# Introduction to Paleoanthropology/Hominids Early Behavior


in human evolution is about the diet of our earliest ancestors. The
presence of primitive stone tools in the fossil record tells us that 2.5
million years ago, early hominids (*A. garhi*) were using stone
implements to cut the flesh off the bones of large animals that they had
either hunted or whose carcasses they had scavenged.

Earlier than 2.5 million years ago, however, we know very little about
the foods that the early hominids ate, and the role that meat played in
their diet. This is due to lack of direct evidence. Nevertheless,
paleoanthropologists and archaeologists have tried to answer these
questions indirectly using a number of techniques.

-   Primatology (studies on chimpanzee behavior)
-   Anatomical Features (tooth morphology and wear-patterns)
-   Isotopic Studies (analysis of chemical signatures in teeth and
    bones)

## What does chimpanzee food-consuming behavior suggest about early hominid behavior?

### Meat consuming strategy

Earliest ancestors and chimpanzees share a common ancestor (around 5-7
million years ago). Therefore, understanding chimpanzee hunting behavior
and ecology may tell us a great deal about the behavior and ecology of
those earliest hominids.

In the early 1960s, when Jane Goodall began her research on chimpanzees
in Gombe National Park (Tanzania), it was thought that chimpanzees were
herbivores. In fact, when Goodall first reported meat hunting by
chimpanzees, many people were extremely sceptical.

Today, hunting by chimpanzees at Gombe and other locations in Africa has
been well documented.

We now know that each year chimpanzees may kill and eat more than 150
small and medium-sized animals, such as monkeys (red colobus monkey,
their favorite prey), but also wild pigs and small antelopes.

Did early hominids hunt and eat small and medium-sized animals? It is
quite possible that they did. We know that colobus-like monkeys
inhabited the woodlands and riverside gallery forest in which early
hominids lived 3-5 Myrs ago. There were also small animals and the young
of larger animals to catch opportunistically on the ground.

Many researchers now believe that the carcasses of dead animals were an
important source of meat for early hominids once they had stone tools to
use (after 2.5 million years ago) for removing the flesh from the
carcass. Wild chimpanzees show little interest in dead animals as a food
source, so scavenging may have evolved as an important mode of getting
food when hominids began to make and use tools for getting at meat.

Before this time, it seems likely that earlier hominids were hunting
small mammals as chimpanzees do today and that the role that hunting
played in the early hominids\' social lives was probably as complex and
political as it is in the social lives of chimpanzees.

When we ask when meat became an important part of the human diet, we
therefore must look well before the evolutionary split between apes and
humans in our own family tree.

### Nut cracking

Nut cracking behavior is another chimpanzee activity that can partially
reflect early hominin behavior. From Jan. 2006 to May 2006, Susana
Carvalho and her colleagues conducted a series of observation on several
chimpanzee groups in Bossou and Diecké in Guinea, western Africa. Both
direct and indirect observation approach was applied to outdoor
laboratory and wild environment scenarios. [^1]

The results of this research show three resource-exploitation strategies
that chimpanzees apply to utilize lithic material as hammers and anvils
to crack nut: 1) Maximum optimization of time and energy (choose the
closest spot to process nut). 2) Transport of nuts to a different site
or transport of the raw materials for tools to the food. 3) Social
strategy such as the behavior of transport of tools and food to a more
distant spot. This behavior might relate to sharing of space and
resources when various individuals occupy the same area.

The results demonstrate that chimpanzees have similar food exploitation
strategies with early hominins which indicate the potential application
of primate archaeology to the understanding of early hominin behavior.

## What do tooth wear patterns suggest about early hominid behavior?

Bones and teeth in the living person are very plastic and respond to
mechanical stimuli over the course of an individual\'s lifetime. We
know, for example, that food consistency (hard vs. soft) has a strong
impact on the masticatory (chewing) system (muscles and teeth). Bones
and teeth in the living person are therefore tissues that are remarkably
sensitive to the environment.

As such, human remains from archaeological sites offer us a
retrospective biological picture of the past that is rarely available
from other lines of evidence.

Also, new technological advances developed in the past ten years or so
now make it possible to reconstruct and interpret in amazing detail the
physical activities and adaptations of hominids in diverse environmental
settings.

Some types of foods are more difficult to process than others, and
primates tend to specialize in different kinds of diets. Most living
primates show three basic dietary adaptations:

-   insectivores (insect eaters);
-   frugivores (fruit eaters);
-   folivores (leaf eaters).

Many primates, such as humans, show a combination of these patterns and
are called omnivores, which in a few primates includes eating meat.

The ingestion both of leaves and of insects requires that the leaves and
the insect skeletons be broken up and chopped into small pieces. The
molars of folivores and insectivores are characterized by the
development of shearing crests on the molars that function to cut food
into small pieces. Insectivores\' molars are further characterized by
high, pointed cusps that are capable of puncturing the outside skeleton
of insects. Frugivores, on the other hand, have molar teeth with low,
rounded cusps; their molars have few crests and are characterized by
broad, flat basins for crushing the food.

In the 1950s, John Robinson developed what came to be known as the
dietary hypothesis. According to this theory there were fundamentally
two kinds of hominids in the Plio-Pleistocene. One was the \"robust\"
australopithecine (called Paranthropus) that was specialized for
herbivory, and the other was the \"gracile\" australopithecine that was
an omnivore/carnivore. By this theory the former became extinct while
the latter evolved into *Homo*.

Like most generalizations about human evolution, Robinson\'s dietary
hypothesis was controversial, but it stood as a useful model for
decades.

Detailed analyses of the tooth surface under microscope appeared to
confirm that the diet of *A. robustus* consisted primarily of plants,
particularly small and hard objects like seeds, nuts and tubers. The
relative sizes and shapes of the teeth of both *A. afarensis* and *A.
africanus* indicated as well a mostly mixed vegetable diet of fruits and
leaves. By contrast, early *Homo* was more omnivorous.

But as new fossil hominid species were discovered in East Africa and new
analyses were done on the old fossils, the usefulness of the model
diminished.

For instance, there is a new understanding that the two South African
species (*A. africanus* and *A. robustus*) are very similar when
compared to other early hominid species. They share a suite of traits
that are absent in earlier species of Australopithecus, including
expanded cheek teeth and faces remodeled to withstand forces generated
from heavy chewing.

## What do isotopic studies suggest about early hominid behavior?

Omnivory can be suggested by studies of the stable carbon isotopes and
strontium(Sr)-calcium(Ca) ratios in early hominid teeth and bones.

For instance, a recent study of carbon isotope (13C) in the tooth enamel
of a sample of *A. africanus* indicated that members of this species ate
either tropical grasses or the flesh of animals that ate tropical
grasses or both. But because the dentition analyzed by these researchers
lacked the tooth wear patterns indicative of grass-eating, the carbon
may have come from grass-eating animals. This is therefore a possible
evidence that the australopithecines either hunted small animals or
scavenged the carcasses of larger ones.

There is new evidence also that *A. robustus* might not be a herbivore.
Isotopic studies reveal chemical signals associated with animals whose
diet is omnivorous and not specialized herbivory. The results from 13C
analysis indicate that *A. robustus* either ate grass and grass seeds or
ate animals that ate grasses. Since the Sr/Ca ratios suggest that *A.
robustus* did not eat grasses, these data indicate that *A. robustus*
was at least partially carnivorous.

## Summary

Much of the evidence for the earliest hominids (*Sahelanthropus
tchadensis*, *Orrorin tugenensis*, *Ardipithecus ramidus*) is not yet
available.

*Australopithecus anamensis* shows the first indications of thicker
molar enamel in a hominid. This suggests that *A. anamensis* might have
been the first hominid to be able to effectively withstand the
functional demands of hard and perhaps abrasive objects in its diet,
whether or not such items were frequently eaten or were only an
important occasional food source.

Australopithecus afarensis was similar to *A. anamensis* in relative
tooth sizes and probable enamel thickness, yet it did show a large
increase in mandibular robusticity. Hard and perhaps abrasive foods may
have become then even more important components of the diet of *A.
afarensis*.

*Australopithecus africanus* shows yet another increase in postcanine
tooth size, which in itself would suggest an increase in the sizes and
abrasiveness of foods. However, its molar microwear does not show the
degree of pitting one might expect from a classic hard-object feeder.
Thus, even *A. africanus* has evidently not begun to specialize in hard
objects, but rather has emphasized dietary breadth (omnivore), as
evidenced by isotopic studies.

Subsequent \"robust\" australopithecines do show hard-object microwear
and craniodental specializations, suggesting a substantial departude in
feeding adaptive strategies early in the Pleistocene. Yet, recent
chemical and anatomical studies on *A. robustus* suggest that this
species may have consumed some animal protein. In fact, they might have
specialized on tough plant material during the dry season but had a more
diverse diet during the rest of the year.


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