Evolution of languages
The evolution of languages encompasses the historical diversification and transformation of human speech systems through cultural transmission, involving mechanisms such as regular sound changes, grammatical innovations, lexical borrowing, and population movements that parallel aspects of biological descent with modification.[1] Languages diverge from common ancestral forms, known as proto-languages, which are reconstructed via the comparative method by identifying systematic correspondences in phonology, morphology, and syntax across related tongues.[2] This empirical approach has delineated over 100 language families worldwide, with robust evidence for divergences spanning several millennia, though deeper connections beyond approximately 10,000 years often lack sufficient cognate retention due to heterogeneous rates of change.[3] Key defining characteristics include the tree-like branching of families under isolation, interspersed with reticulate networks from contact-induced convergence, challenging simplistic cladistic models.[4] Notable achievements encompass the reconstruction of Proto-Indo-European, ancestral to languages spoken by billions, linking migrations like those of steppe pastoralists to linguistic spreads, and the application of computational phylogenetics to date splits with greater precision than traditional lexicostatistics.[3] Controversies persist regarding the uniformity of evolutionary rates—punctuated by substrate influences or elite dominance in conquests—and the limits of reconstruction, as unwritten prehistory obscures origins, with polygenetic emergence of language faculty debated against monogenesis but empirical focus remaining on post-dispersal diversification.[1] Recent advances integrate geospatial data and Bayesian modeling to correlate linguistic phylogenies with archaeological and genetic evidence, enhancing causal insights into how geography, demography, and ecology shape linguistic trajectories.[5]Foundations of Language Evolution
Biological and Cognitive Origins
The capacity for human language emerged through evolutionary adaptations in hominins, integrating biological modifications to vocalization and neural structures with cognitive advancements enabling symbolic reference and recursive syntax. Genetic evidence highlights the role of the FOXP2 gene, where two amino acid substitutions distinguish the human variant from that in chimpanzees and Neanderthals, coinciding with enhanced fine motor control for speech articulation and observed in fossils dating to approximately 200,000 years ago.[6][7] These changes likely facilitated vocal learning, as demonstrated in songbirds and mice engineered with humanized FOXP2, which exhibit accelerated sequence learning relevant to syllable production.[8] Anatomically, the descent of the larynx and remodeling of the hyoid bone in Homo sapiens around 100,000–50,000 years ago enabled phonation for complex vowels and consonants, distinguishing human speech from primate calls limited by higher laryngeal positions.[9] Fossil records of larger-brained species like Homo heidelbergensis (circa 700,000–200,000 years ago) show preliminary adaptations in the basicranium and mandible supporting prolonged vocal tracts, though full articulatory precision appears tied to modern Homo sapiens.[9] Genomic surveys indicate that core language-related neural circuitry, including variants in genes influencing synaptic plasticity, predates symbolic artifacts by at least 135,000 years, suggesting a proto-language capacity before widespread cultural expression.[10] Cognitively, language evolution built on hominin enhancements in social cognition and executive function, such as theory of mind and working memory, which underpin reference and displacement—referring to absent entities.[11] Paleoneurological evidence from endocasts reveals disproportionate expansion of Broca's area (Brodmann areas 44 and 45) in the left inferior frontal gyrus across hominin evolution, correlating with combinatorial processing of sounds and gestures as precursors to syntax.[12][13] This asymmetry, evident by 2 million years ago in early Homo but refined in later species, aligns with gestural theories positing manual signaling as a bridge from primate communication to vocal language, driven by ecological pressures for collaborative foraging.[14] Empirical models of evolutionary dynamics further indicate that selection for prosocial duetting and error-signaling in groups favored recursive embedding, a uniquely human trait absent in other primates despite shared vocal grooming precursors.[15][16]Evolutionary Preconditions in Hominins
Anatomical adaptations in the vocal tract and associated structures formed critical preconditions for articulate speech in hominins. The reconfiguration of the supralaryngeal vocal tract, including a lowered larynx position relative to the oral cavity, enabled the production of a diverse range of formant patterns necessary for distinguishing vowels and consonants. Fossil evidence, such as the hyoid bone from the Neanderthal site of Kebara Cave (dated to approximately 60,000 years ago), exhibits a morphology similar to that of modern humans, indicating that Neanderthals possessed a vocal apparatus capable of producing speech-like sounds.[17] Reductions in jaw size and masticatory muscle mass, observed in the hominin fossil record from the late Pliocene onward (around 3–2 million years ago), correlated with vocal tract lengthening and flexibility, reducing constraints on tongue mobility for precise articulation.[18] Genetic factors underpinned neural circuits for vocal-motor control. The FOXP2 gene, which regulates developmental processes in brain regions involved in speech production such as the basal ganglia and cortex, features two derived amino acid substitutions unique to the human lineage after divergence from chimpanzees approximately 6–7 million years ago. This variant was shared with Neanderthals, as evidenced by ancient DNA from specimens dating to over 40,000 years ago, implying fixation in the common ancestral population before the Neanderthal-modern human split around 500,000–800,000 years ago.[19] Mutations in FOXP2 in modern humans are associated with impaired speech motor coordination and language processing, underscoring its role in fine-tuning orofacial movements essential for phonation.[20] Cognitive capacities for sequential planning and intentional signaling provided behavioral foundations. Early hominins, from Homo habilis onward (circa 2.3–1.4 million years ago), exhibited hierarchical action sequencing in Oldowan stone tool production, reflecting cortical-basal ganglia circuits homologous to those repurposed for linguistic syntax.[21] Self-monitoring and iterative skill refinement, prerequisites for inventing proto-lexical signals, are inferred from the progressive complexity of Acheulean tools by Homo erectus around 1.8 million years ago.[22] These abilities, combined with limbic-mediated social communication, enabled the coupling of motor planning with referential gesturing or vocalization, setting the stage for protolanguage through mimetic practices like pantomime in shared cultural activities.[22] Such preconditions, while present in multiple hominin species, did not necessarily equate to fully modern symbolic language, which archaeological evidence suggests crystallized in Homo sapiens after 100,000 years ago.[23]Mechanisms of Linguistic Change
Phonetic and Phonological Shifts
Phonetic shifts encompass gradual alterations in the articulation or perception of speech sounds, often beginning as subphonemic variations among allophones before potentially restructuring the phonological inventory. These changes contrast with phonological shifts, which modify the systemic distribution or contrastiveness of phonemes, such as through mergers (where distinct phonemes become identical) or splits (where one phoneme diversifies into multiple)./04%3A_Word_Forms_-_Processes/4.06%3A_Phonological_Change) Empirical evidence from comparative reconstruction demonstrates that such shifts occur regularly and exceptionlessly within speech communities, as posited in the Neogrammarian hypothesis of the late 19th century, though later refinements account for conditioned exceptions via analogical leveling or subsequent rules.[24] Common mechanisms include assimilation, where a sound adopts features of a neighboring one to facilitate articulation—such as nasalization spreading regressively in English "can't" from /kænt/ toward [kæ̃nt]—and its inverse, dissimilation, which increases perceptual distinctness by differentiating similar sounds, as in Latin "peregrinus" yielding "pilgrim" in English via partial dissimilation of liquids.[25] Lenition (weakening, e.g., stops to fricatives) and fortition (strengthening) further exemplify phonetic drift, often conditioned by prosodic environment like intervocalic position.[26] Vowel shifts, typically chain reactions preserving contrasts, arise when perceptual or articulatory pressures displace one vowel, prompting adjacent ones to follow; acoustic overlap in formant spaces provides empirical basis for mergers, as reconstructed via comparative method across dialects.[27] [28] A paradigmatic consonant shift is Grimm's Law, operative in Proto-Germanic around the first half of the 1st millennium BCE, whereby Indo-European voiceless stops (*p, *t, *k) systematically fricativized to *f, *θ, *x (e.g., PIE *pṓter > Proto-Germanic *fader, yielding English "father"), voiced stops (*b, *d, *g) became voiceless (*p, *t, *k), and aspirates (*bh, *dh, *gh) devoiced to voiced stops (*b, *d, *g).[29] This unconditioned change, affecting all environments, exemplifies causal regularity driven by internal systemic pressures rather than external borrowing, with archaeological correlations to Nordic Bronze Age expansions around 1200–500 BCE supporting its temporal bracketing.[30] In vowels, the Great Vowel Shift in English, initiating circa 1400 CE and substantially completing by 1750 CE, raised and diphthongized Middle English long vowels—e.g., /iː/ to /aɪ/ (bite), /uː/ to /aʊ/ (house)—while preserving short-long distinctions through compensatory adjustments, evidenced by rhyming patterns in Chaucer (late 14th century) versus Shakespeare (early 17th).[31] [32] Causal factors, grounded in articulatory phonetics and first-language acquisition data, include gestural timing slips during rapid speech, leading to lenition, and perceptual reanalysis by children who map variable adult outputs onto stable categories, propagating innovations probabilistically across generations.[33] [34] Empirical support derives from cross-linguistic typological patterns and experimental phonetics showing chain shifts minimize homophony risks, as in quantified formant trajectory models; external influences like dialect contact accelerate but do not originate regular shifts, per reconstructions of isolated proto-languages.[35] [28] These processes underpin family-level divergences, with phonological evidence enabling glottochronological estimates of split timings, such as Proto-Indo-European dispersal circa 4000–2500 BCE.[24]Morphological and Syntactic Transformations
Morphological transformations encompass changes to the internal structure of words, including the erosion, regularization, or innovation of inflectional and derivational morphemes, often driven by phonological erosion and analogical leveling. In Proto-Indo-European, reconstructed with eight noun cases and complex verbal conjugations, daughter languages exhibited widespread simplification; for instance, Germanic languages reduced cases from eight to four or fewer by the attested stages, as sound changes like vowel reduction in unstressed syllables obscured distinctions.[36][37] This loss is evidenced in Old English texts, where dative and accusative mergers occurred progressively from the 5th to 11th centuries CE, culminating in Modern English retaining primarily genitive and common forms.[36] Analogical processes further contributed, as irregular paradigms were leveled; in English strong verbs, over 200 ablaut patterns in Old English dwindled to about 10 by Middle English through extension of weak -ed endings.[38] Reanalysis, a covert mechanism, frequently underlies morphological innovation by reinterpreting ambiguous forms; for example, Middle English "a napron" was reanalyzed as "an apron," shifting the morpheme boundary and altering perceived derivation.[39] Such changes often correlate with typological shifts from fusional (portmanteau morphemes encoding multiple categories) to analytic structures, as seen in the Romance languages' reduction from Latin's six cases to two or none, compensated by prepositional phrases.[40] Empirical evidence from comparative reconstruction and diachronic corpora confirms this unidirectional trend in many Indo-European branches, attributed to learnability pressures and contact-induced simplification rather than random drift.[41] Syntactic transformations involve rearrangements in phrase structure, clause combining, and dependency relations, frequently interlinked with morphological decay as languages compensate for lost inflectional cues with rigid ordering or functional elements. Proto-Indo-European likely featured flexible but predominantly subject-object-verb (SOV) order, with many branches shifting to subject-verb-object (SVO); Latin's SOV dominance transitioned to SVO in Vulgar Latin by the 3rd-5th centuries CE, as attested in inscriptions and early Romance texts, enabling reliance on preverbal subjects for agent marking.[42][43] This reordering is documented in Germanic too, where Old Norse SOV elements yielded to SVO under Scandinavian influences by the 13th century.[44] Grammaticalization drives syntactic evolution by converting lexical items into functional operators, expanding auxiliary systems; in English, Old English "habban" (to have) grammaticalized into a perfective auxiliary by the 15th century, altering periphrastic constructions from possessive to aspectual roles, as seen in Chaucer's works versus Shakespeare's.[45] Such shifts increase syntactic complexity in analytic languages, with evidence from parsed historical corpora showing rising dependency on adverbials and particles for tense-mood-aspect, countering morphological loss without net simplification.[46] Contact scenarios accelerate these changes, as pidgins and creoles often emerge analytic with fixed SVO order, later acquiring layered syntax through relexification, per studies of Atlantic creoles formed post-1500 CE.[40] Overall, these transformations reflect causal interplay between phonological attrition, cognitive processing efficiencies, and sociolinguistic pressures, yielding diverse outcomes across families rather than uniform progression.[39]Lexical Evolution and Semantic Drift
Lexical evolution involves the dynamic alteration of a language's vocabulary through mechanisms such as neologism formation via coinage, compounding, and derivation; lexical borrowing from contact languages; and the gradual obsolescence or replacement of existing terms due to cultural, technological, or social shifts. These processes reflect adaptations to new realities, with empirical studies showing that core vocabulary tends to persist longer than peripheral items, though even basic terms can evolve under pressure from innovation or disuse. For example, quantitative models of 104 core vocabulary items across languages indicate that lexical replacement rates vary, with semantic stability influenced by frequency and cultural salience.[47] Semantic drift, a subset of lexical evolution, refers to the gradual reconfiguration of a word's core meaning over time, often without abrupt replacement, driven by intralinguistic factors like analogy or polysemy extension rather than external cultural upheavals. This contrasts with localized cultural shifts, where meanings pivot around specific semantic neighbors; drift manifests as broader, systemic reorientations detectable in diachronic corpora. Historical linguistics identifies key types of semantic change, including broadening (extension to more general senses), narrowing (restriction to specific subsets), amelioration (acquisition of positive connotations), pejoration (shift to negative associations), metaphorical transfer (mapping from one domain to another), and metonymy (contiguity-based shifts).[48] [49]| Type of Semantic Change | Description | Example |
|---|---|---|
| Broadening | Word meaning expands to encompass more referents. | English "holiday," originally "holy day" referring to religious observances, broadened by the 19th century to include secular vacations.[50] |
| Narrowing | Meaning contracts to a subset of original senses. | English "meat," from any food in Old English, narrowed post-14th century to animal flesh specifically.[49] |
| Amelioration | Connotation improves from neutral or negative to positive. | English "knight," evolving from a mere servant or boy in Old English to a noble warrior by the Middle Ages.[51] |
| Pejoration | Connotation worsens. | English "silly," from "happy" or "fortunate" in Old English, degraded to "foolish" by the 16th century.[49] |
| Metaphor | Meaning transfers via analogy between domains. | English "grasp," literal hand action extending metaphorically to comprehension by Middle English.[52] |
| Metonymy | Shift based on association or contiguity. | English "will," from "desire" or "want" in Old English, metonymically extending to future intention by the 15th century.[50] |
Borrowing, Contact, and Hybridization
Language borrowing arises from contact between speakers of distinct languages, typically through trade, migration, conquest, or colonization, resulting in the adoption of lexical items, phonological features, or grammatical structures from a donor language into a recipient language.[54] Lexical borrowing predominates, often involving nouns for cultural innovations like technology or administration, while structural borrowing requires prolonged bilingualism and social dominance by the donor language's speakers.[55] Contact intensity correlates with borrowing rates; for instance, unequal power dynamics, as in colonial settings, accelerate superstrate influence on substrate languages.[56] In the case of post-conquest scenarios, the Norman Conquest of England in 1066 exemplifies massive lexical borrowing, with Norman French—spoken by the ruling elite—introducing over 10,000 words into Middle English, particularly in domains such as governance (government), law (justice), and cuisine (beef).[57] This influx elevated French-derived vocabulary to about 29% of modern English's lexicon, though core everyday terms remained Germanic.[58] Such borrowings often underwent phonological adaptation to fit English patterns, illustrating recipient-language constraints on integration.[59] Hybridization emerges in extreme contact zones, yielding pidgins—simplified auxiliary languages for intergroup communication—and creoles, which stabilize as native tongues with expanded grammar. Pidgins form in trade hubs or plantations, recombining elements from multiple sources; for example, West African Pidgins blend English lexicon with local syntax.[60] Creolization follows when children nativize pidgins, as in Haitian Creole (17th-18th century French superstrate with African substrates), developing full morphological systems absent in progenitors.[61] These processes challenge genetic classification, as creoles exhibit hybrid phylogenies rather than pure descent.[62] Areal convergence, or sprachbunds, demonstrates contact-induced isomorphism without genetic ties; the Balkan Sprachbund, spanning Albanian, Greek, Romanian, Bulgarian, and Serbo-Croatian since antiquity, shares features like enclitic definite articles, inferential evidentials, and periphrastic future tenses due to millennia of multilingual coexistence under empires like Ottoman rule.[63] Empirical studies quantify such diffusion, with genetic admixture models revealing borrowing rates mirroring population mixing in contact zones.[64] While academia sometimes overemphasizes convergence over inheritance—potentially due to institutional preferences for diffusionist narratives—reconstruction via comparative methods confirms borrowing's secondary role to internal evolution in most families.[65]Prehistoric Language Diversification
Earliest Communication Systems (Pre-50,000 BP)
Early hominin communication systems, emerging in the Pliocene around 4–2 million years ago with Australopithecus species, primarily involved multimodal signals akin to those in extant great apes, including intentional gestures, vocal grunts, and facial expressions for immediate social functions like reconciliation, mating solicitations, and predator alerts.[14] Comparative ethology reveals chimpanzees employ approximately 66 distinct gestures with contextual meanings, such as arm extensions for play invitations, a repertoire likely inherited and adapted by bipedal hominins whose upright posture freed manual gesturing from locomotion constraints around 6 million years ago.[66] These systems lacked symbolic reference or recursion but supported basic coordination in foraging and group defense, as inferred from dental microwear and isotopic evidence of shared resource exploitation in early Homo habilis sites dated to 2.3–1.4 million years ago. The advent of Homo erectus circa 1.9 million years ago marked a shift toward more structured signaling, driven by behavioral complexities like Acheulean handaxe production, which required multi-stage planning and skill transmission across generations, implying proto-referential communication beyond mere emotional displays.[67] Controlled fire use, evidenced at Wonderwerk Cave around 1 million years ago, and cooperative big-game hunting further necessitated reliable inter-individual information transfer, potentially via an expanded gestural lexicon combined with graded vocalizations, as bipedalism and encephalization (brain volume increasing to 900–1200 cm³) enhanced cognitive prerequisites for intentional signaling.[68] Gestural primacy theories posit that visible manual actions preceded vocal dominance, leveraging mirror neuron systems for rapid comprehension in daylight social contexts, though direct fossil evidence remains absent, relying instead on experimental replications of tool pedagogy showing gesture's efficacy in silent transmission.[14] By the Middle Pleistocene around 780,000–130,000 years ago, archaic Homo species like heidelbergensis exhibited anatomical correlates for vocal tract flexibility, including a repositioned hyoid bone and laryngeal descent, enabling phonation diversity beyond primate hoots, yet syntactic complexity appears limited based on the absence of symbolic artifacts pre-100,000 years ago.[69] Some models reconstruct a rudimentary proto-language in late Homo erectus populations around 1 million years ago, integrating lexical gestures with simple predicates for spatial and causal descriptions, supported by genetic divergence estimates aligning with enhanced neural circuitry for sequencing; however, these remain speculative without corroborative archaeological proxies like sequential markings.[70] Overall, pre-50,000 BP systems prioritized pragmatic efficacy over generative syntax, evolving causally from ecological pressures for social hunting and territorial expansion rather than innate linguistic universals.[71]Upper Paleolithic Innovations (50,000–10,000 BP)
The Upper Paleolithic period witnessed a marked proliferation of symbolic artifacts and behaviors among Homo sapiens, interpreted by archaeologists as evidence for cognitive advancements that underpinned or co-evolved with complex language capabilities. Sites across Eurasia yield non-figurative signs, engravings, and geometric markings dating from at least 42,000 years ago, appearing in over 400 European caves and suggesting proto-symbolic systems for encoding information beyond immediate sensory input.[72] These developments align with the onset of behavioral modernity around 50,000 BP, characterized by abstract representation that requires referential communication, a hallmark of linguistic displacement where speakers discuss absent or hypothetical entities.[73] Symbolic material culture, including ochre processing for pigments and personal ornaments like shell beads from ~40,000 BP, indicates social signaling and identity markers that likely demanded nuanced verbal descriptors and narratives, fostering syntactic elaboration for conveying kinship, status, or shared myths.[74] While direct linguistic fossils are absent, the standardization of tool assemblages—such as Aurignacian blades and later Gravettian points—implies cumulative cultural transmission reliant on protolanguage or full syntax to instruct apprentices in sequential manufacturing techniques spanning multiple steps.[75] This era's innovations contrast with sparser pre-50,000 BP evidence, where symbolic storage appears episodic, pointing to a threshold in cognitive integration where language enabled scalable social networks amid population dispersals.[76] Migratory expansions during this interval, including into Europe ~45,000 BP and Sahul ~50,000 BP, exposed groups to varied ecologies, promoting lexical innovations for novel fauna, tools, and rituals while isolation in refugia accelerated divergence from ancestral communication systems.[77] Genetic studies of ancient DNA reveal effective population sizes as low as 1,000-10,000 individuals in early UP Eurasia, conditions conducive to rapid linguistic drift via founder effects and reduced gene flow, laying groundwork for proto-family splits without preserving reconstructible vocabularies.[78] Such dynamics underscore language's role in adapting hunter-gatherer strategies, with evidence of coordinated big-game hunting via atlatls ~20,000 BP necessitating descriptive planning and deception signaling, traits demanding hierarchical embedding in speech.[79] Overall, these innovations reflect not a sudden genesis but an intensification of linguistic expressivity tied to ecological pressures and cultural feedback loops.Neolithic Transitions and Proto-Families (10,000–3,000 BCE)
The Neolithic era, beginning around 10,000 BCE in the Fertile Crescent, introduced agriculture, animal domestication, and settled villages, fostering population growth from small foraging bands to communities exceeding hundreds of individuals. These demographic expansions, coupled with enhanced trade networks and migrations, are inferred to have promoted linguistic divergence as isolated groups developed specialized vocabularies for crops, tools, and social hierarchies, though no direct records exist and causation remains correlative rather than proven. Archaeological evidence of farming dispersals, such as from the Levant to Europe and East Asia, aligns temporally with reconstructed proto-language timelines, suggesting that sedentism amplified rates of phonetic drift and lexical innovation beyond Paleolithic baselines.[80][69] Comparative linguistics reconstructs proto-families—ancestral languages yielding modern branches via the family-tree model—as emerging or branching in this period, with dates estimated through shared cognates, glottochronology, and calibration against archaeological milestones like pottery styles or haplogroup spreads. Proto-Afroasiatic, encompassing Semitic, Egyptian, Berber, Cushitic, and Chadic branches spoken by over 500 million today, is dated to approximately 12,000–18,000 years ago, potentially originating among pre-Neolithic foragers in the Horn of Africa or Levant who adopted early herding by 8000 BCE; its farming lexicon, including terms for grains and livestock, supports ties to Natufian semi-sedentary cultures. This family diversified as pastoralists expanded into arid zones, evidenced by cognate roots for "barley" and "goat" across branches, though deeper time depths exceed reliable reconstruction limits due to sound-shift erosion.[81] In Eurasia, Proto-Indo-European (PIE), ancestor to Indo-Iranian, Greek, Italic, Germanic, and others, is placed around 4500–2500 BCE in the Pontic-Caspian steppe, during the late Neolithic Yamnaya horizon characterized by kurgan burials and wheeled vehicles. Genetic data from ancient DNA, showing R1a/R1b haplogroup radiations, corroborates linguistic models of PIE speakers as mobile herders overlaying earlier farmer languages, with core vocabulary for horses, wheels, and patrilineal kinship reflecting pastoral adaptations absent in Anatolian farmer hypotheses. Competing Anatolian-origin theories, linking PIE to 7000 BCE spreads from Turkey, falter against Anatolian branch archaisms and lack of steppe-specific terms, favoring the steppe model via Bayesian phylogenetic analysis of cognate distributions.[82][83] East Asian Neolithic transitions around 8000 BCE in the Yellow River basin coincide with proto-Transeurasian (including Turkic, Mongolic, Tungusic, Koreanic, Japonic) divergences, tied to millet and rice cultivation dispersals; linguistic evidence includes shared roots for "to sow" and "millet," calibrated to 9000–6000 BCE via cognate density and admixture with Australoasiatic farmers. In contrast, American language clusters like Algic or Uto-Aztecan show proto-forms around 5000–3000 BCE, linked to maize diffusion from Mesoamerica, but isolation limited macro-family formation compared to Old World connectivity. These proto-families represent initial splits from broader Paleolithic continua, driven by Neolithic bottlenecks rather than uniform "farming-language" packages, as substrate influences and horizontal borrowing complicate pure descent models.[84][85]Macro-proposals like Nostratic, uniting Indo-European, Uralic, Altaic, and Afroasiatic circa 15,000–10,000 BCE, invoke Neolithic climate amelioration post-Last Glacial Maximum for Eurasian spreads, but lack consensus due to insufficient shared morphology and reliance on questionable long-range comparisons; empirical validation requires integrating genomic admixture data, which reveals hybrid zones rather than monolithic origins. Overall, this era's linguistic record, inferred from 21st-century methods, underscores causal realism in tying language stocks to subsistence shifts, yet highlights reconstruction uncertainties beyond 6000–4000 BCE where daughter attestations anchor trees.[86]