Tuesday, August 21, 2007


On the first day of class we had a brief lecture that attempted to define the perspective toward human ecology that we will be developing in this class and gave a few examples of the relationships we'll be looking at later on. I'll give a brief breakdown of some of the main points of the lecture here.

The first goal was to define our approach to human ecology as a macroscopic transdisciplinary enterprise aimed at identifying mechanisms, simple governing principles, and explanations for complex large scale patterns. The specifics of the macroscopic perspective is defined in the chapters by Brown. Our perspective differs quite a bit from the sorts of topics generally associated with human ecology (see journal by this name for examples). We often refer to our perspective as human macroecology to make a distinction. We are interested in very large scale patterns and we draw from several disciplines.

The forager lifestyle and the EEA:
Anthropologists traditionally had a great deal of interest in the study of human foragers - populations that subsist by some combination of hunting, gathering, and horticulture. Unfortunately, detailed field studies of the few remaining indigenous populations who still subsist with a forager economy are very few in number, embarrassingly low I would argue, given that anthropology should be the field responsible for the description, documentation, and explanation for the depth and breadth of diversity of human cultures and lifeways of the past and present. But that's the subject of another blog.
We are interested in foragers because the overwhelming majority of our evolutionary past was spent as foragers. A concept often used in evolutionary psychology is the EEA, which stands for environment of evolutionary adaptedness. The EEA is an important concepts because in many ways our psychological and behavioral predispositions were molded in an environment much different from the modern industrial context. We evolved under conditions of much smaller group sizes where cooperation and food sharing were essential and prevalent and where we hunted and/or gathered our food. The industrial economy and lifestyle is very different from the EEA and we might want to know what sorts of patterns in human behavior, organization, or demography of humans has changed as a function of this change in lifestyle. This change might also have affected the way humans impact other ecological systems and species.

Human Uniqueness:
It is striking how different the lifestyles of modern humans can be. We hear a lot about human uniqueness in both anthropology and ecology. Anthropology is practically built on the idea that humans are outside of nature and therefore biological concepts are not relevant to the social sciences - there are plenty of exceptions to this notion but it is still very common.
If we wonder why humans have so much behavioral and organizational diversity we might wonder if its because we are especially diverse genetically. This is not the case. Individual populations of chimpanzees have more diversity than all living humans combined (see figure).

So, while humans may be unique in their diversity at the phenotypic level (at least with respect to behaviors and lifestyles) they are unique in the homogeneity at the genetic level. This is a very interesting combination of observations. Now, it may be that time is responsible for the lack of genetic diversity, as humans are a relatively recent mammal, but that still begs the question as to what happened to allow so much diversification in such a short time?

Humans have grown very rapidly (some say exponentially) and spread over most of the globe in a fairly short period of time. Is it possible that some of the adaptations that allowed for this rapid spread and growth are related to our modern day impacts on the environment and sustainability issues?
From the observations presented up to this point (there were more in the original lecture) some fundamental questions might be asked: Why do humans have so much variability? What are the patterns of this variability? How do these patterns compare with other ecological patterns? What laws and patterns determine which patterns we follow and which ones we don't?

We then gave a few examples of human patterning. We want to be skeptical of assuming that humans are unique with respect to some pattern or attribute. Uniqueness needs to be demonstrated. (Also, we wouldn't suggest that humans are NOT unique either - all biological species are unique by definition).

The first example is latitudinal gradients. Diversity in languages seems to map onto diversity patterns in plants. Is it possible that the underlying processes are also similar?

Ex. 2: Modern human fertility often is taken as a case where humans must be very unique. Many countries in Europe have below replacement fertility and the wealthiest classes in most or all countries have the lowest fertility rates. How can this be? Does it mean that humans are not following biological patterns with respect to an important Darwinian parameter, fertility?
That depends on your perspective. To the extent that energy budget is related to fertility rate it can be shown that across species those with higher metabolic rates have lower fertility rates (as those with larger body sizes have lower fertility rates). But if we consider the possibility that all of the energy available to an organism, not just what it can eat and drink, determines its fertility we might see a different picture. The next two figures illustrate this. The first shows the pattern with metabolic rate and the second plots industrial nations with an energy budget determined as the average power consumption of an individual in that country (see Moses and Brown 2003 for explanation).

One should always be skeptical of scaling plots, at first. What is this measure on the x-axis anyway? Can we trust it? The next figure suggests that the relationship is at least something more than a statistical artifact. It shows the relationship for two measure of fertility for every year in the United States from 1850 - 2000.

So, maybe there is something to this relationship and maybe modern human fertility is not a complete mystery after all. In one sense our fertility patterns seem really unique in terms of number of offspring. But what is more unique, relatively, about humans - the number of kids they have or the amount of energy they consume per individual and the lack of constraints on the delivery of this energy? These plots suggest that on average humans are making the same basic tradeoffs between energy and fertility as other species. This may not be correct but it certainly deserves our attention.

I think most people see themselves as really autonomous agents and we don't like the idea that we are points following some huge pattern - well some of us don't. And it might seem odd, given how personal fertility decisions are, that such a simple pattern with energy availability should emerge. There's a huge black box of complexity that influences what might affect ferlity. the fact that we can put energy in on one side and get the theoretically predicted exponent out on the other, is quite astounding. We haven't talked about how theory predicts this exponent, but we will. We will read this paper later in the semester too.

We might also think about what the implications are of this plot, if the relationship survives future scrutiny. What are the most important variables to consider with respect to the sustainability of human populations? Certainly the number of people and the amount of energy the consume are among the most important of these. Here, these two variables are connected, but the relationship is the opposite of what we might ideally desire. What do we do if the only way to lower birth rates is to increase per capita energy consumption? that would be a bind. I'm not suggesting that this is the case, but its an issue that we should confront and think about.

Just for fun, note in the following that an additional and important demographic variable also varies with per capita power consumption:

So, we've seen two cases where humans more or less follow ecological and biological patterns.
Now lets look at urban ecology - clearly the human imprint on the ecosystems they interact with tends to be especially robust, particularly in industrial contexts.
Eco-footprint analysis calculates the amount of area it takes to support the average consumer of a country (or other defined region/area) based on typical consumption patterns.
Here's a figure made by William Rees that I got from a handout he used (and emailed to me when I asked him for it) for a presentation at the AAAS meetings in Seattle a few years ago:
The world average is 4 ha per individual. We can ask questions like, 'if everyone in the world lived like the average US citizen, how many earths would it take to support the world?'
One student asked if increasing agricultural outputs would affect this picture. In one sense the answer is yes - the calculation of the productivity of arable land has an impact on the size of the footprint. But I might also caution against accepting those claims that agricultural lands have become more productive in some regions because often those estimates don't factor in the costs of the inputs. That is, we put more and more energy into equipment, fertilizers, and pesticides, etc and the actual productivity of the land is the difference between what goes in and what comes out - not just a measure of the harvest...

We also talked about a paper we'll read later in the semester that looks at cities at metabolizing structures. Its a great perspective that also focuses on energetic features of human societies that helps us understand how the human city, as a system, compares to and influences ecological systems.

In addition to these topics, during the semester we'll also discuss:
1) variation in human growth and development
2) the human role in the extinction of birds and mammals
3) patterns in the distribution of wealth and poverty
4) human cultures as complex systems

Finally, we feel that this class is really unique in format and content. It will be challenging but fun. We are trying to convey not only a different approach to thinking about human ecology but a different approach to science.
The ultimate goal is to discover, describe, and explain emergent phenomena that characterize human systems.

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