Human Macroecology at AAAS/SWARM

We at human macroecology are proud to announce that we have organized a symposium for this year's SWARM meetings, which will be held here in Albuquerque, New Mexico from the 9th to 12th of April 2008. SWARM is the southwest and rocky mountain regional division of the AAAS, the publishers of the journal Science. The symposium features the work of several authors whose work represents the backbone of the approach we conveyed in our class last semester. They also provide the exemplary examples of what this style of social science research will strive to emulate in the future. We hope that anyone who can travel to the event considers stopping in and enjoying the papers, which will prove to be diverse, exciting, and novel in their perspectives and analyses. Information about registration can be found here and lodging info is here.

The keyword for this year's SWARM meeting is collaboration, thus human macroecology fits the theme very well.

The abstracts for the symposium and each of the papers are presented below. We'll periodically add information about the symposium to this blog so check back in from time to time if you're interested.

The symposium will be held on Thursday April 10th, 2008. Papers should start at 9:00 am but the official schedule has not yet been completed. I'll post new information as it becomes available.

Cheers,
Oskar

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Symposium Schedule:

Thursday, April 10, 2008.

Order	time	Speaker	Affiliation
1	9:00 - 9:20	Oskar Burger and Bill Burnside	University of New Mexico
2	9:20 - 9:40	James H. Brown	University of New Mexico
3	9:40 - 10:00	Bill Burnside and Jordan Okie	University of New Mexico
4	10:00 - 10:20	Larry Todd	Colorado State University
5	10:20 - 10:40	Mary Stiner	University of Arizona
	10:40 - 11:00	break	break
6	11:00 - 11:20	Peter Turchin	University of Connecticut
7	11:20 - 11:40	Alison Boyer	University of New Mexico
8	11:40 - 12:00	Helen Davis et al.	University of New Mexico
	12:00 - 1:00	lunch	lunch
9	1:00 - 1:20	Robert Walker et al.	Max Planck Institute
10	1:20 - 1:40	Paul Hooper	University of New Mexico
11	1:40 - 2:00	Marcus Hamilton	University of New Mexico
12	2:00 - 2:20	Melanie Moses	University of New Mexico
13	2:20 - 2:40	Louis Bettencourt	Los Alamos National Laboratory
	2:40 - 3:00	break	break
	3:00 - 4:00	round table discussion

Each presentation is allotted 20 minutes, 15 for the talk with 5 for questions.

Symposium Title:

Human Macroecology: Emergent Patterns and Processes in Large-Scale Human Ecology

Symposium Abstract:

Through a multidisciplinary team of speakers and a panel discussion, this symposium explores the developing field of human macroecology, the study of emergent patterns in human-environment interactions across scales. This collaborative approach to social science emphasizes law-like generalizations of human dynamics that occur at scales larger than what can be observed in a single study, survey, or field site. Within this framework, we borrow from a diverse range of fields, including evolutionary ecology, statistical mechanics, complex systems, biogeography, and others. The talks are connected by the spirit of the analyses and the nature of the questions asked, and provide examples of studies that human macroecology will strive to emulate in the future. These include studies of life history variation in primates and humans that emphasize emergent features of human evolution and energetic tradeoffs among essential demographic variables. Other presentations explore biogeographic trends and large-scale human-environment interactions. To this end, archaeological and paleobiological perspectives are utilized to explore the dynamic feedbacks of demographic trends, dietary shifts, adaptations and their impacts on the environment. We examine the form and structure of human settlements by analyzing how properties of cities and road networks change with population size and geography. Explicitly considering the flow of energy, materials, and information that power human societies highlights the importance of a metabolic framework for human ecology. In many instances, analogies with biological systems are employed to gain novel insights into human dynamics. By encompassing a wide range of topics and datasets we take a macroscopic view of the complexity and diversity of human systems, identifying underlying regularities, mechanisms, and organizing principles. Our approach bridges historic disciplinary divides while building a perspective that is needed to confront many of our most pressing issues of population growth, energy use, and sustainability.

Organized by Oskar Burger and Bill Burnside

9:00 - 9:20 am

Title: Orientation to the Goals, Motives, and Definition of Human Macroecology

Authors: Oskar Burger¹ and Bill Burnside²

1 Department of Anthropology, University of New Mexico

2 Department of Biology, University of New Mexico

Abstract: We present the definition and rationale behind the developing field of human macroecology. We emphasize the interdisciplinary and collaborative nature of this approach to social science by outlining its connections to a wide range of other areas of research that also focus on big picture dynamics in human systems. In doing so, we present some of the more salient emergent patterns that have been examined empirically and discuss some of their likely underlying mechanisms. Additionally, we provide framework for the symposium by highlighting commonalities in theme and approach among the papers which follow.

9:20 - 9:40 am

Title: Toward a Metabolic Theory of Human Ecology

Author: James H. Brown

Department of Biology University of New Mexico

Abstract: The developing metabolic theory of ecology (MTE) uses metabolism – the uptake, transformation, and allocation of energy and materials by organisms – to conceptualize, synthesize, and unify diverse environmental sciences. Since ecological interactions involve exchanges of energy, matter, and information, it is possible to use first principles (e.g., conservation of mass and energy, second law of thermodynamics, chemical stoichiometry) and biological processes (e.g., scaling of metabolic rate with body size and temperature, and dependence of resource use, life history, demography, and species diversity on metabolic rate) to build models and test their predictions. The principles, models, and approaches of MTE are directly applicable to human ecology. In collaborations among colleagues and students in biology and anthropology, we have begun to compile ‘macroecological’ data and to apply MTE. Our goal is to understand how energy and material resources are acquired, transformed, and allocated by aboriginal hunter–gatherers and modern technological societies. Preliminary results highlight the potential to use metabolism as well as genetics to cross the interdisciplinary interfaces between the natural and social sciences.

9:40 - 10:00 am

Title: Ecology of Range Size among Traditional Human Foragers: Macroecological Implications for Cultural Diversity Patterns

Authors: Bill Burnside and Jordan Okie

Department of Biology, University of New Mexico

Abstract: Indigenous human cultures display consistent geographic patterns of ethnic and linguistic diversity and group and territory size. As with biological species, cultural groups are more concentrated in the tropics. In species and populations generally, the geographic range reflects foraging ecology and energy requirements. We hypothesize that similar forces constrain range sizes of human societies: 1) environmental productivity will decrease territory size by supporting given populations with less land, while 2) reliance on hunting will increase territory size because energy is lost ascending food chains. Using a database of 339 traditional foraging societies, we used OLS regressions to test correlations between range size and climate; range size and mobility; and range size and foraging mode (gathering, hunting, fishing). We develop mathematical theory to explain the resulting macroecological patterns, guided by the effects of temperature on productivity and kinetics, or the rates of biological reactions and ecological interactions. Analyses of datasets on both traditional foraging societies and global indigenous cultural diversity support our theory. Combining macroecological analyses of ethnographic data with mechanistic ecological theory helps explain general patterns of human foraging ecology and cultural diversity.

10:00 - 10:20 am

Title: Scale, Boundaries, and Bridges: Human Dimensions in Paleoecology

Author: Lawrence C. Todd

Colorado State University

Abstract: One of the more difficult hurdles for research that examines multi-scale, transdisciplinary ecological processes can be the widespread perception that human actions and cultural transmission of information preclude inclusion of our species. One approach that makes this partition more permeable uses human paleoecology and archaeology as a basis for placing human behaviors within a framework of macroecological analysis. Fundamental to this approach is the effort to refocus archaeological research toward an integrated study of landscapes in which human actions are approached in ways that can be investigated in concert with other biological and physical processes. This approach emphasizes that only the most reductionist of research programs can investigate ecological relationships that do not consider aspects of all three domains of landscape formation and evolution (i.e., the cultural, the biological, and the physical). Examples for the Greybull River Sustainable Landscape Ecology project (GRSLE) in northwester Wyoming’s Greater Yellowstone Ecosystem are used to illustrate the basic components of this approach, which is referred to as “landscape taphonomy.” Investigations of this sort help bridge the unfortunate gap between research in the social and natural sciences.

10:20 - 10:40 am

Title: Changes in the ‘Connectedness’ and Resilience of Paleolithic Societies in Mediterranean Ecosystems

Author: Mary C. Stiner

Department of Anthropology, University of Arizona

Abstract: Human predator-prey relationships changed dramatically in the Mediterranean Basin between 250,000 to 9,000 years ago. Many of these changes can be linked to increases in Paleolithic human population densities. Small game species are particularly diagnostic of increases in human hunting pressure and are a major source of evidence for demographic change after 40-45,000 years ago. Biomass-corrected data on prey choice also indicate increasing use of those species that possess higher reproductive efficiencies. Step-wise, apparently irreversible shifts in human predatory niche are apparent in the Mediterranean Basin, beginning with the earliest Upper Paleolithic in the east and spreading westward. Evidence of demographic pressure and greater use of resiliant prey populations is followed by technological innovations to exploit these animals more efficiently. The zooarchaeological findings suggest that Middle and Lower Paleolithic reproductive units probably were not robust at the micropopulation scale, due to the rather narrow set of behavioral responses that characterized social groups at the time, and that localized extinctions at the micropopulation level were likely to have been common. Upper Paleolithic groups were the quintessential colonizers and, in addition, uniquely good at holding on to habitat gained. Upper Paleolithic archaeological “cultures” have shorter histories of existence than those of earlier periods, but they were even more widespread geographically. The demographic robustness of the Upper Paleolithic systems may stem from wholesale strategies for evening-out or sharing risk and volatility in technology. Micropopulations were larger and often denser on landscapes, more connected via cooperative ties, and thus more robust.

11:00 - 11:20 am

Title: Dynamical Feedbacks between Population Growth and Sociopolitical Instability

Author: Peter Turchin

Department of Ecology and Evolutionary Biology, University of Connecticut

Abstract: Most preindustrial states experienced recurrent waves of political collapse and internal warfare. One possible explanation of this pattern, the demographic-structural theory, suggests that population growth beyond the means of subsistence leads to state instability and breakdown, which in turn causes population decline. In several cases (e.g., early modern England and ancient China) we have data on both population dynamics and sociopolitical instability that can be analyzed using standard time-series approaches. Such analyses confirm that periods of sustained and vigorous population growth are followed, with a time lag, by waves of instability. Industrialization was made possible by rapid gains of agricultural productivity, and the general expectation is that the Malthusian component of the demographic-structural theory should lose relevance. Nevertheless, a survey of industrializing states (Western Europe, the U.S., Russia, and Japan) shows that periods of popular immiseration (proxied by declines in the average body height) were also followed, after a time lag, by waves of instability.

11:20 - 11:40 am

Title: Human Colonization and Pacific Island Biodiversity

Author: Alison G. Boyer

Department of Biology, University of New Mexico

Abstract: Human arrival on every landmass around the world has been associated with elevated extinction probability in the native fauna, which has been a major contributor to biodiversity loss and global change. Human impacts, through direct predation, habitat change and the introduction of exotic species, have been implicated as extinction drivers, but aside from one or two well-analyzed locations, the relative roles of these environmental impacts are much debated. Regression trees built on zooarcheological data from over 40 islands were used to assess the relative importance of these extinction drivers in island bird extinctions across the tropical Pacific. Prehistoric extinctions showed a strong bias toward larger body sizes and flightless, ground-nesting species, even after accounting for preservation bias, indicating a significant human predation component. In many cases endemism was also associated with extinction, possibly through impacts of exotic predators and habitat destruction. Human societies on small, isolated islands can be thought of as replicated microcosms which provide crucial information on the dynamic interplay between humans and biodiversity in natural communities.

11:40 am - 12:00 pm

Title: People as Islands: The Theory of Island Biogeography and Patterns of Disease across Human Populations.

Authors: Helen Elizabeth Davis¹, Oskar Burger¹, and Michael Gurven², and Hillard Kaplan¹.

1 Department of Anthropology, University of New Mexico,

2 Department of Anthropology, University of California- Santa Barbara,

Abstract: Infectious disease plays a major role in human population dynamics. Here we investigate host-parasite interactions across space and time using data collected among the Tsimane, a traditional forager-horticulturalist society in lowland Bolivia. Community ecology and human macroecology models are used to address the co-evolution of hosts and disease with respect to parasite virulence and spread, and human infection and re-infection rates. GIS mapping provides a spatial distribution pattern for 17 helminth and protozoa infections across the population (n=3,000). Application of MacArthur and Wilson’s (1967) theory of island biogeography allows us to identify disease reservoirs and analyze their contribution to population dynamics and disease spread. Counter-intuitively, higher population density (nodes) did not correlate with parasite density, suggesting that other factors such as wealth and immune system integrity are important. Particular attention is given to children’s health, with cognitive performance correlating significantly with parasitic burden and a measure of immune system integrity (IgE). Finally, we discuss the relationship of pathogen load across human populations and how these patterns have global significance.

1:00 - 1:20 pm

Title: The Tradeoff between Number and Size of Offspring in Humans and other Primates

Authors: Robert Walker¹, Michael Gurven², Oskar Burger³, Marcus Hamilton³

1 Max Planck Institute for Evolutionary Anthropology

2 Department of Anthropology, University of California- Santa Barbara,

3 Department of Anthropology, University of New Mexico

Abstract: Life-history theory posits a fundamental trade-off between number and size of offspring that structures the variability in parental investment across and within species. We investigate this ‘quantity–quality’ trade-off across primates and present evidence that a similar trade-off is also found across natural-fertility human societies. Restating the classic Smith–Fretwell model in terms of allometric scaling of resource supply and offspring investment predicts an inverse scaling relation between birthrate and offspring size and a -1/4 power scaling between birth rate and body size. We show that these theoretically predicted relationships, in particular the inverse scaling between number and size of offspring, tend to hold across increasingly finer scales of analyses (i.e. from mammals to primates to apes to humans). The advantage of this approach is that the quantity–quality trade-off in humans is placed into a general framework of parental investment that follows directly from first principles of energetic allocation.

A .pdf of a paper that this talk is based on can be found here.

1:20 - 1:40 pm

Title: Understanding the Effects of Braininess on Primate and Human Lifespan Evolution

Author: Paul Hooper

Department of Anthropology, University of New Mexico

Abstract: Explaining variation in animal lifespans is a central goal in life history theory and the metabolic theory of ecology. Understanding why primates in general, and humans in particular, are especially long-lived for their body size is a particularly relevant problem in this area. While previous life history approaches have taken adult mortality rates (and thus adult lifespan) as given, it has become apparent that lifespan should be treated as a partially endogenous decision variable, mediated by investments in mortality reduction throughout life (e.g. cellular maintenance and repair). The goal of this paper is to evaluate the conceptual continuity between two life history models—Kaplan & Robson 2002 and Charnov 2001—in which investment in survival is an endogenous decision variable. I show that Kaplan & Robson's result—that a more learning-intensive niche leads to greater investment in longevity—can be replicated within Charnov's framework using a numerical example. I then briefly discuss these results with respect to the allometry of mammalian and primate life history variables.

1:40 - 2:00 pm

Title: Scaling the Metabolism of Human Socio-Economies from Hunter-Gatherers to Nation States

Author: Marcus J. Hamilton

Department of Anthropology, University of New Mexico

Abstract: Like all biological species, human socio-economies are embedded within complex ecosystems that are structured by the fluxes and flows of energy and information between organisms and their environments. To meet energy demands, humans harvest resources from their environments by tapping into these flows thus creating nonlinear feedbacks between human and ecological systems. In this paper I use scaling theory to quantify the rate at which humans extract, distribute, and expend energy and information within different socio-economies, from hunter-gatherers to nation states. Preliminary data from over 1,030 human cultures show that human energy use scales at approximately the same sublinear rate across the range of human socio-economies. These results suggest a potential scaling law for human energy use, and the implications for understanding human evolution and ecology are discussed.

2:00 - 2:20 pm

Title: Cities as Organisms: Allometric Scaling of Urban Road Networks
Authors: Melanie E. Moses and Horacio Samaniego

Computer Science Department, University of New Mexico

Abstract: Just as the cardiovascular network distributes energy and materials to cells in an organism, urban road networks distribute energy, materials and people to locations in cities. Understanding the topology of urban networks that connect people and places leads to insights into how cities are organized. We study statistics of road networks and traffic patterns across 425 US cities and show that urban road networks are much less centralized than biological vascular networks. As a result, per capita road capacity is independent of the spatial extent of cities. In contrast, driving distances depend on city area, although not as much as is predicted by a completely centralized model. This intermediate pattern between centralized and decentralized extremes may reflect a mixture of different travel behaviors. The approach presented here offers a novel macroscopic perspective on the differences between small and large cities and on how road infrastructure and traffic might change as cities grow.

2:20 - 2:40 pm

Title: Urbanization, Social Adaptation and Sustainable Development

Author: Luís Bettencourt

Theoretical Division, Los Alamos National Laboratory

Abstract: The problem of creating solutions for sustainable development is increasingly predicated on the management of the resource demands of social economic life in cities. Urbanization is the most conspicuous social force at play worldwide today. Developing countries such as China and India are less that 50% urban, but are expected to reach the levels observed in developed nations (80-90%) in the next 3-4 decades. The consequences of urbanization for human demands on natural ecosystems is somewhat ambivalent. While certain forms of consumption (energy, changes in diet) per capita certainly increase on average, urbanization can partially liberate land from human occupation while increasing the efficiency with which a dense population can be serviced. Quantifying these potentially contradictory trends has been a challenge in the past. We show however that scaling, i.e. the analysis of the systematic variation of urban properties with population size reveals scale invariant statistical regularities that capture systematically and predict the course of cities as their population sizes change. We use these insights to frame the discussion of a transition to sustainability in terms of the consumption of several resources used to quantify human footprint, and show how urbanization may be compatible, and even accelerate, the achievement of continued economic growth that is compatible with the preservation of the Earth's support systems.

Natural selection and culture

A paper was published this week in PNAS on rates of culture change and has an interesting commentary by Stephen Schennan. As its open access you can get it here.

Here's the basics on the paper:

Natural selection and cultural rates of change

Deborah S. Rogers and Paul R. Ehrlich^*

Department of Biological Sciences, Gilbert Building, 371 Serra Mall, Stanford University, Stanford, CA 94305

Contributed by Paul R. Ehrlich, December 17, 2007 (received for review November 5, 2007)

It has been claimed that a meaningful theory of cultural evolution is not possible because human beliefs and behaviors do not follow predictable patterns. However, theoretical models of cultural transmission and observations of the development of societies suggest that patterns in cultural evolution do occur. Here, we analyze whether two sets of related cultural traits, one tested against the environment and the other not, evolve at different rates in the same populations. Using functional and symbolic design features for Polynesian canoes, we show that natural selection apparently slows the evolution of functional structures, whereas symbolic designs differentiate more rapidly. This finding indicates that cultural change, like genetic evolution, can follow theoretically derived patterns.

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I like papers that suggest that we shouldn't just assume that certain features of culture are immune to scientific inquiry.

Cultural evolution is one of those areas of anthropology/social science with lots of baggage - both in terms of misguided criticisms and in terms of misused analytical techniques and models - but its an area that is rapidly growing and seems to consistently make provocative findings - as this paper does.

So they study boats from Polynesia:
"Finding cultural traits with which to test such ideas proved difficult. The traits we settled on were the design elements of canoe building across Polynesian societies. We have since learned that the French philosopher Alain (Émile-Auguste Chartier) in 1908 proposed that boat design would be subject to natural selection (26). "Tout bateau est copié sur un autre bateau... Raisonnons là-dessus à la manière de Darwin. Il est clair qu'un bateau très mal fait s'en ira par le fond après une ou deux campagnes, et ainsi ne sera jamais copié... On peut donc dire, en toute rigueur, que c'est la mer elle-même qui façonne les bateaux, choisit ceux qui conviennent et détruit les autres" (pp 41–42). [Every boat is copied from another boat... Let's reason as follows in the manner of Darwin. It is clear that a very badly made boat will end up at the bottom after one or two voyages, and thus never be copied... One could then say, with complete rigor, that it is the sea herself who fashions the boats, choosing those which function and destroying the others. (Translated by D.S.R.)]"

They divide traits of the canoes into those that seem likely to directly impact the canoe's performance (functional or design characteristics) from those that do not (stylistic), so you need to be comfortable with that dichotomy.

that state: "Our expectation was that the functional traits would change at a significantly different rate from that of symbolic traits."

They statistically evaluated what the differences in rates of change were between the stylistic and functional groups across the islands through time. The statistical technique was interesting - they compared a randomized assignments of functional vs. stylistic to a Wilcoxon signed rank frequency distribution for the recalculated Jaccard distances. I don't know if there were better ways to conduct this test or not. They found that the rates were different, with functional traits changing at a slower rate.

They conclude that: 1) such evolutionary perspectives are indeed good for the study of culture change (a rah rah team conclusion); 2) this identifies the different mechanisms that might act on culture change, and; 3) design features don't change randomly or 'mutations' indicating the link between canoe design and actual survival characteristics. Changes must be conservative and thought out... etc.

enjoy,
O

Levy Walks in the Ocean

A paper published this week in Nature about Levy Walks among marine predators.

Reference info, title, and abstract follow:

Letter

Nature 451, 1098-1102 (28 February 2008) | doi:10.1038/nature06518; Received 17 October 2007; Accepted 29 November 2007

Scaling laws of marine predator search behaviour

David W. Sims, Emily J. Southall, Nicolas E. Humphries, Graeme C. Hays, Corey J. A. Bradshaw, Jonathan W. Pitchford, Alex James, Mohammed Z. Ahmed, Andrew S. Brierley, Mark A. Hindell, David Morritt, Michael K. Musyl, David Righton, Emily L. C. Shepard, Victoria J. Wearmouth, Rory P. Wilson, Matthew J. Witt & Julian D. Metcalfe

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability¹. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology^{1, 2, 3}. Lévy walks⁴ are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes⁵. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested^{6, 7}. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators—sharks, bony fishes, sea turtles and penguins—exhibit Lévy-walk-like behaviour close to a theoretical optimum². Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms³, from microbes⁸ to humans⁹, as a 'rule' that evolved in response to patchy resource distributions.

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So there has been a lot of attention to this Levy Walk stuff in recent years. Do animal movements form power law distributions in terms of the length of each 'flight' they take? If you track an animal as it moves, it goes in a straight line for a while and then turns. These straight line lengths between turns are called paths or flights. A Levy Flight distribution is one where the histogram of these flights has a really long tail toward long flights and the probability of finding a flight of any given length is a power law distribution with an exponent between about 1 and 3 (around 2 being typical). This means there are a lot of small lengths and a few really long ones and that as length increases by some factor the probability decreases by a constant factor (the exponent). Some folks think the importance of these Levy Flights is way overblown and some people think its a big deal. If its a big deal its because we are learning something fundamental about how foraging behavior is organized and presumably how that organization reflects something about the underlying ecology or prey distribution. Are these things adaptive? To get a visual, imagine taking 'flights' while foraging that were all the same length. You might deplete all the resources in your immediate surroundings efficiently but what happens when you have to move a long way? So lots of small steps and a few long ones might be the way to go to efficiently search in your foraging habitat - and that is more or less what the Levy Flight is about.

Here they argue that Levy Flights are optimal foraging strategies that reflect the underlying distribution of prey. Hopefully we'll know more about the mechanistic links between path length distributions and prey distributions in the future. Also note that the book on Foraging that I have been blogging about does not cover this new work on Levy Flights even though this would certainly be a hot topic to some. Of course I don't blame the editors of the book as you can't fit in everything.

Anyway, its an interesting paper that is worth checking out.

Best,
Oskar

Reproducing in Cities: recent paper by R. Mace

A recent perspective by Ruth Mace published in Science (subscription required) gives a perspective on the demographic transition - the transition to reduced fertility rates among wealthy nations and economic classes. The argument is based on the costs of childrearing that seem to increase with urbanization and the lowered rates of infant and child mortality that can accompany city life in contexts where sufficient health care and sanitation are available.

Here's the paper's abstract:

"Reproducing in cities has always been costly, leading to lower fertility (that is, lower birth rates) in urban than in rural areas. Historically, although cities provided job opportunities, initially residents incurred the penalty of higher infant mortality, but as mortality rates fell at the end of the 19th century, European birth rates began to plummet. Fertility decline in Africa only started recently and has been dramatic in some cities. Here it is argued that both historical and evolutionary demographers are interpreting fertility declines across the globe in terms of the relative costs of child rearing, which increase to allow children to out compete their peers. Now largely free from the fear of early death, postindustrial societies may create an environment that generates runaway parental investment, which will continue to drive fertility ever lower."


The paper provides an interesting perspective on fertility in urban life and of course on the demographic transition in general. Mace essentially argues that the demographic transition is the result of the quantity quality tradeoff.

"Industrialization and urban living enable new professions to emerge, some of which are only available to those invested with considerable capital or training." .... "Whether perceived relative costs are equivalent to actual costs is a moot point; but, in essence, historical and evolutionary demographers are converging on similar explanations for demographic change. The cost of raising a child includes enabling it to compete with its peers—for marriage partners, for jobs, or for the means to support a family—and if that competition increases costs, then basic evolutionary ecology predicts that optimal fertility will decline (16). Education introduced a new mechanism through which children could compete for future employment opportunities. School also adds pressure on parents to present adequately fed and dressed offspring for public scrutiny."

Figure 2, pasted in below, represents the basic schematic for the argument. Mace says that in many instances wealth and fertility are often positively correlated within these 'homogenous subpopulations'. While this may indeed be true (I think that it is and would argue in favor of that point), the data supporting it are really not that good and the source Mace cites as proving
that wealth and family size are usually positively correlated really provides only weak support and is based on little data.

Fig. 2. Schematic diagram of how different levels of parental investment per child can generate positive relationships between fertility and wealth in subpopulations (where each of the diagonals represents a different subpopulation within a larger society) but a negative relationship between wealth and fertility over a large heterogeneous population. Levels of parental investment per child may be highest in urban areas.

Mace is skeptical the opinion that these trends in fertility decline simply represent shifts in cultural values that have rapidly swept over the globe and I think for good reason. Clearly the pattern is consistent in very different cultural contexts (Europe, Americas, and Africa have all gone through similar demographic transitions following broadly similar correlations between economic diversification and urbanization). Instead, there is good evidence for a general evolutionary mechanism at work. So the general trend of having "few higher quality offspring" started as initially advantageous, accelerated with lower levels of child mortality and the increased importance of inherited wealth and status, and then became subject to runaway selection.

"Transfers of resources from parents to offspring are key to understanding human life-history evolution (23). In wealth-owning societies, siblings compete with each other for their parents' material and intellectual resources (24–26). If parental investment is a key influence on children's future success, and the ability to invest effectively in children is heritable (and cultural traits such as wealth and status are usually highly heritable), then it is possible that runaway cultural selection has occurred in preferred levels of investment in each child (27), driving the quantity/quality trade-off further in the direction of offspring quality. Hence, I argue that the emergence of postindustrial life, now largely free from the fear of early mortality, seems to have generated conditions under which a runaway process of ever-escalating levels of investment in our children continues to drive fertility ever lower."

The link to 'cultural selection' could be a bit more clear in order to differentiate it from the widely spreading cultural shift idea of some cultural demographers which she criticizes earlier in the paper. Readers who are not already on Mace's side of the argument may not see the difference, and its not entirely clear. However, I am on Mace's side of the argument and think that evolutionary mechanisms do indeed underly fertility decisions of this sort. The runaway selection idea is one that deserves more attention. I'd like to see some modeling or analytical work showing exactly how it could lead to below replacement fertility. Perhaps some of the references in the paper accomplish this. On the whole, its good to see this sort of approach being applied in human demography. Being a UNM graduate student though, I couldn't help but notice that some of the highly relevant work done by some faculty and/0r grad students here was not cited or included in the paper (e.g., Moses and Brown 2003; Kaplan 1996), but that is clearly only a gripe driven by hometown bias.



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Kaplan H. (1996) A Theory of Fertility and Parental Investment in Traditional and Modern Human Societies. Yearbook of Physical Anthropology, 39, 91 - 135

Moses M.E. & Brown J.H. (2003) Allometry of human fertility and energy use. Ecology Letters, 6, 295-300

Some Mac Links

A paper has recently been published in Plos one about the peopling of the new world that uses a large sample of mtDNA from Native Americans to assess population history. They argue for a three stage model that essentially supports the idea that the new world was colonized by northeast Asian groups who crossed Beringia and an ice-free corridor through northwest North America. They do argue that the origin of Clovis culture may go back to 16,000 years or more, which is a bit older than generally thought.
Blogs on this paper can be found here (Anthropology.net) and here (Dienekes).

Also of potential interest is a recent proposal to start an institute of human origins at the University of California San Diego. The news article explains that:
"The Center for Academic Research and Training in Anthropogeny will be “trans-disciplinary,” said Varki, who will be co-director with Gage and Schoeninger. (Anthropogeny is the study of human evolution.)

“It will be more than multidisciplinary,” he said. “CARTA will transcend disciplines, bringing together biologists, social scientists, neuroscientists, chemists, medical specialists – anybody who can bring insight into the question of where we come from.”

Said Schoeninger: “The center will allow us to move well beyond the bounds of any given field of study. Looking at the biological and cognitive links between humans and other primates or other animals – and doing so not only with the breadth afforded by different disciplines, but also with the depth offered by an evolutionary perspective – will give us a richer picture of the past and of today.”"

Sounds pretty cool. We need more work on figuring out what makes humans human.

Human macroecology is interested in underlying mechanisms of the growth and form of human institutions/groups/populations at multiple scales. A recent study in Science magazine covered geometric principles of the growth and form of cities that is covered by Science Daily and worth a quick read.

Cheers,

O

Quantity/quality offspring tradeoff in humans and other primates

The following article is available online in firstcite with the Proceedings of the Royal Society B.

Title: The tradeoff between number and size of offspring in humans and other primates

Abstract: Life-history theory posits a fundamental trade-off between number and size of offspring that structures the variability in parental investment across and within species. We investigate this ‘quantity–quality’ trade-off across primates and present evidence that a similar trade-off is also found across natural-fertility human societies. Restating the classic Smith–Fretwell model in terms of allometric scaling of resource supply and offspring investment predicts an inverse scaling relation between birth rate and offspring size and a −¼ power scaling between birth rate and body size. We show that these theoretically predicted relationships, in particular the inverse scaling between number and size of offspring, tend to hold across increasingly finer scales of analyses (i.e. from mammals to primates to apes to humans). The advantage of this approach is that the quantity–quality trade-off in humans is placed into a general framework of parental investment that follows directly from first principles of energetic allocation.

Authors: Robert Walker, Michael Gurven, Oskar Burger, Marcus Hamilton

I have a biased perspective but I think this is a really good paper. It combines the classic model of the quantity/quality tradeoff in life history theory developed by Smith and Fretwell with a recent model by Charnov and Ernest (citations below).
The Smith-Fretwell model basically says that the relative cost of a kid C is the total energy budget mom has to put toward making kids R divided by the number of kids she has N. so C = R/N. This also means that the number of kids then is given by N = R/C. This is a pretty straight forward model that works well. So the higher the cost of an average kid to an average mother in a species or population the fewer kids the average mom will have. We know from life history theory that mom's energy budget R is a function of her mass and that a 3/4 power allometry of body mass is a pretty reasonable estimate for this energy budget. We also know that a reasonable estimate of the cost of a kid seems to be mass at weaning, which is a linear function of mom's mass - about .3M among mammals where M is mom's mass. This means that on average mammal offspring are dependent on their moms for energy until they are about 1/3 her size (Charnov 1993 and others). Anyway, these two observations can be placed into the Smith-Fretwell model to predict another well-known allometric relationship, the -1/4 power scaling of fertility rate with body mass. This happens because R is proportional to M^3/4 and C is proportional to M^1 so we get that N can be predicted by M^3/4 divided by M^1 which gives us M^-1/4. Or we can use these same expressions to look at the relationship between the number and size of offspring, which is predicted to be an inverse relationship (N/R = 1/C ~ M^-1). Our analysis demonstrates that the theory predicts the actual empirical trends in humans and primates.

If this is kind of thing is new to you just realize that when we look for patterns across large numbers of species - like all mammals or all birds - we find these really consistent relationships where a lot of important traits seem to be largely constrained (or at least well-predicted) by the average adult mass of the species. Three of these traits used here are metabolic rate, which is taken to be energy budget, the size of the offspring when its independent from its mom (important because that's when the mom can start making new kids if she wants so its a key constraint on fertility), and these two predict another - that fertility rate is slower with larger animals than with smaller ones.

We need to keep in mind that mass at weaning is generally a good proxy for the measure we are really interested in which the energetic cost of the offspring to the mother. For primates and in humans in particular, however, this may not be a good approximation. Human mothers invest much more in their offspring as human kids are often dependent long after they are weaned.
We take this into account by looking at mass of the offspring at ages older than the typical age at weaning and find that the model works better as a result. So this basic prediction of life history theory, that a tradeoff exists between the number and size of offspring, is met with data on human groups (natural fertility, small-scale populations) and among primates. There are some other points to the paper as well and we hope people find it interesting and that it provokes further research in this area. comments welcome of course.

I'll post a stable link to the pdf of the paper as soon as I can but something is wacky with UNM's server so I can't right now. [Ok, here's a link to a pdf of the paper.] If you are on a computer that has access to the proceedings of the royal society then you should be able to get it here.

best,
Oskar



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Charnov, E.L. & Ernest, S.K.M. 2006 The offspring-size/clutch-size trade-off in mammals. Am. Nat. 167, 578–582, (doi:10.1086/501141).

Charnov, E.L. 1993 Life history invariants: some explorations of symmetry in evolutionary ecology. Oxford, UK: Oxford University Press.

Smith, C.C. & Fretwell, S.D. 1974 The optimal balance between number and size of offspring. Am. Nat. 108, 499–506, (doi:10.1086/282929).

"Evidence for declines in human population densities during the early Upper Paleolithic in Western Europe"

In PNAS's first issue of the New Year, Eugene Morin elegantly combines a macroecological approach with archaeological data to investigate forager ecology and the evolution of modern humans. Amongst other things, Eugene Morin finds a strong correlation between hunter-gatherer population density and mammalian species richness (see Morin's figure pasted on the right). Please post any comments you have of this paper on the blog.

"Evidence for declines in human population densities during the early Upper Paleolithic in Western Europe", 2008, PNAS, 105, pp. 48-53.

Abstract

"In western Europe, the Middle to Upper Paleolithic (M/UP) transition, dated between 35,000 and
40,000 radiocarbon years, corresponded to a period of major human biological and cultural changes. However, information on human population densities is scarce for that period. New faunal data from the high-resolution record of Saint-Ce´ saire, France, indicate an episode of significant climatic deterioration during the early Upper Paleolithic (EUP), which also was associated with a reduction in mammalian species diversity. High correlations between ethnographic data and mammalian species diversity suggest that this shift decreased human population densities. Reliance on reindeer (Rangifer tarandus), a highly fluctuating resource, would also have promoted declines in human population densities. These data suggest that the EUP represented for humans a period of significant niche contraction in western Europe. In this context, the possibility that a modern human expansion occurred in this region seems low. Instead, it is suggested that population bottlenecks, genetic drift, and gene flow prevailed over human population replacement as mechanisms of evolution in humans during the EUP."

Darwin2009: The Beagle Project

I just learned about the Beagle Project from John Hawkes' blog.
As the page for the Beagle Project explains:
"2009 is one of the most significant anniversary years in science: it marks the 200th anniversary of the birth of Charles Darwin (12 February 1809), and the 150th anniversary of the publication of his book On the Origin of Species by Means of Natural Selection."

and then,

"Our contribution to this [celebration of this great anniversary] will be to build a sailing replica of HMS Beagle, the ship on which Darwin circumnavigated the globe between 1831 and 1836. It was during the shore expeditions he made from the Beagle that he collected the specimens which would later inspire the theory of Natural Selection and the Origin of Species.

The replica HMS Beagle will be launched in 2009 and will spend the year opening its decks to the public, teachers and scientists and supporting the Darwin200 celebrations."

So they are going to build a replica Beagle and then sail over the same ground that Darwin covered when he participated on this epic voyage. They are going to bring modern equipment and do a number of inspired projects along the way.

What a phenomenal sounding adventure. All I can say is 'take me take me!!'. Don't you think they need an archaeologist? Especially one that is interested in things like island biogeography, primate life history variation, foraging behavior, conservation biology, scaling/metabolic theory, natural history in general, and oh of course -human macroecology- and who is tons of fun to work with? Sign me up. Yeah, there's no way this is a complete voyage without a human macroecologist. Somebody please convince them for me.


Best,
Oskar

Special Feature: Foraging with Charnov

This semester I'll be taking a 1 hour seminar from Dr. Ric Charnov that meets every Friday, in which we'll be going through a new book on Foraging theory that just came out a few months ago. (also available at Amazon).

Foraging: Behavior and Ecology (Paperback)
by David W. Stephens (Editor), Joel S. Brown (Editor), Ronald C. Ydenberg (Editor)



The book contains 14 chapters and we'll be going through each one sequentially, one per week.
Each week after class I'll write a short blog about the chapter and try to summarize any highlight's from our class discussion. I really hope some of you out there who are interested in foraging will read along and chime in on the blog. It should be a good way to get up to date on this challenging and always rapidly expanding field.

I probably wouldn't argue that all things foraging theory are necessarily part of what we call human macroecology but foraging behaviors and the models used to understand them are fundamental to a vast range of ecological and evolutionary questions. Moreover, foraging behaviors may often be part of the rule sets generating complex emergent social/group level/population patterns. That is, they may be part of the simple rules of interaction that generate emergent macroecological trends.

Anyway, starting next Friday for all weeks of the semester except springbreak there will hopefully be a blog about the chapter we discussed that week. Next week we start with chapter 1 ; Foraging: an overview, by R. C. Ydenberg, J. S. Brown, and D. W. Stephens.
see you then,
Oskar

"Wallace should hang" ?

The New York Times has just published an interesting opinion piece called "Wallace should Hang" by evolutionary biologist and science writer Olivia Judson in recognition of Alfred Russel Wallace. Wallace was an independent 'discoverer' of the process of evolution by natural selection and a founding father of the field of biogeography. He often plays the role of an unsung hero and his contribution to the field seems to be misscharacterized in many settings. He anticipated many of the important issues of and processes of biogeography and was a great thinker although he had some nuances that the story does a good job of presenting. Check out this interesting read!