Next time we will meet in the library, in the computer room behind the reference desk (NOT the circulation desk!)
for a useful session on how to find information for class presentations and the research paper
Handout: description of class presentations
Handout: list of suggested class presentation topics
Circulate at the very end of class: the schedule of classes and suggested presentations
so you can sign up for your first presentation, if you wish.
You may study the list and wait until Thursday to sign up
but the topics will be taken on a first-come, first-served basis, and we can't have more than two or maybe three in any single class
You may email me your choice if you like, but give me a second and third option in case your other choices are already taken
Again, I won't talk specifically about the readings in Feder
but you will notice that chapter 4, about the Piltdown man hoax, is directly related to today's subject.
I encourage you to think about the questions at the very end of each of his chapters. In particular, the "Critical Thinking Exercises" at the end of the Piltdown chapter should help you get to some of the interesting points about the Piltdown and Cardiff giant cases.
The setting for the emergence of our early ancestors and their culture
Fagan very briefly touches on the early evolution of our ape ancestors and relatives; I'll jump over that here
and cut directly to the time when we start getting the first archaeological evidence, that is, evidence of activities of our ancestors, rather than just physical structure
As Fagan points out, the period in which the hominid lineage (the branch that led to us and some now-extinct relatives) diverged from the lineage that led to modern chimpanzees around 5 mya (million years ago)
and we have just the tiniest fragments of primate fossils, and no archaeological evidence at all, from that period (basically from 10 mya to 4 mya)
the picture only starts to get detailed around 3.5 mya
the best-known probable ancestor of ours at that time was Australopithecus afarensis
there may have been other, similar species at the same time
A. afarensis
had a brain the size of a chimp's, but its face was less projecting, with smaller canine teeth and larger molars
The arms and hands, though evolving in the direction of humans, still had features that probably helped them move around up in trees
While the pelvis, legs, knees, and feet had features that undeniably point towards bipedal (two-legged), more-or-less human-like walking
for more detail on this, take a biological anthropology course!
there is no evidence that they made stone tools
although they might, like modern chimps, have made very simple tools from sticks, twigs, leaves, etc., or pounded on things like nuts with unmodified rocks
so what are they doing in an archaeology course?
The footprints at Laetoli: the world's oldest archaeological site
a series of footprints made in freshly-fallen volcanic ash
the tracks were gently covered by additional ash as the eruption continued
they are the footprints of one or two adult creatures and a younger one, walking with an almost-human bipedal gait
the adult footprints are not as clear; one possibility is that a second adult walked along the same path, carefully placing it's feet in the footprints that were already there
the young one walked in a parallel path, off to one side
it is appealing to think of these as a family that walked across the ash together, but the footprints might also have been made at slightly different times, by individuals walking alone
they date to 3.75 - 3.59 mya
dated by potassium-argon dating, which gives the time since a volcanic rock cooled from a molten state
volcanic ash is formed from molten and vaporized rock that is sprayed up in an eruption and solidifies into fine particles in the air before it reaches the ground
Fagan's discussion of this is so confusing that I feel obliged to try to straighten it out
Potassium (atomic symbol K) is a common component of rocks, and some of it is radioactive 40K that decays very slowly to form argon gas (40Ar).
The argon gas is trapped in the crystal structure of the minerals in the rocks, so it gradually accumulates
when the rock is melted, all the argon gas can bubble out
after it cools and solidifies, the radioactive potassium that is left keeps decaying, and the argon starts building up again
the dating method takes crystals from the rock and measures how much radioactive potassium is in them, and how much argon has accumulated.
The higher the ratio of argon to potassium, the more time has passed since the rock solidified.
the method works for rocks from about 100,000 years old to 2 billion years old
so it is good for fossil hominid sites, but not for most archaeology we will see in this course
also, notice that it dates the cooling of volcanic rock
since few human activities take place in molten lava, it is not useful for directly dating most sites or fossils
instead, you usually date a lava or ash deposit that was laid down before the archaeological site was formed, then date another one that was deposited over it, to bracket the site in time
Laetoli is an exception: the footprints were made in volcanic ash that had probably just fallen from the sky in an eruption
so the date should be within hours of the time when the footprints were made
what creatures could have made these tracks?
the most likely suspect is A. afarensis, since the tracks date to the period that A. afarensis existed, and fossils of numerous individuals have been found in the general area
but there may have been other, related primate species around at the time
the important thing about these footprints is that they prove beyond any doubt that there were bipedal creatures at the time of A. afarensis
even if you doubt the skeletal analyses, you can't really doubt the tracks
and the date shows that there were bipedal creatures walking around about a million years before the first signs of stone tools
why might bipedalism be important?
efficient distance travel
allows use of widely scattered patches of food and water
improves ability to track, follow, and run down animals
raises head to see over tall grass
improved temperature control in a hot, sunny climate
reduces area exposed to sun (smaller area when viewed from above, compared to a quadruped)
improves cooling by getting part of the body away from the hot air near the ground, and up into the breeze
frees hands to carry things
weapons?
plant food?
bags?
children?
note that bipedalism came long before big brains or toolmaking
quite the opposite of what the Piltdown "fossil" seemed to suggest, with big brains being an early feature
so what first set our ancestors apart was bipedalism
by around 2.7 mya, there were several kinds of australopithecines in Africa
all upright and bipedal, surprisingly human-like from the neck down
all with brains a bit bigger than a chimp's
Australopithecus robustus
, a more robust (massively built) type
specialized on chewing tough plant foods
clearly not our ancestor
led to several different species
Australopithecus africanus
, a more gracile (lightly built) type
also a plant chewer, but less exaggerated
probably not our ancestor (although not everyone agrees)
quite possibly more variants along similar lines
much as there are now chimps and gorillas in the same general areas of Africa
by around 2.5 mya, in addition to the australopithecines, there was also a larger-brained variant, Homo habilis
the first member of our genus
brain a bit bigger than australopithecines
H. habilis
: 600 - 700 cc
australopithecines: 400 - 500 cc
chimpanzees: 400 cc
modern human: 1000 - 2000 cc, average for males: 1450 cc
as Fagan notes, the fossils that are often lumped as H. habilis are also sometimes split into several species by people who are more impressed by the differences between the fossils from different times and places
that is, there may actually have been several similar species of early Homo
Fagan's "bush" version of the hominid lineage is pretty much how our evolution is now visualized
he summarizes it as a series of adaptive radiations
first, there was a radiation (burst of creation of new species) of bipedal creatures
then, some of these lineages radiated (split up into multiple new species) into the niche of heavy chewers, especially the robust australopithecines
while others radiated into a niche for larger-brained, presumably more behaviorally complex variants of early Homo
So, what evidence do we have for how these early ancestors of ours lived?
Stone tools
Is it correct to define humans as "the animal that uses tools"?
chimps use tools
stones as hammers and anvils to break nuts
twigs to fish for termites and get marrow out of bones
wadded leaves used as a sponge to get water out of pockets in trees
why would this be hard to recognize archaeologically?
so how is human tool use different?
tools are made, not just found and used as is?
but chimps strip leaves off twigs to use them...
what are broken rocks good for?
Imagine yourself in the forest, hungry, with a freshly killed pig. How are you going to eat it?
You want to make a spear or a bow and arrow. How are you going to do it?
what about wood? bone?
percussion flaking
hammerstone, core, flake, debitage
which resulting piece of rock is used as the tool?
unifacial vs. bifacial tools
retouching
making stone tools requires coordination and some mental abilities, like visualization and planning
if you have any doubts, just try it and see!
The earliest stone tool "style" or technology: Oldowan
oldest examples around 2.6 mya
that is, right about when Homo habilis appears: coincidence?
although it is possible that australopithecines made tools
rounded cobbles with a few flakes knocked off
forming bifacial but very irregular, casual edges
or are the "tools" just cores, left over from the production of flakes for use? Or were both used?
study of microscopic wear on the edges of the tools indicates that the flakes were extensively used
also important that they clearly had preferred stone types, and carried tool material up to 13 km to places where tools were made and used
the sites where they were used suggest that these "made" stone tools were used more or less in the way that chimps use simpler "found" tools
lets look at some specific cases
early hominid archaeological sites
the Plio/Pleistocene environment
warm, mixed savanna and woodland, with shallow, seasonal lakes
so-called "living floors" at several sites
around 2 mya
ancient ground surfaces with scatters of Oldowan tools, tool production debris, and broken animal bone
once thought to be remains of living places or camps (home bases; central places; etc.), similar to those occupied by recent foragers
to which hominids would bring hunted, scavenged, and/or gathered food
where whole families would process the food, eat, and sleep
perhaps with simple shelters or windbreaks
staying for one or more days
now interpreted as something rather different...
how are "sites" and "tools" distinguishable from naturally dead animals or natural broken rocks?
broken rocks from materials naturally found only in distant spots (up to 10 km / 6 miles) must have been brought there: tools
numerous broken rocks with consistent patterns of flaking that are unlikely to happen naturally: artificially made tools
broken rocks concentrated in and near animal bones: tools left at a butchery site
broken rocks concentrated in and near bones with cutmarks: tools left at a butchery site
edges of broken rocks have microscopic wear like that seen on tools used on meat, wood, etc.: tools that were used
Olduvai sites
such as the one where the cranium of Zinjanthropus, the first robust australopithecine fossil, was found
discovered and excavated by Mary Leakey
one circular area had a fairly dense scatter of stone tools, flakes, and bone fragments of many different animals
surrounded by a ring of ground with much lower density of debris
a little away from that spot, another area had piles of stone tools and flakes, along with smashed bones
perhaps where marrow was extracted
the stone was brought in from several km away, presumably specifically to make tools out of
Mary Leakey and others suggested that the circular area might have been the interior of a brush shelter, with the lower density area having been covered by the windbreak
but, at all of these sites
there is a high proportion of carnivore bones at these sites, unlikely to have been hominid prey
more likely that there were fighting carnivores at the site -- hardly a good place to sleep with the kids!
many of the animal bones have both cutmarks from stone tools, and toothmarks from carnivores
again, it doesn't sound like a safe place to be
the bones show different degrees of weathering
some had been laying on the surface up to 10 years before being buried, while others were fresh
so the site did not accumulate in a single event, but in many, separated by years
each of which must have involved relatively few animals
more like a place the hominids came to occasionally to butcher an animal, rather than a home base
a likely alternative: stone cache sites for butchery
rather than lugging lots of stone tool material around, the hominids may have left piles in certain places
then, when the killed or scavenged an animal, they would carry all or part of it to one of the cache sites to cut it up
probably in a hurry, to get away from carnivores
this would explain the many different animals at a single place
and the repeated use of the same place over many years
and the presence of carnivores, which does not fit with a living place
this would be different from modern human forager behavior
more like chimp behavior, where they take nuts to a place where there are rocks to crack them open
which hominid created the sites?
a robust australopithecine, whose bones were found at some of them?
Homo habilis
, who existed in the region at the same time, but whose bones were not at the sites?
why would a creatures bones end up on the ground?
Koobi Fora sites
about 1.8 mya
a hippopotamus skeleton and stone tools made from material that had to be carried there from 14 km away
clear evidence of butchering the animal
what species might have produced this site?
2.0-1.5 mya: H. habilis? robust australopithecine?
Koobi Fora Site FxJj50
like Olduvai sites, lots of stone tools, plus bones of at least 20 different animals
with both cutmarks and carnivore toothmarks
but these bones were all "fresh", not weathered
that is, buried quickly, not exposed to sun, so more likely to be roughly as hominids left it
so some of the worries about whether the Olduvai sites were really created by hominids at all do not apply here
also, the bones accumulated in a shorter period of time, so maybe the activities were different
A hotly debated question: were the hominids hunting these animals, or scavenging from carnivore kills?
lots of bones from animals' torsos
hunters will often cut off the meaty limbs and carry them home, leaving the heavy, less valuable body behind
but there are a lot of these second-rate body parts in the hominid sites
not what you would expect of hunters using "home bases"
cutmarks can address the issue of hunting vs. scavenging
presence of carnivore bones and cutmarks on the same bones, at the same sites
when cutmarks and carnivore toothmarks cross, you can tell which was made first
in fact, they are all mixed up
sometimes carnivore chewing before stone tool butchery, sometimes after
suggests scavanging, and that carnivore were still around when hominids got there, or came back after they left
Fagan presents a mixed foraging and scavenging model
hominids forage for plants in the wet season
tooth wear evidence suggests australopithecines and H. habilis ate a similar diet to chimps, heavy on plants
scavenge meat in the dry season when there are fewer plants to eat
focussing on kills by carnivores in wooded areas near rivers
because the hominids need the protection of the trees
and because their large brains give them an advantage in finding these kills before other carnivores and scavengers get there
Fagan discusses a lot of other evidence about early hominid social behavior, language, etc.
in a frustratingly vague way
take a biological anthro course for this
the evidence is mostly biological, not archaeological, so I have an excuse to pass it by here
but the results are:
H. habilis
probably lived in fairly large groups
probably with a lot of complex social behavior
going with a very varied, flexible diet
maybe with early forms of communication, but almost certainly not real language
For next time:
Meet at the library, in the computer room behind the reference desk!
Catch up with the reading
and think about what topics you want to choose for your class presentations