Seasonality, Climate and Diet

Evolution and seasonality are inextricably intertwined. This isn’t a negotiable, controversial statement, because evolution describes an organism’s response to environmental pressures, and the seasons are part of the environment. Another uncontroversial statement is that the study of human evolution can give us insight into what constitutes a healthy lifestyle for modern humans. I think it’s reasonable, then, to suggest that understanding how seasonality affected human evolution might give even more insight into best practices.

Most examinations of prehistoric climate change deal with average global temperatures, which can explain overall worldwide trends in climate, but when we’re talking about human evolution – that is, on the changes in the human organism that resulted from immediate, localized environmental pressures – knowing the mean global average doesn’t tell us much. To understand how seasonality affected our development, we need to look beyond the global trends. We need to look at specific climate conditions.

The seasons change in many ways. There’s the obvious one – winter to spring to summer to fall – but how that inter-seasonal transition plays out depends on the overall climatic conditions of the environment. That is, winter has meant different things in different regions and at different times in history. Some places, winter is cold and dry, others warm and wet. Seasonality depends heavily on climate.

Okay, so let’s take a look at our data. We’ve got a glacial period lasting 111,000 years, or half the time modern humans have been around (the last half). Throughout this glacial period, common geological features in the north included glaciers, huge sheets of continental ice, changing warm/cold seasons, and arid conditions, all of which make vegetation seasonal and life fairly difficult.

Man grew up in the tropics. Yeah, there are subtropics and neotropics and whatever other distinctions you want to make, but the bulk of our evolution took place in tropical Eastern Africa, where and when it was warm. We also came of age during a glacial period that only just (11,000 years ago) ended. That glacial period was part of a larger ice age that began around 2 to 3 million years ago. We’re still in an ice age, technically, though popular parlance gets “ice age” and “glaciation” mixed up. An ice age is composed of glacial and interglacial periods. Today, we’re in the middle of an interglacial period.

That last glacial period (what we generally refer to as “the ice age,” incorrectly so) began around 111,000 years ago and lasted 100,000 more. Modern humans (Homo sapiens sapiens) have been around for 200,000 years – that’s us. So, about half our time on Earth has been spent dealing with a glacial period. What’s involved in a glacial period, you might be wondering? Well, popular notions of glacial periods include barren tundra, steadily encroaching ice sheets, unstoppable glaciers (hence “glaciation”), hairy men (and women, I suppose) in animal pelts, seasonal vegetation, and wild game with massive stores of saturated back fat. For the northern latitudes, this is pretty accurate imagery. Canada and the northern United States were completely covered by ice. The Scandinavian ice sheet spanned the British Isles, Germany, Poland, Russia, and western Siberia. The Himalayas, Caucasus, and Alps experienced considerable glaciation. Glaciers reached Taiwan, the Japanese Alps, as well as the mountains of Morocco, Algeria, and Ethiopia. The hominids living in the affected areas, then, probably embodied the classic “caveman” lifestyle (the ones who survived, that is).

Sixty thousand years ago, when Europe was icy and forbidding, modern humans weren’t there. Neanderthals were, though, and they were undoubtedly made for the region. Bulky, robust, heavy set, muscular, with pronounced brow ridges – these guys were your archetypal cavemen. But they were not modern humans. When we finally did head northward out of Africa into Europe, around 40,000 years ago, we actually displaced the extant Neanderthals. We mingled and interacted with them along the way, and we may have even interbred with them, but we are not Neanderthals. Those early Europeans were still Africans, genetically, as the famous Hofmeyr Skull showed.

So, what does seasonal, evolutionary eating actually mean? To whom do we look for ultimate guidance?

In the Primal community, there’s a tendency to hone in on the European hunter-gatherer experience for guidance in all things dietary. The big-game hunting, cave-painting Cro-Magnon is the first thing that comes to mind for most of us. That’s fine, to a point, but not when it means excluding from consideration of other hunter-gatherer populations living in completely different climates. We have to take it all in. It’s all relevant. They’re all humans.

If it’s human, it’s relevant, and we have to pay attention.

East Africa, the predominant site of human evolution, experienced the seasons as wet and dry, rather than hot and cold. It was always warm. There wasn’t widespread glaciation, except in the mountains. There were no African ice sheets. Glacial periods affected African climate, sure, but not by creating a winter wonderland. Glacial periods manifested as droughts and in the development of arid deserts and grasslands. Vegetation and game were available. Now, drought and desert undoubtedly altered the scope of human evolution by heavily impacting the humans (our ancestors) living there; it’s just a mistake to assume glacial periods meant fur coats and holing up in caves for the winter for everyone worldwide.

Put another way, when eating seasonally, do we eat according to the seasonal patterns experienced by our East African ancestors or our European/North American/Australian/Asian ancestors? Do we look to the past as a road map, or do we merely eat what’s in season at local farmers’ markets?

I’m not sure, but I’ll venture the safest guess I can muster.

All of the above. Everything matters. One thing is for certain, though: we’ve all got that African Homo sapiens sapiens blood running through our veins. Each of us – irrespective of nationality, ethnicity, or recent ancestry – has several hundred thousand years of tropical evolution to account for. That’s when we developed our taste for animal flesh and our big beautiful brains. But we’re adaptable creatures, us humans. We can thrive on different diets with different macronutrient ratios.

As long as you stick with the basics and avoid those foods that weren’t available, regardless of season, stuff like refined sugar, vegetable oils, grains, and legumes, everything else is just fudging with the margins. Keep one eye on the tropics and another on the Paleolithic climatic region of your choice. Could a descendent of Northern Europeans, a regular Norseman, thrive on a tropical diet of fish, coconuts, pork, and yams? I bet he could. Could a Native American grow old and strong on the modern Primal hybrid eating plan of Big Ass Salads, omelets, and crock pot recipes? Sure, why not.

Seasonality shouldn’t be limiting. The fact that our ancestors evolved with perennial warmth and were still able to thrive in regions with actual seasons means we can handle just about anything. It means we can eat according to any season as long as we remember the basic nutritional laws that bind us all together, rules that were initially written in the tropics and then expanded upon in myriad other climates, seasons, and regions.

Thank you for reading this series of posts in which I explored the role seasonality plays in the human diet and health. If you missed any you can catch up here:

The Question of Seasonality in Human Health and Nutrition

The Question of Seasonality in Fructose Availability

Seasonality for the Birds

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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43 thoughts on “Seasonality, Climate and Diet”

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  1. So basically, don’t worry about it? Not that I really did anyway, but I’m glad to read that the seasonality issue doesn’t have to complicate the PB way, or make it more restrictive (not that I see it as restrictive at all!) Eat what we would’ve eaten way back then, don’t eat what we didn’t, no matter where we lived.

  2. If you think about it from an evolutionary standpoint, every American is an African-American.

  3. “Seasonality shouldn’t be limiting. The fact that our ancestors evolved with perennial warmth and were still able to thrive in regions with actual seasons means we can handle just about anything.” – Mark Sisson

    Without disagreeing with your overall premise, I would have to submit here that the main way that migrating humans “handled” the climate shock was to die en masse while a lucky few with positively adaptive gene variants carried on and reproduced. Hence the wide variation in human form. Ancestry is going to have to play *some* role in how each of us best thrives, though I still agree that we can each thrive on a wide variety of natural food inputs, and thrive *very well* on the common Paleo diet to which we’re all rooted.

    1. “… the main way that migrating humans ‘handled’ the climate shock was to die en masse while a lucky few with positively adaptive gene variants carried on and reproduced”

      The same happened during the rise of agriculture. Does this mean we are adapted to it? No, merely that we can tolerate it.

      1. Well, other than the fact that the process of populating new continents beyond Africa occurred over a time frame substantially longer than 6000-10,000 years, your retort didn’t address my point which is that individuals can’t simply “adapt” to new conditions with instantaneous physiological transformation. In this context “adaptation” equals “natural selection”.

        1. In the light of evolution both environments are new. We are practically the same as we were before these environments were a pressure for adaptation.

          Claiming to be better adapted to a glacial diet than to a tropical African paleo diet because of your ancestors is, at some level, parallel to claiming that an Italian is better adapted to eating grains than to eating paleo. That last statement is just meant to be thought provoking, I don’t really believe the two can be compared that way, but I do emphasize that 100,000 years is still little time when compared to our complete evolutionary history, and that our species was already defined by the time that happened.

          I think a better explanation of why some people are better “adapted” to a glacial paleo diet might be more related to the damage that has already been done by eating non-paleo than to ancestry.

          At the end it doesn’t matter, if it works for you there is no need for justification.

        2. I never made any of the claims you’re refuting. I made the points that a) species level adaptation doesn’t translate into organism level adaptation and b) personal ancestry logically has to have some measurable relationship (of any magnitude) to optimal dietary conditions. These are both sound premises so I don’t really understand the purpose of your argument. Your emphasis on glacial eating is also mystifying. I was making a general case that could be equally applied to a NW Euro eating a fat heavy diet or a Kitavan eating a carb heavy diet. I wasn’t arguing for the acceptance of my personal eating habits.

  4. I dont know if you can answer this, but someone told me more than once that if you live in a very humid climate, that the scale will be heavier on more humid days than less humid ones?

    true or false?

    1. Well generally we zero our scale before we step on it. So the weight of the air on the scale is accounted for. That said, on humid days there is more water in the air, and water had weight, so it could be true.

      Air pressure is around 15 pounds per square inch normally (a little under). That means every square inch of your body and the scale has 15 pounds of air pressing it down. But this doesn’t really matter because we zeroed the scale before hand to account for that weight.

  5. Great post! It had occurred to me that the way people seemed to be thinking about “Grok” was weighted towards a northern bias, and this post provides a nice counterbalance.

  6. Excellent series of posts, really thought provoking. I think you have really hit the nail on the head with this final one, and yesterday’s too. What makes us truly human is the infinite ways in which we have been able to adapt. Keeping it real, not processsed, keeping it simple, not over complicating things, that’s the crux.

    Thanks, I can’t tell you how much you have changed my life!

  7. Love the series…but can I ask one thing…you keep referring to “Big Ass Salads”..but by eating them, that’s what we are most likely to avoid!

    1. rats…I meant to put a big smiley on that last comment. So here it is! 🙂

      1. It took me a second to figure out what you were talking about…losing the Big Ass by eating salads…funny!
        My wife and I have been doing the BAS for 3 weeks now and love it! I don’t have to cook as often because my leftovers from dinner no longer have to be part of my lunch the next day.

  8. Mark, speaking of East Africans, how do you reconcile your “Chronic Cardio” theory with the “Born to Run” theory? According to Prof. Lieberman at Harvard, chronic cardio at some level accounts for our evolutionary development into man…

  9. One of the things I like the most about your writing is the sense of balance. You never take the idea of primal beyond the point of being reasonable. As you say, the idea is a starting point only.

    Just because our ancestors didn’t have something doesn’t necessarily mean that we should deprive ourselves, but when it comes to food, I think caution is the order of the day. It’s best to eat things that you can tell what they are by looking at them, as opposed to “edible food-like substances” as Michael Pollan calls them, like Twinkies. It’s not the fruit of the Twinkie Tree is it?

    I think all hunter gatherer societies experienced periods of relative abundance and relative deprivation, but without the start famines that characterizes agriculture. I remember reading about how Kalihari bushmen continued to eat full meals while working two hours a day on food gathering in the depth of a three year drought, while the local ranchers were all going on government assistance. While the bushmen weren’t necessarily eating their favorite foods, their knowledge of the are gave them access to a more stable food supply, immune to the type of shock that can kick our monoculture teeth in.

    “Stuff like refined sugar, vegetable oils, grains, and legumes, everything else is just fudging with the margins.” I completely agree with this. These things are in many ways both the foundations of our great success as a species and the causes of our society’s most troublesome diseases.

  10. “Could a Native American grow old and strong on the modern Primal hybrid eating plan of Big Ass Salads, omelets, and crock pot recipes? Sure, why not.”

    Hell yea… I ate an omelet yesterday (well, scrambled eggs with veggies and bacon), just finished my big ass salad for lunch about 2 hours ago, and for dinner there is a soup with chicken, dill, and many other veggies for dinner!

    How about that… I LOVE it 🙂

  11. well, what this about big ass salads? im almlost a vegetarian,eating a family sized salad, and what?, where’s the loss?, still waiting months later…

  12. Hi Mark: Now that you’ve finished your series of seasonality posts (which I’ve enjoyed) how about re-posting some of the most important posts like the PB Definitive Guides from June 4th and July 30th, 2008, and the definitive guides to proteins, fats, etc. I know they are all available if people search for them but I think it’s time for the basics to be highlighted again, especially for folks new to MDA. It never hurts to hear the basics over again, and even us oldsters may pick up a few pointers that we’ve forgotten.

  13. I think a big proportion of the paleo community is misguided when thinking about cavemen in harsh winter climates. In reality that cold, harsh, winter environment is almost as new to us as grains. Thanks for making a post about this, maybe some other people will take it into consideration when shaping their diet.

    I am doing a tuber experiment myself, so this post comes nicely (as some HGs living in the warm African environment surely made use of tubers). Nothing crazy, I keep carbs to 20-30%. I have only seen positive results so far. I increased performance in explosive moves (which are important to me as I play racquetball). I meet my “RDAs” without a problem, which have previously been a problem when I was eating very low carb (only for a couple of nutrients, I was eating way too low carb, not saying it cannot be done, it was just hard for me). I recover faster from my lifts. And the most unexpected of all, I have dropped some body fat and finally got into the single-digit zone!

    At the same time, I am 20 and have not had enough time to completely mess up my metabolism by eating SAD (I am Cuban so I was not even eating SAD initially). I understand it probably wouldn’t work for the older tribe that has a more “damaged” metabolism. But maybe it is something some might be interested in trying.

    1. “In reality that cold, harsh, winter environment is almost as new to us as grains.”

      Modern humans were present in Europe no later than 40,000 years ago based on direct archaeological evidence, which means they must have been there considerably longer. Neolithic culture didn’t make it’s way through Europe until 7000-6000 years ago. Whether 40k years is evolutionarily significant is debatable, but at least the two figures are not in the same ballpark.

      1. When compared to our entire evolutionary history, the two numbers are right next to each other. Our genetic makeup has not changed much in the 200,000 years we have existed anyways. I think this is a point Mark tries to make.

        1. Our genetic makeup should have seen the same variation from 200k to the onset of civilization that it did any time prior. Actual speciation has occurred over less time than that. I doubt that Mark would find 190 thousand years of natural selection to be insignificant, but if he does, he’s wrong.

      2. I agree with you. For any doubters, try reading _The 10,000 Year Explosion_. Evolution did not stop 40,000 years ago, it is an ongoing process.
        That being said, for most of us the big picture remains the same, but (and this is a big BUT) there have definitely been some significant genetic adaptations. I am a living example, as I have the lactase persistence gene. This gene is at MOST only 4,000 years old. A drop in the time bucket, but that’s all the time a mutation takes. I find it highly improbable that there haven’t been other, less specific but nevertheless real changes.
        On another note, cold climates haven’t affected us as much as we might think, because we brought some of the tropics with us – in the form of fire. Having fire in those lovely caves was what made living in a cold climate possible, without the need to genetically change. Our Euro ancestors also figured out how to “steal” animal genes (after a fashion) by tanning their hides and furs and using them for ourselves. Why wait for a gene for fur when you can just take somebody else’s?

        1. Remember that just because you can tolerate milk it doesn’t mean it is good for you. I think the same can be said about other recent adaptations, just because we can tolerate them it doesn’t mean it is “natural” or beneficial.

          I understand your point, and I don’t think there’s much evidence either way. I guess it’s a personal choice, trying it out is the best way to know how much one is “adapted” to the changes the cold climates brought.

  14. Thanks Mark – I’ve read the seasonality series with great interest.

    I certainly try to eat fresh and in season. This is usually less expensive and doesn’t affect my meal choices but it is hard not to buy frozen berry mixes etc year round. I don’t think there is much harm in eating frozen fruit/veg that is not in season, apart from the fact that it isn’t going to be quite as fresh as when it was picked.

  15. Great article!

    I’m so glad to see the bit about who, exactly, was living in Europe during the ice age. I keep seeing people making judgements that we should eat only meat based on the idea that “we made it through the ice age, didn’t we?” and then pointing to the Inuit who ate a diet that simply cannot be replicated, not even close, in the lower 48.

  16. The “tendency to hone in on the European hunter-gatherer experience for guidance in all things dietary” in the Primal-Paleo community is IMO attributable to it being In my observation (I could be mistaken) currently being a phenomenon peculiar to Europe and countries of European origin such as the U.S., Canada etc. This may well change in the future.