The Dawn of Human Culture (13 page)

Still, despite the apparent sameness over long periods, early and late Acheulean artifact assemblages do differ in some important respects. Early Acheulean hand axes tend to be much thicker, less extensively trimmed, and less symmetrical (Fig. 4.4). They were commonly shaped by fewer than 10 flake removals, and the flake scars were usually deep. Modern experiments indicate that such scars result from the use of “hard” (meaning stone) hammers. Later Acheulean hand axes are sometimes equally crude, but many are remarkably thin and extensively trimmed, and they are highly symmetric not just in plan form but also when viewed edge on. The final flake scars are shallow and flat, and replication efforts indicate that they were probably produced with “soft” (wooden or bone) hammers.

In addition, later Acheulean hand axes are often accompanied by more refined flake tools that anticipate those of the (Mousterian and Middle Stone Age) people who succeeded the Acheuleans. Like their 04 True Humans.r.qxd 1/29/02 5:04 PM Page 109

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1

2

3

4

5

6

FIGURE 4.6

Stages in the manufacture of a classic Levallois flake whose size and shape have been predetermined on the core (redrawn after F. H. Bordes 1961,
Science
134, fig. 4).

successors, later Acheuleans also knew how to prepare a core so that it would provide a flake of predetermined size and shape (Figure 4.6).

Archeologists call such deliberate core preparation the Levallois technique, named for a western suburb of Paris where prepared cores were found and recognized in the latter part of the nineteenth century. The term Levallois refers strictly to a method of stone flaking, not a culture or tradition, and Levallois flaking was practiced by people of various cultures or traditions, including especially the late Acheuleans and their immediate successors. At any given time, people in some places 04 True Humans.r.qxd 1/29/02 5:04 PM Page 110

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employed the technique frequently, while people in others hardly used it at all. Most of the variation probably reflects differences in the avail-ability of suitable stone raw material.

Most Acheulean assemblages are only weakly dated within the long Acheulean timespan, but future research may show that there were actually two periods of Acheulean stability, representing the early and late Acheulean respectively. They may have been separated by a short burst of relatively rapid artifactual change roughly 600,000 years ago that resulted in the more refined hand axes of the late Acheulean and that may have coincided with a relatively abrupt increase in human brain size.

* * *

To understand why, we must back up a little and address the discovery and dating of its east Asian descendant,
Homo erectus
. The story begins with the Dutch physician and visionary Eugène Dubois.

Dubois was born in 1858, a year before Darwin published his signal classic
On the Origin of Species,
in which he showed how natural selection could drive evolutionary change. Dubois developed a pas-sion for human evolution, and he became the first professional paleoanthropologist when he decided to search full time for human fossils. He focused on Indonesia, which was then a Dutch colony and which he and others reasoned was a logical place to start, since it still contained apes that might broadly resemble protohumans. He obtained a medical appointment in the Dutch East India Army, and he arrived in 04 True Humans.r.qxd 1/29/02 5:04 PM Page 111

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Hoxne

the “Movius line” marking the

Abbeville

approximate eastern limit of

&
St. Acheul

the Acheulean (hand axe)

Mauer

Dmanisi

Industrial Tradition

Gran Dolina

Yiyuan

Nihewan

‘Ubeidiya

Zhoukoudian

Lantian

Buia

Yunxian

Melka Kunturé

Hexian

Nanjing

Konso

Nariokotome

Koobi Fora

Olorgesailie

Isimila

Kalambo Falls

Olduvai
&
Peninj

Sangiran,

Kathu Pan

Sambungmachan,

Ngandong, Trinil

Elandsfontein

&
Mojokerto

Sterkfontein

&
Swartkrans

FIGURE 4.7

Locations of the sites mentioned in this chapter.

Indonesia in December 1887. He started his quest immediately, and in October 1891, he hit pay dirt in river deposits near the village of Trinil on the Solo River in central Java (Figure 4.7). Here, together with bones of ancient animals, he found a low-domed, angular, thick-walled human skullcap with a large shelf-like browridge. In August 1892, in what he thought were the same deposits, he recovered a nearly complete human thigh bone that was fully modern in every anatomical respect. The thigh bone and the skullcap convinced him that he had discovered an erect, ape-like transitional form between apes and 04 True Humans.r.qxd 1/29/02 5:04 PM Page 112

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people, and in 1894, he decided to call it
Pithecanthropus erectus
(“erect ape man”). It was later transferred to
Homo erectus
by scientists who benefited from a much fuller fossil record and a more contemplative approach to the use of species names. The implication of the transfer was that
erectus
did not differ from living people (
Homo sapiens
) as much as Dubois believed. The change in naming is partly a matter of taste, however, and the truly important point is that
erectus
was far removed from its ape ancestors in both anatomy and time.

Dubois’s claim for
Pithecanthropus
met broadly the same kind of resistance that Dart’s claim for
Australopithecus
did thirty years later. Dubois was discouraged, and after his return to the Netherlands in 1895, he gave up the search for human fossils. He was fully vindicated beginning only in 1936, when G. H. R. von Koenigswald described a second skull of
Pithecanthropus
from Mojokerto in eastern Java. The Mojokerto specimen represented a child between the ages of 4 and 6, but it still exhibited incipient browridges, a flat, receding forehead, an angular (as opposed to rounded) rear profile, and other features that recalled Dubois’s Trinil find. Then, between 1937 and 1941, von Koenigswald reported three additional partial adult skulls, some fragmentary lower jaws, and isolated teeth from Sangiran, about 50

kilometers (30 miles) up the Solo River from Trinil in central Java (Figure 4.8). Associated animal bones suggested that two of the Sangiran skulls were about the same age as the Trinil skull and that the third was somewhat older.

Between 1952 and 1977, the deposits at Sangiran produced three additional skulls, some skull fragments, and six partial lower jaws, and there have been sporadic discoveries since. The most recent is a skullcap that turned up in 1999 in a New York City shop that 04 True Humans.r.qxd 1/29/02 5:04 PM Page 113

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flat,

receding

shelf-like

forehead

relatively long,

browridge

low braincase

rear

of skull

composed

of two

planes

meeting

at an

angle

0

5 cm

forwardly

0

2 in

projecting

jaws

no chin

classic Indonesian
Homo erectus

(Sangiran)

receding

relatively long,

forehead

low braincase

shelf-like

browridge

rear

of skull

composed

of two

planes

meeting

0

5 cm

at an

angle

forwardly

0

2 in

projecting

no chin

jaws

classic Chinese
Homo erectus

(Zhoukoudian)

FIGURE 4.8

Franz Weidenreich’s reconstructions of classic Indonesian and Chinese
Homo erectus
skulls (redrawn by Kathryn Cruz-Uribe partly after originals by Janis Cirulis in W. W. Howells 1967,
Mankind in the Making
. New York: Doubleday, pp. 156, 169).

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purchases and resells fossils and ancient artifacts. The owner recognized the skullcap for what it was, and he made it available to scientists at the American Museum of Natural History. It was subsequently returned to Indonesia for curation. Still, in the most extreme way imaginable, the New York City discovery illustrates a problem that besets all the Javan fossils, beginning with Dubois’s original find—their stratigraphic context was not carefully documented in the field.

Sometimes, even the precise find spots are uncertain, because the discoverers were farmers who sold the fossils to scientists.

Java is a land of volcanoes, and in theory, it offers the same potential to date fossils as eastern Africa, since the fossil-bearing deposits often contain volcanic rock fragments or ash layers that are amenable to potassium/argon dating. In some places, the deposits also contain tektites—glassy rocks of meteoritic origin that were molten before they hit Earth and that can be dated in the same way as lava or ash. The dates on various Javan materials range from 2 million to 470,000 years ago, but their meaning is difficult to assess, since the stratigraphic relationship of the materials to the fossils and to each other is largely unknown.

Garniss Curtis, director of the Berkeley Geochronology Center, and his colleague, Carl Swisher, now at Rutgers University, have produced the most credible and most widely publicized dates. Curtis was instrumental in the revolutionary potassium/argon dating of Olduvai Gorge and other east African sites in the 1960s, and he made his first attempt in Java in 1974. He collected a sample of volcanic rock from the vicinity of the Mojokerto site that produced the child’s skull in 1936, and he obtained an age of 1.9 million years ago. However, few authorities took this date seriously, mainly because the stratigraphic relationship between the dated sample and the skull was unclear.

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In 1992–93, Curtis returned to Java with Swisher for another try. They collected fresh volcanic samples from Mojokerto, and they also examined the Mojokerto skull. They found that volcanic material was still stuck to its base, and Swisher borrowed Curtis’ pocket knife to pry some away. The small sample from the skull proved to be too poor in radioactive potassium to provide a reliable age, but in chemical and mineralogical composition it closely matched larger samples collected in the field. When Swisher analyzed the larger samples, he got an age of 1.81 million years, only slightly younger than Curtis’s original result.

While Swisher was in Java, he also collected volcanic samples from near Sangiran, which has now provided more than thirty
erectus
fossils, and he obtained an age of 1.65 million years. If the Mojokerto and Sangiran dates are taken at face value, they imply that
Homo erectus
reached Java about the same time that
Homo ergaster
emerged in eastern Africa. In this event, we would either have to abandon the species distinction between
ergaster
and
erectus
or we would have to argue that they shared an even older and as yet unidentified common ancestor. This ancestor could even have lived in eastern Asia rather than eastern Africa.

So why not accept the dates and revise our understanding of human evolution? Mainly because we lack fundamental stratigraphic observations at either Mojokerto or Sangiran. The Mojokerto date is clearly the more persuasive one, because it is based on volcanic material like that still attached to the skull, but experience in eastern Africa shows that older volcanic particles can be introduced by stream action into much younger deposits, and thorough fieldwork is necessary to detect the possibility of such redeposition. To assess the relevance of both the Mojokerto and Sangiran dates, we would need to know, for 04 True Humans.r.qxd 1/29/02 5:04 PM Page 116

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example, whether volcanic samples from stratigraphically superim-posed horizons provide stratigraphically consistent dates, that is, whether deeper layers provide consistently older dates. If not, redeposition is strongly suggested, and the date on any given layer may overestimate the time of its formation, perhaps by a substantial interval.

The 1.81- to 1.65-million-year ages for Mojokerto and Sangiran
erectus
cannot be simply dismissed, but they contradict other age estimates for the same deposits based on animal fossils, paleomagnetism, and fission-track dating. The fission-track method is a cousin of potassium/argon dating that depends on the radioactive decay of naturally occurring uranium within ancient volcanic rocks or tektites, and like the potassium/argon method it estimates the last time the rocks were heated to a very high temperature. If the Javan fission-track dates are correct, the Mojokerto and Sangiran
erectus
fossils are unlikely to be older than 1 million years. Fossils of
erectus
are also known from China, and so far, the oldest reliable Chinese sites are dated to only about 1 million years or slightly before. For the moment then, there is no persuasive reason to doubt the postulated descent of
erectus
from
ergaster
.

* * *