Rapid decline in a country’s birth and death rates creates a “kinship gap”, leaving people born just years apart with vastly different family support networks. Sha Jiang discusses the ensuing inequalities between adjacent generations, arguably requiring policy attention.
Families are getting smaller as birth rates fall and lifespans increase. In a recent publication (Jiang et al., 2025), we highlight the importance of the speed of this demographic transition, an often overlooked factor that can fundamentally reshape family networks. Using demographic tools that model kinship over time (Caswell & Song, 2021), we address a critical question: can two individuals born only five or ten years apart end up with very different family structures? Our findings show that the answer is yes, and this has profound implications for individuals and society.
The great family divide: how speed creates a gap
Not surprisingly, the faster the demographic transition, the larger the gap in the number of living relatives between people of nearly the same age. Slow changes produce noticeable effects only after several decades, but when they happen rapidly, within a single generation, they create abrupt and significant divides.
We can see this clearly in real-world examples, comparing countries like Thailand, which experienced a very rapid transition (fertility decline especially), and Nigeria, where the demographic transition has been much more gradual. Figure 1 illustrates the stark differences for cousins and daughters:
• Cousins (top panel). In Thailand, a 15-year-old in 2000 had, on average, nearly 30% fewer living cousins than a 25-year-old. This gap was far less pronounced in Nigeria, where the difference was less than 10%.
• Daughters (bottom panel). In Thailand, a 65-year-old in 2020 had, on average, 15% fewer living daughters than a 70-year-old, while in Nigeria in the same year, the opposite dynamic was observed: a 65-year-old had approximately 7% more daughters (thanks to survival improvement).
New generations not only have fewer kin, they are also differently distributed by age (younger daughters and older mothers, for instance), and both phenomena are likely to affect the dynamic of intergenerational support within the family.
We focus on these specific relationships because they represent crucial support systems at different life stages. Living daughters are often primary caregivers for old individuals, so their numbers are a key indicator of available family support in old age. For young people, cousins typically form their first and largest peer group outside of siblings, shaping their social integration and network.
Processes matter more than snapshots
These findings challenge how social support systems are planned. Effective planning requires understanding the entire demographic transition process – including its speed, timing, and sequence – rather than focusing only on a “snapshot” of current fertility or mortality levels. For example, two societies with identical demographic rates today can have vastly different kinship structures simply because their transition histories were different.
The key takeaway is that the process of transition matters more than the endpoint. Social planning must therefore recognize the large disparities in family resources that can exist between near-age peers. In some countries, for example, individuals born in 1975 may have significantly less family support than those born in 1965, just 10 years earlier. This reality demands that social services move beyond static analysis and tailor support based on how the number and age of an individual’s relatives have been shaped by past demographic transitions.
Implications for policy and fairness
The rapid transformation of traditional family networks has social implications. In societies undergoing fast transitions, the need to develop formal support institutions – like public pensions and elder care – arises much sooner than historical patterns would suggest. This raises serious concerns about intergenerational equity. The speed of demographic change can create a birth lottery, where one’s year of birth determines access to traditional family support, placing an unequal burden on the welfare state to support those with fewer kin.
Societies experiencing these rapid transitions must accelerate the development of alternative support mechanisms. Failing to do so may mean that vulnerable groups will fall through the emerging gaps between the shrinking traditional family network and the formal social safety net. To build fair and resilient societies, we must look beyond simple numbers and plan for the dynamic process of demographic change itself.
References
Caswell, H., & Song, X. (2021). The formal demography of kinship III: Kinship dynamics with time-varying demographic rates. Demographic Research, 45, 517-546.
Jiang, S., Zuo, W., Guo, Z., & Tuljapurkar, S. (2025). Changing demographic rates reshape kinship networks. Demography, 62 (3): 899–922. https://doi.org/10.1215/00703370-11996578