Unreal Nature

February 2, 2013

The Immune System

Filed under: Uncategorized — unrealnature @ 6:55 am

… it is arguably a striking irony that the often remarked centrality of individualism in the last 200 years of social theory has perhaps been the greatest obstacle to seeing the profoundly social, or anyhow cooperative, nature of life more generally.

This is from Processes of Life: Essays in the Philosophy of Biology by John Dupré (2012):

… it is an increasingly familiar idea that we … have … a characteristic genome in each cell of our body, and that this genome is something unique and distinctive to each of us.

… It’s pretty clear, however, that we cannot generally admit that parts of a clone are parts of the same individual. Whether or not there are technical contexts for which it is appropriate, I doubt whether there are many interesting purposes for which two monozygotic human twins should be counted as two halves of one organism. Or anyhow, there are certainly interesting purposes for which they must be counted as distinct organisms, including almost all of the regular interests of human life. An obvious reason for this is that most of the career of my monozygotic twin (if I had one) would be quite distinct from my own. And for reasons some of which should become clearer in light of the discussion below of epigenetics, the characteristics of monozygotic twins tend to diverge increasingly as time passes. The careers of monozygotic twins may carry on independently from birth in complete ignorance of one another; but it is hardly plausible that if I were now to discover that I had a monozygotic twin, this would drastically change my sense of who I was (i.e. a spatially discontinuous rather than spatially connected entity). Some kind of continuing connection seems needed even to make sense of the idea that these could be parts of the same thing.

… A good way of approaching the subject matter of epigenetics is to reflect on the question why, if indeed all our cells do have the same genome, they nevertheless do a variety of very different things. It is of course very familiar that not all the cells in a complex organism do the same things — they are differentiated into skin cells, liver cells, nerve cells, and so on. Part of the explanation for this is that the genome itself is modified during development, a process studied under the rubric of epigenetics or epigenomics.

… Whether epigenetic research shows that genomes are diverse throughout the animal body of course depends on one’s definition of ‘genome’ and one’s criterion for counting two as the same. It needs just to be noted that if we choose a definition that pace the points made in earlier sections, counts every cell as having the same genome, we will be overlooking differences that make a great difference to what the cell actually does.

… I want to suggest that the organisms that are part of evolutionary lineages are not the same thing as the organisms that interact functionally with their biological and non-biological surroundings. The latter, which I take to be more fundamental, are composed of a variety of the former, which are the more traditionally conceived organisms.

… about 90 percent of the cells that make up the human body belong to … microbial symbionts and, owing to their great diversity, they contribute something like 99 percent of the genes in the human body. It was once common to think of these as little more than parasites, or at best opportunistic residents of the various vacant niches provided by the surfaces and cavities of the body. However, it has become clear that, on the contrary, these symbionts are essential for the proper functioning of the human body. This has been recognized in a major project being led by the US National Institutes of Health, that aims to map the whole set of genes in a human, the Human Microbiome Project.

The role of microbes in digestion is most familiar and is now even exploited by advertisers of yoghurt. But even more interesting are their roles in development and in the immune system. In organisms in which it is possible to do the relevant experiments it has turned out that genes are activated in cells by symbiotic microbes, and vice versa. … [I]t seems plausible that the complex microbial communities that line the surfaces of the human organism are the first lines of defence in keeping out unwanted microbes. Since the immune system is often defined as the system that distinguishes self from non-self, this role makes it particularly difficult to characterize our symbiotic partners as entirely distinct from ourselves.

… contrary to the assumption that is fundamental to the one genome, one organism idea, the biological entities that form reproducing and evolving lineages are not the same as the entities that function in wholes in wider biological contexts. Functional biological wholes, the entities that we primarily think of as organisms, are in fact cooperating assemblies of a wide variety of lineage-forming entities. In the human case, as well as what we more traditionally think of as human cell lineages, these wider wholes include a great variety of external and internal symbionts. … [T]he role of cooperation in forming the competing wholes has been greatly underestimated. And there is a clear tendency in evolutionary history for entities that once competed to form larger aggregates that now cooperate.

… it is arguably a striking irony that the often remarked centrality of individualism in the last 200 years of social theory has perhaps been the greatest obstacle to seeing the profoundly social, or anyhow cooperative, nature of life more generally.

My most recent previous post from Dupré’s book is here.

-Julie

http://www.unrealnature.com/

 

4 Comments

  1. I read this through the «spectacles» of having recently reread Algis Budrys’ Rogue Moon. Written in 1960, it includes a pre-cloning exploration of duplicated organisms … instead of physically sending a human being to the moon, an identical copy is transmitted there ad reassembled in situ. An important part of the fiction is consideration of how far, and for how long, the original and the copy remain the «same» person.

    When I read it around age 14, all of that philosophical stuff went straight through the cavity between my ears without troubling the brain cells … but now, of course, the reality of cloning made it very relevant – and it recycled as I read the opening passages of your extract here. Then it came back again to rattle around in the last partial sentence too.

    It’s interesting, if nothing else, to muse on how far “the entities that we primarily think of as organisms” are not only “cooperating assemblies of a wide variety of lineage-forming entities” but also cooperating assemblies of «selves» … but, having once started on that track, to further wonder how one then defines «self» at all in a way that is both coherent and precise (a sort of bioheisenbergianism!) – either downwards or upwards

    Comment by Felix — February 2, 2013 @ 5:26 pm

  2. System crash before I finished. To continue…

    The immune system can’t, as we get deeper into what we now know of our plurally hierarchical biologies, perhaps be seen as a «system» at all, except in a provisional sense at a single parochial level. Which ends up making me cross eyed but exhilarated :-)

    Comment by Felix — February 2, 2013 @ 5:41 pm

  3. My enjoyment of Dupré’s essay pretty much parallels yours. (I’m delighted that you picked up the wider “system” I wanted to suggest with my post title.)

    Comment by unrealnature — February 3, 2013 @ 5:09 am

  4. Always delighted to discover that I’ve delighted you! :-)

    Comment by Felix — February 3, 2013 @ 7:52 am


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