Regular and irregular sound changes in Bantu languages of Central Africa: �Significance and historical implications

Rebecca Grollemund

grollemundr@missouri.edu

University of Missouri-Columbia, MO

3^rd Conference on Bantoid languages (Banto3d)

57^th Annual Conference on African Linguistics (ACAL57)�May 19-23, 2026 – University at Buffalo (NY)

BANTU HISTORY

BANTU HISTORY AND PALEOCLIMATOLOGY

Map: Rainforest 2,500 years ago �(Maley 2001)

Map: Rainforest 5,000 years ago �(Adam & Faure 1998)

BANTU �HOMELAND

Sangha River �Interval

BANTU HISTORY AND PALEOCLIMATOLOGY

Map: Rainforest 2,500 years ago �(Maley 2001)

Map: Rainforest 5,000 years ago �(Adam & Faure 2004)

BANTU �HOMELAND

Sangha River �Interval

“Our study indicates that the SRI was never a major passageway for the expansion of the first villagers through the forests of Central Africa because when it was at last settled (ca. 1900 BP), other communities had reached the lower-Congo in the DRC and in northern Angola some 800 km away to the south” 

Clist et al. (2025)

2015

2015

2025

BANTU HISTORY AND ANTHROPOLOGY

Map: Geographical location of historical “Pygmy” groups and their languages (Verdu 2016, adapted from Bahuchet 2012)

Is there a hunter-gatherer linguistic substratum in Bantu languages?

(Bahuchet 2006)

BANTU HISTORY AND ARCHEOLOGY

Maps: Villages in Central Africa at different time periods�Clist (2006)

Neolithic

Neolithic & Iron Age

Neolithic & Iron Age

BANTU HISTORY AND ARCHEOLOGY

→ “Spread-over-spread events” hypothesis

2021

“Il se peut donc que des branches entières de l’arbre généalogique de la famille bantoue aient disparu à cette époque, sans laisser de traces dans les langues bantoues parlées encore aujourd’hui.” Bostoen et al. (2024: 173)

➔ “It is therefore possible that entire branches of the Bantu family tree disappeared at that time, without leaving traces in the Bantu languages ​​still spoken today.”

Oslisly et al. (2013)

> lack of human activities

BANTU HISTORY AND ARCHEOLOGY

• But we need to be cautious…

“Rather than a hiatus between the EIA and LIA, the lack of empirical data for the LIA is to be linked to academic disinterest, differing fieldwork practice, soil preservation conditions, and a low demography suggested by historical and ethnographical accounts from Central Africa all pointing to low population densities.” �Clist et al. (2021: 2)

BANTU HISTORY

• Various factors contributed to the complexity of the Bantu history

​

• As a result, reconstructing the chronology and the geography of the Bantu Expansion is challenging

​

• Different migration routes proposed over the years

LINGUISTICS & MIGRATION ROUTES

Early split

Late split

Bastin et al. (1999), Möhlig (1981), Nurse and Philippson (2003)

Heine (1973), Henrici (1973), Heine et al. (1977), Holden (2002), Holden et al. (2005), Holden et al. (2006), Rexova et al. (2006), Currie et al. (2013), Grollemund et al. �(2015), Koile et al. (2022)

Heine (1973), Henrici (1973), Heine et al. (1977), Holden (2002), Holden et al. (2005), Holden et al. (2006), Rexova et al. (2006), Currie et al. (2013), Grollemund et al. (2015), Koile et al. (2022)

LINGUISTICS & MIGRATION ROUTES

CW

WC

SW

Eastern

CW

WC

SW

Eastern

NW

NW

Adapted from �Koile et al. (2022)

Adapted from �Grollemund et al. (2015)

Adapted from �Grollemund et al. (2015)

LINGUISTICS & MIGRATION ROUTES

CW

WC

SW

Eastern

CW

WC

SW

Eastern

NW

NW

Adapted from �Koile et al. (2022)

Adapted from �Grollemund et al. (2015)

Adapted from �Grollemund et al. (2015)

→ Different migration paths in Central Africa

ARCHEOLOGY & MIGRATION ROUTES

Clist (2021)

1- Obobogo: 3500-3000 BP

2- Okala: 2700- 1900 BP

3- Tchissanga: 2700-2350 BP

5- Imbonga: 2400-2100 BP

Clist et al. (2022)

“To my knowledge its [Imbonga traditions] most southern occurrence is in Cameroon where, at Obobogo, […] P. de Maret (1982) has recently excavated pottery bearing this very peculiar decoration” Eggert (1987: 131)

CENTRAL AFRICA: ZONE OF DISAGREEMENTS

• Results from different disciplines highlight disagreements about early migration routes in Central Africa
• Discrepancies within linguistic classifications
• Conflicting migration routes proposed by archeologists and linguists (e.g., coastal migration wave?)
• Different views on the role of environmental factors (e.g., did the corridor facilitate migration?)
• Disagreements over specific archeological interpretations (e.g., population collapse?)

​

WHAT CAN WE DO?

• To (possibly) help resolve the conflicting findings observed in Bantu studies in Central Africa
• Need to move beyond approaches that rely solely on the study of lexicon
• Need to examine other types of linguistic data �(e.g., non-lexical data)

​

​

PHONOLOGICAL INNOVATIONS

• These past ten years in Bantu comparative studies, we have seen an increase of papers on sound changes
• How can the study of shared phonological innovations help refine or corroborate the validity of the Bantu clades identified with lexicon-based classifications?

​

PHONOLOGICAL INNOVATIONS

2020

Sara Pacchiarotti, Guy Kouarata & Koen Bostoen 2024

2022

PHONOLOGICAL INNOVATIONS

2022

2022

In prep.

2026

PHONOLOGICAL INNOVATIONS

• These papers have shown that:
• Diachronic phonological innovations can be used to support clades identified with lexicon-based classifications (Pacchiarotti and Bostoen 2020), especially when we have uncertainties in the trees
• But, they may also challenge these clades, suggesting the possible need to consider alternative hypotheses (Philippson 2022; Grollemund and Philippson 2026)
• Irregularity in Bantu sound changes may indicate complex history caused by possible substrate influence, spread-over-spread events or ancient prolonged contacts (Pacchiarotti and Bostoen 2022; Grollemund et al., in prep.)

​

WC VELAR MERGER

Pacchiarotti and Bostoen (2020)

PB *k and *g > /k/

WC VELAR MERGER

• Significance of this velar merger
• Phonological innovation that supports the validity of the WC clade
• Strong innovation: rare to have a fortition (PB *g > /k/)
• It separates the WC group from other Bantu clades

​

NW PHONOLOGICAL INNOVATIONS

BLR3 1662 *-kádà ~ �BLR3 2335 *-kádàɡà: “charcoal”

Grollemund and Philippson (2026)

PB *k > Ø

NW PHONOLOGICAL INNOVATIONS

BLR3 1274 *-ɡàb-: “divide”

Grollemund and Philippson (2026)

PB *ɡ > /k/

NW PHONOLOGICAL INNOVATIONS

• With the exclusion from the NW:
• Mbam (A40-A60)
• Some Kele (B20) > WC velar merger
• Myene-Tsogo (B10-B30)

BLR3 1662 *-kádà ~ �BLR3 2335 *-kádàɡà: “charcoal”

BLR3 1274 *-ɡàb-: “divide”

Grollemund and Philippson (2026)

NW PHONOLOGICAL INNOVATIONS

• Importance of these NW phonological innovations
• It takes time for PB *k to be fully lost
• PB *g > k (same fortition observed in WC but triggered by the loss of PB *k)
• PB *k > Ø and PB *g > /k/ distinguish clades
• By isolating languages presenting PB *k > Ø (vs WC, SW or Eastern Bantu that kept PB *k)

NW/CW PHONOLOGICAL INNOVATIONS

• Interestingly:
• Some Bantu languages spoken in Congo and the DRC belonging to the CW clade present the same NW phonological innovations!
• With PB *k > Ø and PB *ɡ > /k/ (Grollemund, Philippson and Johnson, in prep.)

​

​

NW/CW PHONOLOGICAL INNOVATIONS

BLR3 1662 *-kádà: �“ember, charcoal”

Grollemund, Philippson and Jonhson (in prep.)

PB *k > Ø

NW/CW PHONOLOGICAL INNOVATIONS

BLR3 1274 *-ɡàb-: “divide”

Grollemund, Philippson and Jonhson (in prep.)

PB *ɡ > /k/

NW/CW PHONOLOGICAL INNOVATIONS

• With the exception of:
• Boa languages �(C401, C43A, C44, C45)

​

BLR3 1662 *-kádà: �“ember, charcoal”

BLR3 1274 *-ɡàb-: “divide”

Grollemund, Philippson and Jonhson (in prep.)

NW/CW PHONOLOGICAL INNOVATIONS

• Significance of these NW phonological innovations found in CW languages?
• How can we interpret the sound changes PB *k > Ø and PB *ɡ > /k/?
• If two clades identified through lexicon-based classifications share the same phonological innovations, what does that suggest?

​

• What are the historical implications?

ANALYSIS

*k > Ø + *ɡ > k

*k > k + *ɡ > k

*k > k + *ɡ > ɡ

New NW-CW?

New WC + Kele (B20)?

*k > Ø + *ɡ > k

ANALYSIS

CW

WC

SW

Eastern

CW

WC

SW

Eastern

NW

NW

Adapted from �Koile et al. (2022)

Adapted from �Grollemund et al. (2015)

Adapted from �Grollemund et al. (2015)

*k > Ø + *ɡ > k

*k > Ø + *ɡ > k

*k > k + *ɡ > k

*k > k + *ɡ > k

*k > Ø + *ɡ > k

*k > Ø + *ɡ > k

*k > Ø + *ɡ > k

INTERPRETATION

• Debates about the putative superiority of sound change for subgrouping over lexical change
• See Nurse (1997); Ringe, Warnow, and Taylor (2002); Nurse and Philippson (2003); Smith (2017, 2023); Pacchiarotti et al. (2024); Grollemund and Philippson (2026)

​

• Most reasonable and balanced answer:
• We need both > need to combine lexical and phonological evidence

INTERPRETATION

• Why?
• Both types of evidence are revealing different (but complementary) histories
• The discrepancies observed may be interpreted as manifestations of putative historical layers, with shared phonological innovations representing one layer and lexical innovations another

​

• Nurse (1997: 362)
• Shared phonological innovations indicate common developments in the related languages after the proto-community disintegrated (Nurse 1997: 362)
• Phonological innovations are later supplemented by lexical innovations

​

INTERPRETATION

• Bantu history consists of multiple historical layers
• That can be uncovered by comparing and contrasting lexical and non-lexical data (phonological innovations)

​

• Grollemund, Nurse and Watters (2026: 8) wrote about the language contact situation in Cameroon (Bantoid/Bantu)
• “Even though lexical changes may at times represent deep history, they often represent more recent history. In contrast, the shared non-lexical phonological and morphological changes tend to have occurred early in the life of these languages and have more value in reconstructing the older history of Bantoid.”

“PEELING THE ONION”

• But are there more layers to unravel?

​

“PEELING THE ONION”

• Möhlig (1981a) already proposed a similar analysis:
• Bantu (linguistic) history is composed of multiple strata
• And traces of these strata can be discovered through the study of the development of PB consonants (and vowels)
• In Möhlig’s view (1981b, cited in Bostoen et al. 2024: 175), strata are the result of the non-unilinear evolution of Bantu languages with languages that do not necessarily descend from a single ancestral language but rather underwent “hybridization” through intense linguistic contacts (> superposition of linguistic layers)

​

​

“PEELING THE ONION”

• Bostoen et al. (2024: 175) added:
• “hybridization” (described in Möhlig 1981b) is reflected in the synchronic phonological systems of these languages as they display irregular sound changes when compared with the diachronic patterns established through the application of the Comparative Method

​

• Other layers?
• Irregular sound changes may indicate putative ancient contacts?

IRREGULARITY IN BANTU

• Irregularity in Bantu:
• A “casse-tête” (or conundrum) for historical linguists

​

• Many phenomena described over the years highlighting Bantu irregular sound changes:
• Double reflexes for NW languages (see Philippson 2022 for more details on NW double reflexes)
• “Multiple Unconditioned Reflexes” (MUR) for C2 *k and *g in WC languages (Pacchiarotti and Bostoen 2022)
• Osculant PB reconstructions (Guthrie 1967-1971)
• …

​

​

​

IRREGULARITY IN BANTU

• Proto-sounds and reflexes
• In historical linguistics, when a proto-sound is reconstructed, it corresponds to one reflex in the daughter language (or several reflexes if they are conditioned)

​

• Double reflexes or “Multiple Unconditioned Reflexes” in Bantu (NW mostly and WC)
• Phenomenon observed when a reconstructed proto-sound presents two ore more reflexes without any clear phonological conditioning
• Duala: PB *t > /t/ or /l/

​

WHY?

IRREGULAR SOUND CHANGES

• Example of a new case of double reflexes found for PB *g in Central Africa (WC)
• PB *ɡ in C₁ position > /k/ and Ø�
• Remember:
• We have seen that PB *ɡ > /k/ in �NW, CW, WC (as the result of �different phenomena)

​

​

​

Grollemund, Philippson, Chiantelli-Mosebach, Wills and Bostoen (in prep.)

PB *g > k

PB *g₁ > Ø

IRREGULAR SOUND CHANGES

IRREGULAR SOUND CHANGES

Reflexes of PB *g in C1 position in the 50 Bantu languages selected�(map created by Jordan Chiantelli-Mosebach)

RESULTS

• Intriguing phenomenon
• As we expect to find /k/
• Because these languages underwent fortition and lenition with PB *g₁ > Ø or /k/

​

EXPLANATION

• In brief, multiple hypotheses:
• Phonetic merger, phonetic split
• Language-contact-induced changes
• Prolonged contacts with Bantu languages that presented similar patterns (e.g., South-Western Bantu > PB *g > Ø)
• Ancient contacts with putative now extinct Bantu languages based on the “spread-over-spread events” hypothesis (substrata)
• ?

THE CENTRAL AFRICAN BANTU “MESS”

• Issues at many levels:
• Lexicon-based classifications
• Clades identified through lexical and diachronic phonological innovations (e.g., NW or NW-CW?)
• Numerous irregularities (irregular sound changes) attested in Central Africa (where regularity is expected)

​

• Central African Bantu area
• Complex history shaped by different events

​

PUTTING THE EVIDENCE TOGETHER

• Can these results help explain the mismatches observed between linguistic and archeological studies?

​

PUTTING THE EVIDENCE TOGETHER

• Early coastal migration path?

​

• Irregular sound changes
• MUR interpreted as the result of�a complex scenario of�language contact?

​

• If it is the case:
• Possible older layer of NW languages (now extinct) that may have expanded earlier along the coasts
• Extinct because of the more recent expansion of WC languages

Clist (2021)

NW

WC

PUTTING THE EVIDENCE TOGETHER

• About “Multiple Unconditioned Reflexes” (MUR) found in C2 position, Pacchiarotti and Bostoen (2022: 39) wrote:
• “[…] we entertained the possibility that MUR might be the result of the stratified non-tree-like history of the Bantu languages. […] In this scenario, populations and languages in a given area died out or moved elsewhere and left relics which were then absorbed by a new spread event and so forth successively. Each of these incorporated relic languages might have contributed an unconditioned reflex to the incorporating language.”

PUTTING THE EVIDENCE TOGETHER

• Bostoen et al. (2025: 153) wrote:
• “we have interpreted chronological and spatial misfits between archaeological and linguistic data as indeed possibly diagnostic of the more recent spread of WCB languages over an older layer of NWB languages.”

​

​

PUTTING THE EVIDENCE TOGETHER

• Hinterland migration path?

​

• Secondary expansion
• Reflected in phylogenetic classifications
• Probably NW speakers (with PB *k > Ø) in direction of DRC
• Facilitated by the SRI (corridor)?
• Followed by language diversification with CW > WC

​

​

Clist (2021)

NW

*k > Ø + *ɡ > k

CW

WC

PUTTING THE EVIDENCE TOGETHER

• Clist et al. (2025: 2)
• “the SRI hosted a secondary and much younger expansion of possibly Bantu-speaking pottery using communities through the equatorial rainforest centuries after an initial one, which probably followed the western Atlantic coastline”�

​

Clist (2021)

NW

*k > Ø + *ɡ > k

CW

WC

MIGRATIONS IN CENTRAL AFRICA

• If we want to understand early Bantu migration routes and possibly reconcile results from linguistics and archeology
1. We need to reevaluate how to interpret lexicon-based classifications
2. We need to work with non-lexical data (e.g., diachronic phonological innovations, morphological data?, cultural vocabulary, …)
3. We need to take into account irregularity phenomena

​

​

​

​

Bantu history is complex, composed of multiple layers

Thank you!

ACKNOWLEDGMENTS

• Closest collaborator
• Gérard Philippson

​

​

• Esteemed collaborators
• Koen Bostoen
• Bernard Clist
• Christopher Green
• Derek Nurse
• Jeffrey Wills

​

Grant # 2152822

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