LHT wrap-up

So far we’ve tried to weave together some themes that we will continue to develop during the semester as we look at topics in human ecology. We take a macroscopic viewpoint. We are interested in basic governing principles and law-like generalizations that capture basic large scale, emergent, features of the systems we encounter. We want to identify ways in which humans are unique, given background ecological patterns, and ways in which humans seem to conform to these patterns. Part of this is being critical of ad-hoc claims of human uniqueness or mere assumptions that humans are outside of nature, which are common in the literature.

Given this perspective, we want to address the role of life history theory (LHT) in (human) macroecology. We want it to be as clear as possible why we chose to cover LHT and how it ties into the other themes of the class. Please ask us questions about this…

Life history attributes scale with body size, as do other important ecological variables. Such scaling relationships can be used to make deductive predictions. For example, we know that size at weaning is about one third of adult size, so it’s a constant linear proportion, and by combining this with the Smith-Fretwell model we can deductively predict the -1/4 scaling observed for fertility rate (Charnov and Ernest 2006).

Human uniqueness. Life history points us to some key features of the human life history that are truly unique. Importantly, these differences are quantitative rather than qualitative in that humans differ by going to extremes of a continuum not by having features that in and of themselves are something ‘new under the sun.’ Some key life history features that makes us unique are: 1) a long lifespan; 2) long juvenile (growth) period; 3) slow growth; 4) low mortality rates; 5) high levels of support and/or provisioning from males; 6) support from post-reproductive females (also know as grandmothers). These traits are identified by cross-species comparisons where humans are shown to be consistent outliers. Importantly, LHT ties together and explains the observations on the human life course. By investigating the energetic tradeoffs behind these features we’ve learned a lot about the human evolutionary niche. And we’ve also learned, by studying the adaptive nature of these traits, some things that must have been true about past environments where humans evolved. Embodied capital theory has been proposed to unite these observations into one cohesive framework (see Kaplan et al 2000 in Evolutionary Anthropology or Kaplan and Robson 2002 in PNAS).

Lastly, with respect to the EEA (environment of evolutionary adaptedness) concept, I think Foley’s concerns are valid in that it is an easy concept to misuse. This is especially true if the features of this EEA are too narrowly defined. However, as we saw in the Hill and Kaplan paper, it is common to assume that some behavior we study today, among industrial or foraging populations, is an adaptive attribute from some past selective environment. My take is that the EEA can be a useful concept, in some cases is necessary, as long as we don’t assume that it refers to one narrowly defined place and time.