Ancestry. . . . or convergence?

March 6, 2017 • 2:30 pm

In Experimental Parasitology, two scientists have proposed that “macrophages”—specialized white blood cells that, as part of the immune system, destroy invaders like microbes, are descended from an amoeba. This is based largely on the morphological resemblance of a macrophage and the amoeba, and on the fact that they both eat microorganisms. See the similarity?

But this is surely bogus, for if macrophages were evolutionarily related to the amoebae, their DNA (white blood cells, but not red ones, have their own DNA) would be evolutionarily similar, and this ancestry would be detectable. I’m sure it’s not, and the authors are wrong. The resemblance is a case of evolutionary convergence: independent lineages evolving to have similar traits.  That’s all I want to say.

James McInerney, the chair of evolutionary biology at the University of Manchester (and therefore Matthew’s boss), called out the dreadful paper on Twitter, but Steve Kelly (a Royal Society Research Fellow at Oxford) gave a more humorous response:

Now Kelly didn’t create this comparison, which came from someone named Konbini, but there are other examples of evolutionary convergence, with these created by Karen Zack

Chihuahuas and muffins:

Labreadoodles and fried chicken:

Head over to the Daily Mail to see more (at last—something valuable from that paper!).

44 thoughts on “Ancestry. . . . or convergence?

  1. You joke with that last one, but frankly I’ve eaten at some places that I wouldn’t put it past.

  2. My goodness. How in the world did something this bad get published? Is the Journal of Experimental Pathology a vanity journal with little or no review?

  3. Chihuahuas and muffins converge because they occupy the same environmental niche and are therefore subject to the same natural selection. However science tells us that only one species can occupy a single niche therefore one or the other species will eventually become extinct.

    1. The ecological niches are not equal: chihuahuas are commensals of humans; muffins are preys. A question to chihuahua researchers: can chihuahuas prey on muffins?

  4. I cannot access the entire article, has anyone read it? Is morphology the only evidence they have for this theory? Since eukaryotes themselves likely evolved by parasitizing prokaryotes, I really do not see why this macrophage theory is terribly far-fetched. It has been shown that mitochondria and chloroplasts, for example, have undergone extensive gene reduction and elaborate and complicated gene exchange with host DNA when compared with their presumptive prokaryotic ancestors. I don’t know if macrophage DNA has been sequenced, but it seems that functionally it wouldn’t have to have a full component of host DNA since macrophages only live for a few months. I’d like to know more before laughing this off.

    1. WordPress apparently ate my post! However the organelles in eukaryotes continue to have their own DNA which codes for some of their essential genes (although over time they have passed off a lot of this responsibility). Macrophages are a part of the normal myeloid cell lineage, which means that they are originally derived from the fetal liver of the animal in which they reside. They carry the same DNA – as Jerry noted, as the animal of which they are a part.

      The title of the paper “Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality?” sets up a false dichotomy, the idea is not real – but it also doesn’t fit the status of a myth. It’s just plain false.

    2. The genome of a macrophage cell will be identical to the genome of a nerve cell, and of a lung alveolar cell.
      Yes, they crawling mechanism of an amoeba and white blood cell should be pretty much the same, and that is a kind of convergent evolution, utilizing homologous proteins.

      1. But why couldn’t there be a macrophage cell lineage specific activation of genes that were derived from amoebae? I know that’s weird, but blood cells do undergo some unique and weird genetic events (the whole complicated generation of diversity in t-cells and b-cells, as well as the complete elimination of genes in red cells…both examples that should be kept in mind when folks say ‘DNA in all cells is the same’). Ok, I should probably have quit at one strike, but just sayin’ – isn’t it possible?

        1. Mr Sturtevant already answered your question; “The genome of a macrophage cell will be identical to the genome of a nerve cell, and of a lung alveolar cell.”

          The genomes of all monocytes (which phagocytic cells like macrophages are one type) are identical to all other human cells in the body, apart from the locus specific re-combination you are alluding to in the generation of T and B cell receptor diversity (similar recombination occurs in olfactory genes – a discovery that earned Linda Buck a Nobel Prize). This is because they are derived from hematopoietic stem cells that can become many different cell types. This is well understood and the authors of this paper are being ridiculous.

        2. There are undoubtedly genes that are shared by members of the amoeba genus and all vertebrates. Some are even probably pretty highly conserved. But the whole genome of multiple cultured amoeba species has been fully sequenced as has the human genome now – innumerable times. Human macrophages are not derived from amoebas. Any DNA homology with humans is fragmentary and limited to sequence that probably goes back to the last common eukaryotic ancestor. Mitochondria and chloroplasts do appear to have originated from symbionts and have their own genomes. Human macrophages have the whole human nuclear genome.

  5. Err the journal is Experimental Parasitology I thought the title “Acanthamoeba is an evolutionary ancestor of macrophages: A myth or reality?” would have an easy answer. But the question sets up a false dichotomy, it’s clearly not reality. But it doesn’t reach myth either (defined as either a traditional story or a widely held but false belief). So, “neither of the above”

  6. Oh, mah, gerd… That is the lamest idea I have seen in a long … long time.

    The first cells are similar in that they have converged to similar artifacts introduced by their preparation. They were fixed & freeze-dried (badly, I might add) for viewing under a scanning EM. They do not come close to looking like the living cells.

    1. Ha, I was just thinking that it was ‘the Journal of Experimental Pathological Science’. But it should trivially pass away (I hope).

  7. I will never again be able to bite into a blueberry muffin without thinking about eating the face of a Chihuahua.

  8. Reminds me of the classic “How to Tell the Birds from the Flowers: And Other Wood-cuts” by Robert Williams Wood, in which he demonstrates (with pictures) that the Beet is the missing link between the Bee and the Beetle, and other wonders of natural history.

  9. I bet the authors are calling this refutation fake news. Actually, I imagine they’re embarrassed.

  10. I note that I can pay $41.95 access their teaser: “Here we discuss whether Acanthamoeba and macrophages are evolutionary related.” Well, duh, seems the answer would be a simple ‘yes’.

  11. Reminds me of Williamson’s 2009 paper claiming that caterpillars are onychophorans in moth’s clothing. In PNAS, “communicated” by Lynn Margulis, so no outside review.

    1. There is a much older claim that insect larvae are precocial embryos that hatched early from eggs.

    1. Nuclei are excess baggage for a mature RBC – less room for haemoglobin. Fish RBCs are nucleated – great for getting DNA from blood. Not sure about the other classes.

      1. Billy, how does this hypothesis comport with the fact that birds have nucleated blood cells too? Fish aren’t birds, of course, but if it good for the goose it ought to be good for the gander: no nucleus = more haemoglobin. Birds have high respiratory demands in flight and birds have not “discovered” such benefits via evolution, but they have evolved hollow bones and lost their teeth and tail, all of which help to keep the respiratory load low via having a smaller mass to keep airborne.
        The intelligence of birds is also related to this load-lightening hypothesis. It has been argued that birds also cut down on the mass of their brains by ridding it of unnecessary baggage and just keeping what was necessary for intelligence. Hence the use “bird-brain” as a deprecatory adjective might be out of place.

        1. The plain truth is that birds don’t need to dump the nucleus. Their one-way flow through lung tubules and air-sacs, counter-current gas exchange is all vastly superior to mammalian bellows lungs. So packing the RBCs for the last bit of haemoglobin simply isn’t necessary. See the geese flying over Mount Everest in Winged Migration, As an aspiring endurance athlete, I’d love to have those lungs, even with a lower hematocrit!

          In this and many other ways, I always say that the archosaurs got most of the cool stuff, and mammals simply bodged along [or, rather, optimized a snuffling, near-blind quadropedal burrower body plan. Weighing 2kg or less, living 2yr or less. Fromthis, the argument from design implies that the image of God was a brainy raptor, and that Satan managed to send the big comet. So we were YWHs Plan B…

        2. Don’t know. My guess, though, is that the mechanism that jettisons the nucleus evolved after the mammalian line split from the reptile/bird line. If it had evolved earlier and is indeed a good thing, then I’m sure the other classes would have the same trait.

      2. In mammals, immature red blood cells in the marrow are generated by blood stem cells. At first nucleated, but they expel their nuclei as they mature.

  12. I have not read the article, but this seems a) silly on the face of it and b) absurdly easy to test (and likely refute). Just look at the genome of leukocytes and erythrocyte precursors. Red blood cells are anucleate at maturity, but their progenitor cells have nuclei and can be readily harvested from bone marrow (not mine, thank you). I’ll be a thousand bucks that leukocytes and erythrocyte (precursors) have the same DNA and it’s wildly different from Acanthameba sp. This is close to Trumpian science.

Leave a Reply