Introduction to Archaeology F 2002 / Owen: Archaeobotany and Bioarchaeology p. 1
Introduction to Archaeology: Class 14
Archaeobotany and Bioarchaeology
Copyright Bruce Owen 2002
Today we once again cover two basically unrelated topics: archaeobotany (also called paleoethnobotany) and an introduction to bioarchaeology
do the readings to get more of the story!
Archaeobotany
two terms for the field with different emphases, but generally covering work done by the same experts
archaeobotany: study of ancient plant remains
usually focuses on reconstructing environment, climate, resource availability, etc.
paleoethnobotany: study of ancient plant-human relationships and their changes over time
diet and food preparation (cuisine)
implications about farming and gathering practices
determining if a site was occupied year-round, or only during certain seasons ("seasonality")
craft uses of plants (fibers for textiles, gourds for net floats, reeds for mats or house construction, basketry, etc.)
uses of plants for fuels
can have implications about ethnic, occupational, status, etc. relationships
macrobotanical remains (what Thomas calls "plant macrofossils", even though they are not fossils): pieces of plant material that are big enough to pick out while excavating, or that turn up in the screen
a related kind of macrobotanical find: casts or impressions in ceramics, bricks, etc.
example of wheat and barley impressions from Mehrgarh, Baluchistan, early Neolithic (7000 - 4500 BC)
macrobotanical remains are often used to help to reconstruct diet
Peruvian examples:
kinds of corn and cobs
guavas, peppers, beans, etc.
macrobotanical remains are sometimes found in coprolites, also very useful for reconstructing diet
coprolites: dried feces (human, dog, etc.)
only preserved in special circumstances
usually very dry environments
often contain macrobotanical remains
also small bone fragments, microscopic botanical material, parasites that reflect general health status
a very direct, specific source of data on diet, even specific meals and cuisine
analysis requires specialists!
Peruvian example of coprolites
macrobotanical remains also often help to indicate non-dietary activities, crafts, architecture, etc.
farming for fibers:
cotton bolls, fiber, etc. indicate farming of cotton for textiles and/or seed oil
finding the non-fiber parts of cotton indicates that people at the site were involved in farming it, rather than trading for fibers or textiles made elsewhere
collecting for mats, cordage, etc
reeds, grasses, etc.
along with basketry, these artifacts are often studied by specialists who are not botanists
but they often will have a paleoethnobotanist identify the plants that provided the raw materials
collecting architectural building materials
in the area where I work, two different cultures used different kinds of reeds to build their houses
why?
ritual behavior involving plants
example: "offerings" of whole food or craft items in pits
example: layers of reeds in burial mounds
where did they come from?
what did they "mean"?
Thomas's example of "reading the fuel" from the Mantaro Valley, Peru
this is a project that I worked on
Chris Hastorf and Sissel Johannessen
looked at charcoal from flotation samples
compared proportions of wood chunks, stem (twig) pieces, and grass fragments
found gradual decline in proportion of wood chunks, rise in proportion of twigs during Pancan periods
then shift to more wood in Wanka II and Wanka III (Inka) periods
they saw this as a decline in availability of wood through the Pancan periods, then the rise of tree farming with the appearance of local chiefdoms
they argued tree farming may have had symbolic as well as economic value for emerging elites
there are many reasons to be skeptical, but this does show how far some people may push paleoethnobotanical data
methodological point: note that this is all based on percentage data, which has problems that we talked about last time
bringing in less grass and twigs would automatically make it look like they used more wood, even if no tree farming occurred
we have no way to tell whether the total amount of wood actually increased, as tree farming would suggest
and since the WII and WIII sites are on hilltops, versus Pancan on a reedy lakeshore, it is quite possible that the difference is really less stems and grass, rather than more wood.
what if there was another fuel that is not considered here, like dried camelid dung?
say it became common in WII and WIII
then the shift in the mixture of wood, twig, and grass might be a very small part of the overall fuel picture
point: be very wary of percentage data!
in faunal, botanical, or any other analysis
smaller remains are identified by various terms:
flotation samples, light fraction
phytoliths: silica (opal) deposits that form mostly in the stems of arid-adapted grassy plants, but in some other cases as well
some can be identified as to what species of plant they come from
others are ambiguous
they are microscopic, but durable
must be laboriously extracted from
soil samples
the surfaces of grinding stones
sometimes identifiable ones remain embedded in "sickle gloss" on stone blades used to cut thatch, harvest grain, etc.
example: reconstructing what crops were grown on prehistoric agricultural terraces in the Osmore valley, Peru
work by Tony Ribiero
soil samples contained maize phytoliths (and some others; not yet published)
a different project is currently attempting to do the same at a coastal site
pollen: the male gametes of flowering plants
often commonly included here: spores, which are "packaged" cells that disperse and later grow into plants
microscopic, but durable
can be identified as to what species they come from
extracted from soil samples
also from "pollen washes" from the surface of some artifacts
have evolved specifically to blow around easily, so contamination is a constant worry
soil samples collect the "pollen rain" at the time the soil was at or near the surface
this reflects the plant mix in a fairly large surrounding area, depending on prevailing winds, etc.
good for general climatic and ecological reconstruction
Thomas's example of mesolithic Star Carr, ~7500 BC
pollen indicated a forested environment
and little or no reduction of trees until just when the site was abandoned… or does it?
pollen found in specific contexts like burials or storage rooms is sometimes taken to reflect the activities that happened there, rather than just the general environment
Shanidar cave example
not as bad as Thomas makes it out
there were samples from other areas of the cave deposits that had much less flower pollen in them, making the original claim fairly likely
Pampa de la Llamas, Huaca A example
were the rooms were for storage?
very little evidence of what would have been stored there
not surprising; if it had any value, it would have been removed
pollen from niches suggests cotton, beans, potatoes, peanuts
but it could have blown in on the wind
pollen comes from flowers; it is not typically plentiful on the parts of plants that would be stored, like peanuts or potatoes
lots of rodent bones also suggest storage
Bioarchaeology
basically, the study of human remains
includes a huge range of different kinds of work
paleopathology: study of ancient diseases, injuries, health, and activity-related effects on bones
often based on observations of bone and teeth
but also on soft tissue and hair if present
chemical and isotopic composition of bone
DNA (often of disease organisms, not the victim!)
parasitology (lice in hair; parasites and eggs in coprolites, etc.)
tooth wear, loss, caries, abscesses, etc.
can tell a lot about diet
also cultural practices, like the use of front teeth as tools for preparing hides among Neanderthals
injuries such as parry fractures
characteristic kind of fracture in the forearm that often occurs when someone flings up their right arm in front of their face to deflect a blow
Tiffiny Tung's observations on females with head wounds mostly on the left front…
scarcity of ancient bone cancers compared to modern populations: what does that mean?
auditory exostoses: bony growths in the ear canal that seem to be associated with spending a lot of time in cold water
they probably indicate people who did a lot of diving for shellfish
Tuberculosis: Update to Thomas's account
bony evidence is common in some New World populations
characteristic holes in vertebral bodies and other bones
"collapsed" vertebral bodies that cause a permanent forward bend in the lower spine ("Potts syndrome")
but these might have been caused by other diseases
Buikstra even suggested some now-extinct disease, back when it was assumed that TB was introduced to the New World from the Old
this was a "bone of contention" for a long time
but more recent work on mummies from northern Chile has found the DNA of the TB bacterium in the lung tissues
proving beyond any doubt that TB also existed in the New World well before European contact
and making it very likely that the bone evidence really was caused by familiar TB
and many, many other interesting indicators of activities, accidents, violence, diet, etc.
diet reconstruction using stable isotopes
isotopes that are not radioactive; they do not decay away
the most commonly used are 13C and 15N; these are rarer isotopes that are found in small amounts in the environment along with the common 12C and 14N.
Remember "isotopic fractionation" from our discussion of radiocarbon dating
different plants take up the different isotopes of carbon at slightly different rates
so they are more or less "enriched" in the heavier isotopes
14C decays away, but the 13C and 12C are stable
so the ratio of 13C to 12C does not change, and it depends on the particular chemical pathway that the plant uses to extract carbon from air.
or, in animal tissues, it reflects the mix of plants that the animal ate - or that its prey ate.
there are three common chemical pathways for fixing carbon, called C3, C4, and CAM
C3 is used by most food plants in temperate environments
C3 plants are relatively enriched in 13C
C4 is used mostly by arid-adapted grasses, of which maize (corn), sorghum (a grain most used in sub-saharan Africa), and millet (another grain) are the main one of archaeological interest
C4 plants are "normal" in 13C
CAM is used by plants like cacti, which rarely form a large part of human diets.
CAM plants are in between, but fortunately we can usually ignore them
So, as a first approximation, we can estimate how much of the diet was from C4 plants versus C3 plants by measuring the 13C in ancient human bones
in practice, that means we can identify early farmers in the New World (they started eating maize) and parts of the Old World (they started eating millet or sorghum)
But… (there is always a "but")
seafood (fish and shellfish) is also enriched in 13C
so bone that is enriched in 13C could indicate a diet with a lot of maize, OR a diet with a lot of seafood
so 13C studies are ambiguous anywhere near a coastline where C4 plants were used
in some cases, this is not a problem
in the American midwest, there is no need to worry about seafood in the diet
in studies of Vikings on Greenland, there is no need to worry about maize, millet, or sorghum, since those plants don't grow that far north
but in many coastal regions, both could be present, so the 13C data alone don't allow us to reconstruct the diet
another "but" that people have not taken too seriously yet
many wild plants that foragers might have collected have not been characterized as to whether they are C3 or C4
especially in remote places like the desert coast of Peru
so it is possible that there might be C4 plants in the diet other than maize
that would really complicate things…
A partial solution: look at a different stable isotope: 15N
most nitrogen in the environment is 14N
a small amount of natural nitrogen is 15N, which is also stable
seafood (fish and shellfish) are relatively enriched in 15N compared to terrestrial plants and animals
so the 15N content of ancient bone can indicate the fraction of marine food in the diet
so if we measure both 13C and 15N, we can estimate the relative amounts of C3 vs C4 plants, and the relative amount of seafood vs. terrestrial plants
often done by plotting samples on a graph with 15N on the vertical axis, 13C on the horizontal axis, and boxes enclosing the areas where the bones of eaters of pure diets (all terrestrial C3, all terrestrial C4, and all marine) would fall
But… (as always)
terrestrial plants also vary a little in 15N content
particularly legumes (beans, lentils, etc.) vs. other plants
15N content in animal tissues varies with "trophic level"
trophic level describes how high up the food chain the organism is
plants are at the bottom
herbivores are at the next level
carnivores are above herbivores
carnivores are enriched in 15N relative to herbivores
so when people might have been eating legumes or carnivore meat, the reconstruction of diet gets complicated again
fortunately, both of these effects are smaller than the terrestrial vs. marine difference
but they are large enough to add a lot of error to the method
indicators of stress
porotic hyperostosis and general nutrition or parasite stress in infants
Harris lines
dental hypoplasias
paleodemography: reconstructing the age-sex structure of ancient populations and their changes over time
done by looking at various bony indicators
age
tooth eruption
fusion of symphyses (the growth zones between the head and shafts of various bones)
these eventually stop growing and the parts of the bone fuse together
this happens at different ages for different bones
so the combination of which symphyses are still open and which are fused indicates age up to adulthood
fusion of cranial sutures allows rough age estimate
shape of surface of pubic symphysis
the join at the front of the pelvis
wrinkles and other features change through adulthood, allowing rough age estimate
tooth wear allows rough age estimate
some microscopic methods also work, but are very labor intensive so less often employed
sex
best by certain features of the pelvis
less well by differences in the cranium
the population-wide pattern of age at death of both sexes reflects differences in fertility, mortality, general health status, different causes of death
war vs. childbirth vs. childhood diseases, etc.
high infant mortality shows up clearly
in a highly stressed population, more people die younger
example using changing survivorship curves in the Upper Mantaro
survivorship curves show the fraction of the individuals born that survive to any given age
this highlights the mortality rate at different ages
makes infant mortality obvious
makes mortality of young adults vs. old adults obvious, etc.
suggests overall stress on population, particular kinds of causes of death, etc.
Infant and adult mortality declined strongly from Wanka II to Wanka III
that is, from when they lived in walled hilltop towns that were at constant war (Wanka II)
to when they were conquered by the Inka and resettled into lower, less dense, less defensible towns near farmland (Wanka III)
this was surely done to facilitate control by the Inka empire
and to increase crop production for imperial taxes or tribute
but it proved to be a very healthy change for the Wanka people
although they may not have appreciated it!
next time we will look at more things one can learn from human remains