The beauty of multiple baby daddies

August 16, 2010

God bless LiveScience.com for this little factoid, from a story on the long, troubled history of marriage:

In some South American tribes, a pregnant woman could take lovers, all of whom were considered responsible for her child. According to “Cultures of Multiple Fathers: The Theory and Practice of Partible Paternity in Lowland South America” (University of Florida Press, 2002), 80 percent of children with multiple “fathers” survived to adulthood, compared with 64 percent of kids with just one dad.

The practice of partible paternity – i.e., multiple baby daddies – dovetails nicely with some points raised by the group sex theory of hunter-gatherers, which I blogged about earlier. A Google search turned up the introduction to the volume mentioned above, from which I here excerpt the juicy bits.

First, the construction of singular paternity:

[C]onclusive scientific evidence for singular paternity, for what we can call the One Sperm, One Fertilization Doctrine, is only a little over a century old. Gregor Mendel obtained experimental evidence around 1870 that a single pollen grain introduced into an ovule produced a well developed seed. In 1879, Hermann Fol published evidence of experimentation and microscopic observation demonstrating that in animals “[f]ertilization is always effected by a single spermatozoon” (Mayr 1982, 666).

Before the end of the nineteenth century, although Western law and custom assumed that each child had a single biological father, that premise was simply a folk belief, resting on other folk beliefs about how babies are made and what the mother and the father contribute – beliefs that seem quaint to us now.

The construction becomes normalized, of course:

This happy coincidence of folk doctrine and biological reality within our own intellectual tradition has not been without its unfortunate consequences. It has made it easy for us to presume that our folk beliefs concerning fertilization, conception, and fetal development must be everyone’s folk beliefs, inevitable and universal. The presumption has channeled and perhaps constrained our thinking about both the biological and the social aspects of paternity.

Then the scientists get involved:

Most modern scenarios for human evolution invoke paternity certainty as one of the elements leading from African hominids to modern Homo sapiens, along with the sexual division of labor, food sharing, lengthy juvenile dependency, and continuous sexual receptivity. The idea is roughly that men provision women and their children with foods that the women cannot obtain on their own, because they are burdened with dependent children. Men are willing to share their food because the women, faithful to their mates, provide the men with a high degree of paternity certainty. When a man brings his game home to his woman, he can reliably assume that the children it feeds are his own  (Alexander and Noonan 1979; cf. Washburn and Lancaster 1968.) This scenario, now two decades old, is sometimes called the Standard Model of Human Evolution. It remains the dominant version of the story of the evolution of food sharing and the human family.

I promise I didn’t plan for Pinker to enter into this:

Steven Pinker, for instance, writes in How the Mind Works: “Sexual jealousy is found in all cultures…. In most societies, some women readily share a husband, but in no society do men readily share a wife. A woman having sex with another man is always a threat to the man’s genetic interests, because it might fool him into working for a competitor’s genes” (1997, 488-90; italics Pinker’s).

But then… boom goes the anthropology:

These views of universal human nature, as well as the male-female bargain behind the Standard Model of Human Evolution, are called into question by decades of ethnographic research among tribal peoples in lowland South America. […] This work, old and new, has made two relevant findings about a substantial number of lowland South American societies. First, the people of these societies have a different doctrine of paternity, one that allows for a child to have several different biological fathers. Second, these people act on that doctrine in such as way as to confute such statements as Pinker’s that “in no society do men readily share a wife.”

In addition to the societies discussed in this volume, there are quite a few other societies in lowland South America where the idea that paternity is partible, that more than one man can contribute to the formation and development of a fetus, has been reported. These societies are dispersed over much of the continent, and represent many different languages and language families.

For instance, among the Mehinaku of Brazil, speakers of a language in the Arawak family, Thomas Gregor found two theories of conception: “Both theories assert that one sexual act is insufficient to conceive a child. Rather, the infant is formed through repeated acts of intercourse. Since all but three of the village women are involved in extramarital affairs, the semen of the mother’s husband may form only a portion of the infant…. Joint paternity is further recognized at birth when the putative fathers of the baby honor attenuated versions of the couvade and accept some of the obligations of in-laws when the child grows up and gets married” (1985,84).

The folk theory of semen babies:

Frequently, pregnancy is viewed as a matter of degree, not clearly distinguished from gestation. For the Kulina, for instance, all sexually active women are a little pregnant. Over time, as Pollock reports, semen accumulates in the womb, a fetus is formed, further acts of intercourse follow, and additional semen causes the fetus to grow more. Only when semen accretion reaches a certain level is pregnancy irreversible. Lea reports somewhat similar ideas among the Mebengokre, where there is “neither a notion of fertilization nor of subsequent ‘natural’ growth; rather the fetus is built up gradually, somewhat like a snowball.” Like notions are found among the Yanomami, Curripaco, and Ese Eja. The Barí believe, in contrast, that a single copulation is sufficient to conceive a child, but that the fetus must be anointed repeatedly with semen in order to grow strong and healthy. It follows from these ideas that men in these societies often assert that creating a baby is hard work. Alès reports that Yanomami men say that they expend much energy to make a baby, and become thin from the effort.

Note that these tribal cultures don’t necessarily place much value on women:

Woman’s role in conception and the development of the fetus is widely denied among the cultures considered here; the mother is generally considered as the receptacle in which the fetus grows.

What it all means:

[T]he frequency and distribution of the idea of partible paternity shows that the doctrine is common throughout an entire continent; and that it is found among peoples whose cultural traditions diverged millennia ago, as evidenced by the fact that they live thousands of kilometers apart, speak unrelated languages, and show no indication of having been in contact with each other for many centuries. It is difficult to come to any conclusion except that partible paternity is an ancient folk belief capable of supporting effective families, families that provide satisfactory paternal care of children and manage the successful rearing of children to adulthood.

And finally, the benefits of partible paternity:

Among the hunting and gathering Aché, Hill and Hurtado report: “The results of logistic regression show that highest survivorship of children may be attained for children with one primary and one secondary father…. Our best estimate of the shape of the relationship between age-specific mortality and number of fathers suggests an intermediate number of fathers is optimal for child survival. Those children with one primary and one secondary father show the highest survival in our data set, and one secondary father is also the most common number reported during our reproductive interviews” (1996, 444). Hill has kindly made available some of his unpublished data, which show that in a sample of 227 children born over 10 years ago, 70% of those with only a primary father survived to age 10, while 85% of those who had both a primary  and a single secondary father survived to age 10.

There seem to be two kinds of services that these lovers qua secondary fathers can provide and two people they can provide them to. These men can contribute food (male food: fish and game), either to the mother on behalf of the child, or to the child directly; and they can bestow protection, again either to the mother on behalf of the child, or to the child directly. The papers in this volume provide a number of examples of extra provisioning of children with fish and game, either directly or through the mother or another member of her household […].

There are no manifest examples in this volume of protective efforts by secondary fathers, although the issue is alluded to in passing by a few of the authors.

Keep all this in mind next an evolutionary psychologist tries telling you about evolved sex differences.

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