A Very Simple, But Common Mistake

[This is part of my series of posts on the Malthusian argument. You can find an overview with short summaries here, which is updated as I write more posts.]

Let me explain my point first in an abstract form. I will then apply it to the Malthusian and then the Darwinian argument.

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Suppose someone shows that a mechanism X regularly leads to Y.

Now, consider this claim: If you have an example of Y, then it must be the result of X.

This conclusion is obviously false. Why? Y might also be the result of some other mechanism that is not X. So you cannot conclude that it must have been X.

You could only conclude this if only X can result in Y. However, that would need an additional argument that excludes other mechanisms. You could be more lenient: If there were an argument that, while there can be other mechanisms, those are rare, then at least a conclusion is warranted that X is almost always the mechanism that led to Y. That is a bit vague, but it may do. Yet again, you would have to show this claim first.

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How about someone tried to establish the claim that only X can lead to Y or that X almost always leads to Y in this way:

He takes many examples of Y. Then he discusses them with the implicit assumption that only X can be the explanation or that X is so common that other mechanisms can be dismissed as freak exceptions. Afterwards, he concludes that Y is indeed an example how X led to Y. And then he takes all these examples as confirmation that indeed only X or mostly only X can result in Y.

That would be an incredibly bad argument. Why? To explain that X led to Y, this someone assumes that it cannot be otherwise or that other possibilities are too marginal to be considered. However, if you take that as your starting-point, it is no surprise that you will find it. This is just an example of “begging the question,” you assume the conclusion, a pretty elementary fallacy. And even if you do it for many examples, it shows nothing. The whole argument is circular.

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On an abstract level, I hope the fallacies involved are obvious. It would seem that noone could be so stupid to argue like this. But here are two examples:

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(1) Thomas Malthus in his “Essay on the Principle of Population” proposes the following explanation X for Y, where Y are starvation and famines: Human populations grow exponentially if there is enough food. But the food supply can only increase more slowly. Hence after some time, any human population will hit an upper bound where it is not possible to feed further people. Since the population tries to grow even when it has hit the upper bound, there will be a “redundant population” (Malthus’ own words) and hence Y: starvation and famines.

Now, does this mean you can conclude from your observation of Y, starvation and famines in a population, that X is the reason? In other words: Can you conclude that the population is at maximum size and it is impossible to feed more people, ie. that X is at work?

No, that would only follow if X, the Malthusian mechanism, were the only mechanism that could lead to Y, or if it were almost always the reason for it. Malthus never makes such an argument, though. Hence the conclusion is not warranted.

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To see why the Malthusian mechanism X is not the only mechanism that can lead to Y, starvation and famine, look at the following mechanisms that result in Y, starvation and famine, and are not X:

• During a war, an invading army confiscates so much food that what remains for the population is not sufficient. They will starve now and may even go into a famine. That happened, for example, in the Netherlands or in Eastern Europe under the German occupation during World War II.
• Economic policies crash agricultural production to an extent that the population has too little food. That has happened with the famine in Ukraine in the 1930s and the famine during the Great Leap Forward in China in the 1950s. North Korea is probably another example.
• A natural catastrophe destroys the harvest in a society with little trade. The population cannot make up for the shortfall and a famine ensues. There are many examples where the eruption of a volcano on the other side of the world led to a series of unexpectedly bad harvests, eg. during the Great Famine in the early 14th century.
• Some plant disease, eg. potato blight during the Irish Famine in the 1840s, destroys much of the harvest, and many in the population lack the means to buy other food. That is also why there is too little demand for importing more food.
• An economic crisis throws many people out of work. Charity and public support are inadequate, so a part of the population lacks the means to buy the necessary food, which might in principle be there. Or even without an economic crisis, some people fall on hard times and cannot obtain sufficient support. There will be starvation, and maybe even a famine.

Actually, if you run through actual famines, one or sometimes even several of those mechanisms are plausible as the cause for starvation and famine, ie. Y. They have unfortunately also been common enough that you cannot rule them out as freak events that are too exceptional. So the conclusion is not warranted that the Malthusian mechanism has to be the only explanation for Y, starvation and famine in a population, or even mostly so. You could even be skeptical as to whether it was ever the explanation.

For example, it is a common claim that the Great Famine in the early 14th century was the result of Malthusian “overpopulation.” However, the size of the population had been at that level for half a century before the volcano erupted. There was obviously enough food to feed the population for decades. And even if the Malthusian mechanism had been at work that would imply that the population should have remained at the maximum level, not that it should have suffered a severe setback.

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As I have already noted, Thomas Malthus does not even address the problem. It is obvious for him that only his proposed mechanism can explain starvation and famines. He tries to show that it is practically always so by running through a list of historical and contemporary examples. In the later editions, they fill more than one of the four volumes.

But what he actually does is just interpret any example under the assumption that the only explanation can be that a population has grown until it hits a binding constraint for the food supply. The other mechanisms that I have listed above do not mean that a population has grown to a maximum, though, only that the food supply has collapsed or some people are not able to buy enough food. This can happen even without any population growth and at any population size. It has nothing to do with the Malthusian mechanism.

Still, Malthus treats it as if that were the case, or in other words, he assumes it as obvious. He begs the question. Of course, he then finds what he presupposes. And after a long list of such explanations, it may seem as if it is always or almost always the case that starvation and famines are caused by the Malthusian mechanism.

But as I have explained at the abstract level, the reasoning is circular. It does not prove the case. And making the list ever longer, as Malthus does in the later editions, does not additional force to a fallacious argument.

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(2) It is probably no coincidence that Charles Darwin in his original theory of natural selection pursued a similar line of argument. He was indebted to Malthus and learned much from him, probably also this type of reasoning.

The original theory of natural selection goes like this:

All species behave as Malthus claims, they grow exponentially if they can and until they hit a binding constraint for the food supply. Since they keep on having offspring as if there were no constraint, there are always too many specimens of the species and some in a new generation, or even most of them as Darwin implicitly assumes, have to starve to death. There are only so many slots, and some or even many have to be culled by nature.

Darwin parallels this with artificial selection by a breeder. He sees to it that there is a superabundance of offspring in the next generation. Then he picks some of them to fill a limited number of slots. The rest are culled. For “natural selection,” it is only “Nature” that does all this, not a human being. There is a funny problem here, though: Humans are also a part of nature. So artificial selection is only a special case of natural selection. It is actually the only solid example of “natural” selection that Darwin has.

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Now, the mechanism is plausible that stubborn exponential growth plus a constraint on the food supply would lead to selection. Darwin originally meant the word “selection” in a very concrete sense here: Some are selected to live, the others are culled, just like with a human breeder. If there are heritable features that kill some specimens off early in life before they can procreate, the feature will disappear in the next generation.

If it only leads to worse chances of survival than for other specimens, the share of those with the feature will tend to zero. This is just a drawn-out version of the starker case where specimens die off right away. The same is also true in the other direction. If some new feature appears via “variation” (which is just another word for unexplained change) and if it confers some relative advantage for survival, the relative share of the feature in the population will rise and eventually tend to 100%.

I will skip the problem that Darwin takes the Maltusian argument for granted although that might not be warranted. If we assume it, X, the mechanism via “natural selection,” is a plausible reason why Y obtains, some heritable feature becomes ubiquitous in a population.

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As an aside: I would like to stress that I refer to Charles Darwin’s original theory here, which has been reinterpreted over time. “Natural selection” then becomes a tautological term that just means some feature has gone along with relatively more descendants. It does not have to be “selection” in any meaningful sense — some live, others are culled — anymore, and it could be by something that is not “Nature” in the sense of Darwin’s original theory. For example, it could also be pure chance as I will explain below.

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Darwin now tries to draw the conclusion that if Y, a heritable feature is ubiquitous in a population, then X, natural selection, in the narrow original sense, has to be the explanation. That is just the same fallacy as above, though. It may be so that X leads to Y. But you cannot conclude from Y that X must be the mechanism behind it. That would be the case only if nothing apart from X could produce Y. But Darwin does not provide an argument for that as far as I can see. And for good reason, because it would be false.

Instead, he does the same thing as Malthus. He runs through many examples of Y, a ubiquitous heritable feature in a species, and analyzes them under the assumption that the underlying mechanism can have been only X, natural selection. Of course, that is then what he finds, and it is supposed to prove the point. However, as I have noted above that is just circular reasoning and does not show the claim.

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If you have ever read anything from a Darwinian you will be familiar with such explanations via natural selection:

Y is a heritable feature that is ubiquitous in a population. Since we already know from Darwin that this can only be the result of X, natural selection, ie. better chances of survival, we can skip the question whether it is really so in this specific case. Instead we can immediately focus on the question how this feature improved the chances of survival. A plausible guess is usually good enough, you don’t have to show that it actually worked this way.

There is a funny side to these stories if you read them as what they are: stories. You can throw almost anything at a Darwinian, and he will practically always manage to show you how it was natural selection again. That it must have been natural selection is understood. Even if it is totally implausible, he will just explain that the advantage for survival was so incredibly subtle that you cannot see it. But it must be there because we already know this from Darwin.

Malthus can do the same rope-trick. When confronted with the obvious evidence that not many people in his time starved to death and famines had gone out of fashion, he just tells you that famine can be so subtle that a stupid observer will miss it. Only if you have the trained eye of Malthus is it obvious. But seriously: You shrink back when you see someone who is emaciated to their bones. This is sheer horror even for an observer! No one has to tell you when you see pictures from people who were liberated from a concentration camp that they have suffered from serious starvation. It is not subtle.

Let me parody the genre of explanation why it was natural selection again:

Question: Why do practically all human beings have five separate toes? Our muscles are too underdeveloped to move the four smaller ones independently. They are useless. If two of them grew together, it would not matter for survival at all. If you had one toe less, not either. So why five and why five that are separate?

Throw this at a Darwinian, and I am sure you will get an explanation that the value for survival is just extremely subtle, so it escapes a hasty observer like you. If you look with the deep insight of a Darwinian, it is there because it has to be there. When a lion in the wild savannah came at you, they would look at your feet. And if they saw five toes, they would turn back in fright. However, if it was less than five toes, they felt no compunction to devour you on the spot. Harsh natural selection saw to it that we have five separate toes. And so it was natural selection. Again! Just very hidden. QED.

Sure I made the example up to ridicule this type of Darwinian explanations. But if you read any such book, you will come across hundreds of them. Authors labor for pages to show you that something that is obviously not the result of natural selection is the result of natural selection nonetheless. The contortions are often truly funny. And after they have done this for lots of examples, they feel confident that natural selection is really always the explanation. So with the next example they can just assume it and produce another confirmation.

But if it is not clear that it is (almost) always natural selection, you have to show it is the case for a specific example, not assume it as a given. That would be begging the question and circular.

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Note that the point is not that natural selection can never be the explanation, only that it is not true that it always is. The negation of “always” is not “never,” but “at least once not.” If you tone it down to “almost always,” the negation is still not “never,” but “sometimes, but seldom not.”

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Why is the claim false that only X, natural selection, can explain that Y, a heritable feature is ubiquitous in a species?

Simple: Because there are plenty of other mechanisms that can lead to the same result. There are so many that I will not be able to list them in this post. And it is by no means obvious that they are so rare that you can rule them out as extreme exceptions.

But let me show you a few of many mechanisms that can lead to ubiquity of a feature in a species:

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The first mechanism was one that Darwin himself had to concede later on: sexual selection. Someone pointed out to him or he maybe found it out himself that natural selection, ie. higher chances of survival, could not be the explanation for the fancy feathers of the male peacock. They make the peacock stick out and an easy target for predators. Anything less conspicuous should confer higher chances of survival. But obviously, the male peacock does not seem to bother about natural selection.

Darwin’s additional theory of sexual selection now went like this: It is not only important for having more surviving descendants relatively that a specimen survives, but also that it finds a mate. If that is not a given, some are selected to procreate, and others are not although they still manage to survive to the relevant age. If female peacocks are just nuts for fancy feathers and shun any more modest peacock, that will lead to a similar mechanism as with natural selection. A feature that leads to higher chances of becoming a mate will become ubiquitous.

That is a plausible argument, but it creates a problem. If you are faced with an example Y, a heritable feature that is ubiquitous in a species, what is X? Natural selection or sexual selection? It is no longer obvious that it has to be one or the other. It could even be both: Mate choice is also about features that may improve the chances of survival. Hence, it is actually not possible to resort to the circular reasoning above. It is an open question what the mechanism was in a specific case that led to ubiquity of a feature in a species.

Still, Darwinians are not troubled by this. Even though Darwin had to concede sexual selection, the go-to explantion for any example has remained natural selection with them. That’s why you will get the many stories as in my parody.

Until it becomes just too ridiculous. Then Darwinians will backtrack and explain the ubiquity of a feature via sexual selection. Females just went crazy for five seperate toes! It is noteable here that the blame is mostly on the female side for doing braindead things although sometimes it is inevitable as a further retreat that also males might do stupid things.

So a Darwinian will run through many examples again. Since the standard of proof is very low, almost all of them can be explained by natural selection, maybe very subtle natural selection. But there are a few cases where this becomes too silly, like with the male peacock. Then you concede an exception where the explanation must be sexual selection. What else? It can only be natural or sexual selection!

The upshot of such a “proof” is that you obtain what you plug in: X, the mechanism, is almost always natural selection, and only in exceptional cases it is sexual selection.

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However, that is not even an obvious conclusion given these two theories. Suppose Darwin had by accident come up with sexual selection first. It is very easy to explain almost any case of Y, a heritable feature that is ubiquitous in a species, by sexual selection. All you have to claim is that females could just not resist males with the feature. If it was not braindead, but smart in some way, it could also have been the males who saw to it.

Now, Darwin would have made the same type of circular argument where he finds in any case that it was sexual selection again. However, at some point an example would have presented itself where sexual selection is just too implausible. If, for example, a feature is not observable, it is hard to show how it could form the basis for mate choice. That’s where Charles Darwin would have then come up with the theory of natural selection to sweep up a few exceptional cases. It would have left the presumtion almost intact that it is always sexual selection. Natural selection would then have been the waste basket for difficult examples in the counterfactual, just like sexual selection is in Darwin’s actual theory.

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The outcome seems accidental because Darwin started with natural selection and only then conceded sexual selection as an occasional exception. It could have been the other way around.

My take here is that the theory of natural selection is not only a scientific argument, but also a worldview. I have written about what I mean with the term in my post: “Worldviews, Narratives, and Ideologies.” A worldview is a panoramic and intuitive view of how the world works. And the Darwinian worldview is that there is always a “struggle for existence” (a term actually coined by Malthus) where there are always too many specimens of a species, Most of them are culled, and only the “good” ones survive.

A worldview is on an intuitive level. That means it is very hard to change it even if obvious problems arise. The usual ways to handle contradictions is in this order:

• Just ignore them as long as you can.
• If they are too obvious: Concede them as rare exceptions.
• If they are too frequent to make this plausible: Build them into your worldview, but keep it intact. If you don’t pay attention, it is as before. Only if it is in your face, you resort to some fix. But once it is out of view again, you are back to your worldview.

I would say that is what you see here at work with Darwin and later with Darwinians. Although the concession of sexual selection would have to lead to a complete rethink what is the go-to explanation, Darwinians just regularly default to natural selection anyway. Sexual selection is built into the worldview as a backstop for cases that become too silly, once you cannot avoid them.

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But still sexual selection is something that bothers Darwinians. There have been attempts to reduce it to natural selection. But that is absurd: If something obviously lowers the chances of survival, it cannot at the same time raise them. It cannot be both ways for purely logical reasons. At best a feature could be neutral and in this way both.

But that then this is something that creates other tensions because if you concede features that are neutral, it is no longer obvious why there is natural selection for practically everything. Darwinians have conceded the possibility later, but again they have managed to integrate it into their worldview as a fancy exception. Everything is the result of natural selection — err — this rare case might be from sexual selection. Okay, there might be some even weirder theoretical cases where features are neutral for both. But as long as you can tell a mildly plausible story with natural or sexual selection, which is practically always possible, it must be natural selection because we already know that sexual selection is more of an exception. Go figure.

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But aren’t natural selection and sexual selection the only ways how a heritable feature can become ubiquitous? No, by no means. There are many more. And it is hard to see why you could discard them as exceptions apriori.

Here is an example: All humans have an appendix. It serves no purpose. The only thing that can happen is that you get an appendicitis, which may kill you off. Obviously, having an appendix lowers your chances of survival. You would be better off without it. And no one can see an appendix apart from a surgeon. So it cannot play any role in mate choice, which means sexual selection for having an appendix is also off the table. But still all human beings have one. It is clearly an example of an ubiquitous feature in a species.

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The reason we all have an appendix might just be that it is not possible to build a human being without one. It is what has been termed a “spandrel.” The process of evolving a human being from a fertilized egg only has so many points where it can be influenced. There might simply be no point where you can turn evolving an appendix off. In principle, there could be such a way, but that would perhaps mean so many changes to the whole process that it is very improbable that any mutation would produce it in the foreseeable future. It could happen, but it hasn’t, and maybe won’t ever. It might not become ubiquitous even then.

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Surely, you can try to reduce this example to natural selection. The changes to avoid building an appendix could have other side-effects that lead to problems for survival. Or problems with finding a mate? Another awkward feature arises that lowers your chances of survival or of finding a mate. Or both?

Hence an appendix, useless or even somewhat harmful in and of itself, would just be there as a useless side-effect of something that could be the result of natural and/or sexual selection. For Darwinians, this is a satisfactory explanation because it removes a cognitive dissonance in their worldview: Heureka, it is natural selection again! Or at least sexual selection.

However, just because you can make such a claim, does not show that it is so. It is by no means obvious why an appendix is a “spandrel.” It could be there for necessary reasons because it is not possible to build a human being without one, given a certain process to evolve it from a fertilized egg. Or to change it, you would have to wait some extremely improbable mutation out, or even many of them. There were perhaps never any people where “no appendix” was tried out with devastating consequences. It does not have to be so because of natural or sexual selection for something else then. It might be, but that does not show it has to be so.

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So we have now already two further mechanisms apart from natural or sexual selection why a feature is ubiquitous in a population: it could be a “spandrel” or it could just be impossible or extremely improbable that there is a mutation that would avoid it. But then there are many more mechanisms. Here is another one from a much longer list:

“Random selection” happens when a feature is neutral for both natural and sexual selection: It does not confer higher chances of survival or with mate choice. Such a feature would come into being by a mutation. It then depends on whether it goes to the next generation, which could be purely random. The first person with the mutation is hit by a car at age five, which is totally unrelated with the feature. If that happens, the mutation goes out of business. The same is the case if the person does not find a mate, again for completely unrelated reasons.

I mentioned such a case already in my discussion of natural selection. A mutation might create a feature that improve the chances of survival in general, but which is eliminated from the population anyway by pure chance.

But it can also work the other way around: For purely random reasons, a neutral feature becomes more frequent in the next generation because the first person with the mutation just happens to have many children. Since there is no pull by natural or sexual selection, the share with the new feature in the population drifts around randomly from generation to generation. This is technically something like a Brownian motion, which describes, for example, how a particle in a fluid gets kicked around accidentally.

Now such a process will drift around more and more over time. The probability that it reaches any frequency in the population rises over time and actually goes to 100%. That may mean that it disappears at some point when it hits zero. However, if it has reached a certain share in the population, this becomes rather improbable. So it will probably stick around.

And it can also randomly drift to 100%. In that case, it becomes fixated: everyone has the feature from then on. But if that happens it was neither because of natural or sexual selection, but because of random selection. Of course, this can and should take very long by comparison because there is no pull to 100%. Yet that depends on the size of the population. If it is very small, it can happen also fast.

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Someone with a Darwinian worldview could try to fit random selection in as a rare exception. It should seldom lead to fixation, while natural or sexual selection would often do the trick. But that depends. If there are many features that undergo random selection, even with a low probability, many could become fixated. It is not obvious why that would have to be a rare case then. And so if you find a heritable feature that is ubiquitous in a population, it is not warranted to conclude that it can only have been natural selection, or maybe sexual selection. It could also have been random selection.

Random selection means the frequency of a feature drifts around like a particle in a fluid. Hence changes should be rather slow in a larger population. As I said, in a small population it might be different. One way to exclude random selection is to show that a feature has become ubiquitous over a short time span. You could perhaps ascertain the frequency some time back and the frequency now. If the change occurred fast, you can perhaps rule out random selection as the underlying mechanism. But the first thing you would have to do for that would be to show that it so. Just assuming it is not enough.

And then if you could rule out random selection in this or some other way, that still does not narrow the range of possible mechanisms down to natural or sexual selection. That would only be the case if there were no other mechanisms that could also work equally fast. But then there are indeed such mechanisms other than natural and sexual selection, and even many of them, which are not just academic counterexamples.

I will get to explain further such mechanisms in later posts. My point here was only to lay the paucity of a certain type of argument bare that both Malthus and Darwin employ.

I have no great hope that that will change the mind of any Malthusian or Darwinian because I am up against a worldview, which is built around the claim that Y can only result from X, apart from some fancy exceptions that can be ignored. Even if I manage to create some short-term “cognitive dissonances,” I am sure a Malthusian and a Darwinian will just turn around and react in this way:

• The Malthusian: Granted there are some weird exceptions. But then Malthus is still right that it is practically always so that human populations grow to maximum size and that causes starvation and famine. If I see an example, it is only interesting to understand how the Malthusian principle worked in this case. It is comfirmed again and again!
• The Darwinian: Granted there are some weird exceptions. But then Darwin is still right that it is practically always so that a heritable feature in a species becomes ubiquitous because of natural selection. Occasionally it can also be sexual selection (or maybe some even weirder theoretical mechanism). If I see an example, it is only interesting to understand how natural selection worked in this case. It is comfirmed again and again!