Poll: which ecological and evolutionary “laws” actually deserve that title?

There’s a lot of discussion in the literature about the question, “Do ecology and evolutionary biology have scientific laws?” One pragmatic (and slightly flippant) answer to that question is, “Yes, of course they do, except sometimes they’re called ‘rules’ rather than ‘laws’: Kleiber’s law, Dollo’s law, Bergmann’s rule…” That is, ecology and evolutionary biology do in fact have many empirical claims that everyone calls “laws” or “rules”. So whatever you think about the existence and nature of ecological and evolutionary laws in theory, you can’t really ignore the fact that, in practice, there is a thing called “Kleiber’s law”, a thing called “Dollo’s law”, etc.

Or to be more precise, there’s an empirical claim called “Kleiber’s law”, an empirical claim called “Dollo’s law”, etc. But those claims might be false! Or, you know, usually false, or sometimes false, or false in some circumstances. In which case, “law” (or “rule”) seems like a misnomer. At a minimum, surely any empirical claim that deserves to be called a “law” had better be true! (or true enough, or true in a sufficiently wide range of circumstances, or etc.)

Further, there might be disagreement over whether some purported “law” or “rule” is actually true (or true enough, or etc.). One might think this couldn’t possibly be the case, at least not for claims on which there’s a fair bit of data. After all, isn’t science supposed to be data-driven? To which, oh you sweet innocent child. ๐Ÿ™‚

So, I got to wondering: how many of the things that ecologists and evolutionary biologists refer to as “laws” or “rules” are widely agreed to be true enough to deserve the title “law” or “rule”? That is, I’m interested in the truth of these claims–but I’m also interested in what ecologists and evolutionary biologists think about the truth of these claims. Hence this poll!

The poll below lists a bunch of ecological and evolutionary claims commonly referred to as “laws” or “rules” (or something else, in a few cases). Apologies if I omitted your favorite named rule/law. I didn’t want the poll to get unwieldy, so I restricted attention to what I felt like were the most widely familiar laws/rules. Also, I deliberately restricted attention to purely empirical rules/laws, which is why the competitive exclusion principle and Hamilton’s rule aren’t listed. For each named rule/law, please indicate on a 3 point numerical scale whether or not you think it’s true (or true enough) to be called a law/rule (3), rarely/never true (1), or somewhere in the middle (2). If you have no opinion, just skip the question. But if you have a tentative opinion please indicate it; this isn’t a poll only of confident experts. There’s a question at the end for you to indicate your level of expertise regarding each law/rule.

p.s. You thought I was going to miss the opportunity to make an “I fought the law” reference didn’t you? YOU THOUGHT WRONG. Here are four of them! Plus a bonus poll question. ๐Ÿ™‚

36 thoughts on “Poll: which ecological and evolutionary “laws” actually deserve that title?

  1. It’ll be interesting to see the results of this. In our search for generalities I do wonder if, as a community, we’re ignoring laws that are so obvious that they don’t have names and are hardly recognised as laws, and yet are fundamental to ecology and evolution. For example:

    – all living things require a source of energy
    – all living things are the product of evolution*
    – all living things interact with other species at some point during their life history**

    Whenever I hear someone say “there are no laws in ecology and evolutionary biology” I point them to these principles, which are at least as fundamental as any laws in physics.

    *I suppose we could called this the Darwin-Wallace Law, but it’s hardly ever expressed in those terms – a quick Google of that phrase turned up half a dozen uses of it.

    **If this one’s up for grabs then I’m happy to call it “Ollerton’s Law” ๐Ÿ™‚

    • I thought about including your second one as a “control”, to see if there’s any statement that everyone would agree is a law. Not sure why I didn’t, but now I wish I had.

      • So it begs the question of what is a scientific “law”. Here’s one definition I scraped off the web:

        “A law in science is a generalized rule to explain a body of observations in the form of a verbal or mathematical statement. Scientific laws (also known as natural laws) imply a cause and effect between the observed elements and must always apply under the same conditions.”

        Those last 7 words seem to me to be crucial here – there are exceptions to all of the “laws” in your poll, but not to the three principles I set out.

      • Yes, some variability in poll responses no doubt reflects variation among respondents in how they define “laws”. In particular, does a claim have to be exceptionless to be called a “law”? If you think so, then you probably don’t think that any of the claims in the poll are “laws”.

    • All laws in all fields are conditioned on certain assumptions .The law of gravity is only true if there is no air resistance, electro-static forces, etc. Ecology just has a few more things to condition on than physics! So to me something is an ecological law if I have a strong prior that it is true and am surprised and interested when it is not.(And yes that is an entirely empirical definition – causality not needed for a law and don’t believe it exists in many physical laws – e.g. law of gravitation).

      • Hmmmm, I’m not entirely convinced that your physics law example is the same as ecological/evolutionary examples. Gravity is still acting on all mass in the universe, all the time. It’s just that under some circumstances it’s acting less strongly. We can’t say the same for the something like Bergmann’s Rule – there’s no evidence that all animals will get larger at the poles unless something acts to stop that body size increase, is there? In some cases they do, in some cases they don’t, for a variety of reasons including physiological trade-offs where there is no advantage in being larger.

      • Bergman’s a bad example for me because I don’t think its particularly supported empirically.

        But mostly I think we agree – in some cases gravity comes to the fore as the dominant process (and everything else is vanishingly small). Sometimes electrostatic forces come to the fore (tiny particles) and sometimes both may be balanced.

        But I think the same applies to ecology. The forces that cause body size to increase with colder temperature are universal. But sometimes they are trumped by other forces acting on body size.

      • “Bergmanโ€™s a bad example for me because I donโ€™t think its particularly supported empirically.”

        Hey, no trying to influence the poll respondents! ๐Ÿ˜‰

      • I find the discussion of ‘law’ interesting, especially in contrast to laws in physics. I suspect most physicists don’t view Newton’s universal law of gravity at the same level as other laws, and I think they view it simply as the inverse-squared-distance dependence of the gravitational force, which is true even with air resistance (though not true for all stress-energy tensors in General Relativity). I like Jeff’s quoted description of law, and think it boils down to principles which are in some sense always true, and which can broadly explain many observed things, and I think gravity somewhat fails this (due to GR breaking it in some cases), but other physical laws fit this definition perfectly.

        Conservation laws are some of the most powerful, as almost all of physics (and much of its applications in other fields) can be derived from simple considerations of conservation (almost all of my research for instance can be viewed as studying very specific applications of conservation of mass and momentum). In this sense, I see some evolutionary principles as being the only possible candidates for laws in Ecology in terms of both being very useful for understanding phenomena, and essentially without exceptions. But I’m not even sure they are that useful in terms of explaining empirical ecological phenomena, and with things like epigenetics and other foundational shocks in some parts of evolutionary theory (e.g. Denis Noble’s 2013 paper on physiology in evolutionary biology), it is not clear to me what specific aspects of evolutionary theory could be considered analogous to conservation or thermodynamic laws in physics.

      • Hi Andrew; The symmetry that underlies sex allocation evolution is analogous to physical symmetries. half the autosomal genes passed to zygotes come from males and half from females, or a RA Fisher put it…everyone has one mother and one father.

  2. At the moment, there is more consensus about who did the best version of “I Fought The Law” (The Clash) than about any of the laws in the poll. ๐Ÿ™‚

    I leave it to you to decide if that is amusing or depressing.

  3. Shoot, I should’ve asked about “constant connectance” as well as the link-species scaling law. That is, there are competing claims in the literature about what “law” describes the relationship between the number of links in a food web and the number of species. Would’ve been interesting to see people’s views of those competing claims. And interesting to see if people’s views are self-consistent. Like, would we have gotten anyone giving scores of 2 or 3 to *both* the link-species scaling law and constant connectance?

    We do have the EER, Kleiber’s law, and Damuth’s law in the poll, and those are closely connected claims, so it’ll be interesting to see how mutually-consistent opinions of those claims are.

    • Delighted “constant connectance” was mentioned! But aware of the ambiguity of “law,” I called it a hypothesis rather than the “link-species scaling law” it challenged. I love this discussion of laws/rules but with no definitions nor clear examples of a scientific law, it’s rather unclear what the poll results will indicate. A more scientifically productive discussion might address, “What are the most general and successfully (accurate and precise) predictive theories in ecology?” with poll entries for generality, accuracy and precision. “Organisms must consume more energy than they store as biomass” and “Natural selection gives rise to new species” are quite general and I think very accurate but not very precise. Our “niche model” of food webs is very general, quite precise, but only moderately accurate. These are easy suggestions to state but much more difficult to enact. Thanks so much Jeremy for taking a compelling step in that direction!!!

    • Wikipedia informs me that you could’ve simultaneously voted for them, the Dead Kennedys, Hank Williams Jr., Sam Neely, The Nitty Gritty Dirt Band, Oystar, Bruce Springsteen, and La Mano Negra by chosing “somebody else” in the poll. ๐Ÿ™‚

      I hadn’t realized there were so many country versions, but now that I know that it makes sense. The lyrics do seem country to me. Or blues.


      • Also Bryan Adams, H2O, and presumably a bunch more. “I Fought The Law” has to be one of the most covered rock songs ever.

        I share the opinion of most ecologists that The Clash version is the best, but I do really like the Bobby Fuller Four and Oysterband versions. The various country versions all strike me as pretty generic country songs. H2O’s version is interesting; the lead singer’s voice is distinctive, and hearing “I Fought the Law” as New Wave at least makes for a change from all the punk and country versions.

      • There’s got to be a Brit or two reading this blog who knows the Oysterband, of the fine headbanging folk tradition. Something universal about those lyrics and earworm beat that cuts across genre’s

      • Speaking of headbanging British (and Irish) folk, and making a link back to ecology, I wonder if Warblefly (who count, or once counted, ecologists Andy Beckerman, Owen Petchey, and Frank Van Veen among their members) ever covered “I Fought the Law”.

  4. Maybe,”all living things have common ancestry”.
    I think this is a interesting example, because it could not be the case, contrary to Jeff’s propositions which are almost direct consequences of physical laws. Current species could have resulted from several independently events of life emergence. But we have so strong evidences for common ancestry that we always assume it.

    Is the Hutchinson’s fundamental niche a law? Something like: all species reproduction and survival are constrained by environmental conditions.

  5. This list of ecological laws/rules illustrates a problem with the state of ecology. Most of these laws – with a few notable exceptions (e.g. Kleiber’s law, Damuth’s law, Taylor’s power law, species-area curves) – make binary predictions that contain relatively little information. In fact, if we assumed that all of these laws/rules were true, many, maybe most, make predictions that somebody who knew nothing of ecology could make correctly 50% of the time using a coin. It seems to me that, if the sum of information contained in a theory results in predictions that could be made correctly by a completely uninformed person 50% of the time, the theory doesn’t contain much information.
    It’s not that I think we’re getting it wrong – in fact, I gave almost all of these a 2 or a 3. It’s that often, ecological laws/rules make predictions that are so imprecise as to little more than “rules of thumb”. If all we can say about the relationship between species richness and latitude is that richness decreases with latitude, it seems like we’re not saying much.

    • Hmm. I think that’s a little unfair Jeff. You yourself listed several exceptions. And some of the other laws and rules on this list take the form of blanket statements that some state of affairs always (or never) occurs–Dollo’s law, Haldane’s rule… Then there’s Rensch’s rule, which says that the direction of association between two variables is reversed depending the value of a third variable. And then there a couple of laws that say that two variables are independent of one another. So there are actually only a few laws/rules on the list that merely state the direction of association between two variables, and so could be thought of as “coin flips” in some sense.

      As to whether it reflects badly on ecology that so many of these laws are imprecise, well, I’d say two things. One, I’d note Brian’s point, above, that many precise laws of physics only literally hold under very specific and special conditions. Second, I think quantitative predictions are great when you can get them, but if you can’t I don’t think it means you’re somehow not doing science or unable to learn anything.

      • I didn’t intend to suggest that we aren’t doing science or able to learn anything – just that many of the assertions we call laws or rules don’t contain much information. There may be lots of reasons for that and I don’t think the list includes that we aren’t doing science or that we aren’t as good at it as other disciplines.
        But, more on point, I think at least a couple of the examples you cite are pretty close to coin tosses – two variables can only be independent of each other or dependent on one another; Rensch’s law allows for four possibilities rather than two; Dallo’s law is so imprecise as to be nearly trivial. But, there was definitely some hyperbole in the “coin toss” assertion. That said, I think if we went through each of these laws/rules and asked – how much of the entire probability space would be excluded by a prediction made by this law/rule, in many cases, the prediction would be so imprecise as to include most of the probability space.
        Not having quantitative predictions says nothing about whether we’re doing science or whether we can learn but it does say something about how much we know.

      • I agree that Dollo’s law is the vaguest one on the list. Not really the sort of thing that I personally would call a “law”.

  6. In light of the COVID-19 pandemic data, I’m surprised and interested to see that we’ve gotten a respondent who feels that Farr’s law is in fact a law. Of all the rules/laws on the list, that’s the only one that I thought wouldn’t get anyone saying that it’s a law. Looking forward to the future post on the poll results, which will give folks an opportunity to explain why they voted as they did. And I mean that seriously–even if I strongly disagree with how someone voted on Farr’s law (or any other law on the list), I’m genuinely curious to hear their thinking.

  7. How could you have missed the Boris Johnson version?

    My personal favorite is the Dead Kennedys.

    And I guess you were hoping for intellectual comments on ecological theory?

  8. Hi Jeremy; restricting attention to merely empirical ‘rules’ may indeed limit the list, but several comments are actually about theory+empirical [ law of gravity]. Hamilton’s rule, Sex allocation’s product rule, Kleiber’s law [ West,etal] and the marginal value theorem are BOTH empirical and theoretical. Perhaps you could do a second poll on these sorts of ‘rules’? would be interesting to know if folks believe the empirical rule and the theoretical underpinnings.

  9. One of the least important casualties of the pandemic is our poll sample size. Only 43 respondents so far after more than 24 hours. That’s less than a quarter of what we might typically get.

  10. Pingback: Poll results: which ecological and evolutionary “laws” actually deserve that title? | Dynamic Ecology

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