Should you try to live like your ancient ancestors?

Key takeaways

• Evidence about our ancient ancestors’ behaviors can’t tell you what you ought to do today. It can hint at behaviors that might have adaptive benefits, but any attempt to straightforwardly derive prescriptions for modern behavior will likely involve oversimplification.

• These five questions can reveal weaknesses in this kind of argument: Is there assumed uniformity in past behavior? Do we really know what happened? Was it optimal for then and now? Can modern behavior match the ancient one? And does the argument unjustifiably shift from ‘is’ to ‘ought’?

• Just-so stories’ are intuitively appealing explanations that sound plausible but go beyond the evidence. In debates about living like our ancestors, just-so stories can appear in appealing narratives that leap from observations about the past to bold claims about what we should do now. You can use the questions in this article to avoid getting duped by such stories.

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Academics have their own unique brand of insults. For example, when a scientist says that someone’s theory is “Not even wrong,” they’re saying that it’s so confused, poorly-reasoned, meaningless, or empirically untestable that it doesn’t even make sense to ask whether it’s right or wrong. 

Another popular pejorative phrase used by academics comes from the title of a novel by Rudyard Kipling, and it can teach us some lessons about what makes a good theory and how to think about arguments that go from “Our ancestors did X” to “You should do X too.” That’s the subject of this article. We’re going to help you by giving you tools to evaluate those kinds of arguments. But before we get to that, can you guess the insult?

Kipling’s novel is a collection of bedtime stories he told his daughter, who wanted to know how animals got various traits. Kipling invented fanciful nonsense explanations that might sound plausible to a child’s mind, but which are obviously not substantiated by real evidence. How did the elephant get its trunk? A crocodile bit its nose and pulled and pulled and pulled! How did the rhinoceros get its wrinkly skin? A man made it so itchy with cake crumbs that it scratched itself until it became wrinkly. And so on.

The novel is called Just So Stories, and the key features of Kipling’s fanciful tales are that they are imaginative, plausible-sounding (to kids, at least), and not at all supported by evidence. Compelling but unfounded. That’s why, when the paleontologist and evolutionary biologist Stephen Jay Gould was criticizing other researchers for going well beyond what empirical evidence supports, to invent plausible-sounding explanations for why evolving certain traits might be advantageous, he accused them of inventing their own just-so stories and dismissed the theories as “facile speculation.” Gould wasn’t the first to use the phrase ‘just-so stories’ as a kind of insult for a theory, but his usage seems to have done the most to make it popular.

So, if you want to show disdain for a theory that starts with some observations about our ancient ancestors and relies on an appealing narrative to leap to wildly-speculative conclusions far beyond what is supported by those observations, you now know something you can say: “Sounds like a just-so story, to me.” 

But there’s a problem: It can be hard to tell which are the just-so stories and which are the well-founded, reasonable theories. That’s what this article aims to help with. 

Examples of Arguments From Ancestors

You might wonder: How common is it that people claim that because our ancient ancestors did a certain thing, or lived a certain way, we should too? If they’re quite rare and quite low-stakes, then it might not be very important to be able to make accurate judgments about them. Well, the answer is that they’re all over the place. But, since examples might not immediately spring to mind, we’ve picked out some controversial ones for you:

1. It is often argued that natural selection is a fundamentally competitive (not cooperative) process, so our fittest ancient ancestors must have been selfish and this means that human nature must have evolved to be fundamentally selfish. Some even go further, saying that this provides moral justification for selfishness and greed.

2. Some people argue that our male ancestors incurred much less risk from reproducing than our female ancestors and therefore ancient men were more promiscuous than ancient women. This becomes an argument from ancestors when it is used to argue (as many do) that this justifies certain modern dating behaviors and prescriptive norms.

3. In the health and wellness industry, there are countless examples of arguments like this. For example, one popular claim starts with the dubious premise that most of our species’ evolutionary history was spent in sub-zero temperatures, and concludes that we are therefore not well-adapted to our modern lives and we should regularly expose ourselves to extreme cold, in order to reawaken natural strengths and immunities.

4. Advocates of certain diets claim that their diets are justified or superior because they match what our ancient ancestors ate.

Do you find any of these arguments persuasive? They’re each very divisive, with many people both for and against them. So, how do you tell the good from the bad? 

How to Spot a Bad One

When you encounter an argument like the ones listed in the previous section, there are useful questions you can ask, to help you figure out where there might be some weaknesses in the argument. We'll show you how to use these useful questions in the context of one specific claim: that you should eat what our ancestors ate. First, three quick caveats: 

1. As with all arguments: the fact that an argument relies on flawed reasoning doesn’t entail that its conclusion is false, but it probably won’t increase your willingness to believe that conclusion. For instance, someone could argue that seat belts save lives because “I wore one last week and didn’t die in a car crash.” Well, they're right that seat belts do save lives, but that's a terrible argument in favor of it on multiple levels.

2. We hope it’s clear that we’re not trying to tell you what to eat. Ultimately, if you feel good on any given diet and it is aligned with your values, then you may well have found something that works well for you. This article is about the quality of the reasoning in certain kinds of arguments, not the accuracy of the conclusions.

3. We've done our best to report the science as we understand it, but we could be wrong. We are not experts in fields like archaeology or paleoanthropology or human nutrition. The most important thing is that the questions we outline here are useful for evaluating the strength of these kinds of arguments, regardless of what the underlying science turns out to show. If you spot any errors please feel free to send us an email to let us know (including a link to robust evidence).

Here's a framework for evaluating whether we should try to live like our ancient ancestors, applied to the claim that we should today be eating a diet intended to mirror the diets of our paleolithic ancestors (e.g., the paleo diet or the carnivore diet, which are not the same thing, but which are both argued for in this way): 

Question 1: Does the argument assume there’s just one primary way our ancient ancestors behaved?

When it comes to arguments about what diet we should eat, this manifests as the assumption that there’s just one way our ancient ancestors ate. In reality, there is rarely a single way that all humans do anything (at once, or across time), and as expert Peter Ungar has pointed out: “Human evolution is a work in progress, and diets likely varied along a continuum in both time and space.” There is evidence that that our ancient ancestors ate an extremely diverse set of foods. This suggests that humans are highly omnivorous and ate what they had access to (if sufficiently hungry, people will eat anything that provides nutritional value that they believe is safe to eat), and what was available to eat varied a great deal by region and time period, so there is reason to be skeptical of claims that there was a single “diet of our ancestors”, or anything close to that.

In fairness, more nuanced advocates of ancestral diets acknowledge this and make the stronger and more defensible argument that we should be cautious of eating a lot of any food that none of our ancient ancestors regularly ate. Of course, just because none of our ancient ancestors ate a food doesn’t guarantee it’s harmful, but that does seem like reasonable grounds for taking extra precaution, since if our ancient ancestors didn't eat any significant quantities of it, there's a lower chance we're biologically adapted to it.

On the other hand, it's not true that just because some of our ancient ancestors had something in their diet, it was healthy. Due to low availability of food, some groups may have lived on food that provided calories but was otherwise bad for them (e.g., slightly toxic) for a substantial amount of time (at least, until other food sources became available or until they developed adaptations to those foods). But if many of our ancient ancestors commonly ate a food for hundreds of thousands of years, it is reasonable to assume it isn't acutely harmful for humans living those sorts of lifestyles in the quantities they typically consumed.

In general, it’s worth reflecting on how narrowly or uniformly an argument from ancestors portrays human behavior. Does the argument assume limited variation or an unusually high degree of homogeneity? If so, that doesn’t mean it’s definitely wrong, but we’re suggesting that it's a reason for pause.

Question 2: Does the argument assume we accurately know what our ancient ancestors did?

We know less about what our ancient ancestors did than most people think. This is true for all sorts of things, including for their diet. A lot of figuring out what they ate involves inferences from indirect evidence, such as looking at the patterns of wear on their teeth or stable isotopes in remains. Piecing these together gives some broad idea of their diets, but leaves a lot of details unknown (such as macronutrient ratios).

However, methods of diet reconstruction are continually improving, and there are some patterns about our ancient ancestors' diets we can be somewhat confident in, such as that their diets were likely often high in fiber (though this likely had exceptions), and that they probably mostly didn’t consume large quantities of sugar or simple carbohydrates (with some potential exceptions as well, like forager groups that had high availability of honey or naturally sweet fruits). It’s also of course true that they didn’t have the ability to create the ultra-processed foods we eat today. 

In general, our knowledge of what our ancestors were up to is limited to what can stick around to be discovered by scientists. This means that some theories are necessarily harder to support with evidence than others, and some questions likely just can’t be answered. If an argument from ancestors appears to be overstating how much is known about our ancient ancestors, that could also be a mark against it.

Question 3: Does the argument assume that the behaviors that were optimal for our ancestors’ survival are optimal for ours now?

Heart disease, cancer, strokes, and dementia, which are some of the ailments we’re most likely to die from, didn’t exert much evolutionary selection pressure on our ancient ancestors. This is because our ancient ancestors usually died earlier from other things (like infectious disease, injury, and starvation), and because evolutionary pressure is much weaker after childbearing age than before it. If a person dies before having children, their genes don’t pass to the next generation. But if they die 20 years after having children, their genes are still likely to live on (though their children may miss out on some help, which could provide a minor detriment to survival). So even if our ancient ancestors ate what was optimal for their survival, that’s not a strong argument that those foods are the best for our longevity today. If we were to conclude that a diet was optimal for the survival of our paleolithic ancestors (which is hard to do), that would only be modest (rather than strong) evidence that the food is optimal for longevity after age 50.

A fact further complicating the story is that some diet-related genes are widespread now that were not widespread among our ancient ancestors (e.g., genes related to lactase persistence), so we may even process food in certain meaningfully different ways than they did. We usually think of evolution as taking hundreds of thousands or millions of years, but if a gene already exists in a population (but is quite rare), it can become common quite quickly if it provides a strong survival advantage (e.g., growing exponentially in a population until most people have it).

Another version of the pro-ancestral diet argument says that we should eat like hunter-gatherers because hunter-gatherers didn’t often get the chronic late-life diseases prevalent in our society. This argument also has some challenges, though. First, hunter-gatherers had much shorter average lifespans, and it’s hard to know what hunter-gatherers died of (but insofar as they died young, of course they didn't get chronic late-life disease). If we consider only modern hunter-gatherers, and try to generalize from them, then we might as well study all cultures that have low rates of chronic late-life diseases (because there’s no reason to focus just on hunter-gatherers in that case). A challenge with doing so, however, is that these cultures differ in many ways from each other (foods eaten, macro nutrient ratios, exercise, sunlight, genetics, and many more), and it’s hard to isolate specific variables to figure out which are driving less chronic late-life disease. While we can get hypotheses from this kind of data, randomized controlled trials allow for much cleaner isolation of variables. 

It’s likely not a surprise to you that things have changed a lot over tens of thousands of years. In general, if an argument relies on the idea that what was advantageous back then must be advantageous now, that is a weakness in the argument.

Question 4: Does the argument assume that a certain modern behavior closely resembles what our ancient ancestors did?

Suppose you wanted to adopt a diet that matched what our ancient ancestors ate. How well would you be able to do so? One hurdle is that the animals humans eat today were domesticated and selectively bred, and differ dramatically from the wildlife at the time of our ancient ancestors. The same goes for fruits and vegetables - they barely resemble the fruits and vegetables that our paleolithic ancestors had available. Evidence suggests that some groups of humans were even eating grains 100,000 years ago, long before the “agriculture” period.

Some advocates of ancient ancestral diets take these arguments into account and suggest eating game meats in particular, and including organ meats in their diet. But for some reason, they seem to typically focus on finding meat that’s similar to what existed hundreds of thousands of years ago, and not, for instance, tubers and fruits (or insects, for that matter).

One thing that’s certain is that some foods we eat today that didn’t exist in our ancient ancestors' time are unhealthy for us (e.g., deep-fried Oreos). But that’s not the same claim as saying that for optimal health, we should attempt to match our ancient ancestors’ diet. It’s reasonable to be more cautious about foods that none of our ancient ancestors were likely to have encountered in meaningful quantities, but that’s not the same as trying to use their diets as a template for ours.

Question 5: Does the argument slip from ‘is’ to ‘ought’?

Many arguments from ancestors jump from claims about how our ancient ancestors did behave back then, to prescriptions about how you should behave today. But is that jump justified? The Enlightenment philosopher David Hume famously thought not. He argued that no matter how many facts about the world you point to (‘is’ statements) you can’t validly derive a moral or prescriptive claim (an ‘ought’ statement) from them alone. This is sometimes called ‘Hume’s Law’, or ‘the is-ought problem.’ This means that, in order to justify a claim about what modern people should do, an argument from ancestors needs more than just a description of ancestral life: it needs an ought statement in it somewhere. And that means it’s going to rely on values.

People who argue that because our ancestors ate a certain way, we ought to eat that way too, might be valuing all sorts of things, such as:

• Health: If they think it’s healthier to eat that way and more healthiness is good.

• Naturalness: If they think that acting as our ancient ancestors did is more natural and naturalness is good.

• Tradition: If they think that our ancient ancestors lived in some kind of golden age that it would be good to return to.

But even if you agree with all claims about how our ancestors lived, their argument will only be compelling to you if you share the value they’re appealing to in their argument and it’s not overridden by other values you hold. For example, you might be someone who values health and agrees with all the health claims made by advocates of diets that mirror our ancient ancestors’, but if you also value reducing animal suffering enough, then that value might still lead you to reject the conclusion that you should eat as advocates of those diets recommend.

So, in general, when you’re encountering an argument from ancestors, you can ask: Is this argument telling me I should or should not behave a certain way? If so, what is it valuing? And do I value the same thing enough to agree?

For an informative discussion about what our ancestors ate, we recommend this interview that Gil Carvalho conducted with Dr. Peter Ungar.

Things to Remember

Ultimately, evidence that our ancient ancestors did X might provide some evidence that doing X has adaptive advantages. But it’s very, very far from decisive evidence and it has little bearing on the question of whether you should do X. The questions we’ve discussed here can help you to evaluate arguments from ancestors, regardless of what they’re about. 

Those questions are:

• Does the argument assume there’s just one way our ancient ancestors behaved? If so, how true is that, really?

• Does the argument assume we accurately know what our ancient ancestors did? If so, how accurate is our actual knowledge?

• Does the argument assume that the behaviors that were optimal for our ancestors’ survival are optimal for ours now? If so, do we really have good reason to believe this?

• Does the argument assume that a certain modern behavior closely resembles what our ancient ancestors did? If so, how close is that behavior to the behavior of our ancestors, really?

• Does the argument slip from ‘is’ to ‘ought’? If so, can that really be justified, and do I share the values that it relies on?

If one or more of these questions casts doubt on the argument, you might be dealing with a just-so story - a tidy tale that can sound like robust science, but isn’t.

As a reminder: we’re not saying you shouldn't eat any particular diet. If you feel good on such a diet and it is aligned with your values to eat it, then you may well have found something that works well for you. The truth is that while some diets would be unhealthy for everyone (such as one very high in mercury), what works best diet wise varies from person to person, based on factors like their lifestyle, environment, income, preferences, genetics, and values.

If you want to dive further into evaluating arguments, why not try our Can You Detect Weak Arguments tool!

Launch Can You Detect Weak Arguments?