Once in a Lifetime

The current issue of American Journal of Human Biology (Sept/Oct 2007) has several interesting articles relating to an AAPA symposium called "Is Adaptation Healthy: Interpreting growth patterns in adverse environments" and described in the introduction (Bailey and Schnell 2007) below

This symposium focuses on the multiple interpretations of growth decanalization. In contemporary human biology, decanalization typically means a pattern of individual growth that departs from some expectation seen as characteristic of that individual or population. There are apparent gaps, however, between those who see decanalization as indicative of poor health, and those who believe decanalization can reflect a successful adaptation to environmental stressors. In a broad sense, the former stance is associated with auxology and biomedicine, while the latter is associated with evolutionary biology and anthropology.

Two of the articles I found particularly interesting were this one by Bogin et al. entitled Life history trade-offs in human growth: Adaptation or pathology?" with this abstract.

Human beings growing-up in adverse biocultural environments, including undernutrition, exposure to infection, economic oppression/poverty, heavy workloads, high altitude, war, racism, and religious/ethnic oppression, may be stunted, have asymmetric body proportions, be wasted, be overweight, and be at greater risk for disease. One group of researchers explains this as a consequence of developmental programming (DP). Another group uses the phrase predictive adaptive response (PAR). The DP group tends to view the alterations as having permanent maladaptive effects that place people at risk for disease. The PAR group considers the alterations at two levels of adaptation: (1) short-term adaptive responses for immediate survival and (2) predictive responses required to ensure postnatal survival to reproductive age. The differences between the DP and PAR hypotheses are evaluated in this article. A life history theory analysis rephrases the DP versus PAR debate from disease or adaptation to the concept of trade-offs. Even under good conditions, the stages of human life history are replete with trade-offs for survival, productivity, and reproduction. Under adverse conditions, trade-offs result in reduced survival, poor growth, constraints on physical activity, and poor reproductive outcomes. Models of human development may need to be refined to accommodate a greater range of the biological and cultural sources of adversity as well as their independent and interactive influences.

The second one is here is by Kuzawa (2007) and entitled Developmental origins of life history: Growth, productivity, and reproduction with the abstract here

There is now much evidence that early life undernutrition elevates risk of diseases like cardiovascular disease. Less clear is whether the underlying developmental plasticity in metabolism and physiology evolved to serve an adaptive function, beyond these effects on pathophysiology. This review builds from principles of life history theory to propose a functional model linking early environments with adult biology. An organism has metabolic potential in excess of survival requirements, called productivity, that supports growth before being shunted into reproduction after growth ceases. This concept from inter-specific studies leads to the prediction that plasticity in growth rate will be positively correlated with components of future adult reproductive expenditure. Consistent with this idea, evidence is reviewed that early nutrition or growth rate predict offspring size in females, and increased somatic investment related to reproductive strategy in males. Thus, population birth weight and sexual size dimorphism are predicted to increase in response to improvements in early nutrition. A striking feature of the continuity of metabolic production is its perpetuation not merely during the lifecycle but across generations: in females, growth rate predicts future nutritional investment in reproduction, which in turn determines fetal growth rate in the next generation. Growth and reproduction serve as mutually-defining templates, thus creating a phenotypic bridge allowing ecologic information to be maintained during ontogeny and transmitted to offspring. Resetting of metabolic production in response to maternal nutritional cues may serve a broader goal of integrating nutritional information within the matriline, thus providing a more reliable basis for adjusting long-term strategy.

References:

Bailey SM, L. Schnell (2007) "Introduction" Am. J. Hum. Biol., 19 (5) 603-605

Bogin B. MIV Silva, L Rios (2007) Life history trade-offs in human growth: Adaptation or pathology?Am. J. Hum. Biol., 19 (5) 631-642

Kuzawa CW (2007) Developmental origins of life history: Growth, productivity, and reproduction
Am. J. Hum. Biol., 19 (5) 654-661