in plants (e.g. wood is made primarily of cellulose). Starch is used to store carbohydrates in plants and wild plants generally do not have significant stores of starch. Those plants that do (e.g. tubers which store starch in their roots) usually poison these stores so that animals are not tempted to eat them. Therefore, cooking (to detoxify plants with significant natural stores of starch) and agriculture (to selectively breed plants like corn, rice or wheat to produce more significant stores of starch) would likely be required before starch could become a significant part of the human diet.
 
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  • #13
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Could you please elaborate? As far as I know inbreeding is actually detrimental to reproductive success as it increases chances of recessive diseases.
That's true. But you have to also remember that it's disgusting emotionally to a lot of people, so that everyone's not exactly running through the streets screaming to marry your sister (i.e. we have a bias).

Since we have kin-detection systems, inbreeding leads to better game theory strategies between kin. Note that the inbreeding can be distant (cousins) to almost completely eliminate chance of disease. So you get a group of inbred primates that work together to defend a chunk of forest, taking turns doing border patrols, affording the group larger survival odds.

http://www.ucl.ac.uk/~ucbhdjm/courses/b242/InbrDrift/InbrDrift.html


Also I really didn't get the drug part of it.
Different hypothesis that humans are so susceptible to psychoactive effects (moreso than other animals) that the things our ancestors ingested in our evolutionary history led to crazy ideas like horticulture/agriculture.
 
  • #14
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On the subject of the evolution of salivary amylase, a paper in the journal Nature Genetics (citation below) compared the number of copies of the salivary amylase gene AMY1 in various populations of humans that have traditionally high starch or low starch diets. The authors found that the human populations with traditionally higher starch diets had a greater number of copies of the AMY1 gene than human populations that ate traditionally lower starch diets. Indeed, the copy number variation of the AMY1 gene correlated more closely with the groups' diet than with their geography. These results help to show that copy number expansion of the AMY1 gene was selected for by the shift in human diet toward more high starch foods.

It is imporant to note, however, that even the low-starch populations of humans had significantly more copies of the AMY1 gene (5.44 copies) than other primate species (2 copies). The article does note that a subfamily of old world monkeys, the cercopithecines (which includes species such as macaques and mangabeys) have high amounts of the salivary amylase enzyme even compared to humans. So, perhaps this trait, while definitely important in human evolution, is not quite so unique to humans.

Citation:
Perry et al. (2007) Diet and the evolution of human amylase gene copy number variation. Nat. Genet. 39: 1256-1260. http://dx.doi.org/10.1038/ng2123
Freely available on PubMed Central
Summary by http://scienceblogs.com/pharyngula/2008/12/amylase_and_human_evolution.php [Broken]
 
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  • #15
That's true. But you have to also remember that it's disgusting emotionally to a lot of people, so that everyone's not exactly running through the streets screaming to marry your sister (i.e. we have a bias).
I have always thought that this disgust was selected for.

Since we have kin-detection systems, inbreeding leads to better game theory strategies between kin. Note that the inbreeding can be distant (cousins) to almost completely eliminate chance of disease. So you get a group of inbred primates that work together to defend a chunk of forest, taking turns doing border patrols, affording the group larger survival odds.
Yes inbreeding is only effective if one mates with at least a third or a fourth cousin (by this time the shared percentage of genes is less than 1%).

The link you provided is also very nice. It is going to take some time to properly analyze it. However I really cannot understand how this could happen.

One assumes deleterious recessives in habitually inbreeding species have mostly been purged by selection.

Different hypothesis that humans are so susceptible to psychoactive effects (moreso than other animals) that the things our ancestors ingested in our evolutionary history led to crazy ideas like horticulture/agriculture.
haha interesting, never heard of it before; thanks for sharing.
 
  • #16
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The reason the prodynorphin gene is of interest is because it's regulation appears to be shaped by natural selection right around the time of man's origin and it has significant implications for the brain (our prized organism).

We found that positive natural selection altered the cis-regulation of human prodynorphin, the precursor molecule for a suite of endogenous opioids and neuropeptides with critical roles in regulating perception, behavior, and memory. Independent lines of phylogenetic and population genetic evidence support a history of selective sweeps driving the evolution of the human prodynorphin promoter. In experimental assays of chimpanzee–human hybrid promoters, the selected sequence increases transcriptional inducibility. The evidence for a change in the response of the brain's natural opioids to inductive stimuli points to potential human-specific characteristics favored during evolution.
Rockman MV, Hahn MW, Soranzo N, Zimprich F, Goldstein DB, et al. 2005 Ancient and Recent Positive Selection Transformed Opioid cis-Regulation in Humans. PLoS Biol 3(12): e387.http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0030387" [Broken]
 
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  • #17
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The increased expression of prodynorphin does not necessarily suggest a role for psychoactive drugs in human evolution. As the authors mention in the PLoS Biol paper, prodynorphin activates receptors that are important in social attachment and bonding as well as in learning and memory. Thus, the increase in prodynorphin expression could simply be an adaptation to a society where social bonding, learning, and memory are more important.

Furthermore, psychoactive opiates actually compete with prodynorphin for binding to opiate receptors. Therefore, if human evolution selected for psychoactive drug use, one might expect to see a decrease in prodynorphin expression (since the use of psychoactive opiates could replace some of the roles of prodynorphin). A line of evidence that would be more convincing that evolution selected for psychoactive drug use would be increased expression of the opiate receptors without corresponding increase in the expression of their endogenous ligands.
 
  • #18
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The increased expression of prodynorphin does not necessarily suggest a role for psychoactive drugs in human evolution. As the authors mention in the PLoS Biol paper, prodynorphin activates receptors that are important in social attachment and bonding as well as in learning and memory. Thus, the increase in prodynorphin expression could simply be an adaptation to a society where social bonding, learning, and memory are more important.

Furthermore, psychoactive opiates actually compete with prodynorphin for binding to opiate receptors. Therefore, if human evolution selected for psychoactive drug use, one might expect to see a decrease in prodynorphin expression (since the use of psychoactive opiates could replace some of the roles of prodynorphin). A line of evidence that would be more convincing that evolution selected for psychoactive drug use would be increased expression of the opiate receptors without corresponding increase in the expression of their endogenous ligands.
No argument, you would have a better idea than I. The hypothesis came from a senior seminar that I attended.

Just to be clear, the implication was that humans ingested trace amounts in their regular diet, not that they were munching on poppies and actually getting wasted.
 
  • #19
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Okay Ygggdrasil, with all due recognition of your greater knowledge and experience in these matters, I am going to see fit to challenge your assertion that selection for amalyse genes came after humans took up agriculture. My basic objection is based purely on my understanding of how recently (relatively of course) humans took up agriculture and my understanding of the kind of time spans usually involved in anything that can be regarded as evolution. Believe me, I accept the possibility that the flaw is either in my knowledge of history or in my understanding of evolution. But reading the paper you referred to in your post #9 and also returning to the piece about the Amy1 gene that I referred to in the original post, there is a quite different account that I take from it that makes a great deal more sense to me.

Firstly, let me quickly deal with this reference that I am talking about. It is actually a couple of years ago that I first came across this piece while engaged with another forum, but I have managed to recover the reference. It is nothing like so deep and involved a paper as the one you referred to, but it was what first brought my attention to this Amy1 gene and its importance in our evolution, and it does appear to me to support what I am taking from the paper you referred to. In any case, here’s the reference:


So, my summary of the account that makes more sense to me is this: The preferred foods of our distant, vegetarian ancestors would have been fruits and seeds. The central problem with these is their seasonal availability. There would have been long periods every year when such foods were not available and our ancestors had to rely on what Wrangham et al refer to as ‘fallback’ foods. The most effective and reliable fallback foods would have been what Wrangham et al call ‘underground storage organs’ – that is starchy tubers. The really significant insight then is that there is also a very viable explanation for exactly why it was only our ancestors that employed this particular solution to winter food shortages. Baboons, for example, would only dig to a depth of about 10cm. Only our ancestors had the necessary ingenuity, perseverance, whatever to dig deep enough to access these underground storage organs. In answer to my original question, yes there is another species that uses starchy food – one that tends to operate at those depths in any case:

‘…although pigs eat [underground storage organs], the only nonhuman mammalian taxa in Africa known to depend closely on them are mole rats.’​

It is not difficult to understand why mole rats’ good use of starchy food did not lead to the same level of advancement for them!

But of course, there is a glaring flaw in the idea that our use of starchy food was in any way central to our emergence as the dominant species. As you pointed out, what this paper is really about is the importance to our ancestors of the ability to cook food. That of course required the ability to control fire and that ability requires a highly advanced degree of intelligence. None of the modern species that we regard as ‘intelligent’ come anywhere close to having that ability. So, while cooking and the use of starchy foods may have been important in the development of our big brain, the species that first developed these habits had already emerged from the crowd as being one of exceptional intelligence.
 
  • #20
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Yggg, I don't have access to pubmed, but what do you think? This is now more general:

We discuss hypotheses of selective benefits of substance use, including the idea that neurotransmitter-analog plant chemicals were exploited as substitutes for costly, nutritionally constrained endogenous neurotransmitters. However, even if substance seeking was adaptive in the environment of our hominid ancestors, it may not still be so in the contemporary environment. Thus, the implications of our argument are not that the mismatch concept does not apply to human substance-using phenomena, but that it must be reconsidered and extended to incorporate the implications of a substance-rich, rather than substance-free, evolutionary past.
Psychotropic substance-seeking: evolutionary pathology or adaptation?
Sullivan RJ, Hagen EH
Addiction. 2002 Apr;97(4):389-400.
http://www.ncbi.nlm.nih.gov/pubmed/11964056
 
  • #21
My basic objection is based purely on my understanding of how recently (relatively of course) humans took up agriculture and my understanding of the kind of time spans usually involved in anything that can be regarded as evolution. Believe me, I accept the possibility that the flaw is either in my knowledge of history or in my understanding of evolution. But reading the paper you referred to in your post #9 and also returning to the piece about the Amy1 gene that I referred to in the original post, there is a quite different account that I take from it that makes a great deal more sense to me.
Evolution is not as slow as you think it is. A lot can happen in 10,000 years. Take for example the evolution of lactase. It is an enzyme that helps humans digest lactose found in milk. In humans it is coded by the LCT gene on chromosome 2. Although found in all mammals, its production greatly decreases after weaning, since the ingestion of milk normally stops. But a mutation in the LCT gene about 9000-10,000 years ago, coinciding with the domestication of cattle, has enabled approximately half the world's population to successfully digest milk in adulthood without showing any symptoms of lactose intolerance. Something similar could also have happened with starch.
 
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  • #22
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Evolution is not as slow as you think it is. A lot can happen in 10,000 years. Take for example the evolution of lactase. It is an enzyme that helps humans digest lactose found in milk. In humans it is coded by the LCT gene on chromosome 2. Although found in all mammals, its production is greatly decreases after weaning, since it ingestion of milk normally stops. But a mutation in the LCT gene about 9000-10,000 years ago, coinciding with the domestication of cattle, has enabled approximately half the world's population to successfully digest milk in adulthood without showing any symptoms of lactose intolerance. Something similar could also have happened with starch.
That is what I was going to say. Once the new habit starts to come in there could be a lot of selection pressure for the starch-processing activity. It allows population explosions of the favoured population.

You pose a very interesting question I had not thought of before. So I quickly looked up the starch content of foods at http://www.kickas.org/ubbthreads/ubbthreads.php?ubb=showflat&Number=143543 . There is a long list which just makes you realise how almost everything we eat is far from 'natural'! Very little of it in a chimp's diet. However fruit and leaves contain little starch, even bananas!

If you come across new revealing info let us know!
 
  • #23
Ygggdrasil
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Ken, after reading a little more on the subject, I do think it is plausible early hominids ate underground storage organs (USOs) before the invention of agriculture. Since these are relatively starch-rich, this food source would provide a means to explain why human evolution selected for mutations aiding in starch-digestion. In fact, Nathaniel Dominy, an anthropologist at UC Santa Cruz, published a paper (1) suggesting that Australopithecus may have even relied on USOs in its diet. In the study, he collected a variety of different species of USOs from Africa and tested their mechanical properties too see whether early hominids would be able to actually bite into and chew some species. A diet containing some reliance on these types of USOs would also be consistent with the dental morphology of the early hominids, the observed dental wear found in remains of early hominid teeth, and carbon isotope ratios on the teeth suggesting that early hominids ate some amount of C4 plants (which the species of USO fall into). Of course, this evidence is very speculative as other food sources or combination of food sources could explain these observations equally well. But, at least the hypothesis is plausible. Unfortunately, archaeological evidence that early hominids ate USOs is lacking (although such evidence would be very difficult to find), so we do not know exactly when early humans began eating USOs.

Is a diet rich in starchy USOs coupled with the ability to more easily digest starch the key to human evolution? Probably not. It may have been an important factor, but as I noted in post #14, there are some species of monkey, such as macaques, that produce just as much, if not more, salivary amylase as us and probably have a similar capacity to digest starch (2). So, there were probably other factors involved as well. It's hard to distinguish whether higher cognitive function just happened to evolve in a species of primate that ate a relatively starch-rich diet, or whether such a diet helped to facilitate the changes that lead to increased cognitive function.

References:
1. Dominy NJ, Vogel ER, Yeakel JD, Constantino P, Lucas PW (2008). Mechanical properties of plant underground storage organs and implications for dietary models of early hominins. Evolutionary Biology 35:159-175. doi:10.1007/s11692-008-9026-7
Summarized here

2. McGeachin, R.L. & Akin, J.R. (1982). Amylase levels in the tissues and body fluids of several primate species. Comp. Biochem. Physiol. A 72, 267–269. http://dx.doi.org/doi:10.1016/0300-9629(82)90045-7 [Broken]


Pythagorean, I'll respond to your post once I have time to read the paper more fully.
 
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  • #24
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Thanks Ygggdrasil and the others who have contributed, believe me, I do not take the effort you have made to respond to me lightly.

Yes, reading further into the Wrangham et al paper, there is a section where various other scientists from various disciplines (of course this is more of an anthropological discussion than a biological one) comment on Wrangham et al’s assertions, and to the greatest extent disagree with them! Wrangham et al then respond with what I thought was a telling point:

‘The point of our article was not to claim proof. Instead, we argued the value of our scenario because it incorporates variables that have previously been ignored, fits the data at least as well as previous stories, and makes testable predictions.’​

So it is clear that none of this is absolute fact, and all Wrangham et al were doing was proposing a model that might offer some insights. At one level, this paper might be seen as killing this thread because it discusses pretty much all of the points I had thought to discuss very authoritatively. But then the comments are all just as authoritative and largely contradictory. I hope everyone agrees, that doesn’t mean that it is all pointless and we should just give up. It is in the discussion that something of a deeper understanding does emerge.

I see the significance of mishrashubham’s account of our recent adaptation to dairy. There is another similar one in the case of alcohol. The story, as I heard it, is that the original use of alcohol was simply as a highly effective way of making fluids safe to drink. But this was a culture that appeared very recently in the West. Asian populations did not employ this solution and today, Westerners tend to be much better adapted to coping with alcohol than are people of Asian origin, because we have been using alcohol for much longer. But the time spans we are talking about are at most, a few thousand years.

However, I do know, there is also a concept used in evolutionary science that talks about an adaptation becoming ‘fixed’ in a species. Although Westerners are better adapted to alcohol than Asians, the very existence of the variability of ability to cope with it might be seen as evidence that the adaptation is not yet ‘fixed’. Does the prevalence of the condition of lactose intolerance suggest that the adaptation to dairy, though widespread, is still not ‘fixed’? Is it perhaps arguable that the adaptation to starch – the prevalence of AMY1 in the human genome – is fixed and thus more deeply rooted in the ancestral history of humanity?
 
  • #25
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Regarding examples of very recent human evolution, the New York Times had a very nice article detailing a few examples (http://www.nytimes.com/2010/07/20/science/20adapt.html), including a discussion about alcohol tolerance (rather than the differences being due to encountering alcohol later in evolution, the article suggests that European and Asian populations had different strategies to adapt to the invention of alcoholic drinks). The article also cites research into a gene in Tibetans that arose to cope with low oxygen levels that may have evolved as early as 3,000 years ago.

With respect to the Wrangham et al. paper, I do agree that a lot of it is speculative, especially the social and cultural changes that Wrangham ascribes to cooking. However, clearly the invention of cooking has had an important impact on human evolution (for example, allowing humans to evolve smaller teeth and a smaller digestive system) and should be included in a discussion of how diet has affected human evolution. As with the starch digestion hypothesis, it is difficult to asses how much the invention of cooking has allowed humans to evolve more intelligence, but it is certainly plausible that it played an important role.

Copy number expansion of the AMY1 gene does seem to have been fixed in the population since it is so widespread, suggesting that it arose fairly early in human evolution (perhaps before the species left Africa). However, because Perry et al observe differences in copy number of the AMY1 gene between different human populations, it is also clear that this trait has undergone selection in more recent times as well (see paper referenced in post #14).
 

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