11 September 2011

Nathaniel Dominy PhD. and the True Human Diet.

Dartmouth Associate Professor of Anthropology, Nathaniel Dominy PhD, talks about his research and why he believes the true human diet is one based in ...

I'm a biological anthropologist so I'm

interested in how humans and non-human primates discern and acquire food resources and how the act of acquiring those food resources may have exerted a select pressure on their Anatomy in particular food is vital for life you if you don't eat you don't survive and so it stands to reason that evolution or natural selection would strongly favor the abilities the behaviors then the morphologies are the anatomies that allow organisms to acquire food efficiently you have to have food first before you can think about other evolutionary activities like reproduction so food is first and foremost the most vital thing an organism does on a daily basis and the importance of getting it is expected to affect its its adaptations and so when we look at ourselves when we look at humans and we look at the unique traits that we have a large brain the ability to walk on two feet the ability to use tools language these things can be linked at least in part to the importance of acquiring food at least that's what I think we have a constellation of very unusual traits and so something extraordinary happened in

human evolution and we need to link that to some some ability to acquire resources so whatever those resources were they were probably not tapped by other organisms humans evolved an ability to acquire a resource that other organisms didn't have an ability to acquire and that took intelligence and so I think humans to explain the human career you have to find something extraordinary and I think food resources particular food resources may help explain that human beings were the most excellent animal long before agricultural products became an important part of the diet so to understand how human beings became excellent animals we have to look before we have to look at the diet that existed before humans started growing plants for their own benefit or harvesting and husband maintaining animals for their own benefit so yeah I think it's safe to say that the factors that caused humans to be extraordinary cannot be linked to those domesticated foods it has to be something that happened prior to the domestication of those foods we know that humans had a mixed diet we can verify that in part by

looking at modern humans that continue to hunt and gather foods and we know that they have a very mixed diet so things like honey are particularly important for people things like starch your resources that come from underground are particularly important for example tubers and bulbs and corns these tissues that have a lot of starch and carbohydrates meat is important to an extent but not as important as the popular media might lead you to believe it's usually 25% or less of their diet and it's very variable that's unpredictable it's hard to get so humans tend to rely first and foremost on plant foods that they can find in the environment humans don't turn down sugars from fruits of course that if they find a fruit they can eat it but fruits are not particularly reliable either they're seasonal the starches the sugars that are kept in underground storage organs of plants are much more ubiquitous in the environment and much more reliable and are there pretty much year-round behaviorally people are plastic and some people eat meat but anatomically I would say we're not adapted to meat at all or our teeth are

too big or enamels too thick the cusp on our teeth are too short so we simply don't have the adaptations that you would need to chew meat efficiently I mean anyone can look at the teeth of their dog or cat and they can see what teeth should look like if you're going to eat meat our teeth don't match so you could say that we've evolved a face and a mouth that's for eating something else that's not me and most people believe that's plant foods that's one of the great things about culture is that it releases us from some of these evolutionary constraints that most other organisms face so culture for example involves cooking and processing foods adding spices all sorts of other things that we do on a behavioral basis to widen the diversity of our diet and make ourselves far more eclectic feeders than any other organism on the planet starch is a difficult thing to eat actually the starch granule is actually semi crystalline so it's extremely hard and sternly difficult to digest and that's that's for a reason the plants don't really want you to be eating their storage reserves so they protect it as much as

possible the way we humans in the way some other animals have overcome these defenses is by evolving a particular enzyme that allows us to hydrolyze which is to say to break down that semi crystalline structure and the enzyme that does it is called amylase and we humans are blessed with an abundance of amylase in our saliva and you probably all have the experience of thinking about food and then your mouth starts to water so saliva is a pretty important part of the feeding process it allows you to to digest foods very quickly in the mouth and you can convert the starch in the mouth directly to to sugar with the amylase in your saliva so one of the lines of research that we've been interested in pursuing is to try to understand the genes that are responsible for producing saliva amylase in this live in the mouth and we find that humans vary in the number of copies they have at this particular gene and that copy number matters those people that have more copies produce more amylase and so are better able to convert starch into sugars more quickly in the mouth and we find that that ability varies globally so that

populations that have historically eaten a lot of starch tend to have more copies of this particular gene so this is one of the first examples of a diet exerting a pressure on genetic variation and how copies of a gene can affect the way a protein is expressed in the body which is to say the amount of protein that we see in a particular tissue so so humans are pretty extraordinary compared to other primates for producing a lot of the salivary amylase which we can attribute to the importance of starch in human diet well it means that we can rely on starchy foods to a greater extent and in early human evolution you can imagine that some of those starchy foods may have been relatively toxic and so humans may have struggled to consume some of those starches so by having genetic adaptations that allow you to process more efficiently you can expand your overall range of edible foods and ultimately the more things you can eat the more opportunities you have to to grow a larger population to to resist diseases more efficiently to tolerate environmental changes more effectively so ultimately human success may be tied

to its ability to eat a greater variety of food option of food options and starch the ability to digest starch is intimately tied to that ability as humans emerge and spread around the globe they're going to be faced with a variety of different habitats and the foods that they may have been familiar with in one habitat may not be available may not simply exist in a different habitat so the one thing that all plants have in common is that they have starch and so if you have the ability to digest starch you can go anywhere you can go into any habitat and find similar food resources that have that one uniting thing in common that they're all based on starch so if you can digest starch you can live almost anywhere except maybe the Arctic all plants produce starts so when a plant photosynthesizes it's converting sunlight to starch basically and that's what the leaves are there for they're the starch creating organs of the plant then the plant sends that starch down through the bark down into the roots that's ultimately where it needs to go so plants vary in the mountain and the amount of starch that they have based on where they decide to

store it so some plants like to store that starch underground in the form of a big tuber for example or or a bulb or a corm but all plants all tissues and all plants have some starch it's just some tissues have more than others the seeds of a plant are another starch storage organ and the purpose of storing starch in a seed is so that presumably the seed gets deposited somewhere else so the plant wants the sea to be dispersed away from itself and then it wants the germinating plant to use up those starch reserves to grow so we humans have recognized that that there's starch in these seeds and we can access the starch before before it germinates we know from the fossil record that humans consume animal foods we know that for a fact the importance of the of those kinds of foods for brain size development is a bit more ambiguous because what we see in the hominid fossil record is we see a gradual change in brain size throughout the lineage and then we see a relatively large surge in brain size at about two million years ago with it with the origin of our own genus the genus Homo so what we don't know is whether or not

increasing meat consumption parallels those changes in a very in a very accurate way so because there's not a very strong match between meat consumption and increasing gradual increases in brain size scientists have looked to other options and given that plant foods are such an important part of modern humans that hunt and gather Foods the money is on plant foods and a shift in the kinds of plant foods as being the major driving factor in increasing brain size I would say the a mix of plant foods with a large amount of starch coming from tubers and seeds that's the that's the fundamental component of the human diet