A key consideration when embarking on an agent-based modelling focused project is ‘what are we going to write the model in?’. The investment of time and effort that goes into learning a new software tool or a language is so considerable that in the vast majority of cases it is the model that has to be adjusted to the modellers skills and knowledge rather than the the other way round.
Browsing through the OpenABM library it is clear that Netlogo is archaeology’s, social sciences and ecology first choice (51 results), with other platforms and languages trailing well behind (Java – 13 results, Repast – 5 results, Python – 5 results)*. But it comes without saying that there are more tools out there. A new paper published in Computer Science Review compares and contrasts 85 ABM platforms and tools.
It classifies each software package according to the easy of development (simple-moderate-hard) as well as its capabilities (light-weight to extreme-scale). It also sorts them according to their scope and possible subjects (purpose-specific, e.g., teaching, social science simulations, cloud computing, etc., or subject-specific, e.g., pedestrian simulation, political phenomena, artificial life) so that you have a handy list of software tools designed for different applications. This is, to the best of my knowledge, the first survey of this kind since this, equally useful but by now badly outdated, report from 2010.
Abar, Sameera, Georgios K. Theodoropoulos, Pierre Lemarinier, and Gregory M.P. O’Hare. 2017. “Agent Based Modelling and Simulation Tools: A Review of the State-of-Art Software.” Computer Science Review 24: 13–33. doi:10.1016/j.cosrev.2017.03.001.
* Note that the search terms might have influenced the numbers, e.g., if the simulation is concerned with pythons (the snakes) it would add to the count regardless of the language it was written in.
An older version of this tutorial used the now-deprecated ncdf package for R. This updated version makes use of the ncdf4 package, and fixes a few broken links while we’re at it.
You found it: the holy grail of palaeoenvironmental datasets. Some government agency or environmental science department put together some brilliant time series GIS package and you want to find a way to import it into your model. But oftentimes the data may be in a format which isn’t readable by your modeling software, or takes some finagling to get the data in there. NetCDF is one of the more notorious of these. A NetCDF file (which stands for Network Common Data Form) is a multidimensional array, where each layer represents the spatial gridded distribution of a different variable or set of variables, and sets of grids can be stacked into time slices. To make this a little more clear, here’s a diagram:
The basic structure of a NetCDF file
In this diagram, each table represents a gridded spatial coverage for a single variable. Three variables are represented this way, and these are stored together in a single time step. The actual structure of the file might be simpler (that is, it might consist of a single variable and/or single time step) or more complex (with many more variables or where each variable is actually a set of coverages representing a range of values for that variable; imagine water temperature readings taken at a series of depths). These chunks of data can then be accessed as combined spatial coverages over time. Folks who work with climate and earth systems tend to store their data this way. It’s also a convenient way to keep track of data obtained from satellite measurements over time. They’re great for managing lots of spatial data, but if you’ve never dealt with them before, they can be a bit of a bear to work with. ArcGIS and QGIS support them, but it can be difficult to work them into simulations without converting to a more benign data type like an ASCII file. In a previous post, we’ve discussed importing GIS data into a NetLogo model, but of course this depends on our ability to get the data into a model-readable format. The following tutorial is going to walk through the process of getting a NetCDF file, manipulating it in R, and then getting it into NetLogo.
Step #1 – Locate the data
First let’s locate a useful NetCDF dataset and import it to R. As an example, we’ll use the Global Potential Vegetation Dataset from the UW-Madison Nelson Institute Sage Center for Sustainability and the Global Environment. As you can see, the data is also available as an ASCII file; this is useful because you can use this later to check that you’ve got the NetCDF working. Click on the appropriate link to download the Global Potential Veg Data NetCDF. The file is a tarball (extension .tar.gz), so you’ll need something to unzip it. If you’re not partial to a particular file compressor, try 7-Zip. Keep track of where the file is located on your local drive after downloading and unzipping.
Step #2- Bring the data into R
R won’t read NetCDF files as is, so you’ll need to download a package that works with this kind of data. The ncdf package is one of a few different packages that work with these files, and we’ll use it for this tutorial. First, open the R console and go to Packages->Install Packages and download the ncdf4 package from your preferred mirror site. Then load the package by entering the following: library(ncdf4) Now, remembering where you saved your NetCDF file, you can bring it into R with the following command: data <- nc_open(filename) If you didn’t save the data file in your R working directory and want to navigate to the file, just replace filename with file.choose(). For now, we’ll use the 0.5 degree resolution vegetation data (vegtype_0.5.nc). Now if you type in data and press enter, you can check to see what the data variable holds. You should get something like this:
This is telling you what your file is composed of. The first line tells you the name of the file. Beneath this are your variables. In this case, there is only one, vegtype, which according to the above uses a number just shy of nine hundred quintillion as a missing value (the computer will interpret any occurences of this number as no data).
Next come your dimensions, giving the intervals of measurement. In this case, there are four dimensions: longitude, latitude, level, and time. Our file only has one time slice, meaning that it represents a single snapshot of data; if this number is larger, there will be more coverages included in your file over time. The coverage spans from 89.75 S to 89.75 N latitude in 0.5 degree increments, and 180 W to 180 E longitude by the same increments.
To access the vegtype data, we need to assign it to a local variable, which we will call veg:
ncvar_get(data,"vegtype") -> veg
The ncvar_get command extracts an identified variable (“vegtype”) and extracts it from the NetCDF file (data) as a matrix. Then we assign it to the local variable veg. There are a number of other commands within the ncdf4 package which are useful for reading and writing NetCDF files, but these go beyond the scope of this blog entry. You can read more about them here.
Step #3 – Checking out the data
Now our data is available to us as a matrix. We can view it by entering the following:
image(veg)
R visualization of potential vegetation dataset (upside down)
Oops! Our output reads from bottom to top instead of top to bottom. No problem, we can just invert the latitude of the matrix like so:
image(veg, ylim=c(1,0))
R visualization of potential vegetation dataset (right side up)
However, this only changes the view; when we get the data into NetLogo later on, we’ll need to transpose it. But for now, let’s add some terrain colors. According to the readme file associated with the data, there are 15 different landcover types used here:
Tropical Evergreen Forest/Woodland
Tropical Deciduous Forest/Woodland
Temperate Broadleaf Evergreen Forest/Woodland
Temperate Needleleaf Evergreen Forest/Woodland
Temperate Deciduous Forest/Woodland
Boreal Evergreen Forest/Woodland
Boreal Deciduous Forest/Woodland
Evergreen/Deciduous Mixed Forest/Woodland
Savanna
Grassland/Steppe
Dense Shrubland
Open Shrubland
Tundra
Desert
Polar Desert/Rock/Ice
We could choose individual colors for each of these, but for the moment we’ll just use the in-built terrain color ramp:
image(veg,ylim=c(1,0),col=terrain.colors(15))
R visualization of potential vegetation dataset using terrain colors
Step #4 – Exporting the data to NetLogo
Finally, we want to read our data into a modeling platform, in this case NetLogo, so let’s export it as a raster coverage we can work with. Before we do any file writing, we’ll need to coerce the matrix into a data frame and make sure we transpose it so that it doesn’t come out upside down again. To do this, we’ll use the following code:
veg2<-as.data.frame(t(veg))
The as.data.frame command does the coercing, while the t command does the transposing. Now we have to open up the file we’re going to write to:
fileCon<-file('vegcover.asc')
This establishes a connection to an open file which we’ve named vegcover.asc. Next, we’ll write the header data for an ASCII coverage. We can do this by adding lines to the file:
This may look like a bunch of nonsense, but each \t is a tab, and each \n is a new line. The result is a header on our file which looks like this: ncols 720 nrows 360 xllcorner -179.75 yllcorner -89.75 cellsize 0.5 NODATA_value 8.99999982852418e+20 Any program (whether a NetLogo model, GIS, or otherwise) that reads this file will look for this header first. The terms ncols and nrows define the number of columns and rows in the grid. The xllcorner and yllcorner define the lower left corner of the grid. The cellsize term describes how large each cell should be, and the NODATA_value is the same value from the original dataset which we used to define places where data is not available. Now just need to enter in our transposed data.
This will take our data frame and write it to the file we just created, appending it after the header. It’s important that your separator be a space (sep=” “) in order to assure that it is in a format NetLogo can read. Also make sure to get rid of any row and column names as well. Now we can read our file into NetLogo using the GIS extension (for an explanation of this, see here). Open a new NetLogo file, set the world window settings with the origin at the bottom left, a max-pxcor of 719 and and max-pycor of 359, and a patch size of 1. Save your NetLogo model in the same directory as the vegcover.asc file, and the following NetLogo code should do the trick:
to setup
clear-all
set vegcover gis:load-dataset "vegcover.asc"
gis:set-world-envelope-ds gis:envelope-of vegcover
ask patches [
set pcolor white
set vegtype gis:raster-sample vegcover self
]
ask patches with [ vegtype <= 8 ] [
set pcolor scale-color green vegtype -5 10
]
ask patches with [ vegtype > 8 ] [
set pcolor scale-color pink vegtype 9 15
]
end
This should produce a world in which patches have a variable called vegtype with values that correspond to the original dataset. Furthermore, patches are colored according to a set scheme where forested areas are on a scale of green, while non-forested areas are on a scale of pink. The result:
NetLogo visualization of potential vegetation dataset
If you’re truly curious as to whether this has worked as it should, you might download the ASCII version of the 0.5 degree data from the SAGE website, save it to the same directory, and replace vegcover.asc with the name of the ASCII file in the above NetLogo code to see if there is any difference.
Going further
So far, this has been meant to provide a simple tutorial of how to get data from a NetCDF file into an ABM platform. If you’re only dealing with a single coverage, you might be more at home converting your file using QGIS or another standalone GIS. If you’re dealing with multiple time steps or variables from a large dataset, it might make sense to write an R script that will extract the data systematically using combinations of the commands above. However, you might also make use of the R NetLogo extension to query a NetCDF file on the fly. To proceed with this part of the tutorial, you’ll need to download the R extension and have it installed correctly.
First, let’s find a NetCDF file with a temporal component. In honor of the impending winter my Northern Hemisphere colleagues are about to endure, I’m going to use the Northern Hemisphere EASE-Grid Snow Cover and Sea Ice Extent dataset from NOAA, which gives monthly (derived from weekly) snow cover data from 1971 to 1995. Go to the website and download the Monthly Mean dataset and save the file ‘snowcover.mon.mean.nc’ to your local drive, keeping track of the its location.
We’ll start a new NetLogo model, implement the R extension, and create two global variables and a patch variable:
extensions [ R ]
globals [ snowcover s ]
patches-own [ snow ]
The snowcover variable will be our dataset, while s will be a placeholder for monthly coverages. The patch variable snow will be the individual grid cell values from our data which will be updated monthly. Next, we’ll run a setup command which clears the model, installs the ncdf library, opens our NetCDF snowcover file, extracts our snowcover data, and resets our ticks counter. You may need to edit the code below so that it reflects the location of your NetCDF file.
to setup
clear-all
r:clear
r:eval "library(ncdf4)"
r:eval "data<-nc_open(\"C:/Users/me/Downloads/snowcover.mon.mean.nc\")"
r:eval "ncvar_get(data, \"snowcover\") -> snow"
reset-ticks
end
Now, we could automate the process of converting to ASCII and importing the GIS data here, but that’s likely to be a slow solution and generate a lot of file bloat. Alternatively, if our world window is scaled to the same size as the NetCDF grid (or to some easily computed fraction of it), we can simply import the raw data and transmit the values directly to patches (not unlike the File Input example here). To do this, right click on the world window and edit it so that the location of the origin is the bottom left, and that the max-pxcor is 359 and the max-pycor is 89 (this is 360 x 90, the same size as our Northern Hemisphere snowcover data). We’ll also make sure the world doesn’t wrap, and set the patch size to 3 to make sure it fits on our screen.
NetLogo world window settings
Next, we’ll generate the transposed dataframe as in the above example, but this time for a single monthly coverage. Then we’ll import this data from R into the NetLogo placeholder variable s:
to go
tick
r:eval (word "snow2<-as.data.frame(t(snow[,," ticks "]))")
set s r:get "snow2"
ask patches [ get-snow ]
if ticks >= 297 [ stop ]
end
Because our snowcover data has a time component, we need to tell it which month we want to use by inserting a value for the third axis. For example, if we wanted the value for row 1, column 1 in month 3, we would send R the phrase snow[1,1,3]. In this case, we want the entire coverage but for a single month, so we leave our the values for row and column and only feed R a value for the month. We use the word command here to concatenate the string which will serve as our R command, but which incorporates the current value from the NetLogo ticks counter to substitute for the month value. As the ticks counter increases, this will shift the data from one month to the next. The if ticks >= 297 [ stop ] command will ensure that the model only runs for as long as we have data for (which is 297 months). When we import this data frame from R into our NetLogo model, it will be imported as a set nested lists, where each sublist represents a column from the data frame (from 1 to 360).If we enter s into the command line, it will look something like this:
What we’ll want to do is pull values from these lists which correspond with the patch coordinates. However, remember that our world originates in the bottom left and increases toward the top right, while our data originates in the top left and increases toward the bottom right. What we’ll need to do is flip the y-axis values we use to reflect this (note: originating the model in the top left would give our NetLogo world negative Y-values, which would likewise need to be converted). We can do this with the following:
to get-snow
let x pxcor let y ((89 - pycor) / 89 ) * 89
set snow item y (item x s)
set pcolor scale-color grey snow 0 100
end
What this does is create temporary x and y values from the patch coordinates, but inverts the y-axis value of the patch (so top left is now bottom left). Then the patch sets its snow value by pulling out the value that corresponds with the appropriate row (item y) from the list the corresponds with the appropriate column (item x s). Finally, it sets is color along a scale from 0 to 100. When we run this code, the result is a lovely visualization of the monthly changes in snow cover from the Northern Hemisphere, like so:
NetLogo visualization of first three years of snowcover data
So there you have it; a couple of different ways to get NetCDF data into a model using R and NetLogo. Of course, if you’re going to all of this trouble to work with such extensive datasets, it may be worth your while to explore alternativeplatforms which can build in native NetCDF support. Or you might build a model in R entirely. But I reckon the language is largely inconsequential as long as the model is well thought out, and part of that is figuring out what kind of input data you need and how to get it into your model. With a bit of imagination, there are many, many ways to skin this cat.
Data references:
Ramankutty, N., and J.A. Foley (1999). Estimating historical changes in global land cover: croplands from 1700 to 1992, Global Biogeochemical Cycles 13(4), 997-1027.
Cavalieri, D. J., J. Crawford, M. Drinkwater, W. J. Emery, D. T. Eppler, L. D. Farmer, M. Goodberlet, R. Jentz, A. Milman, C. Morris, R. Onstott, A. Schweiger, R. Shuchman, K. Steffen, C. T. Swift, C. Wackerman, and R. L. Weaver. 1992. NASA sea ice validation program for the DMSP SSM/I: final report. NASA Technical Memorandum 104559. 126 pp.
This video, brought to you by our friends over at the Barcelona Supercomputing Center, does a great job of explaining in easy-to-understand terms what agent-based modeling is, and how it can be useful for both understanding the past and making the past relevant to the present. No small feat to accomplish in about 3 minutes. Have a look!
You may remember the SPUHH (Simulating the Past to Understand Human History) event in Barcelona in 2014. It was a satellite to the Social Simulation Conference – an annual gathering of researchers whose models are concerned with complex social systems. This year edition of the SSC is taking place in Rome, September 19-23. The paper abstract deadline is 18th April.
Although there are no sessions dedicated specifically to archaeology this year, this is a great opportunity to get a bit of an insight into what our colleagues [working on humans you can actually talk to because they are not so very dead] are up to. Often you can find many commonalities between their and our problems, models and interpretations. Not to mention, an occasional check on what is going on in the world of social theory is always useful.
Like every year, the conference is followed by a week long summer school in social simulation using NetLogo. For more details see here: http://www.ssc2016.cnr.it/essa-s4/
You can now procrastinate for hours learn about agent-based modelling by playing a computer game!
Yep, life research doesn’t get any better than this.
Our colleagues from the Supercomputer Centre in Barcelona and Simulpast have released a game! Evolving Planet has an archaeologically inspired plot, easy to grasp interface and cool graphics making it an absolutely outstanding procrastination tool (what do you mean ‘stop wasting time playing computer games’? I’m doing research here!).
You steer a group of bots trying to achieve tasks such as obtaining resource, arriving at a specific location or influencing another group within precise time brackets. You can give them certain qualities (ability to move faster, a boost to fertility, etc) but the internal workings of the bots are set in stone (well, code), which is a nice way of showing the methodology behind simulation. By manipulating the bots characteristics, what you are in fact doing is testing different behavioural scenarios: would a bigger but slower group be more successful in dispersal? Can you achieve the goal faster with a highly militaristic group or with a friendly ‘influencing’ group?
I breezed through the ‘dispersal’ part but struggled in several of the later missions indicating that the game is very well grounded in the most current research. However, archaeologists who do ABM (of dispersal…) on a daily basis are probably not the target audience since the whole point of the game seems to be helping non-modellers understand what the technique can and what it cannot do and what kind of questions can you approach with it (+ having some fun). So get your non-coding friends on board and hopefully, they won’t get an idea that all we do whole day long is gaming. And even if they do, they’ll join rather than cut our funding.
Evolving Planet can be downloaded from the apple and android app stores for free. For more information: http://evolvingplanetgame.com
The Simulating Complexity team is all coming home from a successful conference in Oslo. Highlights include a 2-day workshop on agent-based modeling led by the SimComp team, a roundtable on complexity and simulation approaches in archaeology, and a full-day session on simulation approaches in archaeology.
We are all looking forward to CAA 2017 in Atlanta. Dates were announced at Oslo, so start planning.
CAA2017 will be held at Georgia State University March 13th-18th. This leaves 2 weeks before the SAAs, so we hope to have a good turnout on simulation and complexity approaches at both meetings!
Archaeologists often use the term ‘palimpsest’ to describe many archaeological deposits. By my reckoning, very few disciplines use the term more than archaeology, which may be keeping us from being invited to parties. By definition, a palimpsest is a piece of parchment from which previously inscriptions have been scraped away in order to add new inscriptions, leaving marks or evidence of older inscriptions. But clearly we’re not talking about parchment, so when we call the record a ‘palimpsest’, what do we mean?
Often, it seems as though the term gets used very broadly to refer to archaeological deposits that are messy or lacking clear stratigraphic relationships, and this is used to dismiss their interpretive value. However, some argue that all archaeological deposits are palimpsests of one form or another. In a recent publication, Lucas suggests that it might be fruitful to consider different parts of the archaeological record as sitting between two extremes: a true stratigraphy, where are all archaeological deposits occur in separable geological contexts, and a true palimpsest, where each depositional event erases the one that came before.
Recently, I put out a paper with colleagues Simon Holdaway and Patricia Fanning that explores this idea as a model for the formation of surface scatters in a region of arid Australia. The model uses a simple agent-based structure to look at how the temporal distribution of datable features visible on the surface might be affected by localized sequences of sediment erosion and deposition. Among other things, we find that organized patterns such as increasing frequencies of dates and chronological gaps that are often explained through demographic changes, could also be explained as resulting from a sufficiently dynamic landscape. Expectations from the model are borne out in additional patterns in the archaeological record, suggesting that, rather than dismiss palimpsests, archaeologists would do well to consider what kinds of palimpsests their records come from.
The paper, published in the journal The Holocene, can be found here.
What approach do you use if you have only partial information but you want to learn more about a subject? In a recent article, I confronted this very problem. Despite knowing quite a bit about Gaulish settlements and distributions of artifacts, we still know relatively little about the beginnings of the wine industry. We know it was a drink for the elite. We know that Etruscans showed up with wine, and later Greeks showed up with wine. But we don’t know why Etruscan wine all but disappears rapidly within a few years. Is this simple economics (Greek wine being cheaper)? Is this simply that Etruscan wine tasted worse? It’s a question and a conundrum; it simply doesn’t make sense that everyone in the region would swap from one wine type to another. Also, the ceramic vessels that were used to carry the wine—amphorae—those are what we find. They should last for a while, but they disappear. Greek wine takes over, Greek amphorae take over, and Etruscan wine and amphorae disappear.
This is a perfect question for agent based modeling. My approach uses a very simple model of preference, coupled with some simple economics, to look at how Gauls could be drivers of the economy. Through parameter testing I show that a complete transition between two types of wine could occur even when less than 100% of the consumers ‘prefer’ one type.
Most importantly in this model, the pattern oriented approach shows how agent-based modeling can be useful for examining a mystery, even when the amount of information available might be small.
I think everyone who had anything to do with modelling came across an innocent colleague/supervisor/another academic enthusiastically exclaiming:
“Well, isn’t this a great topic for a simulation? Why don’t we put it together – you do the coding and I’ll take care of the rest. It will be done and dusted in two weeks!”
“Sure! I routinely build well-informed and properly tested simulations in less than two weeks.” – answered no one, ever.
Building a simulation can be a long and frustrating process with unwelcome surprises popping out at every corner. Recently I summarised the 9 phases of developing a model and the most common pitfalls in an paper published in Human Biology: ‘So You Think You Can Model? A Guide to Building and Evaluating Archaeological Simulation Models of Dispersals‘. It is an entirely jargon free overview of the simulation pipeline, predominantly aimed at anyone who want to start building their own archaeological simulation but does not know what does the process entail. It will be equally useful to non-modellers, who want to learn more about the technique before they start trusting the results we throw at them. And, I hope, it may inspire more realistic time management for simulation projects 🙂
You can access the preprint of it here. It is not as nicely typeset as the published version but, hey!, it is open access.
I took a sabbatical in the mid-1990s and was fortunate to be able to do it at the Santa Fe Institute. Being there right when Chris Langton was developing Swarm, and just looking over his shoulder while he was developing it, was highly influential; Swarm was the original language that we programmed the Village Ecodynamics Project in. Having the opportunity to interact with scientists of many different types at the Santa Fe Institute (founded in 1984) was a wonderful opportunity. This was not an opportunity available to many archaeologists, so one of the burdens I bear, which is honestly a joyful burden, is that having had that opportunity I need to promulgate that to others who weren’t so lucky. This really was my motive for writing Complex Systems and Archaeology in “Archaeological Theory Today” (second edition).
What complexity tools do you use and how?
I primarily use agent-based modeling, although in Complex Systems and Archaeology I recognize the values of the many other tools available. But I’d point out that I do an awful lot of work that is traditional archaeology too. I recently submitted an article that attempts to look at household-level inequality from the Dolores Archaeological Project data, and this is traditional archaeological inquiry. I do these studies because I think that they contribute in an important way to understanding whether or not an exercise in a structure like the development of leadership model, gives us a sensible answer. This feeds in to traditional archaeology.
In 2014 I published an article calculating levels of violence in the American Southwest. This is traditional archaeology, although it does use elements of complexity. I can’t think of other instances where archaeologists have tried to analyze trajectories of things through time in a phase-space like I did there. The other thing that I do that is kind of unusual in archaeology (not just complexity archaeology) is that I have spent a lot of time and effort trying to estimate how much production you can get off of landscapes. Those things have not really been an end in themselves, although they could be seen as such. However, I approached trying to estimate the potential production of landscapes so that it could feed into the agent-based models. Thus these exercises contribute to complex systems approaches.
What do you think is the unique contribution that complexity science has for archaeology?
I got interested in complexity approaches in early to mid 1990s; during that time when you look around the theoretical landscape there were two competing approaches on offer in archaeology: 1) Processualism (the new archaeology), and the reaction to processualism, 2) Post-processualism, which came from the post-modern critique.
First, with processualism. There has been a great deal of interesting and useful work done through that framework, but if you look at some of that work it really left things lacking. An article that really influenced my feelings on that approach was Feinman’s, famous article “Too Many Types: An Overview of Sedentary Prestate Societies in the Americas” from Advances in Archaeological Method and Theory (1984). He does a nice analysis in the currency of variables having to do with maximal community size, comparison of administrative levels, leadership functions, etc. I would argue that these variables are always a sort of abstraction on the point of view of the analyst. And people, as they are living their daily lives, are not aware of channeling their actions along specific dimensions that can be extracted along variables; people act, they don’t make variables, they act! It’s only through secondary inference that some outcome of their actions (and in fact those of many others) can be distilled as a ‘variable.’ My main objection to processualism is that everything is a variable, and more often these variables are distilled at a very high level abstraction for analysis. Leadership functions, the number of administrative levels… but there’s never a sense in processual archaeology (in my view) for how it is through people’s actions that these variables emerge and these high levels came to be. I thought this was a major flaw in processualism
If you look at post-processulism, at its worst people like Tilley and Shanks in the early 1990s, you have this view of agency… People are acting almost without structures. There’s no predictability to their actions. No sense of optimality or adaptation that structure their actions. Although I would admit that these positions did have the effect of exposing some of the weaknesses in processual archaeology, they didn’t offer a positive program to make a path going forward to understand prehistory.
I thought what was needed was a way to think about the archaeological record as being composed of the actions of agents, while giving the proper role to these sorts of structures that these agents had to operate within (people within societies). I also thought that a proper role needed to be given to concepts like evolution and adaptation that were out the window for the early post-processualists. That is what complexity in archaeology tries to achieve. A complex-adaptive system approach honors actions of individuals but also honors that agents have clear goals that provide predictability to their actions, and that these take place within structures, such as landscapes or ecosystems or cities, that structure these in relatively predictable ways.
How does complexity help you understand your system of interest?
Complexity approaches give us the possibility to examine how high-level outcomes emerge from the outcomes of agent-landscape interaction and agent-agent interaction. These approaches to a great measure satisfy the weaknesses of those the two main approaches from 90s (processualism and post-processualism). So we have both high level outcomes (processualism) and agent level actions (post-processualism) but complexity provides a bridge between these two.
What are the barriers we need to break to make complexity science a main-stream part of archaeology?
Obviously barriers need to be broken. Early on, although this is not the case as much any more, many students swallowed the post-processual bait hook, line and sinker, which made it so they wouldn’t be very friendly to complexity approaches. They were, in a sense, blinded by theoretical prejudices. This is much less true now, and becomes less true each year. The biggest barrier now to entry is the fact that very few faculty are proficient in the tools of complex adaptive systems in archaeology, such as agent based modeling, scaling studies, and faculty even are not proficient with posthoc analyses in tools like R that make sense of what’s going on in these complex systems. Until we get a cadre of faculty who are fluent in these approaches this will be a main barrier.
Right now the students are leading the way in complex adaptive systems studies in archaeology. In a way, this is similar to how processual archaeology started—it was the students who led the way then too. Students are leading the way right now, and as they become faculty it will be enormously useful for the spread of those tools. So all of these students need to get jobs to be able to advance archaeology, and that is a barrier.
Do you think that archaeology has something that can uniquely contribute to complexity science (and what is it)?
I would make a strong division between complex adaptive systems (anything that includes biological and cultural agents) and complex nonadaptive systems (spin glasses, etc.) where there is no sense that there is some kind of learning or adaptation. Physical systems are structured by optimality but there is no learning or adaptation.
The one thing that archaeologists have to offer that is unique is the really great time depth that we always are attempting to cope with in archaeology.
The big tradeoff with archaeology is that, along with deep time depth, we have very poor resolution for the societies that we are attempting to study. But this gives us a chance to develop tools and methods that work with complex adaptive systems specifically within social systems; this, of course, is not unique to archaeology, as it is true for economists, biologists, and economists
What do you think are the major limitations of complexity theory?
I don’t think complexity approaches, so far at least, have had much to say about the central construct for anthropology—culture. Agent-based models, for example, and social network analysis are much more attuned to behavior than to culture. They have not, so far, tried to use these tools to try to understand culture change as opposed to behavioral change. It’s an outstanding problem. And this has got to be addressed if the concept of culture remains central to anthropology (which, by definition, it will). Unless complexity can usefully address what culture is and how it changes, complexity will always be peripheral. Strides have been made in that direction, but the citadel hasn’t been taken.
Does applying complexity theory to a real world system (like archaeology) help alleviate the limitations of complexity and make it more easily understandable?
Many people who aren’t very interested in science are really interested in archaeology. So I think archaeology offers a unique possibility for science generally, and complexity specifically, by being applied to understanding something that people are intrinsically interested in, even if they aren’t interested in other applications of same tools to other problems. It’s non-threatening. You can be liberal or conservative and you can be equally interested in what happened to the Ancestral Puebloans; you might have predilection to one answer or another, but you are still generally interested. But these things are non-threatening in an interesting way. They provide a showcase for these powerful tools that might be more threatening if they were used in an immediate fashion.
What do you recommend your graduate students start on when they start studying complexity?
I learned an enormous amount by a close reading of Stu Kauffman’s “Origins of Order.” I read this during my first sabbatical at SFI, and if you were to look at the copy you’d see all sorts of marginal annotations in that. We don’t see him cited much nowadays, but he did make important contributions to understanding complex systems.
In terms of technology or classes, the most important things would be for them to get analytical and modeling tools as soon as they could and as early as they can. In the case of Washington State University, taking agent-based modeling course and taking the R and Big Data course would be essential. But to be a good archaeologist you need a good grounding in method and theory, so taking courses that fulfill that as early on as possible is essential.
And a final question…
What are two current papers/books/talks that influence your recent work?
I’m always very influenced by the work of my students. One of my favorites is the 2014 Bocinsky and Kohler article in Nature Communications. Another is upcoming foodwebs work from one of my other students. These papers are illustrative of the powers of complexity approaches. Bocinsky’s article is not in and of itself a contribution to complex adaptive systems in archaeology, except that it is in the spirit of starting off from a disaggregated entity (cells on a landscape) and ending up with a production sequence emerging from that for the system as a whole. It shows how we can get high-level trends that can be summarized by amounts within the maize niche. So it deals, in a funny way, with the processes of emergence. It’s a prerequisite for doing the agent-based modeling work.
2012 (first author, with Denton Cockburn, Paul L. Hooper, R. Kyle Bocinsky, and Ziad Kobti) The Coevolution of Group Size and Leadership: An Agent-Based Public Goods Model for Prehispanic Pueblo Societies. Advances in Complex Systems15(1&2):1150007.
