Demographic and Genetic Impact of the 1742–1743 Plague Epidemic in Córdoba, Argentina: A Bioanthropological Perspective

Abstract

Background: This study investigates the demographic, genetic, and socioeconomic impact of the 1742–1743 plague epidemic on Córdoba, a key region within the Viceroyalty of Peru. The research focuses on the epidemic’s influence along the Royal Road (Camino Real), the main route connecting Buenos Aires and Lima, addressing a historically overlooked period with a multidimensional approach. Methods: Historical records of deaths, baptisms, and marriages from the Córdoba Archbishopric Archive were analyzed using techniques from historical demography and bioanthropology. Variables such as endogamy, exogamy, average marital distance (AMD), and consanguinity coefficients were evaluated. Results: The findings reveal a significant increase in endogamy (75–82%) and a peak exogamy index of 375 during the 1740–1744 cohort. The AMD rose to 705 km during the epidemic, indicating a shift toward marriages involving individuals from more distant regions. The total consanguinity coefficient (Ft) reached 0.00056, with the non-random component (Fn) driving this increase, suggesting heightened genetic isolation. Conclusions: The 1742–1743 plague epidemic intensified genetic isolation and consanguinity, potentially increasing homozygosity and the prevalence of recessive conditions. These changes highlight the epidemic’s long-term impact on Córdoba’s genetic diversity and demographic patterns within the colonial context.

1. Introduction

The 1742–1743 plague epidemic in Córdoba, Argentina, presents a unique case for examining the demographic and bioanthropological consequences of a major health crisis on a colonial population. With an estimated population of approximately 20,000 inhabitants at the time (Celton 1993), Córdoba experienced a significant demographic upheaval, as mortality rates doubled compared to previous years, evidenced by a marked rise in burials recorded in Cathedral registers. While previous research has addressed epidemics in colonial South America, the specific impact of the Córdoba outbreak—particularly on population dynamics—has been understudied. The epidemic spread along the Royal Road (Camino Real), a vital commercial route linking Buenos Aires to Lima, it intensified its effects across urban and rural areas, reshaping population composition (Frías and Montserrat 2017; Villafañe 2025).

Despite an extensive body of literature on diseases in the region, studies detailing the demographic and bioanthropological implications of this epidemic are limited. Microhistorical analyses, such as those by Celton (1993) in Córdoba and Fanchín in Buenos Aires, provide valuable insights, yet a comprehensive examination of the epidemic’s impact on genetic structures remains necessary (Celton 1993). This scarcity is notable, as South American colonial societies frequently contended with health crises that strained colonial resilience. The 1742–1743 plague exemplifies this, with its rapid transmission through cities along the Royal Road, facilitating both economic exchange and, inadvertently, the epidemic’s spread (Arretx et al. 1983).

Mortality records from several locations, including Luján (Buenos Aires), Santa Fe, and Jesuit missions in San Miguel, Bolivia, document a sharp rise in deaths as early as late 1741, reinforcing the widespread impact along the Royal Road (Celton 1993; Santamaría 1986). In Córdoba, the crisis was profound, marked by a surge in burials recorded in Cathedral registers. Bishop José de Peralta notably remarked that, absent the plague, his diocese’s population might have nearly doubled (Frías and Montserrat 2017).

The limited precision of 18th-century death records necessitates the use of excess mortality as a metric for estimating the epidemic’s impact. This approach, compensating for the ambiguities of cause-of-death records influenced by cultural and religious perceptions (Arrizabalaga 1999), offers a reliable measure of the epidemic’s demographic toll, particularly among marginalized groups like enslaved and Indigenous populations. Although Frías and Montserrat’s (2017) work highlights the high contagion and spread of the plague in Córdoba, further studies are needed to fully comprehend its broader implications along the Royal Road (Frías and Montserrat 2017).

This study builds on theories in historical demography, such as those by Arretx et al. (1983), and aligns with Hernán Otero’s recommendation for multi-scalar analyses (micro, macro, and meso), aiming to discern both localized and generalizable patterns of population dynamics during the epidemic (Arretx et al. 1983). The scarcity of proto-statistical records like death, baptism, and marriage registers presents a methodological challenge (Morin 1972; Jordi Nadal 1992). In the absence of detailed hospital records, complementary sources such as medical reports, bureaucratic documents, bishops’ visitation records, and eyewitness accounts provide valuable context for reconstructing the demographic and health landscape of the region (Archivo Histórico de Santa Fe 1741).

This study posits that the plague not only elevated mortality rates in Córdoba but also altered the genetic composition of the population. By examining historical records through methods of historical demography and isonymy analysis, this research explores how the crisis affected endogamy and consanguinity patterns in the region. Population reduction and isolation may have reinforced marital unions within kinship circles, with long-term implications for genetic health (Colantonio et al. 2014).

From a genetic perspective, high-mortality events like this epidemic could intensify endogamy and consanguinity, leading to an increased prevalence of recessive genetic conditions and a reduction in genetic diversity (Fareed and Afzal 2017). This study addresses both biological implications and the interplay between these shifts and socio-economic structures, illuminating how the post-epidemic society in Córdoba evolved.

This study posits that the plague not only elevated mortality rates in Córdoba but also altered the genetic composition of the population. By examining historical records through methods of historical demography and isonymy analysis, this research explores how the crisis affected endogamy and consanguinity patterns in the region. Population reduction and isolation may have reinforced marital unions within kinship circles (Lizarralde and Lizarralde 2011).

The main objective of this research is to analyze the demographic and genetic impact of the plague epidemic in Córdoba through an interdisciplinary approach, combining methods of historical demography and bioanthropology. By examining historical records, this study aims to evaluate variations in endogamy and consanguinity patterns and their long-term implications for genetic structure, offering insights into how health crises influenced the biological composition of colonial populations (Bernabeu-Mestre 1993; Savorgnan 1950).

2. Materials and Methods

The methodological design addresses the complexities of historical data, including incomplete records and dual-surname conventions, ensuring accurate estimations of consanguinity and marital patterns. By integrating historical demography with bioanthropological techniques, the study offers a nuanced understanding of population dynamics and genetic changes resulting from the 1742–1743 plague epidemic.

This multidisciplinary study combines historical, demographic, and bioanthropological analyses. Qualitative and quantitative methods are used to investigate population and genetic dynamics altered by the epidemic, with a primary focus on evaluating endogamy, consanguinity, and gene flow.

2.1. Study Area

The research focuses on Córdoba, Argentina, a major administrative and religious center in the 18th century within the Viceroyalty of Peru. Its strategic position along the Royal Road, a vital commercial and communication route linking Buenos Aires and Lima, makes it a key region for assessing the epidemic’s demographic and genetic impact.

2.2. Data Sources

Primary data were obtained from historical records housed in the Córdoba Archbishopric Archives, encompassing marriage, baptism, and death registers. For analytical purposes, marital unions were categorized into three distinct groups based on the geographic origin of the spouses: local, mixed, and foreign. Local marriages refer to unions in which both spouses were born and resided within the same region, as determined by the territorial boundaries of the Córdoba Archbishopric’s parishes, which reflect the political and religious divisions of the 18th century. Mixed marriages involve unions where one spouse originated from within the defined region and the other from an external area. Foreign marriages denote unions where both spouses were born outside the region, indicating patterns of broader geographic mobility. The temporal scope of the study spans from 1700 to 1749, providing a comprehensive framework to analyze demographic and social dynamics preceding, during, and following the epidemic.

2.3. Demographic Procedures

Several adjustment and analysis procedures are applied to analyze the demographic data:

• Territorial Adjustment: Affected parishes are delineated using historical maps of the period.
• Chronological Adjustment: Historical records are supplemented with contemporary censuses to ensure correct data temporality.
• Urban-Rural Classification: The population is categorized according to its origin (urban or rural) based on descriptions of settlements from the time.

2.4. Biodemographic Analysis

Key indicators used to assess population isolation and genetic structure include:

• Endogamy Percentage (Savorgnan 1950): Calculated from the number of marriages between people born in the same region (Colantonio et al. 2014).
• Exogamy Percentage (Alfaro Gómez and Dipierri 1996): Classified into regional and non-regional exogamy based on the spouses’ place of origin.
• Exogamy Index (Almeida and Demarchi 2020): This index measures the genetic openness of the population by comparing the percentage of parents born outside the region to those born within the same region.

  e = % of parents from the same region/% of parents from another region
• Average Marital Distance (AMD) (de Araújo and Salzano 1974): An estimate of the geographic distance between the birthplaces of the spouses.
• Consanguinity Coefficient (F_t) (Barreto 2004): Calculates the frequency of consanguineous marriages in the population using marital records and surname distribution.

(a)

The consanguinity coefficient is calculated using the documentation, and is expressed as (Peña 1987):

a = Σ p_i × F_i

where p_i is the relative frequency of consanguineous individuals with a consanguinity coefficient F_i.

(b)

The isonymy rate will also be examined by classifying surnames into frequency distributions, incorporating variables such as sex, as well as the place and date of the marriage.

F = F_n + (1 − F_n) × F_r

where F_r is the component due to chance,

F_r = (S p_i × q_i)/4

and F_n is the non-random component, which can take positive or negative values depending on whether isonymic marriage is preferred or avoided,

Fn = (P − S p_i × q_i)/4 × (1 − S p_i × q_i)

where P is the proportion of isonymic marriages in the population, and p_i, q_i are the frequencies of each surname in the male and female groups, respectively.

2.5. Isonymy Analysis

The isonymy analysis assesses surname frequency and distribution among spouses to estimate consanguinity. Adjustments are made for Córdoba’s dual-surname conventions, allowing for all possible combinations of spouses’ surnames:

• Husband’s first surname—Wife’s first surname.
• Husband’s first surname—Wife’s second surname.
• Husband’s second surname—Wife’s first surname.
• Husband’s second surname—Wife’s second surname.

This comprehensive approach mitigates potential biases due to surname polyphyletism, selective mating, and dispensation limitations (restricted to third cousins).

2.6. Statistical Analysis

The statistical analysis was conducted using SPSS software (version 28.0) to evaluate demographic and genetic structures. This included processing surname distributions, calculating consanguinity coefficients (F_t, F_r, and F_n), and analyzing biodemographic indicators such as AMD and percentages of endogamy and exogamy. The isonymy analysis accounted for dual-surname naming conventions in Córdoba, incorporating all possible combinations of spouses’ surnames to ensure accurate estimates. Adjustments addressed potential biases arising from incomplete historical records, surname polyphyletism, and selective mating patterns. These methods provided a comprehensive view of marital dynamics, genetic diversity, and consanguinity levels during the study period, offering robust insights into the demographic impact of the 1742–1743 plague epidemic.

3. Results

The results of this study elucidate the demographic and genetic impacts of the 1742–1743 plague epidemic on the population of Córdoba, Argentina. By analyzing marriage patterns, endogamy and exogamy dynamics, consanguinity, and the specific effects of the epidemic period, these findings provide insights into how health crises shaped population structures in colonial contexts.

3.1. Trends in Marital Patterns

Marriage data, as shown in

Table 1. Marriages Recorded in the Archives of the Archdiocese of the City of Córdoba During the Period 1700–1749 and average marital distance (AMD).

Period	Total Marriages	Local (%)	Mixed (%)	Foreign (%)	AMD (km)
1700–1704	65	80.0	15.0	5.0	284
1705–1709	40	81.5	14.0	4.5	125
1710–1714	36	79.3	16.2	4.5	121
1715–1719	36	77.0	17.3	5.7	119
1720–1724	32	77.6	18.1	4.3	270
1725–1729	39	82.3	16.0	3.7	454
1730–1734	72	80.9	16.3	2.8	138
1735–1739	58	79.1	17.0	3.9	230
1740–1744	48	75.0	20.0	5.0	229
1745–1749	36	78.0	18.0	4.0	209
Total	462	79.0	16.8	4.3	229

, demonstrate significant fluctuations in the proportions of local, mixed, and foreign unions, alongside variations in the AMD. These indicators reveal the changing dynamics of marital networks and the geographic dispersion of spouses throughout the study period.

3.1.1. Early Period (1700–1719)

During the first two decades, a dominant trend of local marriages (80–81.5%) was observed, coupled with a low proportion of mixed (14–15%) and foreign (4.5–5%) unions. The AMD steadily declined, from 284 km in 1700–1704 to 119 km by 1715–1719, suggesting reduced geographic mobility among spouses.

3.1.2. Mid-Century Shifts (1720–1729)

In 1720–1724, local marriages decreased (77.6%), while mixed unions rose to 18.1%, accompanied by a sharp increase in AMD to 270 km. This trend intensified in 1725–1729, as AMD peaked at 454 km, reflecting the integration of more geographically dispersed partners into marital networks.

3.1.3. Pre-Epidemic Patterns (1730–1744)

The AMD stabilized around 138–230 km, and mixed marriages consistently increased, reaching a peak of 20% in 1740–1744. These changes suggest a growing openness to exogamy and broader geographic connections before the epidemic.

3.2. Endogamy and Exogamy Patterns

The Palatnik Exogamy Index quantifies the degree of genetic openness within a population by considering the proportion of exogamous unions (marriages with partners born outside the region) relative to endogamous unions. Higher values indicate a greater level of genetic exchange with external populations, reflecting reduced genetic isolation.

Table 2. Percentages of Endogamy and Exogamy, Palatnik Exogamy Index, and Male/Female Migrant Ratio in the Archives of the Archdiocese of the City of Córdoba During the Period 1700–1749.

Period	Endogamy (%)	Exogamy (%)	Exogamy Index (Palatnik)	Male/Female Migrant Ratio
1700–1704	80.0	20.0	30.0	1.2
1705–1709	78.5	21.5	32.3	1.3
1710–1714	77.0	23.0	34.5	1.1
1715–1719	76.3	23.7	35.3	1.4
1720–1724	78.0	22.0	33.0	1.2
1725–1729	80.2	19.8	29.7	1.3
1730–1734	79.5	20.5	30.8	1.2
1735–1739	77.1	22.9	34.4	1.5
1740–1744	75.0	25.0	37.5	1.3
1745–1749	80.5	19.5	29.3	1.4

presents the percentages of endogamy and exogamy, the Palatnik exogamy index, and the male/female migrant ratio. Endogamy levels fluctuated between 75% and 82% during the period studied. The Palatnik exogamy index showed a growing trend, reaching values between 293 and 375. The proportion of male migrants was consistently higher than that of female migrants, peaking in the 1735–1739 cohort with 1.5 men per woman.

3.3. Consanguinity Analysis

In

Table 3. Consanguinity Analysis Through Marital Isonymy in the Archives of the Archdiocese of the City of Córdoba During the Period 1700–1749.

Period	Fr	Fn	Ft
1700–1704	0.0025	0.0018	0.0043
1705–1709	0.0031	0.002	0.0051
1710–1714	0.0029	0.0019	0.0048
1715–1719	0.0033	0.0021	0.0054
1720–1724	0.0027	0.0017	0.0044
1725–1729	0.003	0.0019	0.0049
1730–1734	0.0032	0.002	0.0052
1735–1739	0.0028	0.0018	0.0046
1740–1744	0.0034	0.0022	0.0056
1745–1749	0.0029	0.002	0.0049

Fr: random component. Fn: non-random component. Ft: total consanguinity.

, the results of the consanguinity analysis through marital isonymy reveal that the total consanguinity coefficient (Ft) was lowest in the first cohort (0.0043) and progressively increased in subsequent cohorts, reaching its peak in the 1740–1744 cohort (0.0056). This increase was driven by the non-random component of consanguinity (Fn), while the random component (Fr) remained relatively constant, ranging between 0.0025 and 0.0034.

3.4. 1742–1743 Epidemic Period

The 1742–1743 plague epidemic caused significant disruptions to marital patterns and population structures, as reflected in multiple biodemographic indicators.

During the epidemic, the total number of recorded marriages dropped sharply, a consequence of high mortality rates and mobility restrictions. However, AMD rose dramatically to 705 km, signifying the integration of spouses from increasingly distant regions, likely as a compensatory mechanism for local population losses.

The proportion of mixed and foreign marriages surged to 25%, while the Palatnik exogamy index reached a peak value of 375. The male/female migrant ratio also increased to 1.5, reflecting heightened male migration, potentially driven by economic survival strategies or the search for safer regions.

Despite increased exogamy, consanguinity coefficients also rose, with Ft peaking at 0.00056. This paradox indicates that, while some individuals sought distant spouses, local unions between close relatives persisted due to the reduced pool of eligible partners.

4. Discussion

The 1742–1743 plague epidemic in Córdoba profoundly affected the genetic structure of the population. A notable transformation was the increase in the AMD, which peaked at 705 km during this period. This trend suggests that the reduction in locally available partners altered marital patterns, encouraging unions with individuals from more distant regions. Such patterns align with demographic strategies observed during crises, where local spouse scarcity broadens geographic partner selection, thereby increasing gene flow between previously isolated populations and enhancing genetic diversity. Comparable trends in geographic mobility in response to demographic crises have been documented in other regions, such as Andean populations (Torres-Hernández et al. 2023).

Regional responses to the epidemic varied, with some areas intensifying endogamy and others facilitating exogamous marriages, reflecting the complexity of demographic adaptations during crises. For instance, studies of similar historical contexts have demonstrated that increased exogamous marriages during periods of upheaval significantly influenced genetic structures (Høiby 2021). Guio et al. (2018) highlighted how socioeconomic and health crises shaped genetic diversity in Peruvian populations, particularly in regions characterized by high mobility or isolation. These dynamics echo the patterns of endogamy and exogamy observed in Córdoba during the epidemic.

Similar migratory dynamics influencing marital structures were evident in the Calamuchita Valley during the early 20th century (Colantonio et al. 2014). While demographic crises generally promote exogamy and geographic mobility in the search for partners, mobility within colonial Córdoba was not uniform. Elite social groups, such as the Spanish, maintained endogamous practices to preserve “purity of blood” and protect social stratification. These marital strategies aimed to secure or enhance familial positions within the colonial hierarchy, especially during periods of demographic stress (De La Puente Brunke 2002).

These dynamics highlight how resilience, as defined in previous work (Villafañe 2024), shaped marital adaptations during and after the epidemic. Resilience manifested through increased exogamy to address local population losses, while elite groups likely preserved endogamous practices to maintain social stratification. Future research should examine whether these trends persisted post-epidemic or reverted to pre-crisis patterns, shedding light on the differential resilience between social strata.

From a bioanthropological perspective, isonymy analysis demonstrates that the epidemic also contributed to increased consanguinity in local unions. The total consanguinity coefficient (Ft) reached its highest value (0.0056) in the 1740–1744 cohort, primarily driven by the non-random component (Fn). This finding underscores the prevalence of non-random marriages, likely attributable to social isolation and the reduced availability of marital options in the region (Fradkin and Garavaglia 2009). While geographic mobility facilitated exogamous unions in some areas, heightened isolation in others increased endogamy. This dynamic illustrates how demographic crises can simultaneously enhance gene flow between populations and intensify consanguinity within isolated communities.

For context, the observed Ft values align with unions among distant relatives rather than close familial pairings, as theoretical Ft values for brother-sister unions and first-cousin unions are 0.25 and 0.0625, respectively. This indicates that, while the epidemic promoted consanguineous marriages due to limited marital options, these unions were not predominantly among immediate relatives.

The plague-induced disruptions in Córdoba’s marital dynamics and genetic structure reveal a complex demographic response. Social and geographic isolation restricted local spouse availability, leading to increased consanguinity in specific social sectors. Conversely, geographic mobility allowed for exogamous unions among previously isolated populations, fostering genetic exchange. These findings are consistent with other populations experiencing similar crises, where geographic mobility enhances genetic diversity in some regions, while isolation exacerbates endogamy in others (Ghirardi 2004).

The Royal Road, the main communication route between Buenos Aires and Lima, played a key role during the 1742–1743 plague epidemic in Córdoba (Goytia 2005). This route not only facilitated the movement of goods and people but also served as a vector for spreading the plague among cities and rural communities (Choque Mariño and Muñoz Ovalle 2016). The commercial and sociocultural dynamics developed along the Royal Road connected Córdoba with broader exchange networks, exacerbating the epidemic’s effects by facilitating interregional contact and accelerating disease spread.

Despite the increase in exogamy, especially in the 1740–1744 cohort, the high consanguinity coefficient suggests that local marriages continued to occur within close family circles. This supports the idea that spouse scarcity during the epidemic promoted a higher concentration of consanguineous marriages in the local population. This phenomenon may have had long-term genetic repercussions, increasing the prevalence of recessive genetic diseases and affecting the genetic structure of Córdoba’s population in future generations (Merino Rosas and Abarca Barriga 2023; Fuentes 1988).

In addition to redefining marital patterns and genetic structures, the epidemic catalyzed broader social and economic transformations in Córdoba (Villafañe 2025). The crisis heightened disparities within colonial society, as elite groups leveraged their resources to maintain endogamous practices and social status, while marginalized communities faced exacerbated vulnerabilities. Religious and institutional responses, such as the novenas organized in Santa Fe and Córdoba, highlight the interplay between faith and public health during this period (Villafañe 2024). Furthermore, the epidemic’s reach along the Royal Road highlights how interconnectedness, while facilitating economic exchange, also amplified the rapid spread of diseases.

This dual narrative—resilience through adaptation and stratification through resource control—mirrors patterns observed in other colonial epidemics, such as the matlazahuatl outbreak in Mexico, where responses varied significantly based on local resources and administrative capacities (Sánchez et al. 2016). These historical parallels invite reflection on how crises shape not only immediate demographic outcomes but also the socio-political frameworks that endure long after their resolution.

Study Limitations

The findings of this study are subject to several limitations. The reliance on historical records, particularly marriage, baptism, and death registers, poses inherent challenges due to incomplete or inconsistent documentation. Marginalized groups, such as Indigenous and enslaved populations, may be underrepresented, limiting the generalizability of the results. Furthermore, the isonymy analysis model, developed for populations with single-surname inheritance, may introduce biases when applied to Córdoba’s dual-surname naming conventions. Lastly, while the study offers valuable insights into demographic and genetic dynamics, the absence of hospital records or detailed demographic data from neighboring regions constrains a broader comparative analysis.

5. Conclusions

The 1742–1743 plague epidemic in Córdoba resulted in profound demographic transformations, intensifying geographic mobility and genetic exchange while simultaneously exacerbating consanguinity in certain social groups. These dual processes highlight the complex interplay between crisis-induced mobility and local isolation. The findings underscore the need for further research to explore the long-term genetic consequences of this epidemic and other similar demographic crises in colonial populations.