making the income stream highly variable. This variability in male income streams may shift female strategies of mate choice and family formation. Rather than relying on a single man to provide resources over the long term, women derive support for themselves and their children from a number of different sources: (1) their own market labor; (2) assistance from female kin and other women (Geronimus, 1996; Geronimus and Korenman, 1992; Stack, 1974); or (3) temporary boyfriends, who are chosen in part because they are currently employed (Lancaster, 1989; Tucker and Mitchell-Kernan, 1995).
This pattern results in a system of serial and simultaneous polygynandry, where both women and men have multiple reproductive relationships (Lancaster, 1989; Lancaster and Kaplan, 1992). It also results in residential sibships composed of half-siblings with different fathers. Since it may be difficult for fathers to control the distribution of resources they provide to ex-partners so that they are preferentially directed toward their genetic offspring, men have less incentive to invest in them (Weiss and Willis, 1985; Willis and Haaga, 1996), placing further pressure on women to garner resources from other sources.
In the United States, many women, especially ethnic minorities, who face a mating market where male unemployment is great, choose to reproduce at younger ages while they are still living with their mothers, so that they can receive maternal or grand-maternal assistance in child rearing (Burton, 1990; Geronimus, 1996). The change in the family structure associated with teen childbearing over the second half of the 20th century was dramatic. For example, in 1960 only 15 percent of births to women under age 20 were to unmarried women; by 1994 the figure had risen to 76 percent (Child-Trends, 1995, 1996). Among ethnic groups with high levels of unemployed males, the proportion of all births to unmarried women has shown an equally dramatic increase; for example, by the late 1990s, more than 70 percent of all births to black and Native American women were nonmarital.
This trend is especially pronounced in the developing world, where male unemployment among migrants to the cities is exceptionally high. For example, Figure 7-6 shows the household living arrangements of the students in the Cape Town study discussed above. Less than a quarter of the students were living with both natural parents, about half were living either with their mother alone or with their mother and step-father, and more than a quarter were living with other relatives. It is interesting to note that the switch to the matrifocal family in South Africa from the traditional patrilineal patrilocal form was noted as early as the 1940s, as soon as there was significant migration to urban areas by women (Burman and Preston-Whyte, 1992; Burman and Reynolds, 1986). The global emergence of the matrifocal family in response to urbanization is another example of convergence among people with very different cultural backgrounds.