Retrodictive Disproof of the Onto- Phylogenetic “Just-So Story” and the Role of Narrative in Evolutionary Medicine
Noel T. BOAZ, Ph.D., M.D.
Anatomy Laboratory, Emory and Henry College School of Health Sciences, Marion, VA 24354,
U.S.A.
Laboratory of Biological Anthropology and Anatomy, Integrative Centers for Science and Medicine, Martinsville, VA 24112,
ABSTRACT Whereasmuch of biomedical science relies on the laboratory experiment as its gold- standardmethodology to disprovehypotheses, investigations ofhistorical fact in the evolutionary sciences require a time- controlledmultidisciplinary approachakin to forensic science that is equally rigorous in disproving its hypotheses When detractors, scientific and otherwise, disparage paleobiological hypotheses as “untestable” they may use the term “just - so story” pejoratively to dismiss them as fanciful fiction, drawing a comparison with the popular Just- So Stories publishedby Anglo-Indian author Rudyard Kiplingin the early twentieth century The experimentalmethod tests hypothetical predictionsin a uniformitarian empirical framework that is ahistoricaland mechanism- focused, while the forensic method tests retrodictionsin a uniformitarian empirical framework that is historical and narrative in focus Both methods are fully compatible witheach another, and non-falsified hypotheses must conform withempirical results obtained through eithermethod.A thoroughly tested onto-phylogenetic (“evo-devo”) narrative is an essential component ofEvolutionary Medicine, driving research, educational, and clinical advances Clinical experienceamplydemonstrates that therapies whichignore evolutionary history and rest solely on ahistorical and mechanistic assumptions lead to less-than-optimal patient outcomes To operationalize the retrodictive approachananthropogenic (“human-origins”) matrix isconstructed using an array of 9 paradigmatic tools, including rigorous temporal calibration,applied across 7 categories of narrative elements, including environmental context andadaptations, in order to assess hypotheses Drawing ananalogy to Kipling’s unfalsifiable “How the Rhinoceros Got His Skin” (1902 ) the anthropogenic matrix is used to construct a falsifiable narrative of evolutionary and developmental anatomyof the human integument,with clinicalimplications
U.S.A.TESTING AN ANTHROPOGENIC ONTO-PHYLOGENETIC HYPOTHESIS (AOPH)
Ananthropogenic onto-phylogenetic hypothesis (AOPH) shares two characteristics with a Kipling-esque“just-so” story (JSS) They are both premised on observable phenomena in thenatural world, andthey explain theorigins of thosephenomenabymeans of a narrative They differ fundamentally in that an AOPH is constructed to be falsifiable within a scientific hypothetico-deductive paradigmandby its very nature will change as new data become available The JSS is a non-falsifiable literary creation, despite its author having derivedsome inspiration from Charles Darwin’s Origin of Species (and also Aesop’s Fables). Its essentially unchangeablenature is shown byKipling’s (1902) “HowtheRhinoceros Got His Skin,” originally a bedtime story for his young daughter “Taffy” would correct her father if hemadethe slightest variation in the narrative, giving rise to the appellation “just so” for howthe story and others likeit had to be told Kipling intentionally incorporated whimsical incongruities in the stories, whichcontribute a large part of their allure He was awarded theNobel Prize for Literature in 1908.
The JSS storyline:A lone “Parsi-man”wearing a resplendent hat (see above) bakes a cake in a cookstove improbably set on an exotic beach somewherebetween theIndian Ocean and the Red Sea.A large unmanneredrhinoceros emerges from the “altogether uninhabited interior” to gobble up the cake while the angry Parsi watchesfrom a palm tree He vows revenge Six weeks later a heatwave forces everyone to the shoreto cool off People undress to go into the water buttherhino,which of course does not wear clothes, takes his skin off, leaving it on the beach The Parsi sees hischance and rubs stale cake crumbs into the rhino’s skin Whentherhinoputshis skin backon, buttoning it up in front, it itches terribly Distracted so muchby the itching that he doesnotthink to unbuttonhis skin the rhino rubs against a tree, causing his skin to form large folds andrubbing off thebuttons Therhino wanders off in a badtemper and presumably survives to bequeathhisunique skin and bad disposition to future generations
If viewed as a scientific hypothesis a JSS isfallacious based on all four Baconian criteria (see bottom right) Thus itis untestable and unfalsifiable usingthe anthropogenic matrix proposed here (see right) Science-mindedchildren (unlike “Taffy ”) point out to no avail that rhinosdonot eat cake, removing theirskin would be fataleven if they hadopposablethumbs(whichtheydon’t),rubbing like that wouldinjurethe skin and would not immediately produce callous-like folds, thecrumbsinside would eventually be absorbed,and even if those changes happened they would notbe passed on to the rhino’s offspring(that would beinheritance of acquired characters) An adult scientist labeling a colleague’s evolutionary narrative hypothesis a JSS then is undoubtedly globally condemnatory,but not especiallyspecific nor particularly useful in advancing scientific inquiry Is it possible tore-tell Kipling’s tale about integumentary origins from a human perspective, generating an Anthropogenic Onto-Phylogenetic Hypothesis (AOPH) as a scientific narrative useful for both research anddidacticpurposes,and devise reliablescientificcriteria to test it?
How Humans Got Their Skin: An Anthropomorphized but Disprovable AOPH as Rudyard Kipling May Have Told It
Shortly after the dawn of the world (some 4.567 thousand million [as we British say for “billion”] years ago), ittle single-celled LUCA, the Last U niversal Common Ancestor of us all, first dressedherself up in a lipidbilayer cell membraneand for the first time clothedher naked RNA MotherNature approved and invoked Natural Selection (as I describedpreviously and somewhat imperfectly, as the “Law of theJungle”) to ensure that theseadaptations were bequeathed to subsequent generations This most ancient of adaptations was the first approximation of an “integument” between the “altogether uninhabited” organismal interior (no organelles) and the environment LUCA’s Hadean habitat was a rotten- egg world – sulfurous hot,dark, oxygenless, clay-lined clefts alongside hydrothermal vents deep in the sea Bacteria-like descendants of LUCA, Archaean bacteria, began living in stromatolitic colonies over the next billion and a half years, adhering torocks, covering themselves with a proteinaceous protective film, and producing oxygen as a metabolic byproduct But bacteria hadno manners then andthey have no manners now They just continued proliferating until theypollutedthe world – with oxygen
What to do?
In good time Bacteria began to use the caustic but energy-rich oxygenmolecules in theirmetabolism Bigger bacterial descendants preyed upon and engulfed the oxygen- users butthen made an evolutionarypact with them known as symbiosis The big bacteria didn’t digest the smallerones and used the hydrogen electrons left over from the smaller bacteria’s oxygen respiration for their own energy The smaller bacteriabenefitted by living protected insidethe larger bacteria’s cell membrane The little bacteriawere the ancestors of the mitochondriawho after a billion or moreyearsare still there in our cells today, still producing energy via the electron transportchain The bigger cell became the first eukaryote and enclosed its DNA-containingnucleus with another membrane layer, thenuclear membrane
Like the bacteria before themthe eukaryotes discovered that there was strength in numbers Theyclumped together, utilizing theadherens molecules that their ancestors had evolved originally to cling torocks They began communicating cell- to-cell with receptor and messengermolecules to produce proteins that promoted the survival not just of themselves but of the aggregate The genes that had coded for the protective proteinaceous film of their bacterial stromatoliteancestors evolved to produce anactual skin-like coveringover all the aggregated cells Thusdid the integument appear as a covering enclosingall themulti-cellular creatures on earth, includingour ancestors, the actively moving animals
The ntegument was so important to animalsas theyadapted to the many niches in the seas,jungles, mountains,and plains of theearth that MotherNaturebequeathed to multicellularanimals one entire embryonic germ layer (the ectoderm) and part of a second layer (the mesoderm) for its development The integument became the largest organ in the vertebrate body, serving as an impenetrable barrier in our fishy ancestors between their internal milieu and thesurrounding waters Asouramphibian forebears moved onto the land,their still-moist respiring skinhelped them catch their breath as they wriggled away frompredators Those too slow to escape the jaws of doom, however, didnotdie in vain, for the integument’s noxious toxins provided a bitter reminder to any predator the next timeit contemplated dining on one of their fellows Among the descendent, fully terrestrial amniotes the integument became a major barrierto water loss made possibleby a drynon-living layer of epidermal cells sealed by corneodesmosomes the stratum corneum But 300 million years ago was a time of snowand ice andagain the integument helped our ancestors survive Hair evolved to insulate the body of mammal-like reptiles from the cold When large reptiles, the dinosaurs, took over diurnalniches, a furry integument provedto be a valuable exaptation for their tinynocturnalcousins,the warm- blooded mammals, whohad to stay warm while theyscurriedaround during thehours of darkness Mammals sensed the environment around them via whiskers (integumentary hairs on the face), communicated via smell and cooled themselves off via integumentary sweatglands, and even fed their offspring with nutritious secretions from female integumentary glands that came to be known in humans as “breasts.” Asthe Cenozoic Era dawned some 65 million years ago a group of diurnal, tree-living mammals, the primates, adorned themselves in a stunning array of patterns and colorsof skin and pelage, communicating everything from receptivity to mating togroup membership Paradoxically, human-like primates largely divested themselves of their integumentary hairy raiment in orderto cool off (similar to my earlierdiscussion of this topic relative to therhinoceros [op cit.]). Environmental desiccation 5 to 6 million years ago forced them to adapt to a sweaty, bipedal life on t heopen ground Increased ultraviolet radiation on naked skin, however, disrupted folate metabolismin australopithecine mothers leading to many neurological birth defects fatal to their newborns, until protective dark skinevolved inearly Homo some 1.2 million years ago Variablymelanic integument has been the norm for the human speciesever since, with skin color rapidlyevolving a lighter hue in thosepeople migratingto sunlightdeprivedhigher latitudes (to allow adequate Vitamin D production in the skin)and evolving rapidly to darker skin in peoplemovingback towards theEquator (to prevent ultravioletradiation skin injuryand folate deficiency) Despite a remarkable lability in human skin color and itslack of correlationwith
Steps to Retrodictively Disprove an AOPH
• 1. Construct an Evolutionary Timeline from TimeTree.org for Homo sapiens, showing the geological time scale, evolutionary divergence times as calculated with the molecular clock, and temporally controlled paleoenvironmental parameters (above left).
• 2. Construct a time-controlled phylogeny with extant comparative organisms showing major genomic and morphological adaptations related to the integument from the Last Universal Common Ancestor (LUCA) to the present. Time is plotted on a logarithmic scale. Divergence dates are means from the Time Tree of Life (www.timetree.org). Extant related organisms are shown along the top row. Major adaptations are indicated in boxes at their respective evolutionary nodes, with references (above right).
3. Dissect a narrative (below left) into 7 elements and critically assess them along a core empirical diagonal of paradigmatic tools (in green below). Following Baconian and Darwinian scientific methods and as still practiced in forensic sciences (see lowermost), all narrative elements must a) agree, b) differ (with explanation), or c) concomitantly vary with the core empirical diagonal.
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