Sunday, May 7, 2017

Natural Selection Favors Both Strength and Longevity in Humans

Recently I have been getting comments on my blog to this effect:

“Evolution only favors reproductive success, not necessarily individual health and longevity.”

And:

“The diet that makes you physically strong and attractive (‘look good naked’) may not help you be healthy or live long.”

These widely held beliefs are commonly used to attack the idea that a meat- and fat- based, low plant food diet can support or may be best for health because it is the diet that enabled our ancestors to survive the Pleistocene Ice Age.

I want to show that these beliefs are not supported by scientific evidence and reasoning.

Long Live the Carnivorous Ape

Humans are the most carnivorous and longest lived primate.


Hence, among all of the great apes, greater carnivory is linked to much greater lifespan.   The vegetarian great apes have only half the potential life span of the carnivorous ape. 

In humans, natural selection as a matter of fact has favored longer life span and the increase in human life span compared to other apes evolved along with an increased dependence on hunting and meat- and fat- eating.

On the basis of this evidence:

1) It looks reasonable to hypothesize that increased meat-eating was one of the factors that contributed to the evolution of increased lifespan in humans compared to other apes.

2) It looks unreasonable to hypothesize that reducing meat consumption is a path to greater life span for primates. 

The Ice Age Diet Favored Long-Lived Humans

It is a matter of fact that human life span increased over the past 1.8 million years.  During this period of time, known as the Pleistocene epoch, the ice age climate restricted the availability of carbohydrate-rich fruits and vegetables.  Grass became the dominant form of plant life, and large grass-eating animals (e.g. mammoths and rhinos) became abundant animal species; in turn, predators of those herbivores – cats, canines, and humans – flourished.

Humans moved out of Africa into Europe and Asia during this time.  Animals migrate toward their food sources, not away from them.  Pleistocene Europe offered nothing for an animal adapted to a plant-based, animal-free diet.  Pleistocene humans were "top level carnivores" living by hunting for meat and fat [1, 20].

Increasing meat consumption at the expense of plants necessarily means eating more protein and fat, and less carbohydrate.

Plant foods are rich in carbohydrate and antioxidants. 

A low plant food diet is a low in carbohydrates and antioxidants.

It has been shown that carbohydrate-restriction, reduced glucose metabolism, reduced insulin receptor and insulin receptor substrate, and increased mitochondrial respiration and levels of reactive oxidation species increase lifespan, calling into question the fashion of eating both carbohydrate and antioxidants.[2, 3]

Supplementation with antioxidants has been found to promote cancer growth and increase the incidence of a number of diseases with adverse effects on human longevity.[4] 

Unlike normal cells, cancer cells are glucose dependent, and a low (8-15% energy) carbohydrate, high (58-69% energy) protein diet has been shown to reduce insulin and lactate levels, curtail cancer growth and prevent cancer initiation in mammals.[5]

Low carbohydrate (hence low antioxidant) diets have been shown to reduce cardiovascular risk factors and inflammation in humans.[6]

Caloric restriction is a method of glucose and insulin restriction. Methionine restriction appears to increase lifespan in animal models, but methionine is an essential amino acid.  A methionine-restricted diet impairs fertility because methionine is required for DNA synthesis.  There is some evidence that slowed synthesis of DNA and methionine is a pathogenetic mechanism that promotes both Down's syndrome and Alzheimer's dementia [29].  This underscores the importance of methionine to proper functioning of the human brain, which is the primary tool for survival.  Methionine-deficient humans would be demented and unable to cope with the rigors of the Pleistocene environment. Thus since a methionine-restricted diet could reduce fertility and impair the viability of both children and elders, it could not have played a role in the evolution of human longevity.

In contrast, carbohydrate is not an essential dietary nutrient. Restriction of carbohydrate does not impair fertility; numerous humans have sustained reproduction over thousands of years on low carbohydrate diets, "with no apparent effect on health or longevity," as acknowledged on page 275 of the National Academy of Sciences Food and Nutrition Board Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids:


Restricting dietary carbohydrate  rather than total calories, protein or methionine does not involve courting nutritional deficiency yet according to experimental evidence promotes increased life span. 

Hence, it is reasonable to hypothesize that the low antioxidant, low carbohydrate, animal-based diet consumed by Pleistocene humans may have favored longer life span than found in vegetarian apes, and thus also favored reproduction of long-lived humans.

From a phylogenetic perspective, it appears that among apes, the one that chose to progressively reduce plant food and increase meat and fat consumption, to the point of complete carnivory during the Pleistocene, evolved a lifespan double that of the vegetarian apes. 

This perspective renders implausible both the idea that a plant-based diet is most likely to increase human lifespan, and the idea that an animal-based diet is most likely to reduce human life span.

(NOTE: Before you say "but Inuit had this and that disease," think. Inuit lived in igloos warmed by burning oil.  They cooked food over indoor fires.  Thus they and other hunters who had similar habits had daily sustained exposure to fumes that, like smoking tobacco, can cause health conditions, including heart disease and cancer.  Thus, even if some of these tribes did get heart disease or cancer – which, as recorded in Stefansson's Cancer: Disease of Civilization, is disputed by many first hand reports [30] – diet is not the only environmental influence on health of modern or ancient humans.)

Strength and Muscle Mass Predicts Life Expectancy

Muscular strength “has an independent role in the prevention of chronic diseases whereas muscular weakness is strongly related to functional limitations and physical disability.”[7]  Muscular strength reduces the risk of premature death from cancer and all causes in men [8] and women [9]. 

Aging of muscles leads to disability; disability makes one unproductive and unable to help your children and grand-children survive and thrive. 

Strength training is the only physical training method proven to retard and even reverse aging of muscles.10  Properly performed resistance training can significantly improve strength, cardiorespiratory fitness [11, 12]  and flexibility [13, 14, 15, 16] whereas endurance training does not improve strength or flexibility (actually tends to reduce them), and flexibility training does not improve endurance or strength.  Progressive strength training “produces greater strength, gait and balance improvements in elderly people than a flexibility exercise program.”[17]  Resistance exercise also improves self-esteem, mood, body image, and fatigue.[18] 

Strength is a function of muscle mass.  Therefore, the best diet for functional life span would be one that best maintains muscle mass and strength. 

The available evidence indicates that in general, animal proteins are more effective for promoting muscle protein synthesis and hypertrophy than plant proteins, particularly in older people.[19]

During the Pleistocene, humans in Europe were "all top-level carnivores who derived the vast majority of their protein from animal sources, likely to be large herbivores."[20]

Therefore, animal proteins are best for maintaining strength, particularly in mature adults, and since strength protects against premature death from cancer and all causes (see above), it is reasonable to postulate that the known high consumption of animal protein during the Pleistocene played some role in natural selection for longevity in carnivorous humans compared to vegetarian apes.

Natural Selection Favors Longevity in Humans

In humans, longevity is critical to reproductive success in harsh environments such as characterized the Pleistocene epoch. Since human children require a long period of tutoring and mentoring to be successful adults in a harsh environment, natural selection would have favored those individuals who achieved healthy longevity on their Pleistocene cuisine.

Up until the age of about 20, hunter-gatherers eat more food than they produce, and they don’t have a net productivity – that is, produce surpluses of food sufficient for supporting pregnant and lactating wives and children – until they are past the age of 25 or even 30.[21] 

Source:  The Evolution of the Human Life Course
For example, among the Aché:
“Fifteen- to seventeen-year-old boys acquired 440 calories of meat per day, 18- to 20-year-olds acquired 1,530 calories, and 21- to 24-year-olds acquired 3,450 calories, whereas 25- to 50 year olds acquired about 7,000 calories of meat per day. The fourfold increase between 18 and 25 years of age exists in spite of the fact that by age 18, young men are hunting about as much as fully adult men.” [22]
Note that 50 year old men are among the most productive hunters among the Aché.  If men died at 50 or 60, the family would sustain a huge economic loass.  There is no reason to suppose that the Pleistocene human teens were any more productive.  The Pleistocene family must have depended on the older males for sustenance. 

This means that if paleolithic parents died in their 20s or 30s, their children would have also died of starvation before reaching the age of 20.  Given that due to their lean conditions wild human females are not fertile until about 16 years of age, a mother would have to live at least 30 years beyond this to see her sons become productive enough to support children themselves.  Now consider that the typical hunter-gatherer woman had 4 to 5 children, generally spaced about 4 years apart by the contraceptive effect of intensive lactation.  If she had her first child at 20, she would have her 5th child when she was between 40 and 50 years old.  Then she and her husband would have to live another 30 years – that is, to the age of 75 or 80 – before that last child became productive enough to support children him- or her-self. In the meantime their children and grandchildren would need all the help their parents/grandparents could give.

Thus, in the Pleistocene, menopausal women and elder men living past the age of 50 and up to the age of 80 or beyond would have played an important role in provision of food for their children and grandchildren who would have had lower net productivity.  Given the fact that humans mature quite slowly and foragers do not individually become capable of producing enough surplus food to support pregnant and lactating women and children until they are past the age of 30, natural selection during the Pleistocene would have favored people who had natural lifespans similar to modern foragers, about 70 to 80 years provided they do not die from infection or accident in childhood or later.[23]

Modern man does not live on average much longer than this. Today the people with the longest lifespan are those living in Okinawa where the average life expectancy is 81.2 years––86 for women, 75 for men. In the U.S.A., the average (both sexes combined) is 80.45 years.

Ancient people did as well.  Bond adds: “Look again at some of Alexander the Great’s generals. Antigonus Monophthalmos was a battling veteran who, encouraging his troops from his war-horse, finally succumbed to a hail of javelins at the Battle of Ipsus. He was 81 years old. His opponent, Lysimichos was later killed at the Battle of Coropedium at the age of 70. His ally Selfcos Nicator survived all battles only to be assassinated at the age of 78.”[24]

As I wrote in the Garden of Eating:  “How many modern 80-year-old men would be capable of riding a horse into battle carrying the heavy ancient armaments.  These old men had the virility of youth.”  Humans like other species have more or less fixed potential natural life spans. No diet is going to take you beyond that.  This is why traditional people weren’t obsessed with physical longevity in this one life, but found meaning in a life well lived (honor) and, in traditional European religion, originally the bear cult, a knowledge that individuals who live honorably will reincarnate.






Since it takes one to two decades of tutoring and mentoring for a primitive hunter to gain the skill necessary to become a highly productive hunter, which tutoring could only have been provided by adult males with decades of experience,  it is reasonable to hypothesize that our ancestors’ need to rely on hunting to survive the Pleistocene imposed a natural selection for long-lived humans.

People who maintain health and strength (i.e. muscle mass) for more years remain more productive members of the family and tribe.  Grandparents and great-grandparents who are stronger in old age can contribute more to the survival of their grandchildren and great-grandchildren.  They can tutor, take care of and protect their grandchildren while their children go hunting and gathering, build shelters, or whatever.

This is in fact the proposed evolutionary explanation for menopause.  Women who went through menopause left more progeny than those who did not, because by forsaking reproduction themselves, they were able to invest more resources in their grandchildren.  This is called the Grandmother Hypothesis

The same applies to grandfathers.  The longest lived men would provide the family with the most experience, knowledge, and wisdom, as well as assistance with hunting, building, and so on.  Men who were most intelligent and strongest for the longest life spans were most able to help their grandchildren and great-grandchildren survive and thrive.  Thus, they left more successful progeny than men who died at younger ages.

Thus, a reasonable hypothesis for how humans evolved to be the longest-lived primates during the Pleistocene:

1) the low-carbohydrate Pleistocene cuisine supported longevity
2) the longest-lived, most family-oriented and conscientious men and women had the largest number of successful progeny, with the result that their genetic gift for longevity when supported by the Pleistocene diet became dominant in humanity. (Off the Pleistocene diet, results may be very different.)

Thus, the idea that humans could have achieved maximum reproductive success during the Pleistocene without diet-supported longevity lacks credibility and is severely challenged by the very fact that humans are the longest-lived apes. 

In challenging environments such as posed by the Pleistocene, humans just can’t have maximum reproductive success over the long term – i.e. leave the largest possible number of progeny capable of thriving in the harsh environment and passing that capability on to more and more generations – without optimizing individual longevity.

Stephan Guyenet Ph.D. notes:
"One of the classic counter-arguments that's used to discredit accounts of healthy hunter-gatherers is the fallacy that they were short-lived, and thus did not have time to develop diseases of old age like cancer. While the life expectancy of hunter-gatherers was not as high as ours today, most groups had a significant number of elderly individuals, who sometimes lived to 80 years and beyond. Mortality came mostly from accidents, warfare and infectious disease rather than chronic disease."
In that post, Dr. Guyenet discusses evidence that after contact with Europeans about 25% of Inuit eating their traditional low-carbohydrate diet lived past the age of 60 and some lived into their 90s.  This happened in spite of the fact that contact with Europeans increased adult mortality from infectious diseases that Europeans unintentionally introduced to the Inuit population.  Guyenet aptly notes:
"It's possible that life expectancy would have been higher before contact with the Russians, since they introduced a number of nasty diseases to which the Inuit were not resistant. Keep in mind that the Westerners who were developing cancer alongside them probably had a similar life expectancy at the time."
The most longevous Inuit would most likely have left more descendants – children, grand-children, and great-grandchildren – than those who died younger.  Thus, natural selection would favor the reproduction of longevous individuals, and not those who died young of any cause.  Modern medicine works against natural selection for longevity by preserving the lives of people who in prehistoric times would have died from infections, accidents, warfare or other causes before having a chance to propagate their genes.  Hence over time a population served by modern medicine tends to have a greater proportion of individuals who have weak immune systems, are accident prone, or are either more warlike or more inept in battle.

This is a photo of Chief Seattle (c. 1786 – June 7, 1866) a hunter in quite good shape at the age of 78.

Source:  Public domain, Wikipedia


The idea that the Pleistocene cuisine could have promoted maximum reproductive success while curtailing individual lifespan, making them die at ages similar to other apes (i.e. 35-50) lacks evidential support and credibility. 

Attractiveness – 'Looking Good Naked' – Signals Strength and Potential Longevity

The idea that a diet could make you attractive yet not help you live long lacks credibility.

It is a simple fact that not only people but members of all other species prefer to associate and mate with physically attractive individuals.

Now, suppose that attractiveness did not signal health or potential longevity in humans.

If this were so, our ancestors would have been misled into mating with physically attractive mates who were strong (due to carrying attractive muscle mass) but who would then turn out to be useless for long-term child care and hence reproductive success as described above.

To maximize reproductive success, you need to be attractive, smart, strong, healthy and committed to helping your progeny thrive for as long as possible, across as many generations as possible.

As already discussed above, we know that physical strength protects against premature death from all causes, and also makes one more capable of contributing to the success of your progeny in advanced age.  Strength is produced by muscle mass, and, male or female, muscle mass makes you look good naked.

Physical attractiveness would not contribute to maximizing reproductive success in humans unless it also help people live long enough to help their grandchildren and great-grandchildren thrive. 

If physical attractiveness was deceptive regarding health and led people (or any other species) to choose mates who were actually sick inside and bound to be disabled or die young from atherosclerosis, diabetes, cancer or other diseases, and therefore unable to contribute to grandchildrens’ success, then it would not be favored by natural selection.

Therefore the idea that a lifestyle that makes you look good naked throughout your life could shorten your life is implausible.  

Internal illness makes an animal unattractive.  The longer you maintain health, the longer you maintain attractiveness, the more you will attract the opposite sex, and the more likely you will have a larger number of offspring.  This applies to both sexes.

In Natural Eating, Geoff Bond notes that about 3000 years ago, the poet Homer composed the Iliad, in which he tells us Odysseus’ wife Penelope remained faithful though he was absent 20 years, during which time she had offers of marriage from many men, some the same age as her son Telemachus. Bond says, “In other words, in ancient Greece 3000 years ago, a 40-plus woman was such a marriageable attraction that she was pursued by men half her age.”[25] More than 2300 years ago in Greece, Aristotle recommended men not marry until reaching 35––as Bond says, “hardly the strategy of people expecting a short life or decrepit old age.”

In his report on Germany first published in about 110 A.D., the Roman historian Tacitus wrote that the Germans lived on wild fruit, fresh game, and curdled milk. Given the cold climate and forest cover of Germany of the time, wild fruit was limited and relatively low carbohydrate.[26]  Of the Germans’ reproductive habits he wrote:

“The young men marry late, and their vigour is thus unimpaired.  Nor are the maidens hurried into marriage; the same age and a similar stature is required; well-matched and vigorous they wed, and the offspring reproduce the strength of the parents.”[27]

As Bond said, this is “hardly the strategy of people expecting a short life or decrepit old age.” 

Tacitus goes on to say of the German man:  “But every man’s own children are his heirs and successors, and there are no wills....The more relatives he has, the more numerous his connections, the more honoured is his old age; nor are there any advantages in childlessness.”[28]

From their deliberate delay of marriage yet high valuation on large families we can surmise that it is highly unlikely that the Germans' animal-based diet was killing them prematurely. 

Conclusions

In review:

The fact that humans are the longest-lived and most carnivorous of the great apes, having a life span double that of the vegetarian apes, renders implausible the idea that plant-based diets absent animal protein are best for human longevity. On the other hand it supports a hypothesis that meat-eating was one of the environmental factors that supported the evolutionary increase in human life span compared to non-human apes.

We have experimental evidence and reason to support a hypothesis that the reduced intake of carbohydrate and antioxidants from plants and the increased intake of animal protein and fat by humans during the Pleistocene epoch favored greater life span among humans compared to the vegetarian apes.

The idea that that humans’ evolutionary diet could promote reproductive success for individuals without promoting healthy longevity for those individuals is implausible at best.  On the contrary, the evidence and evolutionary reasoning support the conclusion that humans can not achieve maximum reproductive success in a Pleistocene environment without healthy longevity, and there is reason to believe that the Pleistocene diet, low in carbohydrate and antioxidants, high in animal protein and fat, combats inflammation, heart disease, diabetes and cancer and optimally supports fertility, health, strength, and longevity.

The idea that humans’ evolutionary diet could make an individual strong and attractive yet unhealthy and prone to premature death is inconsistent with evolutionary theory. 

Since human children require a long period of tutoring and mentoring to be successful adults in a harsh environment, natural selection would have favored those individuals who achieved healthy longevity along with successful procreation on the Pleistocene cuisine.

NOTES

1 Ben-Dor M, Gopher A, Hershkovitz I, Barkai R, “Man the Fat Hunter,” PLOS One 2011;6(12): e28689. doi:10.1371/journal.pone.0028689.

2 Schulz TJ, et al., “Glucose restriction extends Caenorhabditis elegans life span by inducing mitochondrial respiration and increasing oxidative stress,” Cell Metabolism 2007 Oct 3;6(4):280-293. 

3 Ristow M, Schemeisser S, “Extending life span by increasing oxidative stress,” Free Radical Biology and Medicine 15 July 2011;51(2):327-336.

4 Ristow M, Schemeisser S, “Extending life span by increasing oxidative stress,” Free Radical Biology and Medicine 15 July 2011;51(2):327-336.

5 Ho VW, et al., “A low carbohydrate, high protein diet slows tumor growth and prevents cancer initiation,” Cancer Research 2001 July;71(13):4484-93.

6 Ristow M, Schemeisser S, “Extending life span by increasing oxidative stress,” Free Radical Biology and Medicine 15 July 2011;51(2):327-336.

7 Volaklis KA, Halle M, Meisinger C.  Muscular strength as a strong predictor of mortality: A narrative review. Eur J Intern Med 2015 June;26(5):303-10.

8 Ruiz JR, Sui X, Lobelo F, et al. Association between muscular strength and mortality in men: prospective cohort study. BMJ : British Medical Journal. 2008;337(7661):92-95. doi:10.1136/bmj.a439.

9 Rantanen T, Vopato S, Ferrucci L, et al. Handgrip strength and cause-specific and total mortality in older disabled women: Exploring the mechanism. J Am Geriatrics Soc 2003 April 29;51(5):636-41.

10 Melov S, Tarnopolsky MA, Beckman K, et al.. Resistance Exercise Reverses Aging in Human Skeletal Muscle. PLOS 23 May 2007. 

11 Artero EG, Lee D, Lavie CJ, et al. Effects of Muscular Strength on Cardiovascular Risk Factors and Prognosis. Journal of cardiopulmonary rehabilitation and prevention. 2012;32(6):351-358. doi:10.1097/HCR.0b013e3182642688.


12 Steele J, Fisher J, McGuff D, et al. Resistance training to momentary muscular failure improves cardiovascular fitness in humans: A review of acute physiological responses and chronic physiological adaptations. J Ex Phys (online) 2012 June;15(3):53-80.

13 Fatouros IG, Kambas A, Katrabasas I, et al. Resistance training and detraining effects on flexibility performance in the elderly are intensity-dependent. J Strength Cond Res 2006 Aug;20(3):634-42.

14 Morton SK, Whitehead JR, Brinkert RH, et al. Resistance training vs. static stretching: effects on flexibility and strength. J Strength Cond Res 2011 Dec;25(12):3391-8.

15 Santos E, Rhea MR, et al. Influence of moderately intense strength training on flexibility in sedentary young women. J Strength Cond Res. 2010 Nov;24(11):3144-9. PubMed PMID: 20940647.

16 Monteiro WD, Simão R, Polito MD, et al.. Influence of strength training on adult women's flexibility. J Strength Cond Res.
2008 May;22(3):672-7. PubMed PMID: 18438255.

17 Barrett C, Smerdely P. A comparison of community-based resistance exercise and flexibility exercise for seniors. Aus J Physiother 2002;48(3):215-19. 

18 Taspinar B, Asian UB, Agbuga B, et al. A comparison of the effects of hatha yoga and resistance exercise on mental health and well-being in sedentary adults: a pilot study. Complement Ther Med 2014 Jun;22(3):433-40. 

19 Witard, Oliver C. et al. “Protein Considerations for Optimising Skeletal Muscle Mass in Healthy Young and Older Adults.” Nutrients 8.4 (2016): 181. PMC. Web. 12 Apr. 2017.

20 National Research Council (US) Committee on Population; Wachter KW, Finch CE, editors. Between Zeus and the Salmon: The Biodemography of Longevity. Washington (DC): National Academies Press (US); 1997. 10, The Evolution of the Human Life Course. Available from: https://www.ncbi.nlm.nih.gov/books/NBK100413/

21 Richards MP, “A review of the archaeological evidence for Paleolithic and Neolithic subsistence,” Eur J Clin Nutr 2002;56. doi:10.1038/sj.ejcn.1601646

22 National Research Council (US) Committee on Population; Wachter KW, Finch CE, editors. Between Zeus and the Salmon: The Biodemography of Longevity. Washington (DC): National Academies Press (US); 1997. 10, The Evolution of the Human Life Course. Available from: https://www.ncbi.nlm.nih.gov/books/NBK100413/

23 Ibid.

24 Bond G. Natural Eating. Torrance, CA: Griffin Publishing Group, 2000:131.

25 Ibid.

26 Tacitus, Germania and Agricola (Ostara Publications, 2016), p. 9.

27  Ibid., p. 8.

28 Ibid.

29  Regland B, Gottfries CG, "Slowed synthesis of DNA and methionine is a pathogenetic mechanism common to dementia in down's sydrome, AIDS and Alzheimer's disease?" Medical Hypotheses 1992 May;38(1):11-19. 

30  Stefansson V. Cancer: Disease of Civilization. New York: Hill and Wang, 1960.

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