Pandas, Humans, and Evolution: What is the state of nature?

Pandas are notoriously picky eaters: they only eat bamboo. But a recent study has found that pandas are actually poorly adapted for their diet. Pandas apparently evolved from omnivorous bears. Whether as a consequence of a decrease in the availability of prey or an increase in bamboo, however, they shifted to an exclusively vegetarian diet about two million years ago. But they did not evolve the kind of digestive apparatus usually seen in herbivores. They have a carnivore’s digestive system, and they lack the gut flora required for extracting the maximum amount of energy from plant-based sources. Hence, perhaps, the fact that they spend so much of their time eating.Why didn’t pandas evolve a more suitable digestive system? There are at least two possible explanations. One is that evolution can only work with the mutations that happen to occur: it can’t select for genetic changes unless they happen, by chance. The second reason is that evolution will only occur if there are pressures favoring one trait over another. Pandas had few predators and the strategy of eating all day worked well enough for them. There was no selection pressure in favor of greater efficiency.

Why is this interesting? I happen to think it’s intrinsically interesting, but it has some relevance for broader issues too. It is quite common these days to come across claims about the kinds of activities or lifestyle to which human beings are adapted. You come across these claims in the popular media and in academic contexts too.

A prominent example in the popular media concerns the ‘paleo’ diet. Proponents of the diet claim that it is best for us because we are adapted to the kinds of food that our Paleolithic ancestors ate. In more academic contexts, the same sorts of claims are sometimes put forward, for instance, by proponents of the ‘mismatch’ theory of mental illness. The claims of such theorists is that we are adapted for a particular kind of life but live a very different one, and that mental illness arises from this mismatch. For instance, it has been claimed that depression arises, at least in part, from the supposed fact that human beings are adapted to living in social groups with around 100-150 members, and the fact that we are acutely attuned to our social status. Today, most of us live in conurbations with millions of members and are unable to place ourselves securely in the social hierarchy; depression results.

I don’t want to dismiss the value of these kinds of hypotheses entirely. We are a distinctive kind of animal with distinctive traits, and some environments are very likely easier for us to flourish in than others. However, too often (as in the Paleo diet fad), people move too quickly from noting that certain conditions obtained in what is sometimes called the environment of evolutionary adaptation – the environment in which modern humans developed from earlier ancestors – to the conclusion that conditions like those are normative for us, in some sense: we will do better in those conditions than others. That ignores several facts, as the panda case illustrates.

First, while it may be true that we are not well-adapted to, say, city living, it doesn’t follow that there is some other way of living to which we are better adapted. Evolution patches together compromises: it doesn’t optimally fit an organism to an environment. Pandas are not well-adapted to eating bamboo; that doesn’t entail that they are better adapted to eating meat. Evolution doesn’t care about them, or us, and doesn’t guarantee that there is any environment to which they or we are well-adapted. We are not likely to find ourselves feeling more at home living a hunter-gatherer lifestyle. Second, even if we discover that there is some environment to which we are best adapted, we have no reason to think that we can’t alter ourselves or our physical and social environment to be better off than we would be in such an environment.

Pandas are an old species, compared to human beings. But they are relatively poorly adapted to the environment in which they find themselves. Obviously they are well enough adapted; otherwise they would have gone extinct. Our ancestors, too, must have been well enough adapted to the conditions in the environment of evolutionary adaptiveness for survival. But good enough is all evolution strives for. Its up to us if we want to do better, and while our evolutionary history can provide useful information for that project, it has no special normative force for us.

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14 Responses to Pandas, Humans, and Evolution: What is the state of nature?

  • Anthony Drinkwater says:

    Rather boringly, I agree : thank you for this dose of well-argued sense !
    (Sad, but true, that most people (myself included!) only bother to comment when they disagree ….)

  • Alex says:

    If we assume that humans have not evolved much since the beginning of civilization, then taken literally, this does not seem to make sense. But it is an interesting way to state your values.

    • Neil says:

      Why doesn’t this make sense, Alex? Nothing here is meant to be taken in any sense that is not literal.

      • Alex says:

        Because humans could not have evolved since the paleolithic in the kind of sub-optimal way that the pandas did, since humans apparently have not evolved much at all. Right?

        • Neil says:

          It doesn’t matter *when* the biggest changes in human evolution occurred. The question is whether there is any particular environment to which humans are uniquely suited by evolution. My claim is that though there are certainly better and worse fits, we have no reason to expect the fit to be all that good. Evolution doesn’t work like that.

          It is controversial how much evolution we have seen over the past 10-15 thousand years. The answer is certainly not “none”. The most famous example of recent human evolution is the development of lactose tolerance in Eurasia.

          • Alex says:

            Okay. To clarify, can you give one candidate for how humans might have evolved in a sub-optimal way?

            • Neil says:

              The argument concerns what we should expect: should we expect a good fit between any particular environment and our suite of dispositions? I pointed to evidence that human beings are adapted to living in small groups (100-150 members). That may be true (there is a reasonable amount of evidence). It doesn’t follow that were we to live in such groups we would feel happier, as some have claimed. because its quit likely that that reflects a compromise.

              Here’s one more concrete example which comes to mind. What political system are humans adapted to? The answer seems to be “none”. Hunter-gatherer groups were (and are) remarkably egalitarian. They made decisions collectively, and though they sometimes had a chief figure, that figure had to negotiate every decision and couldn’t impose his will (I use ‘his’ advisably: there is an ongoing debate about the degree of gender inequality in these groups). So many anthropologists believe that in the EEA we lived in egalitarian bands. So are we adapted for egalitarianism? No; rather these bands arose from the fact that our ancestors hated to be dominated. They didn’t value or like equality; rather, they hated being dominated more than they hated equality. We may have the same dispositions. If that’s so, we shouldn’t expect to find a political system which makes us happy; rather (since we are social animals and living in community is not optional for us) the best we can do is to find the one that makes us least unhappy.

              • Dave Frame says:

                Neil wrote: “Here’s one more concrete example which comes to mind. What political system are humans adapted to? The answer seems to be “none”.”

                In-group relations in prehistoric societies may have been part egalitarian and part hierarchical (depending on the circumstances) but inter-group relations have usually been characterised by anarchy – not always bloody but certainly rivalrous. I vaguely recall Azar Gat’s book War in Human Civilization pointing at evidence that suggested some huge fraction (20%??) of adult men in prehistoric periods died violently – presumably much of this was in-group, though much was inter-group, too. That was the context in which we evolved, but it does not mean that it is normatively ideal, obviously.

                Nor does it mean that the payoffs to violence in the modern era remain as they were. The development of suites of norms and institutions that solve the security dilemma allow for specialisation, and for high returns on investments in human and social capital. Technology and public health have created less precarious existences and have made easier the creation of surpluses that can be (and are) widely shared. And so on. These changes mean (e.g. in my neck of the woods) invading the Kapiti Coast to obtain additional resources looks less attractive than working with Kapiti Coasters to co-create things of value that we can sell for mutual gain.* The returns on clever ideas, adding value and collaboration have never been higher, and those on violent invasion have (in most parts of the world – there are exceptions) never been lower. But that does not mean we are adapted to the new environment (nor does it mean that the current state is the normative ideal.

                *This was less obviously the case 200 years ago for residents of the greater Wellington region, where raiding and tribal rivalry was a strong feature of social interaction.

          • Alex says:

            Of course, you did mention the paleo diet and so forth, but I am wondering why we might suspect these in particular.

          • Alex says:

            Re your 10:51 reply: So the analogy here is “humans don’t like being dominated”:”pandas don’t have efficient digestion”::”humans now live in community due to adaptations”:”pandas now eat bamboo due to adaptations”

            Okay 🙂

  • Sarah says:

    Pandas are quite fat though… Maybe they should go paleo?

  • Ionizer says:

    Yeah it is misleading to think that just because a species evolved in an environment, this would also be the optimal environment for it health wise. But it is equally misleading to assume that evolution can provide us no useful information whatsoever. If we take for example human breast milk, we can make the assumption that since infant mortality has been high, selection pressures to optimize its healthfulness would have been strong. This would lead us to believe that in order to make the healthiest formula for babies we should mimic the composition of breast milk as close as possible. This has not been done though, some components of breast milk, like saturated fat and cholesterol, have been considered suboptimal for health. This lead scientist to produce infant formulas with lower amounts of cholesterol, which was assumed to produce health benefits. What in fact was found out by empirical studies was that formula fed infants had higher mortality rates than breast fed ones. Later science has corrected itself and figured out that cholesterol also has immunological functions and sufficient dietary sources of it reduce deaths caused by infections. One could argue that an evolutionary approach would have saved many and improved the long term health of even more babies, and thus made this whole large scale human experiment redundant.

    • Neil says:

      That’s an interesting challenge. I’m not convinced, though. From the fact that breast milk is high in cholesterol – call that fact H – we can infer that one of the following facts is the case:

      1. H was adaptive in the EEA and continues to be adaptive today.
      2. H was adaptive in the EEA but is no longer adaptive today.
      3. H is a byproduct of some other fact that was itself adaptive.

      Scientists though that 2 or 3 was more likely than 1; if you’re right (I am assuming you are), they were wrong. But was the assumption unreasonable? I don’t think so. First, byproducts of adaptations are common. Second, with regard to our eating habits we routinely discover that hypotheses like 2 are the case. We are evolved to find sweet and fatty foods tempting, because those tastes were adaptive in the EEA. But they are highly maladaptive today.

      I agree that evolutionary hypotheses are always worth exploring (finding that something seems to be true of us is a reason to explore whether that fact was adaptive in the EEA). I also agree that the finding that something was adaptive should lead us to consider whether it is still adaptive. But I think its hasty to move from the discovery that X is the case to the conclusion that X is adaptive in the contemporary world.

      • Ionizer says:

        Thanks for the response. In hindsight the best solution would have been to compare different formulas with real breast milk, on either human or animal models, before launching a population wide experiment. Yet being cautious about cholesterol because empirical studies have detected problems with it was also reasonable, as you point out.

        Our taste for sweet foods evolved in an environment where sweet food was scarce, but contained nutrients that are necessary for good health. A person in the modern world with an aversion to sweet tastes would also end up nutritionally deficient without supplementation, because he would not eat fruits for example. This taste can thus not be entirely maladaptive. The case with fat could be similar. Cravings for fatty foods are common on very low fat diets, while food that is too fatty is not tasty either. This suggests that our taste evolved to prefer a certain composition of macro nutrients, not any harm full one as a evolutionary byproduct.

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