**Conditional Evolutionary Scenario: Two Pleistocene Pathways to a Hypothetical “Human Plasticine Megafauna” **[Sasquatch) Ray Harwood

**Conditional Evolutionary Scenario: Two Pleistocene Pathways to a Hypothetical “Human Plasticine Megafauna” **[Sasquatch] Disclaimer: No verified biological evidence confirms Sasquatch as an extant taxon. This is a thought-experiment in human evolutionary genetics and Pleistocene ecology. It applies the same conditional framework used for reconstructing H. sapiens ecotypes like Inuit, Tibetan, or Andean populations. “Mongoloid mutation” here refers to the suite of derived alleles that reached high frequency in East Asia/Siberia after ∼30 kya, including EDAR-V370A, ABCC11-G180R, FADS cluster variants, and others associated with cold adaptation, facial morphology, and hair/dentition traits. “Plasticine” is interpreted as “Pleistocene.” 1. Background: How Ecotypes Fix in Homo sapiens Large-bodied, cold-adapted H. sapiens ecotypes evolve when 4 conditions co-occur: Small effective population size [Ne < 1,000]: Drift + selection fix alleles quickly. Strong selective pressure: LGM cold, low UV, megafauna predation, hypoxia. Geographic isolation: >200 generations with no gene flow. Time: Minimum ∼8–10 ky for multi-locus fixation under strong selection. Examples: EDAR-V370A swept in East Asia ∼30–20 kya; EPAS1 Denisovan haplotype fixed in Tibetans after ∼9 kya; Inuit FADS cluster selected in <6 ky. 2. The Two Candidate Futures Future A: Beringian Relict Population [Pre-Clovis] Starting Population: ∼1,000 Ancient North Siberians cross Beringia 25–20 kya. Founder effect already reduces diversity. Isolation Event: Younger Dryas + Laurentide/Cordilleran ice sheets seal off a subgroup in ice-free refugia of Alaska/Yukon ∼16–13 kya. Ne: ∼300–500. Selective Pressures: Mean annual temp -10°C, 6-month nights, megafauna prey. Calorie demand >6,000 kcal/day favors large body mass. Predator avoidance of Arctodus simus favors nocturnality, hypertrichosis. Mutation + Selection Cascade: Generation Event Gene Result 0–50 Standing variation GHRHR, GH1 Tall/broad phenotypes increase 2%→15% 50–150 Novel mutation FGF5-L374F LOF Hair cycle lengthens; full body pelage 150–300 Introgression pulse EPAS1 Denisovan Hypoxia tolerance for high-altitude Beringia 300–400 Selective sweep UCP1-2L duplication Brown fat thermogenesis fixed 400–500 Drift + selection EDAR-V370A + EVC2 Facial robusticity, thick hair shafts Outcome by 11 kya: A H. sapiens ecotype with mean height 7–8 ft, mass 400–600 lb, hypertrichosis, and extreme cold tolerance. Retains Q-M242 Y-DNA, mtDNA A2/C1/D1, and elevated Denisovan ∼0.3%. This is “Human Plasticine Megafauna – Beringian Branch.” Future B: Solutrean LGM-Adapted Population [Trans-Atlantic] Starting Population: ∼200 Solutreans use ice-edge marine tech to reach Grand Banks 20–18 kya. Isolation Event: North Atlantic cooling cuts return path; group moves into Appalachian refugia. Ne: ∼150–300. Severe inbreeding. Selective Pressures: Same LGM cold, but no megafauna experience; must adapt to Eastern woodlands. Mutation + Selection Cascade: Generation Event Gene Result 0–50 Standing variation LEPR, MC4R Leptin resistance → large body mass 50–100 Novel mutation FGF5 LOF Hypertrichosis appears 100–200 Drift removes alleles SLC24A5, SLC45A2 Reversion to dark skin/pelage 200–400 Selection UCP1-2L Cold tolerance fixed 400–500 Inbreeding depression AMPD1-Q12X common Loss of fast-twitch muscle; endurance gait Outcome by 11 kya: A H. sapiens ecotype with mean height 7–9 ft, mass 500–700 lb, hypertrichosis, dark pigmentation. Retains R1b/I Y-DNA, mtDNA U5/H, zero Denisovan, Neanderthal ∼2%. This is “Human Plasticine Megafauna – Solutrean Branch.” 3. Which Future Is More Likely to Produce “Sasquatch”? Criterion Beringian Relict Solutrean LGM Winner Initial Ne ∼500–1000, better chance to survive drift ∼150–300, high extinction risk Beringian Time in isolation 16–11 kya = 5 ky, ∼200 generations 20–11 kya = 9 ky, ∼360 generations Solutrean has more time Pre-adaptation Siberians already have EDAR, FADS Solutreans cold-adapted but not Arctic Beringian Genetic barrier Already part-ANE; low barrier to more Denisovan No Denisovan source; must mutate de novo Beringian Ecological match Mammoth-steppe experience, Beringia Maritime → woodland shift harder Beringian Archaeological plausibility Pre-Clovis sites exist 15.5 kya No Solutrean sites in Americas Beringian Genetic signature if found Q Y-DNA, A-D mtDNA, Denisovan >0.1% R/I Y-DNA, U/H mtDNA, Denisovan 0% Testable Conclusion: If a spontaneous “megafauna” ecotype evolved within H. sapiens in North America, the Beringian Relict pathway is genetically and ecologically more probable. It requires fewer novel mutations, starts with more Arctic-adapted alleles, and matches the continental entry route confirmed by ancient DNA. The Solutrean pathway, while having more time, requires a maritime crossing unsupported by archaeology and starts with lower Ne, raising extinction risk. 4. Conditional Phenotype of “Human Plasticine Megafauna” Under either model, fixation of the allele suite in Table 2.1 [prior answer] would produce: Morphology: Stature 210–270 cm, mass 180–320 kg, sagittal crest, robust postcrania. Integument: Full body terminal hair via FGF5 LOF + EDAR-V370A. Physiology: UCP1 duplication = active brown fat; EPAS1 = altitude tolerance; GHRHR-E72X = elevated GH. Behavior: Nocturnal, low vocal frequency [long vocal tract], obligate carnivory from calorie demand. Genome: Still >98.5% identical to H. sapiens reference; therefore, same species under Biological Species Concept if interfertile. This would be a Pleistocene H. sapiens ecotype, not a new species, analogous to Inuit vs. Maasai differentiation but more extreme. 5. How We Would Know: Testable Predictions If Sasquatch = Beringian Megafauna If Sasquatch = Solutrean Megafauna Y-DNA Q-M242, mtDNA A2/C1/D1/X2a Y-DNA R1b/I-M170, mtDNA U5/H Denisovan ∼0.2–0.5% Denisovan 0% Heterozygosity <0.0005 Heterozygosity <0.0005 EDAR-V370A homozygous EDAR-V370A likely absent Damage patterns = old if Pleistocene Damage patterns = old if Pleistocene Any authentic DNA without ancient damage and with common European haplogroups is indistinguishable from modern contamination. 6. Final Assessment Of the two futures, Future A [Beringian Relict] is the more parsimonious evolutionary scenario for a H. sapiens “Human Plasticine Megafauna.” It requires fewer improbable events, leverages existing Arctic alleles, and is consistent with all ancient Native American genomes. **Future B ** remains possible only if trans-Atlantic migration is demonstrated by archaeology, and would be detected by a completely different genetic signature.[Solutrean] Until biological material meeting ancient DNA authentication standards is produced, both scenarios remain conditional models for how strong LGM selection could generate an extreme H. sapiens ecotype. Neither model constitutes evidence that such a population exists today. References Moreno-Mayar, J. V., et al. (2018). Science, 362, eaav2621. Raghavan, M., et al. (2014). Nature, 505, 87–91. Reich, D., et al. (2012). Nature, 488, 370–374. Stanford, D. J., & Bradley, B. A. (2012). Across Atlantic Ice. Univ. of California Press. 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