Friday, November 11th 2011
The Duggars Demonstrate Life History Trade-Offs Around Quality Versus Quantity of Offspring
A picture of the Duggar family (public domain).
Back in the day, when many anthropologists assume we were all egalitarian foragers living off the land, women may not have thought on how many offspring they wanted. Contraceptives and abortifacents have likely been with us a very long time, yet various environmental stressors probably suppressed reproductive function enough of the time that this was rarely necessary. Instead, babies happened. I’m sure many women were quite aware of how and why they happened, but with several years in between each one, cooperative breeding and play groups, overlapping dependent offspring was possible.
But of course, environments vary, and foragers may live in marginal or energy-rich environments. Some are partial agriculturalists or pastoralists. Some are able to hunt and fish as well as gather. And so there was, and is now, plenty of variation in interbirth intervals, or the length of time between births.
In a broader sense, the timing of pregnancies are an interesting way to study life history trade-offs. For instance, one may choose to have many offspring, place them close together and allocate less resource to them, or one may choose to have only a few offspring, spread far apart. This is a classic quantity versus quality trade-off question, and we see trends in these trade-offs within and between species, but also in humans, and even among different cultural traditions. It’s an interesting instance where culture can have a very real effect on one’s physiology.
Compared to other species, humans tend to choose quality over quantity. Human babies take a lot of energy to make and feed, and because of our slow life histories, long learning periods and late pubertal maturation, they are dependent on their parents for food and resources for decades. Offspring that are still asking for handouts well into their twenties, when their primate kin have become independent before turning ten, are not conducive to life history decisions towards quantity of offspring. Even with cooperative breeding and the trading of food and labor that occurs within human societies, human babies are costly, and under some conditions even dangerous.
And so after Tuesday’s announcement that the Duggars are expecting their twentieth child, I decided to read up on them, not having watched more than one or two early episodes. To offset their high reproductive output, the Duggars do seem to have significant resources in terms of an enormous house and a fair bit of money from Discovery Channel, the folks who run TLC, which is the cable channel that the Duggar family show is on. And, at least according to Wikipedia, they have a fair bit of sibling care: older siblings are assigned to younger siblings as mother’s helpers. This is consistent with what we see in some other forager populations like the Pumé: there, we see women give birth relatively young, but the mother’s younger siblings contribute to the offspring’s care to offset the costs of early reproduction (Kramer 2005).
But resources and cooperative breeding only get you so far, particularly when you are giving birth every year and a half for fifteen years. There is such a thing as maternal depletion syndrome. Maternal depletion syndrome comes from the depletion of energy stores and micronutrients (such as folate and iron) from having closely-spaced pregnancies, or living in a poor environment where it’s hard to have good enough access to resources to get food to replete these stores (King 2003).
Not having adequate time and nutritional resources to replete those stores can lead to major health concerns. For the mother, maternal depletion syndrome can mean not having adequate fat stores to feed the next fetus (Lassek and Gaulin 2006), and putting constraints on one’s reproductive output that can decrease the chances for having future children. It can also mean the mother develops nutritional deficiencies, or needs to allocate some of her stores to the fetus. Short interbirth intervals increase the risk of maternal death (Conde-Agudelo and Belizán 2000). And in some populations, the more babies a woman has, the shorter her life span; in others, costs manifest in other ways (Jasienska 2009).
For the fetus maternal depletion syndrome means the mother isn’t really that prepared to provide for the fetus. This can lead to fetal growth retardation (King 2003), to the point that the fetus needs to decide if its chances are better inside or outside the womb. Often, this also means a higher risk of preterm birth (King 2003; Klerman et al. 1998), as the fetus usually needs to take its chances outside where it hopes to get more energy from breastmilk.
This means that in addition to the nineteen, possibly twenty offspring the Duggars will have added to the planet, Michelle Duggar is very likely putting herself at risk with her many and closely-spaced pregnancies. In fact, Duggar experienced preeclampsia with her last baby and delivered three months prematurely as a result, with her daughter Josie weighing just over a pound at birth. Little Josie Duggar spent many long months in the Neonatal Intensive Care Unit of her hospital, and is very lucky to be alive.
Many people politicize and criticize the side of reproductive choice that seeks to limit reproduction through contraception and abortion, though limiting family size is something women and other primates and animals have done throughout our history. Perhaps it’s also time to consider the other end of the spectrum of reproductive choice and its consequences. This is not to politicize it – the Duggars have to make, be responsible for, and live with their own choices, and in general women have enough trouble getting to make reproductive decisions. But we need to realize that all reproductive decisions, not just those that limit the number of children, have costs and benefits.
References
Conde-Agudelo A, and Belizán JM. 2000. Maternal morbidity and mortality associated with interpregnancy interval: cross sectional study. BMJ 321(7271):1255-1259.
Jasienska G. 2009. Reproduction and lifespan: Trade-offs, overall energy budgets, intergenerational costs, and costs neglected by research. AMERICAN JOURNAL OF HUMAN BIOLOGY 21(4):524-532.
King JC. 2003. The risk of maternal nutritional depletion and poor outcomes increases in early or closely spaced pregnancies. The Journal of nutrition 133(5):1732S.
Klerman LV, Cliver SP, and Goldenberg RL. 1998. The impact of short interpregnancy intervals on pregnancy outcomes in a low-income population. American Journal of Public Health 88(8):1182.
Kramer K. 2005. Children’s help and the pace of reproduction: cooperative breeding in humans. Evolutionary Anthropology 14(6):224-237.
Lassek WD, and Gaulin SJC. 2006. Changes in body fat distribution in relation to parity in American women: a covert form of maternal depletion. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 131(2):295-302.
