It happened again back in 2008<\/a> when I encountered Pepper et al<\/em>\u2019s paper on Somatic Evolution<\/a>, a paper that posed a question mindbogglingly obvious in hindsight, but which had never occurred to me: how can multicellular life evolve in the presence of Darwinian processes that should, by rights, turn every individual cell against its neighbors in a competition for resources? Why isn\u2019t every somatic cell in it for themselves, why doesn\u2019t all multicellular life devolve into cancer? That particular question ultimately gave you \u201cThe Things<\/a>\u201d. You\u2019re welcome. <\/p>\n\n\n\n And now, once again: a bolt from the blue that (for me at least) redefines the word \u201cindividual\u201d in a way that could almost be a deliberate response to Pepper et al<\/em>. An individual<\/em>\u2014 an organism<\/em>\u2014 is <\/p>\n\n\n\n \u201ca living system maintaining both a higher level of internal cooperation and a lower level of internal conflict than either its components or any larger systems of which it is a component.\u201d <\/p><\/blockquote>\n\n\n\n What we have here is a definition that not only acknowledges the issue of cellular competition within the individual, but which is actually based upon it. <\/p>\n\n\n\n Here\u2019s a corollary, which elevates us from the perspective of the individual to the shaping of entire populations: <\/p>\n\n\n\n \u201cThe major evolutionary transitions, including those from prokaryotes to eukaryotes and from free-living cells to multicellularity, all increase the scale over which cooperative interactions dominate competitive interactions.\u201d <\/p><\/blockquote>\n\n\n\n Personally I think that\u2019s a bit clunky: I\u2019d have just said symbiosis increases with complexity; antagonism diminishes[1]<\/a><\/sup><\/sup><\/em>. However you put it, it provides an evolutionary rationale for the emergence of hive minds: competition waning between individuals the same way it did between cells, cooperation waxing, as individuals fuse to become a single superorganism. Put it that way and hive minds seem almost an inevitable next step, on the off chance that extinction doesn\u2019t happen first. <\/p>\n\n\n\n I found those little gems of insight quoted in a 2018 paper<\/a> from Fields and Levin. They weren\u2019t talking about hive minds, of course. They were talking about something far more down to earth: those humble, endearingly cross-eyed little flatworms everybody learns about in first-year biology. You know: Planarians. Dugesia et al<\/em>. <\/p>\n\n\n\n Except, if this paper is right, they\u2019re not exactly worms. They\u2019re not even individuals. What they are is habitats: cellular substrates containing<\/em> individuals. Individuals who may not even like each other very much. <\/p>\n\n\n\n There are these things called neoblasts<\/em>\u2014stem cells, basically. They only comprise about 20% of any given planaria, but they\u2019re the ones that keep the whole worm running. A single neoblast can build an entire worm from scratch; they not only produce new neoblasts but they also give rise to the other cells that comprise the remaining eighty percent of the body. Those<\/em> guys don\u2019t even divide; they\u2019re perennially post-mitotic, they just kind of sit there being muscle fibers or digestive cells or neuroconductors for a week or so before dying off. (Fields and Levin compare them to the sterile workers in insect hives; the queens in that scenario being, of course, the neoblasts themselves.) <\/p>\n\n\n\n <\/p>\n\n\n\n Also\u2014and this is especially wild\u2014genetically-different neoblast lineages can be found in the same planarian body<\/em>. Turns out the genes tend to mix it up at wound sites: neoblasts and non-neoblasts exchange genes during wound repair, which changes the gene frequencies (not to mention sharing any mutations which have turned up along the way), effectively forging new lineages. Further, asexual reproduction in planaria is a form of self-inflicted wounding: the worm literally rips itself in two, each piece subsequently regenerating into a whole worm. So neoblast lineages diverge<\/em>, both during reproduction and repair. You end up with gangs<\/em> of neoblasts\u2014tribes, if you will\u2014whose members are bound to each other by genetic similarity and put at competitive odds with less-similar neoblast populations living in the same body. <\/p>\n\n\n\n I\u2019ve been focusing on asexual reproduction, but there are also planarian species that reproduce sexually. And here\u2019s an interesting factoid: you can sexualize an asexual planarian by feeding it a sexual one. Or cut out the cannibalistic middleman and just inject neoblasts from a sexual worm directly into an asexual one. They\u2019ll move right in, take over, sexualize the territory. <\/p>\n\n\n\n So. Neoblasts are Immortal. Autonomous. Mobile. Genetically distinct. Neoblasts are, in other words, a system which maintains a higher level of internal cooperation and a lower level of internal conflict than either its components or the larger system of which it is a component<\/em> (i.e., the worm entire). <\/p>\n\n\n\n There are quantifiers, of course. It wouldn\u2019t be science if you couldn\u2019t hang numbers off it. The paper cites Hamilton\u2019s Rule, invokes \u201czygotic bottlenecks\u201d, describes a model which simulates a day in the life of Joe Neoblast. But the conclusion, the point<\/em>, is that planarians are not the organism here. Neoblasts\u2014in their competing tribes\u2014 are the organisms, the individuals. The worm is merely the niche they happen to be fighting over. The worm is not an individual but an environment<\/em>, highly complex, constructed by neoblasts out of their own \u201creproductively incompetent progeny\u201d. Maybe it\u2019s just me (I am also, after all, reproductively incompetent), but I find this a profoundly exciting thought. <\/p>\n\n\n\n And I haven\u2019t even mentioned somatic mutations, bioelectrical fields that supersede genetic codes, two-headed and headless variants that persist from one generation to the next even though the genes themselves have not been edited. Fields and Levins invoke all that stuff. But for me, their radical conclusions regarding individuality are especially resonant in the context of John Carpenter\u2019s classic \u201cThe Thing\u201d. So much of planarian biology seems, paradoxically, both alien and familiar. The ability to grow new morphological features independent of genetic code<\/a>. A single particle able to regenerate an entire organism (\u201cWe should each prepare our own food. And I suggest we only eat out of cans.\u201d). Even the alien\u2019s Achilles\u2019 heel, the competing agendas of different groups of neoblasts (\u201cBlood from one of you Things won\u2019t obey when it\u2019s attacked. It\u2019ll try and survive\u2014crawl away from a hot needle, say.\u201d) <\/p>\n\n\n\n It all fits<\/em>. <\/p>\n\n\n\n Canonically, The Thing came from outer space. But maybe that\u2019s not where we should have been looking all this time. <\/p>\n\n\n\n Maybe we should have been looking at the puddles under our own feet. <\/p>\n\n\n\n![\"\"](\"https:\/\/www.rifters.com\/crawl\/wp-content\/uploads\/2021\/09\/Lobo-et-al.jpg\")
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