Month: January 2025

Evolution: Foundations of Genetics

PNRJ Logic of Kindness, tribal paradigm , , , , , , , , , , , ,


Jan 26 JDN 2460702

It frustrates me that in American society, evolutionary biology is considered a controversial topic. When I use knowledge from quantum physics or from organic chemistry, all I need to do is cite a credible source; I don’t need to preface it with a defense of the entire scientific field. Yet in the United States today, even basic statements of facts observed in evolutionary biology are met with incredulity. The consensus in the scientific community about evolution is greater than the consensus about quantum physics, and comparable to the consensus about organic chemistry. 95% of scientists agree that evolution happens, that Darwinian natural selection is the primary cause, and that human beings share a common ancestor with every other life form on Earth. Polls of scientists have consistently made this clear, and the wild success of Project Steve continues to vividly demonstrate it.

But I would rather defend evolution than have to tiptoe around it, or worse have my conclusions ignored because I use it. So, here goes.

You may think you understand evolution, but especially if you doubt that evolution is true, odds are good that you really don’t. Even most people who have taken college courses in evolutionary biology have difficulty understanding evolution.

Evolution is a very rich and complicated science, and I don’t have room to do it justice here. I merely hope that I can give you enough background to make sense of the core concepts, and convince you that evolution is real and important.

Foundations of genetics

So let us start at the beginning. DNA—deoxyribonucleic acid—is a macromolecular (very big and complicated) organic (carbon-based) acid (chemical that can give up hydrogen ions in solution) that is produced by all living cells. More properly, it is a class of macromolecular organic acids, because differences between DNA strands are actually chemical differences in the molecule. The structure of DNA consists of two long chains of constituent molecules called nucleotides; for chemical reasons nucleotides usually bond in pairs, adenine (A) with thymine (T), guanine (G) with cytosine (C). Pairs of nucleotides are called base pairs. We call it a “double-helix” because the two chains are normally wrapped around each other in a helix shape.

Because of this base-pair correspondence, the two strands of a DNA molecule are complementary; if one half is GATTACA, the other half will be CTAATGT. This process is reversible. Either strand can be reproduced from the other; this is how DNA replicates. A DNA strand GATTACA/CTAATGT can split into its GATTACA half and its CTAATGT half, and then the original GATTACA half will acquire new nucleotides and make a new CTAATGT for itself; similarly the original CTAATGT half will make a new GATTACA. At the end of this process, two precise copies of the original GATTACA/CTAATGT strand will result. This process can be repeated as necessary.

DNA molecules can vary in size from a few base-pairs (like the sequence GATTACA), to the 16,000 base-pairs of Carsonella bacteria, up to the 3 billion base-pairs of humans and beyond. While complexity of DNA and complexity of organism are surely related (it’s impossible to make a really complicated organism with very simple DNA), more base pairs does not necessarily imply a more complex organism. The single-celled amoeboid Polychaos dubium has 670 billion base-pairs. Amoeboids are relatively complex, all things considered; but they’re hardly 200 times more complex than we are!

The copying of DNA is exceedingly precise, but like anything in real life, not perfect. Cells have many physical and chemical mechanisms to correct bad copying, but sometimes—about 1 in 1 million base-pairs copied—something goes wrong. Sometimes, one nucleotide gets switched for another; perhaps what should have been a T becomes an A, or what should have been an A becomes a G. Other times, a whole sequence of DNA gets duplicated and inserted in a new place; still other times entire pieces of DNA are lost, never to be copied again. In some cases a sequence is flipped around backwards. All of these things (a single-nucleotide substitution, an insertion, a deletion, and an inversion, respectively) are forms of mutation. Mutation is always happening, but it can be increased by the presence of radiation, toxins, and other stresses. Usually cells with mutant DNA are killed by the immune system; if not, mutant body cells can cause cancer or other health problems. Usually it’s only mutations in gametes—the sperm and egg cells that carry DNA to the next generation—that actually have a long-term effect on future generations. Most mutations do not have any significant effect, and most of those that do have bad effects. It is only the rare minority of mutations that actually produces something useful to an organism’s survival.

What does DNA do? It makes proteins. Technically, proteins make other proteins (enzymes called transcriptases and polymerases and so on), but which protein is produced by such a process is dependent upon the order of base pairs in a DNA strand. DNA has been likened to a “code” or a “message”, but this is a little misleading. It’s definitely a sequence that contains information, but the “code” is less like a cryptographer’s cipher and more like a computer’s machine code; it interacts directly with the hardware to produce an output. And it’s important to understand that when DNA is “read” and “decoded”, it’s all happening purely by chemical reactions, and there is no conscious being doing the reading. While metaphorically we might say that DNA is a “code” or a “language”, we must not take these metaphors too literally; DNA is not a language in the same sense as English, nor is it a code in the same sense as the Enigma cipher.

Genotype and phenotype

DNA is also not a “blueprint”, as it is sometimes described. There is a one-to-one correspondence between a house and its blueprint: given a house, it would be easy to draw a blueprint much like the original blueprint; given a blueprint, one can construct basically the same house. DNA is not like this. There is no one-to-one correspondence between DNA and a living organism’s structure. Given the traits of an organism, it is impossible to reconstruct its DNA—and purely from the DNA, it is impossible to reconstruct the organism. A better analogy is to a recipe, which offers a general guide as to what to make and how to make it, but depending on the cook and the ingredients, may give quite different results. The ingredients in this case are nutrients, and the “cook” is the whole of our experience and interaction with the environment. No experience or environment can act upon us unless we have the right genes and nutrients to make it effective. No matter how long you let it sit, bread with no yeast will never rise—and no matter how hard you try to teach him, your dog will never be able to speak in fluent sentences.

Furthermore, genes rarely do only one thing in an organism; much as drugs have side effects, so do genes, a phenomenon called pleiotropy. Some genes are more pleiotropic than others, but really, all genes are pleiotropic. In any complex organism, genes will have complex effects. The genes of an organism are its genotype; the actual traits that it has are its phenotype. We have these two different words precisely because they are different things; genotype influences phenotype, but many other things influence phenotype besides genotype. The answer to the question “Nature or Nurture?” is always—always—“Both”. There are much more useful questions to ask, like “How much of the variation of this trait within this population is attributable to genetic differences?”, “How do environmental conditions trigger this phenotype in the presence of this genotype?”, and “Under what ecological circumstances would this genotype evolve?”

This is why it’s a bit misleading to talk about the “the gene for homosexuality” or “the gene for religiosity”; taken literally this would be like saying “the ingredient for chocolate cake” or “the beam for the Empire State Building”. At best we can distinguish certain genes that might, in the context of many other genes and environmental contributions, make a difference between particular states—much as removing the cocoa from chocolate cake makes some other kind of cake, it could be that removing a particular gene from someone strongly homosexual might make them nearer to heterosexual. It’s not that genes can be mapped one-to-one to traits of an organism; but rather that in many cases a genetic difference corresponds to a difference in traits that is ecologically significant. This is what geneticists mean when they say “the gene for X”; it’s a very useful concept in evolutionary theory, but I don’t think it’s one most laypeople understand. As usual, Richard Dawkins explains this matter brilliantly:

Probably the first point to make is that whenever a geneticist speaks of a gene `for’ such and such a characteristic, say brown eyes, he never means that this gene affects nothing else, nor that it is the only gene contributing to the brown pigmentation. Most genes have many distantly ramified and apparently unconnected effects. A vast number of genes are necessary for the development of eyes and their pigment. When a geneticist talks about a single gene effect, he is always talking about a difference between individuals. A gene `for brown eyes’ is not a gene that, alone and unaided, manufactures brown pigment. It is a gene that, when compared with its alleles (alternatives at the same chromosomal locus), in a normal environment, is responsible for the difference in eye colour between individuals possessing the gene and individuals not possessing the gene. The statement `G1 is a gene for phenotypic characteristic P1‘ is always a shorthand. It always implies the existence, or potential existence, of at least one alternative gene G2, and at least one alternative characteristic P2. It also implies a normal developmental environment, including the presence of the other genes which are common in the gene pool as a whole, and therefore likely to be in the same body. If all individuals had two copies of the gene `for’ brown eyes and if no other eye colour ever occurred, the `gene for brown eyes’ would strictly be a meaningless concept. It can only be defined by reference to at least one potential alternative. Of course any gene exists physically in the sense of being a length of DNA; but it is only properly called a gene `for X’ if there is at least one alternative gene at the same chromosomal locus, which leads to not X.

It follows that there is no clear limit to the complexity of the `X’ which we may substitute in the phrase `a gene for X’. Reading, for example, is a learned skill of immense and subtle complexity. A gene for reading would, to naive common sense, be an absurd notion. Yet, if we follow genetic terminological convention to its logical conclusion, all that would be necessary in order to establish the existence of a gene for reading is the existence of a gene for not reading. If a gene G2 could be found which infallibly caused in its possessors the particular brain lesion necessary to induce specific dyslexia, it would follow that G1, the gene which all the rest of us have in double dose at that chromosomal locus, would by definition have to be called a gene for reading.

It’s important to keep this in mind when interpreting any new ideas or evidence from biology. Just as cocoa by itself is not chocolate cake because one also needs all the other ingredients that make it cake in the first place, “the gay gene” cannot exist in isolation because in order to be gay one needs all the other biological and neurological structures that make one a human being in the first place. Moreover, just as cocoa changes the consistency of a cake so that other ingredients may need to be changed to compensate, so a hypothetical“gay gene” might have other biological or neurological effects that would be inseparable from its contribution to sexual orientation.

It’s also important to point out that hereditary is not the same thing as genetic. By comparing pedigrees, it is relatively straightforward to determine the heritability of a trait within a population—but this is not the same as determining whether the trait is genetic. A great many traits are systematically inherited from parents that have nothing to do with DNA—like language, culture, and wealth. (These too can evolve, but it’s a different kind of evolution.) In the United States, IQ is about 80% heritable; but so is height, and yet nutrition has large, well-documented effects on height (The simplest case: malnourished people never grow very tall). If, as is almost certainly the case, there are many environmental influences such as culture and education that can affect IQ scores, then the heritability of IQ tells us very little.

In fact, some traits are genetic but not hereditary! Certain rare genetic diseases can appear by what is called de novo mutation; the genes that cause them can randomly appear in an individual without having been present in their parents. Neurofibromatosis occurs in as many people with no family history as it does in people with family history; and yet, neurofibromatosis is definitely a genetic disorder, for it can be traced to particular sections of defective DNA.

Honestly, most of the debate about nature versus nurture in human behavior is really quite pointless. Even if you ignore the general facts that phenotype is always an interaction between genes and environment, and feedback occurs between genes and environment over evolutionary time, human beings are the species for which the “Nature or nurture?” question reaches its most meaningless. It is human nature to be nurtured; it is written within our genes that we should be flexible, intelligent beings capable of learning and training far beyond our congenital capacities. An ant’s genes are not written that way; ants play out essentially the same program in every place and time, because that program is hard-wired within them. Humans have an enormous variety of behaviors—far outstripping the variety in any other species—despite having genetic variation of only about 0.1%; clearly most of the differences between humans are environmental. Yet, it is precisely the genes that code for being Homo sapiens that make this possible; if we’d had the genes of an ant or an earthworm, we wouldn’t have this enormous behavioral plasticity. So each person is who they are largely because of their environment—but that itself would not be true without the genes we all share.

On this, my 37th birthday

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Jan 19 JDN 2460695

This post will go live on my 37th birthday. I’m now at an age where birthdays don’t really feel like a good thing.

This past year has been one of my worst ever.

It started with returning home from the UK, burnt out, depressed, suffering from frequent debilitating migraines. I had no job prospects, and I was too depressed to search for any. I moved in with my mother, who lately has been suffering health problems of her own.

Gradually, far too gradually, some aspects of my situation improved; my migraines are now better controlled, my depression has been reduced. I am now able to search for jobs at least—but I still haven’t found one. I would say that my mother’s health is better than it was—but several of her conditions are chronic, and much of this struggle will continue indefinitely.

I look back on this year feeling shame, despair, failure and defeat. I haven’t published anything—either fiction, nonfiction, or scientific—in years, and after months of searching I still haven’t found a job that would let me and my husband move to a home of our own. My six figures of student debt are now in forbearance, because the SAVE plan was struck down in court. (At least they’re not accruing interest….) I can’t think of anything I’ve done this year that I would count as a meaningful accomplishment. I feel like I’m just treading water, trying not to drown.

I see others my age finding careers, buying homes, starting families. Honestly they’re a little old to be doing these things now—we Millennials have drawn the short straw on homeownership for sure. (The median age of first-time homebuyers is now 38 years old—the highest ever recorded. In 1981, it was only 29.) I don’t see that happening for me any time soon, and I feel a deep grief over that.

I have not had a year go this badly since high school, when I was struggling even more with migraines and depression. Back then I had debilitating migraines multiple times per week, and my depression sometimes kept me from getting out of bed. I even had suicidal thoughts for a time, though I never made any plans or attempts.

Somehow, despite all that, I still managed to maintain straight As in high school and became a kind of de facto valedictorian. (My school technically didn’t have a valedictorian, but I had the best grades, and I successfully petitioned for special dispensation to deliver a much longer graduation speech than any other student.) Some would say this was because I was so brilliant, but I say it was because high school was too easy—and that this set me up for unrealistic expectations later in life. I am a poster child for Gifted Kid Syndrome and Impostor Syndrome. Honestly, maybe I would have gotten better help for my conditions sooner if my grades had slipped.

Will the coming year be better?

In some ways, probably. Now that my migraines and depression are better controlled—but by no means gone—I have been able to actively search for jobs, and I should be able to find one that fits me eventually (or so I keep trying to convince myself, when it all feels hopeless and pointless). And once I do have a job, whenever that happens, I might be able to start saving up for a home and finally move forward into feeling like a proper adult in this society.

But I look to the coming year feeling fear and dread, as Trump will soon take office and already looks primed to be far worse the second time around. In all likelihood I personally won’t suffer very much from Trump’s incompetence and malfeasance—but millions of other people will, and I don’t know how I can help them, especially when I seem so ineffectual at helping myself.

Moore’s “naturalistic fallacy”

PNRJ ethics, Logic of Kindness , , , , , , , , , , , , , , , , , , , ,

Jan 12 JDN 2460688

In last week’s post I talked about some of the arguments against ethical naturalism, which have sometimes been called “the naturalistic fallacy”.

The “naturalistic fallacy” that G.E. Moore actually wrote about is somewhat subtler; it says that there is something philosophically suspect about defining something non-natural in terms of natural things—and furthermore, it says that “good” is not a natural thing and so cannot be defined in terms of natural things. For Moore, “good” is not something that can be defined with recourse to facts about psychology, biology or mathematics; “good” is simply an indefinable atomic concept that exists independent of all other concepts. As such Moore was criticizing moral theories like utilitarianism and hedonism that seek to define “good” in terms of “pleasure” or “lack of pain”; for Moore, good cannot have a definition in terms of anything except itself.

My greatest problem with this position is less philosophical than linguistic; how does one go about learning a concept that is so atomic and indefinable? When I was a child, I acquired an understanding of the word “good” that has since expanded as I grew in knowledge and maturity. I need not have called it “good”: had I been raised in Madrid, I would have called it bueno; in Beijing, hao; in Kyoto, ii; in Cairo, jaiid; and so on.

I’m not even sure if all these words really mean exactly the same thing, since each word comes with its own cultural and linguistic connotations. A vast range of possible sounds could be used to express this concept and related concepts—and somehow I had to learn which sounds were meant to symbolize which concepts, and what relations were meant to hold between them. This learning process was highly automatic, and occurred when I was very young, so I do not have great insight into its specifics; but nonetheless it seems clear to me that in some sense I learned to define “good” in terms of things that I could perceive. No doubt this definition was tentative, and changed with time and experience; indeed, I think all definitions are like this. Perhaps my knowledge of other concepts, like “pleasure”, “happiness”, “hope” and “justice”, is interconnected with “good” in such a way that none can be defined separately from the others—indeed perhaps language itself is best considered a network of mutually-reinforcing concepts, each with some independent justification and some connection to other concepts, not a straightforward derivation from more basic atomic notions. If you wish, call me a “foundherentist” in the tradition of Susan Haack; I certainly do think that all beliefs have some degree of independent justification by direct evidence and some degree of mutual justification by coherence. Haack uses the metaphor of a crossword puzzle, but I prefer Alison Gopnik’s mathematical model of a Bayes net. In any case, I had to learn about “good” somehow. Even if I had some innate atomic concept of good, we are left to explain two things: First, how I managed to associate that innate atomic concept with my sense experiences, and second, how that innate atomic concept got in my brain in the first place. If it was genetic, it must have evolved; but it could only have evolved by phenotypic interaction with the external environment—that is, with natural things. We are natural beings, made of natural material, evolved by natural selection. If there is a concept of “good” encoded into my brain either by learning or instinct or whatever combination, it had to get there by some natural mechanism.

The classic argument Moore used to support this position is now called the Open Question Argument; it says, essentially, that we could take any natural property that would be proposed as the definition of “good” and call it X, and we could ask: “Sure, that’s X, but is it good?” The idea is that since we can ask this question and it seems to make sense, then X cannot be the definition of “good”. If someone asked, “I know he is an unmarried man, but is he a bachelor?” or “I know that has three sides, but is it a triangle?” we would think that they didn’t understand what they were talking about; but Moore argues that for any natural property, “I know that is X, but is it good?” is still a meaningful question. Moore uses two particular examples, X = “pleasant” and X = “what we desire to desire”; and indeed those fit what he is saying. But are these really very good examples?

One subtle point that many philosophers make about this argument is that science can discover identities between things and properties that are not immediately apparent. We now know that water is H2O, but until the 19th century we did not know this. So we could perfectly well imagine someone asking, “I know that’s H2O, but is it water?” even though in fact water is H2O and we know this. I think this sort of argument would work for some very complicated moral claims, like the claim that constitutional democracy is good; I can imagine someone who was quite ignorant of international affairs asking: “I know that it’s constitutional democracy, but is that good?” and be making sense. This is because the goodness of constitutional democracy isn’t something conceptually necessary, it is an empirical result based on the fact that constitutional democracies are more peaceful, fair, egalitarian, and prosperous than other governmental systems. In fact, it may even be only true relative to other systems we know of; perhaps there is an as-yet-unimagined governmental system that is better still. No one thinks that constitutional democracy is a definition of moral goodness. And indeed, I think few would argue that H2O is the definition of water; instead the definition of water is something like “that wet stuff we need to drink to survive” and it just so happens that this turns out to be H2O. If someone asked “is that wet stuff we need to drink to survive really water?” he would rightly be thought talking nonsense; that’s just what water means.

But if instead of the silly examples Moore uses, we take a serious proposal that real moral philosophers have suggested, it’s not nearly so obvious that the question is open. From Kant: “Yes, that is our duty as rational beings, but is it good?” From Mill: “Yes, that increases the amount of happiness and decreases the amount of suffering in the world, but is it good?” From Aristotle: “Yes, that is kind, just, and fair, but is it good?” These do sound dangerously close to talking nonsense! If someone asked these questions, I would immediately expect an explanation of what they were getting at. And if no such explanation was forthcoming, I would, in fact, be led to conclude that they literally don’t understand what they’re talking about.

I can imagine making sense of “I know that has three sides, but is it a triangle?”in some bizarre curved multi-dimensional geometry. Even “I know he is an unmarried man, but is he a bachelor?” makes sense if you are talking about a celibate priest. Very rarely do perfect synonyms exist in natural languages, and even when they do they are often unstable due to the effects of connotations. None of this changes the fact that bachelors are unmarried men, triangles have three sides, and yes, goodness involves fulfilling rational duties, alleviating suffering, and being kind and just (Deontology, consequentialism, and virtue theory are often thought to be distinct and incompatible; I’m convinced they amount to the same thing, which I’ll say more about in later posts.).

This line of reasoning has led some philosophers (notably Willard Quine) to deny the existence of analytic truths altogether; on Quine’s view even “2+2=4” isn’t something we can deduce directly from the meaning of the symbols. This is clearly much too strong; no empirical observation could ever lead us to deny 2+2=4. In fact, I am convinced that all mathematical truths are ultimately reducible to tautologies; even “the Fourier transform of a Gaussian is Gaussian” is ultimately a way of saying in compact jargon some very complicated statement that amounts to A=A. This is not to deny that mathematics is useful; of course mathematics is tremendously useful, because this sort of compact symbolic jargon allows us to make innumerable inferences about the world and at the same time guarantee that these inferences are correct. Whenever you see a Gaussian and you need its Fourier transform (I know, it happens a lot, right?), you can immediately know that the result will be a Gaussian; you don’t have to go through the whole derivation yourself. We are wrong to think that “ultimately reducible to a tautology” is the same as “worthless and trivial”; on the contrary, to realize that mathematics is reducible to tautology is to say that mathematics is undeniable, literally impossible to coherently deny. At least the way I use the words, the statement “Happiness is good and suffering is bad” is pretty close to that same sort of claim; if you don’t agree with it, I sense that you honestly don’t understand what I mean.

In any case, I see no more fundamental difficulty in defining “good” than I do in defining any concept, like “man”, “tree”, “multiplication”, “green” or “refrigerator”; and nor do I see any point in arguing about the semantics of definition as an approach to understanding moral truth. It seems to me that Moore has confused the map with the territory, and later authors have confused him with Hume, to all of our detriment.

What’s fallacious about naturalism?

PNRJ core principles, ethics, Logic of Kindness , , , , , , , , , , ,

Jan 5 JDN 2460681

There is another line of attack against a scientific approach to morality, one which threatens all the more because it comes from fellow scientists. Even though they generally agree that morality is real and important, many scientists have suggested that morality is completely inaccessible to science. There are a few different ways that this claim can be articulated; the most common are Stephen Jay Gould’s concept of “non-overlapping magisteria” (NOMA), David Hume’s “is-ought problem”, and G.E. Moore’s “naturalistic fallacy”. As I will show, none of these pose serious threats to a scientific understanding of morality.

NOMA

Stephen Jay Gould, though a scientist, an agnostic, and a morally upright person, did not think that morality could be justified in scientific or naturalistic terms. He seemed convinced that moral truth could only be understood through religion, and indeed seemed to use the words “religion” and “morality” almost interchangeably:

The magisterium of science covers the empirical realm: what the Universe is made of (fact) and why does it work in this way (theory). The magisterium of religion extends over questions of ultimate meaning and moral value. These two magisteria do not overlap, nor do they encompass all inquiry (consider, for example, the magisterium of art and the meaning of beauty).

If we take Gould to be using a very circumscribed definition of “science” to just mean the so-called “natural sciences” like physics and chemistry, then the claim is trivial. Of course we cannot resolve moral questions about stem cell research entirely in terms of quantum physics or even entirely in terms of cellular biology; no one ever supposed that we could. Yes, it’s obvious that we need to understand the way people think and the way they interact in social structures. But that’s precisely what the fields of psychology, sociology, economics, and political science are designed to do. It would be like saying that quantum physics cannot by itself explain the evolution of life on Earth. This is surely true, but it’s hardly relevant.

Conversely, if we define science broadly to include all rational and empirical methods: physics, chemistry, geology, biology, psychology, sociology, astronomy, logic, mathematics, philosophy, history, archaeology, anthropology, economics, political science, and so on, then Gould’s claim would mean that there is no rational reason for thinking that rape and genocide are immoral.

And even if we suppose there is something wrong with using science to study morality, the alternative Gould offers us—religion—is far worse. As I’ve already shown in previous posts, religion is a very poor source of moral understanding. If morality is defined by religious tradition, then it is arbitrary and capricious, and real moral truth disintegrates.

Fortunately, we have no reason to think so. The entire history of ethical philosophy speaks against such notions, and had Immanuel Kant and John Stuart Mill alive been alive to read them, they would have scoffed at Gould’s claims. I suspect Peter Singer and Thomas Pogge would scoff similarly today. Religion doesn’t offer any deep insights into morality, and reason often does; NOMA is simply wrong.

What’s the problem with “ought” and “is”?

The next common objection to a scientific approach to morality is the remark, after David Hume, that “one cannot derive an ought from an is”; due to a conflation with a loosely-related argument that G.E. Moore made later, the attempt to derive moral statements from empirical facts has become called the “naturalistic fallacy” (this is clearly not what Moore intended; I will address Moore’s actual point in a later post). But in truth, I do not really see where the fallacy is meant to lie; there is little difference in principle between deriving “ought” from “is” than there is from deriving anything from anything else.

First, let’s put aside direct inferences from “X is true” to “X ought to be true”; these are obviously fallacious. If that’s all Hume was saying, then he is of course correct; but this does little to undermine any serious scientific theory of morality. You can’t infer from “there are genocides” to “there ought to be genocides”; nor can you infer from “there ought to be happy people” to “there are happy people”; but nor would I or any other scientist seek to do so. This is a strawman of naturalistic morality.

It’s true that some people do attempt to draw similar inferences, usually stated in a slightly different form—but these are not moral scientists, they are invariably laypeople with little understanding of the subject. Arguments based on the claim that “homosexuality is unnatural” (therefore wrong) or “violence is natural” (therefore right) are guilty of this sort of fallacy, but I’ve never heard any credible philosopher or scientist support such arguments. (And by the way, homosexuality is nearly as common among animals as violence.)

A subtler way of reasoning from “is” to “ought” that is still problematic is the common practice of surveying people about their moral attitudes and experimentally testing their moral behaviors, sometimes called experimental philosophy. I do think this kind of research is useful and relevant, but it doesn’t get us as far as some people seem to think. Even if we were to prove that 100% of humans who have ever lived believe that cannibalism is wrong, it does not follow that cannibalism is in fact wrong. It is indeed evidence that there is something wrong with cannibalism—perhaps it is maladaptive to the point of being evolutionarily unstable, or it is so obviously wrong that even the most morally-blind individuals can detect its wrongness. But this extra step of explanation is necessary; it simply doesn’t follow from the fact that “everyone believes X is wrong” that in fact “X is wrong”. (Before 1900 just about everyone quite reasonably believed that the passage of time is the same everywhere regardless of location, speed or gravity; Einstein proved everyone wrong.) Moral realism demands that we admit people can be mistaken about their moral beliefs, just as they can be mistaken about other beliefs.

But these are not the only way to infer from “is” to “ought”, and there are many ways to make such inferences that are in fact perfectly valid. For instance, I know at least two ways to validly prove moral claims from nonmoral claims. The first is by conjunctive addition: “2+2=4, therefore 2+2=4 or genocide is wrong”. The second is by contradictory explosion: “2+2=5, therefore genocide is wrong”. Both of these arguments are logically valid. Obviously they are also quite trivial; “genocide is wrong” could be replaced by any other conceivable proposition (even a contradiction!), leaving an equally valid argument. Still, we have validly derived a moral statement from nonmoral statements, while obeying the laws of logic.

Moreover, it is clearly rational to infer a certain kind of “ought” from statements that entirely involve facts. For instance, it is rational to reason, “If you are cold, you ought to close the window”. This is an instrumental “ought” (it says what it is useful to do, given the goals that you have), not a moral “ought” (which would say what goals you should have in the first place). Hence, this is not really inferring moral claims from non-moral claims, since the “ought” isn’t really a moral “ought” at all; if the ends are immoral the means will be immoral too. (It would be equally rational in this instrumental sense to say, “If you want to destroy the world, you ought to get control of the nuclear launch codes”.) In fact this kind of instrumental rationality—doing what accomplishes our goals—actually gets us quite far in defining moral norms for real human beings; but clearly it does not get us far enough.

Finally, and most importantly, epistemic normativity, which any rational being must accept, is itself an inference from “is” to “ought”; it involves inferences like “Is it raining, therefore you ought to believe it is raining.”

With these considerations in mind, we must carefully rephrase Hume’s remark, to something like this:

One cannot nontrivially with logical certainty derive moral statements from entirely nonmoral statements.

This is indeed correct; but here the word “moral” carries no weight and could be replaced by almost anything. One cannot nontrivially with logical certainty derive physical statements from entirely nonphysical statements, nor nontrivially with logical certainty derive statements about fish from statements that are entirely not about fish. For all X, one cannot nontrivially with logical certainty derive statements about X from statements entirely unrelated to X. This is an extremely general truth. We could very well make it a logical axiom. In fact, if we do so, we pretty much get relevance logic, which takes the idea of “nontrivial” proofs to the extreme of actually considering trivial proofs invalid. Most logicians don’t go so far—they say that “2+2=5, therefore genocide is wrong” is technically a valid argument—but everyone agrees that such arguments are pointless and silly. In any case the word “moral” carries no weight here; it is no harder to derive an “ought” from an “is” than it is to derive a “fish” from a “molecule”.

Moreover, the claim that nonmoral propositions can never validly influence moral propositions is clearly false; the argument “Killing is wrong, shooting someone will kill them, therefore shooting someone is wrong” is entirely valid, and the moral proposition “shooting someone is wrong” is derived in large part from the nonmoral proposition “shooting someone will kill them”. In fact, the entire Frege-Geach argument against expressivism hinges upon the fact that we all realize that moral propositions function logically the same way as nonmoral propositions, and can interact with nonmoral propositions in all the usual ways. Even expressivists usually do not deny this; they simply try to come up with ways of rescuing expressivism despite this observation.

There are also ways of validly deriving moral propositions from entirely nonmoral propositions, in an approximate or probabilistic fashion. “Genocide causes a great deal of suffering and death, and almost everyone who has ever lived has agreed that suffering and death are bad and that genocide is wrong, therefore genocide is probably wrong” is a reasonably sound probabilistic argument that infers a moral conclusion based on entirely nonmoral premises, though it lacks the certainty of a logical proof.

We could furthermore take as axiom some definition of moral concepts in terms of nonmoral concepts, and then derive consequences of this definition with logical certainty. “A morally right action maximizes pleasure and minimizes pain. Genocide fails to maximize pleasure or minimize pain. Therefore genocide is not morally right.” Obviously one is free to challenge the definition, but that’s true of many different types of philosophical arguments, not a specific problem in arguments about morality.

So what exactly was Hume trying to say? I’m really not sure. Maybe he has in mind the sort of naive arguments that infer from “unnatural” to “wrong”; if so, he’s surely correct, but the argument does little to undermine any serious naturalistic theories of morality.