Migration, Partner Selection, and Fertility in Germany: How Many Children are Born in Mixed Unions?

Gawron, Annegret; Milewski, Nadja Article — Published Version Migration, Partner Selection, and Fertility in Germany: How Many Children are Born in Mixed Unions? European Journal of Population Provided in Cooperation with: Springer Nature Suggested Citation: Gawron, Annegret; Milewski, Nadja (2024) : Migration, Partner Selection, and Fertility in Germany: How Many Children are Born in Mixed Unions?, European Journal of Population, ISSN 1572-9885, Springer Netherlands, Dordrecht, Vol. 40, Iss. 1, https://doi.org/10.1007/s10680-024-09710-w This Version is available at: https://hdl.handle.net/10419/318642 Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. Sie dürfen die Dokumente nicht für öffentliche oder kommerzielle Zwecke vervielfältigen, öffentlich ausstellen, öffentlich zugänglich machen, vertreiben oder anderweitig nutzen. Sofern die Verfasser die Dokumente unter Open-Content-Lizenzen (insbesondere CC-Lizenzen) zur Verfügung gestellt haben sollten, gelten abweichend von diesen Nutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte. Terms of use: Documents in EconStor may be saved and copied for your personal and scholarly purposes. You are not to copy documents for public or commercial purposes, to exhibit the documents publicly, to make them publicly available on the internet, or to distribute or otherwise use the documents in public. If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence. http://creativecommons.org/licenses/by/4.0/ Vol.:(0123456789) European Journal of Population (2024) 40:24 https://doi.org/10.1007/s10680-024-09710-w ORIGINAL RESEARCH Migration, Partner Selection, andFertility inGermany: How Many Children are Born inMixed Unions? AnnegretGawron1 · NadjaMilewski2 Received: 19 October 2023 / Accepted: 3 June 2024 / Published online: 28 June 2024 © The Author(s) 2024 Abstract For the German context, we investigate whether the number of children ever born differs between mixed unions (exogamous unions between natives and migrants or migrant descendants) and endogamous unions (unions among co-ethnics). Our theoretical considerations are derived from assimilation theories, which view exogamous unions as indicators of assimilation processes, and the framework on migrant fertility. The migrant (or descendant) partner in an exogamous union may adapt to the majority group, both partners may adapt to each other, or both partners may constitute a selected group in their fertility preferences. However, due to the higher likelihood of conflicts within the partnership and of separation, exogamy may disrupt family formation processes and depress couples’ fertility. Drawing on data from the GSOEP (1984–2020), we estimate generalized Poisson regressions. The results reveal that the number of children ever born is higher in exogamous unions than in endogamous native couples. This general pattern largely persists across migrant generations and regions of origin, but we identify gender differences. While fertility in exogamous unions of native women/migrant (descendant) men is not statistically different from fertility in native/native couples, unions of migrant (descendant) women/native men have more children, especially when controlling for socio-demographic confounders. Our results demonstrate that in the German context, exogamy does not lead to fertility disruptions, and is not straightforwardly associated with assimilation to the fertility of the majority group. Instead, differences in gendered partner choice patterns and life-course transitions may influence the number of children exogamous couples have. Keywords Exogamy· Migration· Fertility· Germany * Annegret Gawron [email protected] 1 Institute ofSociology andDemography, University ofRostock, Ulmenstraße 69, 18057Rostock, Germany 2 Federal Institute forPopulation Research, Wiesbaden, Germany A.Gawron, N.Milewski 24 Page 2 of 29 1 Introduction Over the past two decades, numerous studies have investigated fertility among migrant populations (Kulu etal., 2019). Particularly in countries where fertility has fallen below the replacement level (Morgan, 2003), there is substantial research on the fertility of migrant populations. As migrant women (especially from high-fertility countries) living in low-fertility countries have, on average, more children than native women (Milewski & Adserà, 2023), this research interest correlates with the expectation that fertility in migrant populations may increase fertility in low-fertility countries, and that demographic behaviour is an indicator of assimilation processes (Billari, 2008; Goldstein etal., 2009). However, previous research on migrant fertility largely overlooked the fact that fertility usually occurs within partnerships (Bauer & Kneip, 2013, 2014). Increasing international migration and mobility and globalisation processes (Castles et al., 2013) have made the partner market more diverse, and the numbers of (any) social boundary-crossing couples have risen in both majority and (migrant) minority groups (Braack & Milewski, 2020; Lanzieri, 2012). Hence, migrants, migrant descendants, and natives may choose a partner of their own ethnic group (i.e., endogamy) or a partner of a different group (i.e., exogamy), which can have implications for their fertility behaviour. To investigate the association between migration and fertility on the couple level, we pose the following research question: How many children are born in exogamous unions versus in endogamous unions among native non-migrants? By addressing this research question, this article combines two classical indicators of migrant assimilation. The fertility behaviour of migrants and their descendants is seen as an indicator of their cultural and socio-economic adaptation to the majority group (Coleman, 1994). Additionally, exogamous unions signal the crossing of social group boundaries (Alba & Nee, 2003; Carol & Leszczensky, 2019; Qian & Lichter, 2007), and their offspring may show greater “mixedness”, or diversity. Fertility in exogamous pairings blurs ethnic boundaries, and, as ethnic minority status and social status are highly correlated, this boundary blurring may contribute to the transformation of social structures within destination societies (Alba, 2022). However, whether exogamy contributes to the growth of a multi-ethnic population is unclear. Theoretical considerations regarding this issue are not conclusive. On the one hand, exogamy indicates assimilation, and the fertility patterns of exogamous couples may be similar to those of natives. On the other, fertility may be disrupted in exogamous unions because the partners’ values and norms regarding childbearing are dissimilar (Huinink & Konietzka, 2007). Compared to partners in endogamous unions, partners in exogamous unions tend to differ more in their family backgrounds and values, and in other individual traits, like age and education (Elwert, 2020; González-Ferrer etal., 2018). Moreover, even when exogamous partners (i.e., individuals in exogamous unions) have similar fertility preferences, the realisation of their preferences may be hampered, especially given that exogamy is associated with higher union dissolution risks (Choi & Goldberg, 2021; Milewski & Kulu, 2014). There is limited empirical research on the association between exogamy and fertility. Several previous investigations focused on fertility among interracial Migration, Partner Selection, andFertility inGermany: How… Page 3 of 29 24 couples in the US (Choi & Goldberg, 2018, 2020; Fu, 2008; Qian & Lichter, 2021). Only a few existing studies in Europe have explicitly focused on the impact of exogamy on fertility among migrants and their descendants. Pereiro etal. (2023) examined the fertility intentions of female migrants in exogamous unions in Italy. Elwert (2023) estimated third-birth risks in exogamous unions among female and male migrants in Sweden. Van Landschoot etal., (2017, 2018) analysed the birth transition rates of female migrant descendants with native partners in Belgium. For Germany, Glowsky (2015) investigated the number of children born to male natives with female migrant partners from Poland, Thailand, and Russia. Thus, the question of how fertility intentions and the tempo and the quantum of selected birth transitions translate into the final number of children couples have remains open. As these ideational and behavioural fertility measures may produce different patterns of group differences (e.g., Mussino et al., 2021), investigations of the number of children ever born to couples are needed to understand the long-term impact of mixed unions on demographic developments. Additionally, the current lack of studies on fertility among native women in unions with migrant (descendant) partners mirrors the blind spot of research on the implications of exogamy for the respective majority groups (i.e., natives) in Europe (Braack & Milewski, 2019) and the marginalised position of migrant (descendant) men in fertility studies (Milewski & Baykara-Krumme, 2023). Our study contributes to the literature in several ways. First, we add to the literature on partnership heterogeneity and fertility by investigating exogamy. Second, we provide insight into the consequences of exogamy across the life course from the perspective of “linked lives” (Elder, 1994) by analysing couples’ fertility. Third, whereas previous research on fertility by union type focused on indicators like fertility intentions or single birth transition rates, we examine couples’ number of children ever born. Fourth, we also analyse exogamous unions between male migrant (descendant)s and female natives (i.e., native non-migrants). Our analyses focus on Germany, which has had low fertility since the 1970s, and has been one of the main destination countries for immigrants for about seven decades. We use generalized Poisson regressions on GSOEP data (1984–2020) to investigate couples’ number of children ever born by distinguishing between endogamous and exogamous (marital and non-marital) unions of natives and (first-, 1.5-, and second-generation) migrants. The analysed unions are based on women’s first and second unions during their reproductive years. 2 Theoretical Background Typical explanations for migrant fertility focus on the roles of socialisation, selection, disruption, and adaptation (e.g., Adsera & Ferrer, 2015; Kulu etal., 2019). The fertility of migrants and their descendants may, for example, be linked to norms, values, and preferences they acquired through socialisation in their country of origin’s majority culture or in a minority group subculture. It could also stem from selection, e.g., in terms of family size preferences. Moreover, the migration process may be associated with disruptive factors (e.g., stress during migration, discrimination A.Gawron, N.Milewski 24 Page 4 of 29 experiences) that lead to lower fertility. Migrants and their descendants may also adapt their fertility preferences to the economic, social, and cultural conditions in the destination country. The adaptation perspective views the fertility behaviour of migrants and their descendants as an indicator of their cultural and structural assimilation to the destination country (Milewski & Mussino, 2018). Rather than focusing solely on the individual-level fertility of migrants and their descendants, we analyse the implications of exogamous unions for fertility. The few previous studies on the association between exogamy and fertility provided mixed evidence. Some found that fertility in exogamous unions is higher than that in endogamous unions of the majority group (Choi & Goldberg, 2020; Elwert, 2023), whereas others found that fertility in exogamous unions is lower than (Fu, 2008; Glowsky, 2015) or similar to that in endogamous unions of the majority group (Choi & Goldberg, 2018). In the following sections, we take the different empirical findings as points of departure for our theoretical considerations, which build upon the terminologies of the classical hypotheses on migrant fertility, but expand the potential impact of migrant status on fertility on the couple level using literature on migrant assimilation and exogamy. Based on these considerations, we derive hypotheses that specify the position of fertility in exogamous unions relative to that in endogamous native unions (see Fig.1). We conclude our deliberations on fertility patterns among exogamous couples by summarising the role of selection in these unions. Lastly, we look at within-migrant variation (generation and origin). 2.1 Adaptation asaOne‑Way Process We start with findings indicating that exogamous couples’ fertility differs only slightly (or not at all) from that of endogamous unions with majority group members (i.e., natives) (Choi & Goldberg, 2018). The observation that fertility among Fig. 1 Graphic depiction of the three main hypotheses Migration, Partner Selection, andFertility inGermany: How… Page 5 of 29 24 exogamous couples is similar to that among the majority group may be seen as evidence of migrant adaptation, or assimilation. Classical assimilation theory assumes that exogamous union formation is the final stage in the assimilation processes of migrant groups (Gordon, 1964). Indeed, cultural (e.g., understanding of the host country’s language, but also its values and norms) and structural assimilation (in socio-economic traits like education and income) may contribute to exogamous union formation among migrants and their descendants (Dribe & Lundh, 2008, 2011; Furtado & Song, 2015; Wiik & Bergsvik, 2023). The link between migrant assimilation and exogamy may have implications for couples’ fertility. For example, fertility behaviour in exogamous unions may be similar to that in endogamous native unions. Similar behaviour might occur when exogamous union formation is linked to migrant (descendant)s consciously departing from their culture of origin (mentioned for women: Collet, 2015), and, thus, potentially from their culture of origin’s fertility norms and values, to more closely align their values with those of the majority group in the destination country. Therefore, having (fertility) preferences that mirror those of the majority group may influence exogamous partner choice among migrants and migrant descendants, and affect the fertility outcomes of their unions. Higher education is associated with individualistic attitudes and detachment from family and the community of origin (Kalmijn, 1998). Consequently, higher educated migrants and migrant descendants are more likely to adjust their fertility values and norms to those of the majority group. As higher educated migrant (descendant) women and men rather intermarry (Dribe & Lundh, 2008; González-Ferrer, 2006; Wiik & Bergsvik, 2023), exogamous couples’ fertility behaviour may be similar to that of endogamous natives, independent of the makeup of the exogamous union (i.e., whether the woman or the man belongs to a migrant group). The higher education levels among migrants and migrant descendants in exogamous unions help to explain why they have more favourable labour market positions than their counterparts in endogamous unions (denoted as “intermarriage premium”) (Furtado & Song, 2015; Wiik & Bergsvik, 2023). Given the intermarriage premium, opportunity costs should affect the realisation of fertility preferences among exogamous unions in a manner similar to that among endogamous natives. Note, however, that exogamy may also facilitate migrant (descendant) s’ assimilation to the majority group (Rodríguez-García, 2015). Having ties to natives can also improve exogamous migrant (descendant)s’ cultural adaptation (Rodríguez-García et al., 2015), labour market participation (Furtado & Theodoropoulos, 2010), and income (Meng & Gregory, 2005) following union formation. Considering the complex association between exogamy and cultural and structural assimilation (Rodríguez-García, 2015), we formulate a null hypothesis (independent of whether the woman or the man belongs to a migrant group), which forms the backdrop of our statistical analysis: Assimilation hypothesis (H0) Fertility behaviour in exogamous unions is similar to that in endogamous native unions. A.Gawron, N.Milewski 24 Page 6 of 29 2.2 Adaptation asaTwo‑Way Process Despite this assimilation pattern, some scholars have found that fertility is higher in exogamous unions than in the respective endogamous majority group (Choi & Goldberg, 2020; Elwert, 2023; Qian & Lichter, 2021). This fertility pattern is less likely to be attributable to migrant (descendant) partners departing from cultural values (as assumed for the assimilation pattern), and is more likely be due to the preservation of different values. Research has shown that cultural assimilation may progress more slowly for fundamental life-course events, such as family formation (Carlsson, 2018). Additionally, while structural conditions can offer opportunities for inter-ethnic encounters, the migrant (descendant) partner may partially adapt to the majority group prior to or following exogamous union formation (Collet, 2015). The paths into exogamy can vary greatly, as can the potential adaptation processes between partners. While partnering with a member of a culturally dissimilar group is associated with higher risks (e.g., loss of acceptance by the origin group), the potential partner’s traits may increase the individual gains of union formation (Alba, 2005). These traits might include similar preferences, like those for a larger family. The propensity for exogamy is relatively high among couples in which both partners are religious and have the same religious affiliation (Milewski, 2003). Religiousness is associated with a higher ideal number of children (Bein etal., 2023; Philipov & Berghammer, 2007), and may contribute to higher fertility within unions (Peri-Rotem, 2016). Moreover, religious norms might promote traditional family roles and conservative family formation patterns (McQuillan, 2004; Pearce & Thornton, 2007). Native men with migrant female partners tend to favour traditional rather than egalitarian gender roles (Glowsky, 2011), and these preferences may be associated with a stronger desire for high fertility than that of people with more egalitarian views (Kato, 2018). Furthermore, natives in exogamous unions often have more pronounced familyoriented attitudes than natives in endogamous unions (Braack & Milewski, 2019). These findings suggest that not only migrants and migrant descendants, but also natives in exogamous unions may be selected groups. While partners’ homogamy in socio-cultural traits (such as shared preferences for higher fertility, or, indirectly, sharing a religious affiliation and preferences for traditional gender roles and family solidarity) may facilitate exogamous union formation, it might also lead to these couples having higher fertility than endogamous native unions. Qian and Lichter (2021), who found that exogamous unions’ fertility may lie between that of the respective endogamous minority and majority groups, interpreted this observation as resulting from symmetrical fertility decision-making. This again suggests the relative, or gradual, persistence of migrant (descendant)s’ fertility preferences, even in exogamous unions. Given that openness to and interest in the partners’ cultural differences may drive exogamous union formation (Singla & Holm, 2012), fertility might be higher in such unions because the partners negotiate their cultural differences through mutual adaptation (Collet, 2015). Mutual adaptation is common particularly in relation to conflicting fertility and child-timing preferences within partnerships (Thomson & Hoem, 1998). Partners negotiate their fertility preferences, which leads to a synthesis of their positions (Jansen & Liefbroer, Migration, Partner Selection, andFertility inGermany: How… Page 7 of 29 24 2006). Consequently, natives’ fertility preferences may be adapted to those of the migrant (descendant) partner, while symmetrical adjustments of exogamous unions on the micro level may result in an in-between fertility pattern on the macro level. The abovementioned arguments challenge the traditional view that assimilation is solely a one-way process driven by migrants and their descendants. Instead, they indicate the existence of a two-way dynamic, either by underscoring the diversity among natives and questioning their role as the standard for assessing migrant assimilation, or by suggesting that assimilation at the couple level entails mutual adaptation (Alba & Nee, 2003; Klarenbeek, 2019). These insights form the basis for the first working hypothesis guiding our empirical investigation. It expands the previously observed intermarriage premium, like in the migrant’s economic assimilation (e.g., Meng & Gregory, 2005) or well-being (Milewski & Gawron, 2019; Potarca & Bernardi, 2021) on the couple level to an “intermarriage premium in family size”: Intermarriage premium (H1a) Exogamous unions have higher fertility than endogamous native unions. 2.3 Disruption The previous fertility patterns indicate that exogamous unions have fertility that is similar to or higher than that of endogamous native unions. However, previous research also suggests that exogamous couples could have lower fertility than endogamous native unions (Fu, 2008; Glowsky, 2015; Qian & Lichter, 2021). From the life-course perspective, such a disruption may be the consequence of exogamous partnering. Exogamous unions are more likely to be higher order marriages or cohabitations (Elwert, 2020; Hohmann-Marriott & Amato, 2008). Particularly for women, pre-union fertility may have a negative impact on childbearing intentions and fertility (Stewart, 2002). Moreover, a leading factor for (higher order union) fertility is age (Beaujouan, 2020). Exogamous unions tend to occur later in life than endogamous unions (Elwert, 2020; González-Ferrer etal., 2018; Milewski, 2003; Soehl & Yahirun, 2011). Hence, the fertile phases of exogamous couples may be shorter (Schmidt etal., 2012). Additionally, four mechanisms related to exogamous couples’ circumstances after union formation could lead to disruption. First, as they crossed ethnic boundaries in their partner choice, exogamous couples may experience discrimination by their families and a lack of familial support (Rodríguez-García etal., 2016). As family support is an important resource in childrearing, exogamous couples may need to compensate for this lack of support by devoting more time and energy to parenting (Qian & Lichter, 2021), and by spending more on non-family childcare. Thus, the increased costs of childrearing may lead these couples to have fewer children (Fu, 2008; Qian & Lichter, 2021). Second, internal conflicts due to the partners’ cultural differences may result in fertility disruption. Divergent values and norms heighten the risk of conflicts in exogamous unions (Hohmann-Marriott & Amato, 2008; Rodríguez-García, 2006). A.Gawron, N.Milewski 24 Page 8 of 29 However, differences in partners’ fertility preferences may generally contribute to the postponement of fertility decision-making (Jansen & Liefbroer, 2006). Thus, differences in fertility preferences in exogamous unions may lead partners to postpone fertility or even give up their fertility desires, thereby reducing their family size. Third, fertility disruption may follow after the first birth. Raising children may be particularly demanding in exogamous unions because of the partners’ cultural differences (Gawron & Carol, 2022; Rodríguez-García, 2006). Partners’ experiences with their first child may affect their subsequent fertility decisions (Iacovou & Tavares, 2011). Exogamous couples may not only postpone subsequent births, but adjust (i.e., decrease) their fertility intentions more than other couples typically do, given the difficulties they face in raising children in a “mixed” family. Fourth, the chances of exogamous couples realising their (even conflicting) fertility preferences may be lower when they experience union instability. Exogamous couples’ greater vulnerability to conflict increases their risk of union dissolution (e.g., Dribe & Lundh, 2012; Milewski & Kulu, 2014; Saarela & Finnäs, 2018). Especially unions consisting of a migrant man and a native woman tend to be less stable (Milewski & Kulu, 2014). However, initiating union dissolution may be more difficult for migrant (descendant) women than for native women (Dribe & Lundh, 2012). Moreover, exogamous unions’ potential fragility mayalso create poor conditions for childbearing, as childrearing requires a long-term commitment (Choi & Goldberg, 2018). Therefore, we formulate an alternative working hypothesis, in contrast to that of the intermarriage premium pattern, which focuses on the potentially disruptive effects of exogamy: Disruption hypothesis (H1b) Exogamous unions have lower fertility than endogamous native unions. 2.4 Selection Effects The previous considerations partly imply that the disruption, assimilation, and intermarriage premium patterns may arise from selection into exogamy (i.e., confounders). The tendency for exogamous migrant (descendant)s to have higher education levels compared to their endogamous counterparts may contribute to similar fertility rates between exogamous unions and endogamous native unions (see assimilation pattern). The higher fertility in exogamous unions relative to that in endogamous native unions may be attributed to exogamous partners sharing a preference for more children, sharing a religious affiliation, holding traditional views on gender roles, or valuing family solidarity, even prior to union formation (see intermarriage premium pattern). By contrast, risk factors related to exogamous partnering across the life course may depress fertility in exogamous unions (see disruption pattern). When comparing fertility in exogamous unions and endogamous native unions, accounting for confounders is crucial. Beyond confounders, the link between exogamy and fertility may be influenced by a range of factors that emerge after union formation (i.e., mediators), such as social support levels, conflicts between partners and family, and socio-economic and socio-cultural adaptation processes. Similar to Migration, Partner Selection, andFertility inGermany: How… Page 15 of 29 24 Table 2 Descriptive statistics, by union type and women’s migrant status. Source: Calculations based on GSOEP 1984−2020, N = 7218 Min Max Exogamous unions with … Endogamous unions with … native women migrant (descendant) women native women migrant (descendant) women Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Dependent variable Couple’s number of children ever born in union (metric†) 0 6 1.6 1.1 1.8 1.1 1.7 1.0 2.2 1.1 0 – – 18.2 33 13.5 27 14.6 926 7.2 36 1 – – 24.3 44 22.5 45 23.8 1505 13.4 67 2 – – 38.1 69 42.5 85 43.3 2743 45.1 226 3 + – – 19.3 35 21.5 43 18.3 1162 34.3 172 Confounders Woman’s year of birth (metric) 1940 1980 1962 9.5 1962 11.1 1957 10.2 1960 11.5 Woman’s age at union formation (metric) 16 39 25.8 4.8 26.5 4.5 24.4 4.9 22.8 4.5 Partner’s age difference Woman is ≤ 1year older / ≤ 5years younger than man (woman’s = man’s) – – 64.1 116 58.5 117 73.6 4665 58.7 294 Woman ≥ 6years younger than man (woman’s < man’s) – – 16.6 30 34.5 69 19.1 1212 33.1 166 Woman ≥ 2years older than man (woman’s > man’s) – – 19.3 35 7.0 14 7.2 459 8.2 41 Woman’s children born prior to union No – – 88.4 160 87.0 174 88.2 5587 93.2 467 Yes – – 11.6 21 13.0 26 11.8 749 6.8 34 Woman’s order of union First – – 95.6 173 98.0 196 97.6 6181 99.8 500 Higher – – 4.4 8 2.0 4 2.4 155 0.2 1 A.Gawron, N.Milewski 24 Page 16 of 29 Table 2 (continued) Min Max Exogamous unions with … Endogamous unions with … native women migrant (descendant) women native women migrant (descendant) women Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Partner’s order of union First – – 93.9 170 88.5 177 93.2 5906 96.0 481 Higher – – 6.1 11 11.5 23 6.8 430 4.0 20 Woman’s education None, primary, lower secondary – – 13.8 25 16.5 33 10.1 640 51.3 257 Upper secondary – – 56.4 102 45.0 90 62.6 3967 40.5 203 Tertiary – – 29.3 53 38.0 76 26.9 1704 7.6 38 Mv – – 0.6 1 0.5 1 0.4 25 0.6 3 Partner’s comparative education Homogamy (woman’s = man’s) – – 43.6 79 44.0 88 53.7 3405 41.9 210 Hypergamy (woman’s < man’s) – – 29.3 53 33.5 67 30.3 1918 33.7 169 Hypogamy (woman’s > man’s) – – 26.5 48 21.0 42 14.6 923 23.4 117 Mv – – 0.6 1 1.5 3 1.4 90 1.0 5 Woman having religious affiliation No – – 15.5 28 20.0 40 25.4 1611 7.0 35 Yes – – 75.1 136 73.5 147 63.2 4002 82.4 413 Mv – – 9.4 17 6.5 13 11.4 723 10.6 53 Partner’s comparative religious affiliation Homogamy (woman’s = man’s) – – 42.0 76 49.0 98 61.8 3913 77.0 386 Migration, Partner Selection, andFertility inGermany: How… Page 17 of 29 24 Table 2 (continued) Min Max Exogamous unions with … Endogamous unions with … native women migrant (descendant) women native women migrant (descendant) women Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Mean/ % SD/ n Heterogamy (woman’s ≠ man’s) – – 44.8 81 42.0 84 24.0 1518 11.0 55 Mv – – 13.3 24 9.0 18 14.3 905 12.0 60 Moderators Migrants’ region of origin Low-fertility countries – – 75.1 136 74.5 149 n.a – 56.3 282 High(er)-fertility countries – – 24.9 45 25.5 51 n.a – 43.7 219 Migrant generation First-generation migrants (G1) – – 49.2 89 67.5 135 n.a – 75.6 379 Migrant descendants (G1.5 + G2) – – 50.8 92 32.5 65 n.a – 24.4 122 Total ––2.5 181 2.8 200 87.8 6336 6.9 501 mv = missing values, n.a. =not applicable † mean is based on the birth distribution from 0 to 6 children A.Gawron, N.Milewski 24 Page 18 of 29 Table 3 Determinants of couples’ number of children ever born. Source: Calculations based on GSOEP 1984–2020 Standard errors in parentheses, +p < 0.10, *p < 0.05, **p < 0.01, ***p < 0.001 M1 M2 M3 Coef (S.E.) Coef (S.E.) Coef (S.E.) Union type Endogamous: native women Ref Ref Ref Exogamous: native women − 0.00 (0.05) 0.00 (0.04) 0.01 (0.05) Exogamous: migrant (descendant) women 0.09+(0.05) 0.14*** (0.04) 0.12** (0.04) Endogamous: migrant (descendant) women 0.25*** (0.02) 0.14*** (0.02) 0.10*** (0.03) Woman’s year of birth (mean centered) − 0.00*** (0.00) 0.00*** (0.00) 0.00*** (0.00) Woman’s age at union formation (mean centered) − 0.04*** (0.00) − 0.04*** (0.00) Partner’s age difference Woman is ≤ 1year older / ≤ 5years younger than man (woman’s = man’s) Ref Ref Woman ≥ 6years younger than man (woman’s < man’s) 0.00 (0.02) − 0.00 (0.02) Woman ≥ 2years older than man (woman’s > man’s) 0.11*** (0.03) 0.10** (0.03) Woman’s order of union First Ref Ref Higher − 0.37*** (0.06) − 0.37*** (0.06) Partner’s order of union First Ref Ref Higher − 0.21*** (0.04) − 0.16*** (0.04) Woman’s children born prior to union No Ref Ref Yes − 0.33*** (0.03) − 0.26*** (0.03) Woman’s education None, primary, lower secondary Ref Upper secondary − 0.06** (0.02) Tertiary 0.08** (0.03) Partner’s comparative education Homogamy (woman’s = man’s) Ref Hypergamy (woman’s < man’s) 0.03 (0.02) Hypogamy (woman’s > man’s) − 0.10*** (0.02) Woman having religious affiliation No Ref Yes 0.21*** (0.02) Partner’s comparative religious affiliation Homogamy (woman’s = man’s) Ref Heterogamy (woman’s ≠ man’s) − 0.06*** (0.02) Constant 0.53*** (0.01) 0.55*** (0.01) 0.43*** (0.03) N 7218 7218 7218 Migration, Partner Selection, andFertility inGermany: How… Page 19 of 29 24 endogamous unions with native women. However, exogamous unions with migrant (descendant) women have higher fertility than endogamous native unions, with statistical significance at a 10% level. Thus, our findings suggest an assimilation pattern among exogamous unions with native women, and an intermarriage premium in family size among exogamous unions with migrant (descendant) women. Next, we control for whether the fertility patterns hold after accounting for confounders. Accounting for socio-demographic confounders in Model 2/Table3, the fertility of exogamous unions with native women remains comparable to that of endogamous native unions, although the coefficient shifts from negative to positive. Furthermore, in Model 2, exogamous unions involving migrant (descendant) women have fertility rates similar to those of endogamous migrant (descendant) unions, exceeding the fertility rates of endogamous native unions with a significance level of 0.1%. The changes in the coefficients for both groups of exogamous unions can particularly be attributed to the inclusion of the woman’s age at union formation. Exogamous migrant (descendant) women tend to have the highest mean age at union formation, followed by exogamous native women (see Table2), which correlates with fewer childbirths (see Table 3). However, considering socio-demographic confounders only results in a more pronounced intermarriage premium pattern among exogamous unions with migrant (descendant) women, whereas the fertility pattern of exogamous unions with native women continues to suggest assimilation. In Model 3 (Table3), which introduces socio-economic and socio-cultural variables, the previously observed fertility patterns are maintained, with slight coefficient changes in exogamous unions, mainly due to the inclusion of the woman’s religious affiliation. Both native and migrant (descendant) women in exogamous unions are more likely than those in endogamous native unions to have a religious affiliation (see Table2), which is linked to higher fertility (see Table3). Adding the religion variable diminishes the coefficient for exogamous unions with migrant (descendant) women, but enhances it for those with native women. Despite the adjustments in Model 3 (Table3), the fertility pattern of exogamous unions with native women still indicates assimilation, and that of migrant (descendant) women still points to the intermarriage premium. In summary, our analysis reveals fertility differences between endogamous native and migrant (descendant) unions, with the latter generally exhibiting higher fertility. However, our findings for exogamous unions vary. First, while no statistically significant fertility disruptions (H1b) are observed, a negative coefficient in the first model suggests potential disruptions, particularly in unions involving native women. Second, the results for exogamous unions involving native women consistently support the assimilation hypothesis (H0). Conversely, exogamous unions with migrant (descendant) women exhibit higher fertility than endogamous native unions, especially in Models 2 and 3, in line with our intermarriage premium hypothesis (H1a). Third, we find support for selection (H2), with differing effects for the two groups of exogamous unions. Especially in the case of exogamous unions with migrant (descendant) women, the intermarriage premium becomes more pronounced after considering life-course transitions, particularly women’s older ages at union formation. Additionally, the intermarriage premium of exogamous unions with migrant (descendant) women is partly explained by religious affiliation. Even though migrant A.Gawron, N.Milewski 24 Page 20 of 29 (descendant) and native women in exogamous unions exhibit similar patterns of religious affiliation, fertility in exogamous unions with native women does not decrease when accounting for the woman’s religious affiliation. Thus, the association between religious norms (which often advocate for traditional family roles and conservative family formation patterns) and fertility seems less pronounced in unions of native women/migrant (descendant) men than in unions of migrant (descendant) women/ native men. 4.2 Differences bytheMigrant’s Country ofOrigin andGeneration Next, we examine differences in fertility patterns across union type groups, considering the migrant (descendant)s’ region of origin and migrant generation. Table4, subgroup analysis A, presents the coefficients of the union type groups, distinguishing by different regions of origin. We first focus on high-fertility regions. From Model 2 (Table 4) onwards, the fertility of exogamous unions involving women from high-fertility regions clearly exceeds that of endogamous native unions, resembling the fertility levels of endogamous migrant (descendant) unions. Additionally, the coefficient for unions of native women/men from high-fertility regions falls between those for endogamous native and migrant (descendant) unions from Model 2 onwards. However, due to statistical significance, we can only regard the finding on exogamous unions with women from high-fertility regions as evidence of an intermarriage premium. Focusing on low-fertility regions shows that differences between endogamous native and migrant (descendant) couples vanish by Model 3(Table4). Correspondingly, in Model 3, we see assimilation patterns among exogamous unions with native women and endogamous migrant (descendant) unions. However, exogamous unions with migrant (descendant) women from low-fertility regions display higher fertility than endogamous native unions. Thus, unions of migrant (descendant) women/ native men have a larger family size, regardless of origin. Nevertheless, exogamous unions with female and male partners from high-fertility regions consistently have higher fertility than those with migrant (descendant) partners from low-fertility regions. Subgroup analysis B (Table4) distinguishes between unions involving first-generation migrants and unions involving migrant descendants. The fertility rates of unions with first-generation migrant women, whether endogamous or exogamous, are higher than those of endogamous native unions. While exogamous and endogamous unions with female migrant descendants also have higher fertility than endogamous native unions, the differences are not statistically significant, suggesting an assimilation pattern. Exogamous unions with native women exhibit an assimilation pattern, regardless of the partner’s generational status. However, exogamous unions involving female and male first-generation migrants generally have higher fertility than those with migrant descendants. In summary, the fertility differences between the two groups of endogamous unions are most pronounced when comparing natives with migrant (descendant)s from high-fertility regions, and are notable, albeit less pronounced, when Migration, Partner Selection, andFertility inGermany: How… Page 21 of 29 24 comparing natives with first-generation migrants. Regarding exogamous unions with native women, our findings across all subgroup analyses consistently support the assimilation hypothesis (H0), although some of the results for unions of native women/men from high-fertility regions suggest an intermarriage premium. Conversely, exogamous unions with migrant (descendant) women show an intermarriage premium (H1a) pattern across most subgroup analyses. This pattern is Table 4 Determinants of couples’ number of children ever born, by migrant (descendant)s’ region of origin and migrant generation. Source: Calculations based on GSOEP 1984–2020 Standard errors in parentheses, +p < 0.10, *p < 0.05, **p < 0.01, ***p < 0.001 M1 = +woman’s year of birth M2 = +woman’s and partner’s higher order union, woman’s children born prior to union, woman’s age at union formation, partner’s age difference M3 = +woman having religious affiliation, partner’s comparative religious affiliation, woman’s education, partner’s comparative education Subgroup analysis M1 M2 M3 Coef (S.E.) Coef (S.E.) Coef (S.E.) (A) Migrant (descendant)s’ region of origin: Union type # migrant (descendant)s’ region of origin Endogamous: native women Ref Ref Ref Migrants from high-fertility regions Exogamous: native women 0.02 (0.09) 0.09 (0.08) 0.12 (0.08) Exogamous: migrant (descendant) women 0.10 (0.11) 0.22* (0.10) 0.17+(0.10) Endogamous: migrant (descendant) women 0.35*** (0.04) 0.21*** (0.03) 0.18*** (0.04) Migrants from low-fertility regions Exogamous: native women − 0.01 (0.06) − 0.03 (0.05) − 0.02 (0.05) Exogamous: migrant (descendant) women 0.08+(0.05) 0.11* (0.05) 0.10* (0.05) Endogamous: migrant (descendant) women 0.15*** (0.03) 0.07* (0.03) 0.02 (0.03) Constant 0.53*** (0.01) 0.55*** (0.01) 0.43*** (0.03) N 7218 7218 7218 (B) Migrant generation: Union type # migrant generation Endogamous: native women Ref Ref Ref First-generation migrants Exogamous: native women 0.00 (0.07) 0.01 (0.07) 0.02 (0.07) Exogamous: migrant (descendant) women 0.11* (0.05) 0.16*** (0.05) 0.15** (0.05) Endogamous: migrant (descendant) women 0.25*** (0.03) 0.15*** (0.03) 0.12*** (0.03) Migrant descendants Exogamous: native women − 0.01 (0.06) − 0.01 (0.06) 0.00 (0.06) Exogamous: migrant (descendant) women 0.04 (0.09) 0.11 (0.09) 0.07 (0.08) Endogamous: migrant (descendant) women 0.23*** (0.05) 0.09* (0.04) 0.05 (0.05) Constant 0.53*** (0.01) 0.55*** (0.01) 0.43*** (0.03) N 7218 7218 7218 A.Gawron, N.Milewski 24 Page 22 of 29 not statistically significant only in unions involving female migrant descendants. Despite the varied fertility patterns, Table 4 supports the subgroup hypothesis (H3) for all exogamous unions. 5 Discussion By examining the association between couples’ number of children ever born and exogamy, our paper analyses two measures of migrant assimilation: partner choice and fertility. The empirical analyses have produced rich material, and we conclude by highlighting the main findings. First, the number of children in exogamous unions exceeds that in endogamous native couples, as observed in exogamous unions with first-generation migrant women, and in those with women from both lowand highfertility regions. Additionally, our results suggest that fertility is higher in exogamous unions with female migrant descendants and in exogamous unions between native women and migrant men from high-fertility countries, although these findings are not statistically significant. In particular, the finding of statistically significant higher fertility in exogamous unions than in endogamous native unions supports the hypothesis of an intermarriage premium in family size (H1a). This implies a two-way character of assimilation within exogamous unions (Alba & Nee, 2003; Klarenbeek, 2019). As we cannot adequately account for socio-cultural confounders, whether motivations for union formation—such as both partners having a preference for higher fertility or favouring traditional gender roles and family solidarity before union formation—contribute to the intermarriage premium in family size remains unclear. Additionally, whether alignment in the partners’ values and preferences after union formation plays a role is uncertain. To answer such questions, more research is needed on values, preferences, and attitudes regarding fertility and family among exogamous natives, migrants, and migrant descendants (see also Braack & Milewski, 2019). Specifically, addressing the impact of exogamy on changes in socio-cultural factors, as was previously done for exogamy and well-being (Potarca & Bernardi, 2021) or migrants’ structural assimilation (Dribe & Nystedt, 2015), will provide further insights into assimilation processes at the micro societal level and the link between the two analysed indicators of migrant assimilation. Second, our results point to gendered patterns of assimilation. Although we do not distinguish between exogamous unions with native or with migrant (descendant) women in our hypotheses, our findings reveal that exogamy has different implications depending on whether the female or the male partner is a migrant (descendant). We find that exogamous unions with native women have lower fertility than exogamous unions with migrant (descendant) women. More precisely, after accounting for selection into exogamy (H2), we observe an intermarriage premium in family size (H1a) among exogamous unions with migrant (descendant) women. In contrast, exogamous unions with native women show an assimilation fertility pattern (H0), both before and after accounting for selection into exogamy. The observed differences in fertility between exogamous unions with native women and those with migrant (descendant) women are in line with previous research that found differences depending on exogamous couples’ gender composition. Overall, exogamous Migration, Partner Selection, andFertility inGermany: How… Page 23 of 29 24 couples with native women seem to be more disadvantaged than exogamous couples with native men in terms of their risk of poor mental health (Eibich & Liu, 2021; Milewski & Gawron, 2019) or of divorce (Milewski & Kulu, 2014). The latter finding aligns with our observation that the shortest union durations are in exogamous unions with native woman (see Supplementary TableS-1.1). Moreover, Braack etal. (2021) demonstrated that natives in exogamous unions are more likely than their endogamous counterparts to be the main earner. It seems that exogamous unions involving native women are more likely to have precarious household conditions, and therefore tend to face higher opportunity costs for childbearing, than exogamous unions involving migrant (descendant) women. These different opportunity costs may contribute to the observed differences between exogamous unions with native women and those with migrant (descendant) women. Despite the different fertility conditions in exogamous unions with native women, we do not find a disruption (H1b) in their number of children. However, as our analyses are conducted in the low-fertility context of Germany, the question of whether a disruption in family size would be observed among exogamous unions with native women in destination countries with higher fertility remains open. While relatively minor differences by union type are found after considering confounders, and although confounding effects cannot be entirely eliminated, we conclude that exogamy seems to influence fertility. However, the implications of the union type particularly depend on the gender of the migrant (descendant) partner. The obtained findings highlight the relevance of including information on both partners’ migrant status in analyses on fertility, in accordance with previous research on fertility decision-making that emphasised the roles of both partners (Bauer & Kneip, 2013, 2014) and of migrant (descendant) men (Milewski & Baykara-Krumme, 2023). Moreover, the results suggest a two-way character of assimilation within exogamous unions, raise questions regarding the causal link between exogamy and socio-cultural factors, and indicate that the couple’s employment patterns in particular may mediate the association between exogamy and family size. Lastly, the findings indicate how exogamy may drive social change within the mainstream society (Alba, 2022). Exogamous unions do not have fewer children than endogamous native unions; rather, bigger family sizes in exogamous unions with migrant (descendant) women may contribute to the growth of the multi-ethnic population. While the proportion of exogamous unions is small, the number increases across generations (see Table2). Previous research suggests that migrant descendants, particularly from certain non-Western groups, have higher fertility than the native population (Kulu & González-Ferrer, 2014). Furthermore, we note that exogamous unions involving female migrant descendants tend to have higher fertility than endogamous native unions. Therefore, a detailed analysis of fertility patterns in exogamous unions with migrant descendants by origin could provide further insights into how exogamy influences social change within mainstream society. Like others, this study is not without limitations. Our study has a descriptive character. The smaller case numbers for exogamous unions allowed for only rough categorisations of the migrant (descendant)’s country of origin and migrant generation. As the share of minorities is growing in the population, future research will benefit from the ability to distinguish more precisely between origin groups. A.Gawron, N.Milewski 24 Page 24 of 29 Additionally, due to the limited information on men’s number of children before union formation, future research should explore how this confounder affects exogamous couples’ fertility. This study also raises questions about how individuals in exogamous unions differ from those in endogamous unions in terms of sociocultural traits like fertility preferences and family and gender role attitudes prior to and after union formation. To gain a deeper understanding of how exogamy affects fertility, future research should examine how couples’ employment patterns influence the relationship between exogamy and fertility. Due to insufficient data, this study could not explore mediating factors (like couples’ employment patterns, social support, partner and family conflicts). However, the relationship between these mediating variables and couples’ fertility is particularly complex when focusing on couples’ number of children ever born. For example, while the birth of a couple’s first child can change their employment patterns, the first birth may be influenced by exogamy, and can, in turn, affect the likelihood of subsequent births (“mediator-outcome confounding influenced by the exposure”, Richiardi etal., 2013, pp. 1516). Thus, an initial step may be to consider these variables in studies focusing on first-birth transitions. Despite some limitations, our results are partly in line with previous research on exogamy and fertility. Research on fertility intentions also highlighted the role of selection into exogamy (Pereiro etal., 2023). However, we observe some differences as well. Contrary to our findings, an investigation on fertility intentions (Pereiro etal., 2023) supported the assimilation hypothesis for exogamous migrant women after accounting for exogamous couples’ selectivity. Moreover, whereas studies on other contexts, like the US (Choi & Goldberg, 2018; Qian & Lichter, 2021) and the Swedish context (Elwert, 2023), reported higher fertility in exogamous unions with minority group men, our findings show larger family sizes in exogamous unions with migrant women. It is possible that deviations from Elwert’s results (2023) are attributable to sample selectivity. Elwert (2023) analysed third-birth risks, which may heighten sample selectivity. This is primarily because the investigated women already have two children, and it is especially relevant among exogamous couples with native women due to the shorter duration of these relationships (see Supplementary TableS-1.1). Overall, future investigations of couples’ number of children ever born could clarify whether differences in fertility measures, samples, or minority population compositions contribute to these varied findings. We are identifying a further avenue for research. The observed fertility differences between exogamous unions involving native and migrant (descendant) women raise questions regarding offspring in mixed families. As the experiences of growing up in these unions may differ too, future research on mixed children’s life chances should consider the different constellations of exogamous parents in relation not only to origin (e.g., Irastorza & Elwert, 2021), but also to gender. By combining the two research streams of partner choice and fertility, our study has provided new insights into ethnically diverse societies. As this is the first investigation that has focused on couples’ number of children ever born by considering the different union types of and between migrant (descendant)s, and natives, our results have relevance for studies in migration research and family sociology. The findings challenge existing assimilation theories, which are often gender-blind, omit natives,