CNN science completely botches natural selection in the headline, and is confusing in the text

March 24, 2017 • 10:00 am

I have little time to post this morning, but I call your attention to a really dreadful piece of science journalism at CNN.

It refers to a new paper in PLoS Genetics by Arslan Zaidi et al. (reference below, free access) describing how natural selection based on climate (temperature and humidity) may have molded the nose shape of populations of humans in different parts of the world (I’d call these groups “races” but I’d get my tuchas chewed for that). Here’s the paper’s abstract:


The evolutionary reasons for variation in nose shape across human populations have been subject to continuing debate. An import function of the nose and nasal cavity is to condition inspired air before it reaches the lower respiratory tract. For this reason, it is thought the observed differences in nose shape among populations are not simply the result of genetic drift, but may be adaptations to climate. To address the question of whether local adaptation to climate is responsible for nose shape divergence across populations, we use Qst–Fst comparisons to show that nares width and alar base width are more differentiated across populations than expected under genetic drift alone. To test whether this differentiation is due to climate adaptation, we compared the spatial distribution of these variables with the global distribution of temperature, absolute humidity, and relative humidity. We find that width of the nares is correlated with temperature and absolute humidity, but not with relative humidity. We conclude that some aspects of nose shape may indeed have been driven by local adaptation to climate. However, we think that this is a simplified explanation of a very complex evolutionary history, which possibly also involved other non-neutral forces such as sexual selection.

We know of course that selection has been responsible for many local adaptations in humans (see here for a summary), so this is nothing new, though it’s an interesting piece of work. Sexual selection may also be responsible, as the authors say, though it’s not the kind of sexual selection that leads to sexual dimorphism (in this case, to any different nose shape between males and females).

Now look at the CNN headline reporting this result (clicl on screenshot to go to article):

The headline (which probably wasn’t written by author Susan Scutti) gets natural selection completely wrong, implying that it’s something that involves genetics and the selective pressure itself as different and separable entities. Of course we know that if climate-based natural selection caused evolutionary changes in nose shape, those changes would have to be genetic! Climate, after all, is not some Lamarckian force that molds an nose shape that gets passed on without the intervention of genes. Climate cannot evolutionarily mold nose shape, at least in a heritable way, without genes!

The authors of the PLoS paper discuss the differential replication of gene forms (alleles) based on their contribution to well being mediated through nose shape. That process involves both climate and genes interacting in a nonrandom way. The headline is grossly misleading, though Scutti herself seems to get it pretty much right in the article (but see below).

I was sent this headline by Richard Dawkins, who was just as appalled as I was. Here’s what he wrote (quoted with permission):

But if you read the CNN story it turns out, as you would expect, that the study shows natural selection, in different climates, has shaped the nose. In what possible sense is that NOT genetics?

Well, as I said, the story itself is okay, but the headline is horrible.

But there’s still a bizarre bit of Scutti’s story. Here’s what she reports further:

So it’s easy to understand why many people, past and present, “have this sense that human populations are very distinct and have been separated for a long time,” said Mark D. Shriver, lead author of the study and a professor of anthropology at Penn State University. Still, he noted, “human populations have always split and come back together, split and come back together, so there’s no separate origin.”

In fact, genetic differences between various population groups is not that great. Using noses as just one example, said Shriver, “the surface, the appearance of people in different populations is much greater than what the genetic differences show on average.”

There are three things wrong here. Yes, human populations have exchanged migrants for a while—ever since forms of transportation came about. And this process is accelerating. But the statement that “populations have always split and come back together” and that “there’s no separate origin” is flatly wrong. Populations don’t meld completely and then split again: they simply send individuals back and forth, and historically have maintained many of their genetic and phenotypic differences.

Further, there is a separate origin for many populations. Native Americans, including those in North and South America, came over the Bering Strait about 15,000-20,000 years ago. They did not repeatedly fuse back to their Eurasian ancestors and separate again. Ditto with Polynesians, the indigenous people of Australia, and so on. I have no idea what Shriver is talking about.

In the second paragraph, I am simply confused by Shriver’s statement that “the surface, the appearance of people in different populations is much greater than what the genetic differences show on average.” What genetic differences is he talking about? For surely there are substantial genetic differences involved in the nose shape differences, be they small differences in the frequency of alleles at many loci, big differences in the frequency of alleles at a few loci, or a mixture.

Perhaps he is saying that the allele frequency differences in nose shape (and other distinguishable traits among populations) are greater than those of the “average” gene, including “neutral” sites where different gene forms make no difference in appearance, phyisology, or so on. That would be a nod to the fact that wholesale genetic differentiation of our genome hasn’t had time to evolve over the 60,000-100,000 years since we spread out over the globe from Africa. But if Shriver meant that, why didn’t he say it more clearly, and why didn’t Scutti ask him to clarify it? After all, there’s no good way to compare the differences in the configuration of a character like the nose with the frequency differences of genes in the genome. They are apples and oranges.

This is the kind of dire science reporting, with the journalist not asking the right questions (not atypical for science journalists who haven’t had extensive training in science), and therefore the body of the article (and the headline!) remaining confusing. It was confusing for me, and I’m an evolutionary biologist.


Zaidi A. A. et al. 2017. Investigating the case of human nose shape and climate adaptation. PLoS Genetics

31 thoughts on “CNN science completely botches natural selection in the headline, and is confusing in the text

  1. “The headline (which probably wasn’t written by author Susan Scutti) gets natural selection completely wrong, implying that it’s something that involves genetics and the selective pressure itself as different and separable entities. ”

    Excellent – thank you PCC(E)!

    I had seen this news item come through the information sluice, and dismissed the title as usual with the assumption that a headline conforms to non-scientific and imprecise language, while understanding that a genuine scientific publication is at the bottom of it.

    But yes, I see how deceptive and wrong this one is now!

    1. Meant to say “non-obvious”, more than “deceptive” – it’s not really deceptive actually, since it’s just wrong.

  2. When CNN reports on something you know about first-hand you see they botch it. When CNN reports on things you don’t know first-hand, do you trust them?

    1. For me, it depends on the subject. Some things they do a good job of reporting. However, I doubt any scientists rely on CNN for their science news. Just because a source is bad on one topic, doesn’t mean it’s universally bad. I find CNN pretty good on politics, current events, and similar things. On other stuff, not so good. It also depends who’s doing the reporting – not all journalists are created equal.

      1. You got that right. CNN made the economic decision some time back to kill hard journalism with documentaries and in dept pieces. It shut down most of it’s overseas stations. Now it just does politics and more politics and talking heads and what we refer to as news light. It is the shape of today’s news “so-called”. But it beats the hell out of Fox and MSNBC.

        People can bad mouth Public TV (PBS) if they want but then please name me anything on the Tube that does what Frontline does? Did anyone bother to watch the last frontline show with the female journalist going into Iraq to show the fight with ISIS and the Shia militia. That is investigative journalism at it’s best.

      2. This sounds like you know CNN is unreliable, but you want to trust them on politics anyway. But their political reporting is no better.
        I don’t mean to single out CNN. Pretty much all the major media is like this. Sometimes accurate, sometimes not, but never very reliable.
        I do like Frontline, which Randy mentions. But maybe I am too trusting 🙂

        1. I don’t think any news media anywhere is 100% reliable, and anyone who thinks that is in trouble. Imo we all have a responsibility to educate ourselves on the facts.

          I find CNN useful for hearing different points of view when discussing various topics. On that I find them much better than most other networks. Anderson Cooper’s show is one I watch regularly and like.

          1. We tape his Sunday morning GPS show. He has interesting guests and is a very good moderator as well as commentator.

  3. I think this in a general sense is one of the reasons for Americans’ very poor understanding of evolution. I’m subscribed to an old “44 Reasons why Evolution is a Fairy tale for Adults” thread, and bang my head against it on occastion

    In one comment I stated

    A common ancestor evolved into chimpanzees and gorillas and humans. That is a fact, and no less a fact than water is made up of molecules, which are themselves made up of one oxygen atom and two hydrogen atoms.

    Part of a response I got was

    If you rate the likelihood of say, biblical creationism and evolution being true out of ten- you’re looking at maybe a 1 and 2, respectively. Though 2 beats 1, it’s not close to 10.

    The person doesn’t seem to be religiously motivated, but through poor education and ID propaganda has this “just a theory” nonsense.


  4. The extent of a given gene’s expression (here for nose size) could be arguably dependent on some environmental factors.
    I had two grandfathers well under 6 feet tall, whereas I am 6 feet seven: I would assume that nutrition is the likely contributor here and not genes. (One grandfather had 10 siblings and food was scarcer when he was growing up).

    Its not a Lamarkian argument. Maybe a child growing in a certain climate will have a different development of the respiratory tract than in another climate: like the same species of a plant will grow differently in different countries. Its not a genetic argument at that point. The usual nature and nurture.

    As I understand it, genes define the physical limit of a trait, not its absolute predetermined value.

    For the argument to be principally one of genetics, it would be necessary to propose how a certain nose size confers an increased chance of survival and reproduction in given climates.

    1. I’m a little dubious. I don’t think height is a good analogy to nose shape.

      I think it is pretty well established that environmental factors can affect your height even though there are strong genetic factors affecting height.

      I think it is pretty well established that nose shape is from genetics while environment has little effect.

      I have heard of many cases where malnourishment affected someone’s height. I have never heard of a single case where someone who grew up in a different climate from their parents had a nose shape different from their parents and instead resembled the people in their new home.

      1. I think that is partly the point of the experiment: I used height as an evident example. However there must be factors determining nose size: selection, environmental whatever that have significantly determined nose variation over relatively recent human history.
        You could look at shaded variations in eye colour for example: there are variations in eye colour which may be contributed to by environmental factors.

        Whatever the advantages of wide flat nose in a hot climate, an aquiline nose in a desert or a small nose in the arctic, or a certain nose shape being aesthetically pleasing to a potential mate, those factors might probably be of neutral advantage when that tribal group migrates to an area where nose size is less relevant to survival.

        “I have never heard of a single case where someone who grew up in a different climate from their parents had a nose shape different from their parents and instead resembled the people in their new home.”

        I don’t think anyone is suggesting that: if you look at the US, where there has been massive migration and mixing, in many cases the ‘parents’ are not distinct from ‘people in their new home’: there may be one of each a ‘migrant’ and a ‘local’ and a lot of not indigenous (in the sense of recently imported) physical traits. For nose shape to ‘evolve’ it is necessary that a persons nose may be, ‘on occasions’, genetically different from a parent, otherwise only ‘shuffling’ of existent genes would not allow different nose to develop with new traits. You may not have heard of a single case, but those single cases must have existed, albeit possibly imperceptible.

        If you are looking at a factor in a diverse population where that factor is no longer relevant to the environment in which it evolved, it will be very difficult to do any meaningful statistical research. In this case they are trying to see if there are environmental factors which determine nasal cavity development etc. within the limits of the underlying genetics.

        I think the main issue here is not the research itself, but the way the media is latching on to it.

  5. It seemed to me that the odd line: “the surface, the appearance of people in different populations is much greater than what the genetic differences show on average..” was to imply allegiance to the view that there is no such thing as genetically definable races, so no real races.

    1. Yes. I suspect that many journalists and even some scientists are happy to be misunderstood as claiming some direct Lamarckian influence on the nose, because this will reinforce the modern leftist mantra that race is a social construct.

  6. I’m not seeing what it is about that headline that you and Dawkins object to. The headline doesn’t say “not genetics”; it says “not just genetics”.

    It could have turned out that nose shapes of different populations were entirely attributable to fixation of random alleles by genetic drift — “just genetics” in other words. The headline tells us this is not in fact the case — “not just genetics”. How is this wrong?

    1. That wording still posits that genetics is separable from natural selection as something autonomous. “It’s not just gravity that makes apples fall, it’s also their weight.”

      1. You seem to be claiming that there can be no such thing as genetic change without selection. But that’s exactly what drift is. Presumably you don’t deny that drift exists and can be a significant cause of differences between populations.

    2. Yes, Gregory, I take your point, except that the public has no awareness of what genetic drift is, and therefore wouldn’t even begin with the assumption that nose shape differences between populations could reflect genetic drift. A better headline would be “nose shape differences between populations likely molded by natural selection.”

      A more parsimonious hypothesis than yours is, I think, that the headline writer didn’t know what he/she was talking about.

      1. It may well be that the headline writer doesn’t know what they’re talking about, but I don’t think the headline provides unequivocal evidence of that, and in the absence of such evidence, I’m inclined to interpret it charitably.

  7. I always wondered about these cold noses. On the one hand the Neanderthals had huge sniffers as an adaptation to the cold, but on the other hand the North Asians had tiny ones as an adaptation to the cold. Go figure.

    As an aside, it appears (from Peter Freuchen’s “My Life Among the Eskimo’s”) that the greatest compliment you can make to an Inuit woman is to say: “Your nose is so small, I can hardly see it!”. Appears to point to sexual selection, now doesn’t it? 😆

    1. Some several years ago I read in the NY Times an obituary of a Spaniard famous for his ability to evaluate the efficacy of vino. His nickname was “El Nariz” (IIRC the spelling).

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