- CHAPTER 10: PALEOANTHROPOLOGY: RECONSTRUCTING EARLY HOMININ
BEHAVIOR AND ECOLOGY
- Chapter Outline
- I. Introduction
- a) Definite hominin fossil material has been found in Africa
that dates to just after 5 mya.
- i) The hominin nature of these remains is indicated because
of the way they behaved.
- ii) Hominin biocultural nature of human evolution, this
chapter focuses in the methods scientists use to explore the
secrets of early hominin behavior and ecology.
- II. Definition of a Hominin
- a) Hominin origins date to the end of the Miocene.
- b) Hominins have been variously defined as having: a large
brain, bipedal locomotion, and/or tool-making behavior.
- i) It is clear that these characteristics did not evolve
simultaneously. The phenomenon of different physiological systems
evolving at different rates is called mosaic evolution.
- ii) Bipedal locomotion is the key indication that a fossil
was a hominin.
- c) What's in a name? we refer to members of the human family
- i) Molecular evidence clearly shows that the great apes are
not a monophyletic group.
- ii) Hominoid classification has been significantly revised
adding two further taxonomic levels (subfamily and tribe).
- iii) There is very close evolutionary relationships between
humans and African apes (particularly chimpanzees and
- (1) The former term hominid has a quite different meaning in
this revised classification referring to all great apes and
- d) Biocultural evolution: the human capacity for
- i) The most distinctive feature of humans is our dependence
- (1) Human culture is an adaptive strategy that includes
cognitive, political, social, and economic aspects as well as the
capacity to make and use tools.
- ii) The earliest hominins did not regularly manufacture stone
- (1) They probably had the tool-making capabilities of living
- (a) Stone tools appear in the archaeological record about 2.6
- (2) By 7 to 6 mya, hominins had developed bipedalism and
could carry and transport objects from place to place..
- iii) The dynamics between neuronal reorganization, tool use,
changing social organization, and communication form the core of
- III. The Strategy of Paleoanthropology
- a) Paleoanthropology, the study of ancient humans, is a
multidisciplinary approach that includes geologists,
archaeologists, physical anthropologists, and
- i) The earliest artifact date back to 2.6 mya and were found
in sites from the Gona and Bouri areas in northeastern
- ii) Paleoanthropologists must synthesize information
- (1) Dating of the site.
- (2) The paleoecology of the site.
- (3) Any archaeological traces of behavior.
- (4) Any anatomical evidence from hominid remains.
- iii) The ultimate goal is to "flesh out" the hominids to
produce a more complete and accurate understanding of human
- IV. Paleoanthropology in Action-Olduvai Gorge
- a) Olduvai Gorge, located on the eastern branch of the Great
Rift Valley of Africa, has yielded an immense quantity of
high-quality data on early hominid behavior.
- b) Olduvai has a well-documented sequence of geological,
paleontological, archeological, and hominid remains that span the
last 2 million years.
- i) The earliest hominid site dates to about 1.85 mya, and is
accompanied by the Oldowan tool industry.
- ii) The most famous hominid fossil from Olduvai is probably
the Zinjanthropus skull, discovered by Mary Leakey in 1959.
- V. Dating Methods
- a) The two types of dating methods are relative dating and
chronometric, or absolute dating.
- i) One relative dating method is based on stratigraphy.
- (1) The law of superposition states that (in an undisturbed
deposit) a lower layer is older than a higher layer.
- ii) Another relative dating method is fluorine analysis.
- (1) Groundwater contains fluorine, and the longer a bone is
in a deposit; the more fluorine will accumulate during the
- (2) The fluorine method can only be used to compare bones
found at the same location.
- iii) Chronometric methods are based on the phenomenon of the
radioactive decay of unstable isotopes.
- (1) Depending on the half-life of the isotope used, the time
range for this method varies from the age of the earth (billions
of years) to less than 1,000 years.
- (a) Paleoanthropologists use the K/Ar method extensively to
determine the age of volcanic deposits (and therefore the
associated fossils) in East Africa.
- (i) The 40Ar/39Ar method can be used on smaller samples and
provides more accurate results.
- (b) The C-14 method is used on organic materials and has a
useful time-range of 75,000 to less than 1,000 years.
- (c) Thermoluminescence dates can be obtained from burnt
- b) Applications of dating methods: examples from
- i) Olduvai has several reliable K/Ar dates for the
underlying basalt and the tuffs in Bed I, and the Zinj site has
been dated to 1.79 + .3 mya
- (1) K/Ar dates must be cross-checked, since all dates have
errors associated with them.
- (2) One important cross-check is to use the fission-track
- (a) In fission-track dating uranium 238 (238 U) decays
regularly by spontaneous fission.
- (3) Another way of cross-checking is to use
- (a) With this technique, the orientation of magnetic
sediments is checked to determine whether they were deposited
during a period of normal or reversed magnetism.
- (4) Biostratigraphy, or faunal correlation, is another
- (a) This technique matches faunal remains, such as pigs,
elephants, rodents, and antelopes at the site in question with the
known evolutionary sequences of the same faunal species.
- (5) Cross-checking with different methods lends confidence to
the results because each method has a different source of
- VI. Excavations at Olduvai
- a) There are many hominin sites found at Olduvai.
- i) Mary Leakey excavated close to 20 of these sites.
- ii) There is much controversy regarding hominin activities at
these sites ("campsites").
- (1) These are general-purpose areas where hominins carried
out daily activities.
- (2) The exact nature of the activities carried out at these
sites is not fully understood.
- (a) Initially, they were interpreted as true campsites.
Alternately, the accumulations could have been produced by
nonhominins, or the accumulations could be the result of hominin
gathering and scavenging activities.
- VII. Experimental Archaeology
- a) Archaeologists try to reconstruct prehistoric techniques
of tool-making, butchering, and other activities in order to
answer fundamental questions about hominin behavior.
- i) Stone tool (lithic) technology is the most commonly
preserved aspect of hominin cultural behavior.
- (1) Initially, archaeologists thought that the Oldowan
industry consisted of deliberately fashioned cores and
- (a) Richard Potts believes that only the flakes were being
deliberately produced, and the "core tools" were merely byproducts
of flake manufacture.
- (2) Flakes can be removed from cores by direct percussion
and/or pressure flaking.
- (a) The nodules found in Bed I at Olduvai (1.85-1.2 mya) have
been unifacially flaked by using direct percussion.
- (b) Later, in Bed IV (400,000 ya), most tools are flaked
bifacially with direct percussion, but they could only have been
produced with a "soft" hammer, most likely a piece of bone or
- (c) The microliths found in the upper beds (17,000 ya) must
be produced using the pressure flaking method in which a pointed
piece of bone, antler, or wood is pressed firmly against the
- (3) Microwear analysis is performed by observing stone tools
under high magnification to detect patterns of polish and
striations characteristic of tool use on various materials such as
bone or wood, as well as the way the tools were used (such as
cutting versus scraping).
- (a) Tools observed under a scanning electron microscope may
reveal the presence of the phytoliths of the different species of
plants on which the tool was used.
- ii) Analysis of bone is undertaken to determine how humans
and natural forces affect bone.
- (1) Taphonomy is the branch of paleoecology concerned with
the influence of natural forces on bone deposition and
- (a) Research such as observing human butchering practices, or
analyzing scavenger bone accumulations is conducted to determine
the extent to which these factors can account for the composition
of bone accumulations at hominin sites.
- (b) Another research concern is to determine the effects of
natural forces, such as running water, on patterns of bone
- (2) Bones may also be examined for evidence of hominin
activity in the form of cut marks.
- VIII. Reconstruction of Early Hominin Environments and
- a) The behavioral interpretation of archaeological and
skeletal evidence is speculative and not as amenable to rigorous
testing as are the original data.
- i) Nevertheless, behavioral and environmental
reconstructions (or scenarios) give us a broader view of evolution
and adaptation which can be known from the paleoanthropological
- (1) Environmental explanations for hominin origins focus on
the environment as a major factor in evolution.
- (a) It is possible to oversimplify the complex interactions
between the organism and the environment by making sweeping
generalities about environmental determinism.
- (b) There may have been major ecological changes occurring in
Africa at or around the same time that hominins were evolving
(i.e. a trend towards cooler, drier, and more seasonal
- (i) However, the causal connection between environmental
change and the initial hominoid/hominin transition has not yet
been convincingly demonstrated.
- (c) The evolutionary pulse theory proposes a causal
connection between periods of increased aridity in South and East
Africa and the evolution of new species of hominids.
- (i) In Indonesia, scientists investigate the flora and fauna
enticing early hominins, evident at Sangrian Dome where life there
included the extended habitation of Homo erectus from 1.6 to .9
- (ii) Some experts believe that hominins evolved due to their
flexibility to adapt to many types of environments.
- (2) Why did hominins become bipedal?
- (a) The shift to bipedality is the fundamental hominin
- (b) Hominins are adapted to a more mixed and open-country
habitat than are the chimpanzees, yet no other mixed to
open-country adapted mammals are full-time bipeds.
- (i) There can be no simple environmentally-driven explanation
for the shift to full-time bipedalism.
- (ii) Jolly's seed-eating hypothesis proposes that early
hominins, like living gelada baboons, were highly dependent on
eating seeds and nuts but they stood upright while feeding.
- 1. Fossil evidence indicates that the dental adaptations
predicted by Jolly's hypothesis are not restricted only to the
- (iii) Lovejoy has devised a scenario in which hominins are
tied to a "home base" that requires female provisioning by
- 1. The skeletal evidence suggests early hominins were not
pair-bonded because they are highly sexually dimorphic. A recent
study, however, questions the high level of sexual dimorphism in
- 2. Additionally, notions of food sharing, home basis, and
long distance provisioning are questioned.
- (iv) Falk has proposed the "radiator theory" which proposes a
link between bipedalism and brain expansion.
- 1. Falk argues that the hominins that exploited the hot
savannah evolved a venous drainage system that better cooled the
brain. This particular venous drainage pattern also removed the
constraints for encephalization because it efficiently cooled
larger brains too.
- 2. This hypothesis does not explain the origins of
bipedalism, nor does it explain why brain size increased in the