Masters of the Planet (23 page)

Whatever the details of the transition, exactly how the fulfillment of the neural potential underwriting the invention of the handaxe affected other aspects of the Acheuleans' lives remains anyone's guess. For although a lot of handaxe sites are known, the kinds of activities performed at them seem, at least early on, not to have been hugely different in material terms from those documented at older sites. There is one major exception to this, though. Previous toolmakers had typically made their stone artifacts at butchery places, as and when they were needed. Tools at such places are not usually found in great abundance because of the small quantities of stone that the makers could reasonably carry around for flaking on the spot. In contrast, handaxes were often made in huge quantities, at “workshop” localities, often in close proximity to good sources of appropriate rock. Perhaps the most famous such place is at Olorgesailie, in Kenya, where literally thousands of million-year-old stone tools were found littered in a small area of the ancient landscape. This concentration of tools implies an entirely different approach to life than had been taken by the Oldowan tool makers, including the earliest
Homo ergaster.
It even strongly suggests that some degree of specialization in social and economic roles existed among members of the group.

The suggestion has also been made, though it is quite controversial, that the sites containing unusual quantities of handaxes hint at ritual gatherings, and at a social rather than purely utilitarian function for at least some of these tools. This remains pure speculation; but it is possible to draw this conclusion with more confidence from the spectacularly large size of some of the handaxes found at places like Isimila, in Tanzania. These tools were far too big and heavy to have been used for routine chores, and they have invited speculation that their uses were instead ceremonial. And while this inference may be a little too loaded with implications of our own style of humanity, it is quite possible that such tools were made in a playful spirit, or perhaps even a competitive one
of
showing off at large social gatherings. Expressions like these make it all the more frustrating that we have so little other supporting evidence about Acheulean lifestyles—which may well have become more complex with the passage of time: Isimila is quite late.

At Olorgesailie we also have the best current physical candidate for an actual maker of early handaxes. Not far away from the rich tool site, at the same stratigraphic level, were found fossil bits of a very small individual—far more diminutive than the Turkana Boy—who the excavators of the site suspect may have been a member of the population to which the toolmakers belonged. They described the specimen as a
Homo erectus,
but in truth this is much more because of its date than its morphology. The cranial fragments look nothing like the type specimen from Java, or, for that matter, the Boy. Still, under current standards it is entirely reasonable to attribute it to an early member of the genus
Homo;
and while a guesstimate places its brain size at under 800 cc, this lowish figure is nonetheless within the
Homo erectus/Homo ergaster
range, especially considering the individual's petite size.

BRAINS AND BRAIN SIZES

With
Homo ergaster
and
Homo erectus
we confront for the first time an episode of marked brain-size enlargement among the hominids, and this issue is a uniquely important one to confront. The brain sizes of fossil hominids have attracted a huge amount of attention, not simply because our large brains have for long been our most vaunted organs (at least as they distinguish us from other animals), but also because brain volume is easy to quantify as long as you have a fossil cranial vault that is sufficiently well-preserved to measure, or from which to make an estimate. One fascinating thing about hominid brain sizes over the last couple of million years is that, without any doubt, they show a striking trend toward enlargement with time. Brain sizes had more or less flatlined during the long tenure of the australopiths. The very latest australopiths seem on balance to have had slightly larger brains than the earliest ones; but even if this doesn't simply reflect body size, the difference is too small to be worth noting. But once the genus
Homo
was on the scene, everything changed. On average, the later in time a fossil member of the
genus
Homo
is, the larger its brain is likely to be. This really is important, because the way we process information in our heads most clearly demarcates us modern humans from all other creatures on the planet; and our cognitive abilities are certainly dependent on our large brains, even if size is not in itself the whole story.

So brain size is without doubt a critical factor in human evolution. But we have to be careful how we interpret it. Particularly under the gradualist dictates of the Evolutionary Synthesis, paleoanthropologists have often been tempted to simply join the dots into a single continuum of brain size increase. Two million years ago, our ancestors' brains were basically ape-sized; a million years later, they had doubled in volume; and today they are twice as large again. What could be more suggestive of an inexorable trend, as smarter individuals out-reproduced dumber ones? And what, looking back, could be a greater compliment to our current finely burnished species? When you think about it, this really is the ultimate paleoanthropological feel-good formula.

But there are other ways to look at the brain size picture. For a start, even though we don't have anything like the number of fossil hominid braincases we'd like, we do have enough to know that at any one point in time brain sizes varied widely. Among the australopiths, we're in the fairly tight range of about 400 cc to 550 cc. Among the earliest species of
Homo,
in the period following about two million years ago we're looking at a range of some 600 cc to 850 cc; and by around half a million years, give or take, the range has broadened to around 725 cc to 1,200 cc.

We are also looking at a pretty impressive if often unacknowledged variety of morphologies. Take, for example, four eastern African crania, all dated to roughly one million years ago: that tiny individual from Olorgesailie (reckoned to have had a brain capacity of less than 800 cc); a cranium from Buia in Ethiopia (750–800 cc); a skullcap from Daka in Ethiopia (995 cc); and a braincase from Bed II at Olduvai Gorge (1,067 cc). All have been allocated to the species
Homo erectus;
but all of them look decidedly different, not only from the Javan type specimen of the species, but from each other. There is clearly more going on here than a simple lump categorization as
Homo erectus
or even
Homo ergaster
can reflect, for none of them looks much like the Turkana Boy,
either
.

A crude plot of average hominid brain sizes against time. After an initial flatlining, this plot appears to indicate a consistent enlargement of the hominid brain over the last two million years. But it is important to bear in mind that these brain volumes are averaged across an uncertain number of different lineages within the genus
Homo,
and that it is likely that what the plot actually reflects is the preferential success over this period of larger-brained hominid species, rather than steady increase within a single lineage. Illustration by Gisselle Garcia.

A perfect example of the conflicted mindset that results from the tension between evidence and tradition came a few years ago, when a team working in the Turkana Basin described two new hominid fossils from the Ileret area to the east of the lake. One was a lightly built braincase (691 cc) some 1.55 million years old, that they allocated to
Homo erectus
even though it bears none of the morphological hallmarks of the Javan type specimen. The other was a piece of upper jaw, perhaps a hundred thousand years younger, that they assigned to
Homo habilis.
The researchers hailed these finds as evidence that at least two distinct lineages of the genus
Homo
had occupied the Turkana Basin at about the same time, emphasizing diversity among the hominids of the period. Yet their allocation of the braincase to
Homo erectus
could only have borne any conceivable logic in the context of the view that
Homo erectus
is the middle grade of a single, worldwide, variable, and gradually evolving hominid lineage—precisely the construct that they ostensibly wished to undermine.

Of
course, with modern humans presenting us with brains ranging from roughly 1,000 cc to 2,000 cc in volume, we can hardly use past brain size variation alone to reject the notion of a single variable human lineage that consistently gained in brain volume with time. But the huge variation we see in the morphology of the skulls those brains were contained in is at least highly suggestive. And if multiple hominid species
were
out there in the past—species whose brain size ranges and geological lifespans are, regrettably, unknown to us—then it is just as likely that the trend we see toward increasing brain size over the last two million years is due to the greater competitive success in the ecological arena of larger-brained hominid species, as that it is due to the reproductive success of larger-brained and thus smarter individuals.

A scenario involving the consistent triumph of larger-brained species might be taken to suggest that the pressures favoring hominid brain expansion over time were essentially ecological, and thus external to the species themselves. Nonetheless, there is one important observation that suggests that members of the genus
Homo
have been consistently predisposed in some way toward brain size increase: brain enlargement has occurred independently in at least three lineages within the genus. The earliest
Homo erectus
in Java, dating from perhaps more than 1.5 million to a bit under one million years ago, have brains ranging from around 800 cc to a bit over 1,000 cc in volume. A later Javan group, poorly dated but maybe about a quarter of a million years old, comes in at 917 cc to 1035 cc; and the latest Javan
Homo erectus
group of all, perhaps no more than 40 thousand years old, varies from 1,013 cc to 1,251 cc. Similarly,
Homo sapiens
and
Homo neanderthalensis
diverged from a smaller-brained common ancestor well over half a million years ago, and independently gained their comparably sized large brains. Thus, a 600-thousand-year-old collection of Spanish fossils foreshadowing the Neanderthals had brains some 1,125 cc to 1,390 cc in volume, against the later Neanderthal average of 1,487 cc.

Given that
Homo erectus
lived in tropical eastern Asia, the Neanderthals in Ice Age Europe, and the precursors of
Homo sapiens
in Africa, it is hard to see a common environmental thread in the trend toward bigger brains that all three lineages independently followed. Somehow,
very
early on in its evolution, the genus
Homo
must have acquired some underlying predisposition, biological or cultural, toward brain enlargement. Identifying that factor will be essential if we are ever to have a full account of how we became the extraordinary cognitive entity we are— even though, as we will see, while a large brain is clearly a necessary condition for our unique modern cognitive style, it is not a sufficient one.

Still, predispositions notwithstanding, there is nothing inevitable about the enlarging brain in
Homo.
We were all forcibly reminded of this by the recent discovery of the remarkable “Hobbit” at Liang Bua Cave on the Indonesian island of Flores. The best specimen of this extraordinary hominid, technically known as
Homo floresiensis,
is the skeleton of a tiny individual, dubbed LB1. In life LB1 had stood not much more than three feet tall and, though bipedal, had possessed rather unusual body proportions. LB1 also has a head with a tiny vault that had contained a brain of maybe as little as 380 cc in volume—fractionally smaller even than Lucy's, the smallest australopith brain known. What's more, perhaps most bizarrely of all, the individual had lived only about 18 thousand years ago.

Predictably, the announcement of the entirely unexpected Hobbit was greeted by enormous controversy. The scientists who described LB1 thought it might be a dwarfed descendant of a population of
Homo erectus
that had somehow contrived to reach Flores in the remote past. This is not in itself implausible: “island dwarfing” of mammals and reptiles is not unusual on smallish isolated landmasses such as Flores—and indeed, bones of a tiny elephant are found in the same cave deposits that yielded LB1. But there is little about its anatomy to suggest any close affinity to
Homo erectus,
and LB1's brain is much smaller than you would expect to find as a result of normal processes of dwarfing, even from the typically modest-brained
Homo erectus.
Several different authorities have suggested, alternatively, that LB1 is simply the skeleton of a pathological modern human; but none of the suggested disease conditions fits the case well enough. As more is learned about this specimen, the more likely it appears that LB1 and its kind will in the end prove to be descendants of extremely early émigrés from Africa, preserving archaic features that may well eventually help us learn just what those émigrés were like. Meanwhile, independent of whether or not some degree of island dwarfism is indeed involved in this particular case, LB1 tells us that, larger patterns apart, time and brain enlargement need not necessarily be synonymous among members of the genus
Homo—
if, that is, it is appropriately assigned to our genus at all.