I
was reading my October issue of Scientific
American [yes, I am somewhat behind], and I came across an article
explaining a fairly new hypothesis regarding the longevity of humans in
relation to other primates (Pringle, 2013). The widespread belief is that
modern medicine, sanitation systems, and food availability have allowed humans
to live so much longer – and this is true over the past 200 years. However, extension
of human lifespan began long before these lifestyle modifications were
implemented.
According
to Caleb E Finch (2010), as humans began trading their plant-based diet for more
meaty alternatives sometime between 3.4 and 2.5 million years ago, the extra
calories and protein not only supplied the brain with extra fuel to grow but
also increased pathogen exposure. This risk of infection placed selective
pressure on host-defense adaptations to better fight off disease. As Finch
began to examine changes to immunological genes specific to humans, the
apolipoprotein E (ApoE) gene drew his
attention. ApoE functions in lipid
transport and metabolism, brain development, and immune defense. The gene
contains three alleles, of which ApoE3 and
ApoE4 are the most prevalent. ApoE4 closely resembles chimpanzee ApoE, suggesting that it is one of the
first ancestral variants to arise in the Homo
genus and first to have an effect on human longevity. Notably, ApoE4 greatly enhances the acute phase
of inflammation, with heightened production of pro-inflammatory cytokines such
as interleukin-6 and tumor necrosis factor-alpha. With the ApoE4 allele boosting immunity, humans living two million years ago
had a higher chance of surviving infection. Early humans also benefited from ApoE4 during periods of starvation,
since the allele aids in absorption and storage of lipids that can be drawn on
when food is scarce.
Based
on its function, one would think that the ApoE4
allele would remain at a high frequency in most populations. This is not the
case, however. While ApoE4 confers
advantages early in life, as human lifespan extended those possessing the
allele developed increased risk for chronic diseases of aging such as heart
attacks, strokes, atherosclerosis, and Alzheimer’s disease. This explains the
surprising findings of Randall Thompson and his team (2013) upon observing CT scans
of 137 mummies spanning over 4,000 years. Thompson et al. found that
atherosclerosis was common in the four preindustrial populations examined,
including preagricultural hunter-gatherers. These results challenged the assumption
that atherosclerosis is a modern disease, and point to a more fundamental
predisposition for the illness.
The
acquisition of the ApoE4 allele
presents an interesting trade-off, and is a textbook example of antagonistic
pleiotropy, where a gene affects the young positively and the old negatively.
The fading of ApoE4 from a major
allele in the population to a minor allele, replaced by the milder ApoE3 allele, makes sense in this
context. It is astounding to me that a simple change in diet millions of years
ago allowed us to not only increase our brain volume and gain the prefrontal
cortex that makes us what we are today, but also played a role in augmenting
lifespan and immunity. As a vegetarian, I can’t help but be thankful to my
ancestors for eating meat – and grateful that now I don’t have to!
Finch
CE. 2010. Evolution of the human lifespan and diseases of aging: Roles of
infection, inflammation, and nutrition. Proc Natl Acad Sci U S A. [Internet].
[cited 2013 Nov 26]. 107(Suppl 1): 1718-1724. DOI: 10.1073/pnas.0909606106
Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2868286/
Pringle,
H. 2013. Long live the humans: Modern genomes and ancient mummies are yielding
clues to why the lifespan of Homo sapiens
far exceeds that of other primates. Sci Am [Print]. [cited 2013 Nov 26]. 309(4):
48-55.
Thompson
RC, Allam AH, Lombardi GP, Wann LS, Sutherland ML, Sutherland JD, Soliman MAT,
Frohlich B, Mininberg DT, Monge JM, Vallodolid CM, Cox SL, el-Maksoud GA, Badr
I, Miyamoto MI, Nur el-din AH, Narula J, Finch CE, and Thomas GS. 2013.
Atherosclerosis across 4000 years of human history: The Horus study of four ancient
populations. The Lancet [Internet]. [cited 2013 Nov 26]. 381(9873): 1211-1222.
DOI: http://dx.doi.org/10.1016/S0140-6736(13)60598-X
Available at: http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(13)60598-X/fulltext
I was curious to know as to whether or not the Thompson article went into detail as to what defined a "hunter-gather diet" like that of the mummies? A lot of research I have been doing lately has indicated that heart disease and atherosclerosis can be attributed to the high amounts of saturated fat in our Western diets primarily from animal products (Micha, Wallace, and Mozaffarian, 2010). I would be interested to know more about the comparison of saturated fats in those ancestral diets versus the current Western diet, and the incidence of atherosclerosis among both.
ReplyDeleteMicha R, Wallace S, and Mozaffarian D. 2010 May. Red and Processed Meat Consumption and Risk of Incident Coronary Heart Disease, Stroke, and Diabetes Mellitus. Epidemiology and Prevention.121:2251-2252.
I went back and looked at the Thompson article and they had a really good table (Table 2, pg. 1220) that included the diet of the four populations they looked at [I copied the essentials below]. It seems like they did eat a lot of meat [mainly marine mammals for the hunter-gatherers], so perhaps the trade-off for the excess calories that boosted our immune system and augmented our brain power includes atherosclerosis later in life. It is quite ironic that what extended our lifespan in the past is now preventing our contemporaries from living as long as we potentially could. I'm not familiar with which foods have an unhealthy level of saturated fat, but that would be an interesting way of furthering this research.
ReplyDeleteEgyptians [farmers, animal domestication]: farmed wheat, barley, dates, figs, olive, beans, pomegranates, radishes, onions, cucumbers, lettuce, cabbage; made beer, wine; protein sources included domesticated cattle, sheep, goats, pigs, hyenas, ducks, geese, quail, pheasant, fish.
Peruvians [farmers, animal domestication]: farmed corn, potato, sweet potato, manioc, beans, bananas, hot pepper; protein sources included domesticated alpaca, guinea pigs, ducks, Andean deer, birds, crayfish, fish.
Ancestral Puebloans [forager-farmers]: farmed maize (corn) and squash; collected pine nuts, seeds, amaranth, grasses; protein sources included rabbit, mice, big horn sheep, mule deer, fish.
Unangan/Aleuts [hunter-gatherers]: collected berries; hunted marine mammals (seal, sea lion, sea otter, whales) and fish; collected shellfish, sea urchins, eggs.
This blog is very interesting and reflects a very common debate today on which diet is best (i.e. vegetarian, meatitarian, omnivore, pescatarian, etc.) From the research that you did relates to a lot of aspects of our physiology classes.
ReplyDeleteIn our class, we have learned that different kinds of meats provides the necessary proteins and nutrition needed to give us energy and perform other bodily functions. In class, I remember Dr. Campisi mentioning you can obtain the same about of proteins and nutrients being a vegetarian. The catch is that you have to eat a more of a variety of plants, vegetables, fruits, etc. to gain the same amount of nutrients that could be found in meat. So it is possible to gain the proper amount of nutrients through vegetarianism. But I don't think vegetarianism could have been to our ancestors advantage.
I think it would have been hard for our ancestors go out and gather all of the necessary nutrients through vegetables, fruits, etc. Because this could require them to be out looking for food, exposing them to other predators constantly instead of hunting some of the predators instead.
I think this blog is great because it relates back to our physiology through the digestive system as well as also looking at evolutionary adaptations that could be to our advantage. Now a days though, there is more availability to access the necessary nutrients where you can follow any diet you want and makes you happy.