170 CHAPTER 7 | The First Bipeds
acids, the building blocks of protein. No single plant food
can provide this nutritional balance. Only a combination
of plants can supply the range of amino acids provided
by meat alone.
Lacking long, sharp teeth for shearing meat, our earli-
est ancestors likely foraged for insects, but sharp tools for
butchering made it possible to efficiently eat meat. The ini-
tial use of tools by early Homo may be related to adapting
to an environment that we know was changing since the
Miocene from forests to grasslands (recall Figure 7.14).^25
The physical changes that adapted bipeds for spending in-
creasing amounts of time on the new grassy terrain may
have encouraged tool making. Thus with the appearance
of the genus Homo, a feedback loop between biological
characteristics and cultural innovations began to play a
major role in our evolutionary history. This set the human
line on a steady course of increasing brain size and a reli-
ance on culture as the means of adaptation, as we explore
in detail in the next chapter.failure to do so has serious consequences: stunted growth,
malnutrition, starvation, and death. Leaves and legumes
(nitrogen-fixing plants, familiar modern examples being
beans and peas) provide the most readily accessible plant
sources of protein. The problem is that these raw plants
are difficult for primates to digest; substances in the leaves
and legumes cause proteins to pass right through the gut
without being absorbed unless cooked.^23
Chimpanzees have a similar problem when out on
the savannah. Even with canine teeth far larger and
sharper than ours or those of early Homo, chimpanzees
frequently have trouble tearing through the skin of other
animals.^24 In savannah environments, chimps spend
about a third of their time foraging for insects (ants and
termites), eggs, and small vertebrate animals. Such ani-
mal foods not only are easily digestible, but they provide
high-quality proteins that contain all the essential amino
(^23) Stahl, A. B. (1984). Hominid dietary selection before fire. Current
Anthropology 25, 151–168.
(^24) Goodall, p. 372. (^25) Behrensmeyer, A. K., et al. (1997). Late Pliocene faunal turnover in the
Turkana basin, Kenya, and Ethiopia. Science 278, 1589–1594.
Questions for Reflection
- The spectacular 4.4-million-year-old Ardi specimen has
captured our collective imagination. Does the fact that this
specimen has a name and a face change how you respond
to the scientific facts? How do these ancient bones, which
we know as the individual Ardi, challenge us to think about
what it means to be human? How does the splash made by
Ardi challenge our understanding of the nature of human
origin studies? - Describe the anatomy of bipedalism, providing exam-
ples from head to toe of how bipedalism can be “diagnosed”
from a single bone. Do you think evidence from a single
bone is enough to determine whether an organism from the
past was bipedal?
3. Who were the robust australopithecines? What evi-
dence is used to demonstrate that they are an evolutionary
dead end?
4. How do paleoanthropologists decide whether a fossil
specimen from the distant past is male or female? Do our
cultural ideas about males and females in the present affect
the interpretation of behavior in human evolutionary
history?
5. Do you think that members of the genera Ardipithecus
and Australopithecus were tool users? What evidence would
you use to support a case for tool use in these early bipeds?
Suggested Readings
Falk, D. (2004). Braindance: New discoveries about human
origins and brain evolution—revised and updated. Gainesville:
University Press of Florida.
In this updated and expanded version of her 1994 book, Falk
presents her radiator theory to account for the lag between
the appearance of bipedalism and the increase in the size of
the brain over the course of human evolutionary history.
Johanson, D. C., Edgar, B., & Brill, D. (1996). From Lucy to
language. New York: Simon & Schuster.
This coffee-table-sized book includes more than 200 color
pictures of major fossil discoveries along with a readable,
intelligent discussion of many of the key issues in paleo-
anthropology.