Monday, June 9, 2008

An idea worth spreading

Here's a video of a lecture by Ron Eglash about fractals in Africa. its quite interesting in terms of the small bit of history of fractals you get as well as in terms of those he discovers in African settlements and art. I don't know if its true that fractals are not just as present outside of Africa but this is cool. I thank Chris Millington for sending this.
The video is part of the TED series - I posted one before. Its just shy of 17 minutes long.

Monday, April 7, 2008


The semester got away from me a bit and I've been terrible about getting anything posted for a while now. I was at the Society for American Archaeology meetings in Vancouver last week, which were great fun and I should blog about them. That is why I missed a week in the series on Foraging. I hope to get rolling again soon. The other big event is of course the SWARM meetings, which are later this week - lots to get together for those...

Thursday, March 20, 2008

Humans and extinctions: the flightess sea duck

A paper just published in PNAS argues that since the flightless sea duck didn't got extinct until well into the Holocene humans probably didn't hunt megafauna to extinction. No, seriously.

Here's the title, and abstract:
The protracted Holocene extinction of California's flightless sea duck (Chendytes lawi) and its implications for the Pleistocene overkill hypothesis

T. L. Jones, J. F. Porcasi, J. M. Erlandson, H. Dallas, Jr., T. A. Wake, an R. Schwaderer

Bones of the flightless sea duck (Chendytes lawi) from 14 archaeological sites along the California coast indicate that humans hunted the species for at least 8,000 years before it was driven to extinction. Direct 14C dates on Chendytes bones show that the duck was exploited on the southern California islands as early as {approx}11,150–10,280 calendar years B.P., and on the mainland by at least 8,500 calendar years B.P. The youngest direct date of 2,720–2,350 calendar years B.P., combined with the absence of Chendytes bones from hundreds of late Holocene sites, suggests that the species was extinct by {approx}2,400 years ago. Although the extinction of Chendytes clearly resulted from human overhunting, its demise raises questions about the Pleistocene overkill model, which suggests that megafauna were driven to extinction in a blitzkrieg fashion by Native Americans {approx}13,000 years ago. That the extermination of Chendytes was so protracted and archaeologically visible suggests that, if the terminal Pleistocene megafauna extinctions were primarily the result of human exploitation, there should also be a long and readily detectable archaeological record of their demise. The brief window now attributed to the Clovis culture ({approx}13,300–12,900 B.P.) seems inconsistent with an overhunting event.


There is also an accompanying commentary by Donald Grayson.

The authors have thoroughly documented an interesting relationship between human predation and this species of flightless duck. There seems little doubt that the duck was periodically or frequently preyed upon for millennia before it went extinct. They argue that the early inhabitants of the California coast were more technologically sophisticated than is generally acknowledged - they had some boats/canoes from which to hunt. What I don't understand is the lack of attention to ecology when they try to make the leap of connecting the relationship they document to Pleistocene extinctions in general. So maybe people had boats 12,000 years ago but I think its worth considering that there are some pretty fundamental differences between mammoths and ducks... (!!) and the particular island environments where most island extinctions took place are also different from the California coast. The colonists didn't bring rats, the environment was not as circumscribed as many islands and may have provided more natural refugia from human predation, the people may have had their main populations on the coast rather than on islands (in the california case), and they may have been at lower population densities.

Grayson's commentary is surprisingly even-handed. He seems more conservative with regard to the suggestion that this particular history of this particular species of flightless bird has general implications for our thinking of the loss of megafauna. But rather suggests that understanding the processes of extinction on a species by species basis tells us that there some important nuances that are often overlooked and that in many cases direct predation may not be the mechanism of extinction. Humans alter environments in lots of ways and it may be these indirect effects that are often detrimental. Rats and dogs and pigs all likely accelerated the rate of extinction in the case of Polynesian colonists.

Grayson and Jones et al (and lots of other archaeologists) frequently point out that the evidence for association between unambiguous signs of human activity and the remains of the extinct megafauna are rare in North America. And that is part of the point Jones et al are making. That this species has loads of direct associations with people and hence the extinction process is very visible. So why isn't it more visible for sloths and other really large critters that went extinct and should be very visible? If people were butchering these animals in a more expedient manner and not transporting bones to caves and rock shelters very often, then that could explain the lack of well preserved evidence. (I suppose). They also point out that the process of human mediated extinction seems to take a really long time in some cases, even islands, and yet for 35 genera across the entire continent of North America it was very rapid.

Good points in the article and in the commentary... would have liked to see more discussion of the ecological variables that alter the probability of extinction.


Monday, March 17, 2008

SWARM schedule posted

The blog post for the upcoming SWARM meetings has been updated with more detailed scheduling information. The Human Macroecology symposium will be on Thursday April 10, 2008. Read more about it here.

Tuesday, March 11, 2008

More very small humans found

An exciting discovery was recently made and just reported on in PLoS One. Several (25ish) individuals of very small and potentially insularly dwarfed humans were found on the island of Palau, which is within spitting distance (relatively speaking of course) of the well known and hotly debated finds from Flores.

title and authors are:

Small-Bodied Humans from Palau, Micronesia

Lee R. Berger, Steven E. Churchill, Bonita De Klerk, Rhonda L. Quinn

Its an open access article so you can get it here.
A blog written about the find has been posted on, which you can read here.
These finds are much more recent, dating to the last 3000 years than the ones from Flores, which are 18,000 years old or so. They were found in cave sites which appear to be burial locations as very few artifacts and no other fauna are associated.
The authors interpret the findings as dwarfed homo sapiens rather than some genetic abnormality as has been argued for the Flores finds (and contests as well of course).
There are some similarities between these Paluan finds and the ones from Flores.

Here is the final paragraph of the paper to offer their conclusions:

"Based on the evidence from Palau, we hypothesize that reduction in the size of the face and chin, large dental size and other features noted here may in some cases be correlates of extreme body size reduction in H. sapiens. These features when seen in Flores may be best explained as correlates of small body size in an island adaptation, regardless of taxonomic affinity. Under any circumstances the Palauan sample supports at least the possibility that the Flores hominins are simply an island adapted population of H. sapiens, perhaps with some individuals expressing congenital abnormalities."

It will be interesting to see how the different sides of the Flores arguments react to these findings.
Great stuff. exciting to think about. human biogeography.


Saturday, March 8, 2008

A little primate biogeography

A fairly recent PNAS paper makes some interesting claims about the first primates to arrive in the New World. These little mouse sized guys, called Teilhardina magnoliana may have arrived by crossing the landbridge between Siberia and the New World way before people did (like 60 million years ago or so). They tip the scales at around 28 grams.

A good popular news piece based on the article can be found here.

Here's the stuff on the PNAS paper:

The oldest North American primate and mammalian biogeography during the Paleocene–Eocene Thermal Maximum

K. Christopher Beard{dagger}

Section of Vertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, PA 15213

Edited by Alan Walker, Pennsylvania State University, University Park, PA, and approved January 10, 2008 (received for review October 25, 2007)


Undoubted primates first appear almost synchronously in the fossil records of Asia, Europe, and North America. This temporal pattern has complicated efforts to reconstruct the early dispersal history of primates in relation to global climate change and eustatic fluctuations in sea level. Here, I describe fossils from the Tuscahoma Formation on the Gulf Coastal Plain of Mississippi documenting an anatomically primitive species of Teilhardina that is older than other North American and European primates. Consistent with its antiquity, a phylogenetic analysis of dental characters recognizes Teilhardina magnoliana, sp. nov., as the most basal member of this genus currently known from either North America or Europe. Its stratigraphic provenance demonstrates that primates originally colonized North America near the base of the Paleocene–Eocene Thermal Maximum (PETM), but before an important fall in eustatic sea level. Correlation based on carbon isotope stratigraphy and sequence stratigraphy indicates that the earliest North American primates inhabited coastal regions of the continent for thousands of years before they were able to colonize the Rocky Mountain Interior. The transient provincialism displayed by early North American primates corresponds to similar biogeographic patterns noted among fossil plants. Decreased precipitation in the Rocky Mountain Interior during the early part of the PETM may have been an important factor in maintaining biotic provincialism within North America at this time. These results underscore the need to obtain multiple, geographically dispersed records bearing on significant macroevolutionary events such as the PETM.

Cosmic impacts and the end-Pleistocene extinction: idea seems not to hold up

A while back I posted a blog on a paper published in PNAS arguing that a comet impact was responsible for the extinction of the megafauna in North America. They also argue that the impact was responsible for the disappearance of the Clovis culture - the earliest recognized archaeological culture in the New World known for large well made and very distinctive fluted spear points.
I was skeptical of their ability to link the proposed impact to the strongly size biased nature of the extinctions and wondered about how it extended to the similar patterns in extinction that we see on other continents. There was a lot missing in terms of how to link the impact to mammals - but aside from that it seemed like they may have demonstrated that lots of stratigraphic layers around the United States contain minerals of extra-terrestrial origin. or maybe not...

A news focus just published in Science (authored by Science writer Richard Kerr) reviews the evidence and points out that many of the claims by the authors of the comet study are not holding up. This is probably not surprising on the whole but it is amazing how many of the claims seem to be really thoroughly refuted and experts in the study of cosmic impacts suggest that the hole's in the study were evident long before it was published - that can happen when papers go to non-specialized audiences. Also note that the paper was published in PNAS...

Magnetic spherules believed to be diagnostic of the impact were a key line of evidence for the study by Firestone et al. (the authors of the PNAS paper) but it turns out that such spherules may be regularly introduced to our atmosphere from space and are not useful markers for a specific impact.

Excerpt from the article:
"One problem is that no one has "any of the classic evidence of an impact," says impact specialist David Kring of the Lunar and Planetary Institute in Houston, Texas. Spurred by the 1980s debate over what killed off the dinosaurs, "the community learned a lot about what the threshold of evidence is" for confirming an impact, he explains. But taking all the evidence offered by the group proposing the mammoth-killer impact, "you end up with [markers] that are not diagnostic of impact," says impact specialist Bevan French of the National Museum of Natural History in Washington, D.C. Proponents, meanwhile, are defending some of their published claims and giving ground on others but promising ultimate vindication.

Figure 2 ET? An impactor (top) may have produced magnetic spherules (lower right), but similar spherules (lower left) continually fall from space.


Diamonds not forever
Everyone agrees on one point at least. "Obviously, something really interesting happened 13,000 years ago," as Kring puts it. It was 12,900 years ago, to be precise, that a world staggering out of the last Ice Age suddenly plunged back into a millennium of near-glacial climate before emerging into the current warmth. It was also about then--emphasis on the uncertainties summed up by "about"--that the mammoths and other great beasts disappeared from North America. And the Paleo-Indian Clovis culture vanished from the archaeological record around then, too."
Science 7 March 2008:
Vol. 319. no. 5868, pp. 1331 - 1332
DOI: 10.1126/science.319.5868.1331

Experts question the existence of the nanodiamonds that are thought to be traced to the impact and other lines of evidence, such as the iridium spike in the stratigraphic layers in question, have been fairly extensively criticized and questioned as well.

These criticisms really don't sound like the nay-saying that goes with old stodgy types not like their conventional wisdoms being questioned. They seem pretty solid. Perhaps the debate will continue to play out in the literature.


Tuesday, March 4, 2008

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.


Symposium Schedule:

Thursday, April 10, 2008.






9:00 - 9:20

Oskar Burger and Bill Burnside

University of New Mexico


9:20 - 9:40

James H. Brown

University of New Mexico


9:40 - 10:00

Bill Burnside and Jordan Okie

University of New Mexico


10:00 - 10:20

Larry Todd

Colorado State University


10:20 - 10:40

Mary Stiner

University of Arizona

10:40 - 11:00




11:00 - 11:20

Peter Turchin

University of Connecticut


11:20 - 11:40

Alison Boyer

University of New Mexico


11:40 - 12:00

Helen Davis et al.

University of New Mexico

12:00 - 1:00




1:00 - 1:20

Robert Walker et al.

Max Planck Institute


1:20 - 1:40

Paul Hooper

University of New Mexico


1:40 - 2:00

Marcus Hamilton

University of New Mexico


2:00 - 2:20

Melanie Moses

University of New Mexico


2:20 - 2:40

Louis Bettencourt

Los Alamos National Laboratory

2:40 - 3:00



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

: 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.


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.


Thursday, February 28, 2008

Levy Walks in the Ocean

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

Reference info, title, and abstract follow:


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 ecology1, 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 untested6, 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.


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.


Tuesday, February 19, 2008

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 (2426). 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.

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

Saturday, February 16, 2008

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 ( 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.



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