Scary monsters can materialize out
of the darkness
Apes look like us – the scandal of the fact
that they’re our blood relatives is an open
one. We distance ourselves from it with laughter, a common
human response to uneasiness. Funny-chimpanzee movies used
to be an established Hollywood genre.
Monkeys and baboons – still too close to our species
for comfort – are frequently also thought of as comical
beings. I was struck by the contrast between this stereotype,
and the dignity and gravity on the faces of a row of female
chacma baboons that I saw sitting on the railing of the H12
bridge across the Sabi River in October of 2001. Those faces,
with their intelligent, aware eyes, spoke to me of beings
for whom life – the business of survival, status and
reproduction – is a completely serious matter. It occurred
to me that I wouldn’t be crossing the Sabi in a 4 X
4 – that I wouldn’t be crossing the Sabi period
– if my australopithecine ancestors hadn’t been
equally serious about those biological imperatives.
There’s a great view of the downstream side of the
Sabi from the H12. Alone on the back seat, I moved over to
the other side of the car to take it in. I’d scarcely
done so, however, when our friend Lucy, sitting up front with
Delphine, let out a piercing shriek. I whipped around to see
that one of the female baboons I’d been empathizing
with was now in the car, on the back seat next to me. Before
I could do anything (and what was I going do anyway?),
our hairy passenger grabbed a paper bag lying between the
front seats – empty, unluckily for her – and exited
through the window which I had carelessly left open.
I was left with an image of the narrow, human-like hand that
had reached for that bag. Even the creases in its mat-black
palm seemed to run along human lines. The hands of Australopithecus
africanus must, I imagined, have looked something like
that.
Having a baboon burst into their troop to steal something
would have been a terrifying experience for Australopithecus
africanus. Most baboon species include meat in their diet,
and a thief of that kind could well have been going for a
child. Baboons still kill and eat human infants occasionally.
In africanus’ time, giant baboons in the genus Dinopithecus
might well have been more confident and successful hunters
of hominid prey. The biggest Dinopithecus reached
the size of modern humans. Another baboon, Theropithecus
oswaldi, grew even larger that this – as large,
in fact, as a present-day gorilla – but its diet seems,
mercifully, to have been shifted to the vegetarian end of
baboon omnivory. None of the hominid species living with these
huge baboons were a great deal bigger than present-day baboons.
All the way from its origins around seven million years ago,
up until just over 2 million years ago, the hominid family
seems, as far as we can tell, to have consisted exclusively
of small species. Like baboons, early hominids were “sexually
dimorphous” creatures– the males weighed around
90 lb., and grew about five feet tall, while the females weighed
only about 50 lb., and stood four feet high or less. We would
have been struck not only by the diminutive stature of those
“australopithecine” hominids, but also by the
unfamiliar proportions of their bodies. Whereas our chests
taper down into relatively narrow waists, the thickish mid-sections
of australopithecines tapered upward into a relatively narrow
chest and shoulders. The powerful, sinewy arms that hung from
those narrow shoulders would have seemed too long for their
owner’s short thighs.
* * *
In the classic view of human evolution, hominids split off
from their ape-like ancestors in the process of leaving the
forests in which they had evolved, and starting to live on
the savanna. This view became unfashionable after the tree-climbing
adaptations of the australopithecines we’ve just been
talking about became apparent. More evidence was aligned against
the “we moved on to the savanna” hypothesis when
fragments of forest-plants like lianes were found in the same
deposits as Australopithecus fossils, along with
the remains of forest animals like colobus monkeys, the woodland
baboon Theropithecus brumpti, tragelephine or “bushbuck-type”
antelopes, and reduncine or “waterbuck-type” antelopes.
For a while it looked like the savanna hypothesis would have
to be scrapped completely – and it still looks that
way to some people. Australopithecine remains are not, however,
exclusively associated with those of “moist-woodland”
mammals. They’re found, too, in association with those
of early impalas, which lived in relatively dry bush country,
the savanna baboon Theropithecus dartii, and the
so-called “alcelaphine” antelopes, i.e. the wildebeests
and hartebeests, whose tooth structure provides clear evidence
of the fact that they lived, as their present-day descendants
still live, almost exclusively on grass.
It’s beginning to look, therefore, as if the australopithecines
might have lived in a mosaic of forest and grassland. Back
in the middle Miocene, around 15 million years ago, famous
hominid sites like the middle section of the Awash River in
Ethiopia, Olduvai Gorge in Tanzania, and the Sterkfontein
valley in South Africa, were probably covered, like most parts
of Africa were at this time, by dense forest. Beginning about
10 million years ago, the cooling and drying process we’ll
speak about at the end of Chapter 20, started opening up the
forest-cover in those and other parts of Africa. As I’ll
suggest in that Chapter, that “opening-up process”
didn’t immediately create grasslands as dry or as extensive
as those presently found in Africa. It seems, instead, to
have created regions of relatively diminished rainfall,
in which forest was transformed into the kind of heavily-wooded
savannas that are found today on the margins of the Congo’s
rainforests.
The australopithecines were probably dependent on both the
grassland and the forest components of those Congo-like savannas.
My guess is that the abundance of trees on the Miocene and
early Pliocene savannas provided them with an essential refuge
from dangerous animals.
There were, as we’ll see in the next chapter, no less
than six kinds of big cat in late-Pliocene Africa, as well
as four or five kinds of hyena, ranging from the lion-sized
Pachycrocuta to the cheetah-like Chasmaporthetes.
Some of those carnivores probably killed hominids for food
on a fairly regular basis. Modern-day Leopards are, Jean Dorst
and Pierre Dandelot’s Field Guide tells us,
“...particularly partial to monkeys and baboons.”
That predilection for primates almost certainly extended to
australopithecines. “There is abundant evidence,”
Bob Brain wrote, “...that predation by large cats such
as leopards and sabre tooths was an important factor contributing
to accumulation of hominid remains as fossils at Swartkrans.”
The increases in both size and technological proficiency
which humans have undergone in the last two million years
have made them less desirable prey, but leopards still kill
humans for food occasionally in both Africa and Asia. Walking
through Berg-en-Dal rest camp in the south-western end of
the Kruger Park in April of 2004, I noticed a memorial stone
with fresh flowers on it which read
In memory of our beloved son and brother
Charles Aldridge Swart 18/8/73 - 21/8/98, student ranger
at Berg-en-Dal who was killed on duty by a leopard...
I learned subsequently that the animal had attacked Swart
in a completely unprovoked way, and that it had eaten part
of his body after killing him. Since Swart’s death,
two other people, a ten-year-old son of a park employee and
a fifty-eight year old woman who worked at Skukuza, were killed
in similar circumstances by leopards in the Kruger Park.
Jim Corbett, who became famous for hunting down man-eating
tigers and leopards in India in the early Twentieth Century,
defended India’s big cats by arguing that man-eating
is an “unnatural” activity for them, indulged
in mainly by injured or old animals who can no longer hunt
their normal prey. I suspect, however, that man-eating only
seems abnormal in our time, because we’ve dramatically
lessened the numbers of big cats, and because, under normal
circumstances, we protect ourselves so effectively against
the remaining ones. Cats are intelligent animals who are well
aware of the power that humans usually have at their disposal.
Lions have never attacked the tourists who participate in
the Kruger Park’s organized “bush walks,”
even though they’ve been encountering those participants,
together with their armed escorts, on a regular basis for
decades. Lions regularly encounter unarmed Park employees
traveling on foot, and have not, at least in the last few
decades, killed such people either.
In the early 1990s, however, when refugees from war and famine
in Mozambique were crossing into South Africa through Kruger’s
wilderness, lions quickly realized that those particular humans
weren’t part of the defense and retaliatory network
which protect the other humans in the area. Those unarmed
refugees were, for one thing, spending the night in the veld.
As a result, the cats killed and ate what was, from our species’
point of view, a horrifyingly large number of them.
On August 7, 2005, the BBC reported that well over 500 people
had been killed by lions in Tanzania since 1990. Reports of
relatively large numbers of humans being killed by lions have
also come out of Ethiopia recently, and it’s highly
likely that similar things are happening in other parts of
Africa outside the view of the media. I’d be willing
to bet, too, that the lions who are doing this killing aren’t
predominantly old or injured animals. For well over 99% of
their evolutionary history, lions and leopards preyed on hominids
in an entirely “natural” way. Our instinctual
fears still reflect that state of affairs – our children
get warnings (via the same kind of genetically-encoded messages
that tell them to be careful of spiders, scorpions and snakes)
that scary monsters can materialize out of the darkness.
Predators like big cats and giant hyenas weren’t the
only mammals that posed a threat to the australopithecines.
The pig and baboon species which competed with early hominids
for savanna foods would almost certainly have come into conflict
with them from time to time. Initially, at any rate, those
conflicts would have been one-sided affairs. The overwhelming
size-advantage which the biggest kinds of pigs and baboons
had in the Pliocene, together with the formidable tusks of
the former and fangs of the latter, would have given them
the ability to shred an australopithecine in short order.
* * *
Probably because the ability to climb into a tree in a quick
and agile way was an important defense against these formidable
predators and competitors, the australopithecines were much
better adapted to tree-climbing than modern humans are. The
long, curved finger- and toe-bones of Lucy’s species,
Australopithecus afarensis, as well as its long,
ape-like forearms and short legs, speak of a need to climb
trees that persisted long after hominids started walking upright
some six or seven million years ago. That conclusion is bolstered
by evidence which suggests that both afarensis and
the still-unnamed, 4.2 million-year-old “little foot,”
from South Africa may have had opposable big toes. That would
have enabled their feet to grasp branches, rather
than just stand on them like ours do.
As I see it, the smallness of the australopithecines
was among the most important of their tree-climbing adaptations.
Gorillas aren’t good tree-climbers, despite the fact
that their grasping feet and hands are so well-suited to that
task. That’s so because they weigh, on average, almost
two-and-a-half times as much as humans do. Gorillas can climb
trees, but they do so, as Jean Dorst and Pierre Dandalot’s
Field Guide to the Larger Mammals of Africa tells
us, “with great caution.” Young gorillas do so
far more easily than adults, while chimpanzees, who weigh,
on average, about seventy percent as much as humans do, “climb
trees with consummate agility, and may occasionally jump to
a nearby or lower tree...” Size is, therefore, of critical
importance in the business of getting into trees and moving
around in them efficiently.
Leopards, which weigh between 110 and 180 lb., commonly protect
themselves and their kills by climbing into trees which aren’t
accessible to 360-450 lb. lions. Lions can and do make their
way into relatively easy-to-climb trees, but the simple fact
that they’re so much bigger than leopards, means that
there’s a wide range of trees which are not accessible
to them, but which are accessible to leopards –
even leopards hauling 70 lb. gazelle-carcasses up with them.
This “selective accessibility” of trees is a
result of what we could call the “length-to-volume ratio.”
A four-foot-high cube is two thirds as high as a six-foot-high
cube, but its volume is only 29.6296% of its six-foot counterpart.
The mathematics of cubic volume works the same way for humans:
a four-foot-tall human boy is two-thirds as tall as a six-foot
man, but the boy’s volume is just under a third of that
of the six-footer. Growth tables confirm that four-foot tall
American boys (who reach that height at just over seven years
of age) have a median weight of around 52lb – just less
than a third of the weight of an average six-foot man. It
is not, therefore, only their liking for play and adventure
which make children better tree-climbers than adults –
a child who’s fully two-thirds as tall as a given adult,
only has to haul about one-third of that adult’s weight
up into a tree. An australopithecine who was 80% as tall as
an average modern human, would only have had to haul about
half of such a human’s weight up a tree.
If the ability to climb trees in a quick and agile way was,
in short, important to the survival of the australopithecines,
it makes sense that natural selection would have kept their
size within the chimpanzee range.
It’s easy to imagine a hominid climbing a tree to escape
from large, angry pig, but it seems absurd to think of a member
of the human family doing so to seek refuge from a baboon.
If the hominid in question only weighed around 70 lb., however,
and baboon was as big as a present-day gorilla, then the logic
of the length-to-volume ratio tells us that tree-climbing
could have been an effective, and sometimes, indeed, easy
avenue of escape for the former. 70 lb. hominids could, in
fact, have escaped from 140 lb. leopards on occasion by climbing
quickly enough into the right kind of tree.
The proximity of trees would, therefore, have provided our
Pliocene ancestors with a more-or-less dependable refuge from
a long list of predators and competitors. We can imagine australopithecines
keeping a cautious eye out for climbable trees, therefore,
as they walked across those heavily-wooded Pliocene savannas.
Personal experience informs me that hominids still do this
when they’re walking unarmed in bushveld inhabited by
megaherbivores and big cats.
* * *
Walking across the veld during the day would have posed a
moderate level of risk to the australopithecines, but sleeping
on the ground at night – the prime hunting-time of many
of the big predators – would have been suicidal. (Raymond
Dart named one of their variants Australopithecus prometheus,
but it’s highly unlikely, as we saw in the previous
chapter, that any of the australopithecines had the power
to keep or make fire.) Seeking refuge in the rocky hills or
“koppies” which dot the plains of eastern and
southern Africa would have been a better option than sleeping
on the open veld, but baboons also like to sleep on koppies.
It seems likely, therefore, that at least some of the australopithecines
might have constructed the kind of “nests” or
“platforms” that allow modern-day chimpanzees
to sleep in trees at night.
Australopithecines would also have climbed trees to get at
fruit like the figs, sour plums, Strychnos “oranges”
and merula “apricots” which are still abundant
on the savanna at certain times of the year. But, even though
the heavily-forested Pliocene savannas must have produced
a bigger variety of fruits than their more arid, present-day
counterparts, fruit does not seem to have been the main source
of food for the australopithecines. They seem to have specialized,
instead, in finding and eating relatively hard, dry, fibrous
grassland foods like seeds, nuts, roots, corms, tubers and
bulbs. This is, at any rate, the conclusion which most people
draw from the fact that the molar teeth of the australopithecines
were broader than those of apes, and covered, in addition,
with a thicker layer of enamel. Apes, who live on fruits and
other soft forest-foods like shoots, vines and leaves, don’t
require heavy-duty molars of that kind.
Why would hominids have specialized in hard “grassland
foods” rather than fruits? They were, I suspect, obliged
to do so, because the fruit niche was already occupied by
their closest relatives, chimpanzees-to-be, and other apes.
Apes are regarded as somewhat pathetic creatures nowadays
– animals which urgently require protection against
our species. In the earlier stages of hominid development,
however, they would probably have been formidable competitors
in the business of living on forest food like fruits, shoots
and leaves. Developing a way of eating and living that lay,
for the most part, outside that niche, probably created
our identity as hominids, and allowed us to maintain it in
the face of our anthropoid relatives.
As the writing of this book is being completed in 2006, the
six-to-seven-million-year-old Sahelanthropus tchadensis
appears to be the oldest hominid species yet discovered. One
of several indications that Sahelanthropus is, in
fact, probably a hominid, is the fact that its molar teeth
are slightly broader than those of contemporary chimpanzees,
and covered, in addition, with slightly thicker enamel. By
four million years ago, the molars of Australopithecus
anamensis – a possible ancestor of A. afarensis
– are already considerably broader than those
of apes, and covered with much thicker enamel. It
seems likely, therefore, that hard, dry, and fibrous foods
– savanna foods – may have been part of the hominid
diet from the start.
* * *
We’ll probably never know how many species of australopithecine
there were, because populations which may, as Alan Walker
pointed out, have looked and lived very
different from each other as living beings, could have had
a very similar bone structure. Depending on who’s doing
the counting, there are, for instance, sixteen to eighteen
species of long-tailed or “guenon” monkeys in
Africa. Dramatic differences in fur and skin color –
especially facial patterning – make it easy to tell
most of those species apart, but many of them would, as Walker
has pointed out, probably be indistinguishable on the basis
of skeletal remains.
Even in the cases where there were skeletal differences between
different kinds of australopithecines, recognizing them in
the fossilized fragments at our disposal can be a very subjective
matter. Raymond Dart thought, for instance, that the australopithecines
found at South Africa’s Makapansgat site, which he named
A. prometheus, were distinct enough from the
A. africanus found at Taung and Sterkfontein to be placed
in a different species. The scientific world hasn’t
recognized the former species, but Phillip Tobias’ analysis
of the relevant specimens has brought him to the conclusion
that Dart’s distinction a valid one. In Tobias’
view, the Makapansgat australopithecines show affinities with
A. afarensis, whose remains have hitherto only been
found near the Horn of Africa, thousands of miles to the north.
Australopithecus afarensis was discovered in 1971
when a team led by Don Johansen and Maurice Taieb found a
large number of hominid bones in the Hadar region of Ethiopia,
including the partial skeleton of a three-foot tall individual
that has become known as “Lucy.” As far we can
presently tell, afarensis existed from 3.8 to just under 3
million years ago. (It probably co-existed, therefore, at
least for a short while, with africanus, which seems
to have existed from about 2.8 to 2.3 million years ago.)
In 1996 a team lead by Michel Brunet named a new species
called Australopithecus bahrelghazali on the basis
of a 3.3 to 3 million-year-old jaw fragment that they’d
found in Chad. Then, in 2001, Meave Leakey – Richard
Leakey’s wife – described a 3.5-million-year-old
hominid which she and her colleagues regarded as being distinct
from afarensis. They assigned their find (which they’d
excavated near the western shore of Lake Turkana) to a genus
of its own, calling it Kenyanthropus platyops (Kenya-human
with a flat face).
In 1999 Leakey and her co-workers had described an older-than-afarensis
species on the basis of fragmented remains found at both Allia
Bay on the eastern shore of Lake Turkana and at Kanapoi on
the lake’s western side. Named Australopithecus
anamensis, it dates from between 4.2 to 3.9 million years
ago. A partial tibia which includes part of the knee-joint
(and is very similar to tibias assigned to afarensis),
indicates clearly that anamensis walked upright.
Other features of its anatomy show, however, that it is a
more ape-like species than afarenis. Its teeth are
arranged in the U-shaped arch typical of apes, for instance,
rather than in the open parabola which characterizes later
hominids. Its molars and premolars are, however, broad and
thickly-enameled in enough to provide adequate confirmation
of their owners’ hominid status. Anamensis
might (as Leakey herself has speculated) have been ancestral
to afarensis.
Also in 1999, the uniquely complete skeleton of a still-unnamed
contemporary of anamensis was pieced together in
South Africa. The piecing-together process began when the
British-South African paleontologist Ron Clark found hominid
foot bones in a museum storage box labeled “cercopithecids.”
Following his suggestion to examine the wall of the Sterkfontein
grotto at the place from which the stored remains had originally
dynamited, Clark’s associates Steven Motsumi and Nkume
Molefe managed to identify the location of the rest of the
skeleton. This hominid, nicknamed “little foot,”
has been determined by the cosmogenic burial dating technique
to be 4.17 million years old.
In 1994, Tim White and his colleagues discovered 4.4 million-year-old
fragments of several apparent hominids in Ethiopia’s
Middle Awash district. On the basis of those fragments, they
described a species called Ardipithecus ramidus.
Searching at a nearby location in 1997, Yohannes Haile-Selassie,
a member of Tim White’s team, found the first in a series
of remains of a still-older species which was named Ardipithecus
kedabba. If Ardipithecus is in fact a hominid,
the discovery of kedabba pushed the history of our
family over the 5.3-million-year-ago boundary between the
Pliocene and the Miocene.
Ardipithecus kedabba seems to have been a very ape-like
species. The breadth of its molars, and the thickness of their
enamel coating places are reported to be intermediate between
the living apes and Australopithecus. A single toe-bone,
a few hundred thousand years younger than the other remains
ascribed to this species, resembles that of a bipedal hominid
rather than that of an ape. (the toe-bones of clearly-bipedal
hominids like africanus and afarensis are
much thicker and more robust than those of apes.) Was this
very ape-like but apparently bipedal creature the last common
ancestor (“LCA”) of all the hominids? Its discoverers
obviously thought it might be: “Ardi” means “ground”
or “floor” in the local Afar language; “ramid”
means root, while “kedabba” means “basal
ancestor.”
In 2000, however, Brigitte Senut and Brian Pickford announced
the discovery in Western Kenya of a six-million-year-old hominid
which they named Orrorin tugenensis. This name also
implies a claim to the LCA position – “orrorin”
means “original man” in the Tugen language spoken
in the area where the finds were made. It may also have been
intended to evoke the French word aurore –
“dawn.” Senut and Pickford claim that there’s
clear evidence that Orrorin was bipedal, and that
the enamel on its molars is thicker than that of Ardipithecus.
The history of the earliest australopithecines was made even
more complicated and fascinating in June of 2002 with the
announcement that a 6-7 million-year-old primate with hominid
characteristics had been discovered more than a thousand miles
west of the Rift Valley in west-central Chad by a team lead
by Michel Brunet (the discoverer of Australopithecus bahrelghazali
which we talked about a few paragraphs ago). The discovery
of this enormously ancient species – the Sahelanthropus
tchadensis we talked about in connection with the diet
and tooth structure of the earliest hominids – has cast
serious doubt on the idea that hominid evolution was, in Yves
Coppens’ words, an “east side story” –
i.e. one whose action was restricted to the eastern side of
Africa.
Sahelanthropus’ foramen magnum is reported
to be somewhat shifted to the front, but there are no other
indications at the time of this writing that it was bipedal.
If we haven’t actually reached the time when hominids
were quadrupedal with the discovery of Sahelanthropus,
we must be close to it. Are we certain that there was a time
when hominids were quadrupedal? The answer is “nearly.”
It’s just possible that the chimp-human branch of primates
had become bipedal before humans-to-be separated
from chimps-to-be. If we assume this, however, we must also
assume that chimps later re-evolved their quadrupedal way
of walking. It’s a more economical and therefore more
likely assumption that hominids first split off from
the chimpanzee branch, and then became bipedal.
* * *
The word “australopithecine” doesn’t denote
a formal biological category like a genus or a sub-family.
As I use it in this book, it’s an informal designation,
rather, for hominids whose small size, short legs and long,
ape-like forearms made them more-or-less similar to Dart’s
Australopithecus africanus. Up to about 1.8 million
years ago, when larger, differently-proportioned hominids
start to appear on the scene, all members of the human family
could, according to this definition, be regarded as “australopithecines.”
As the fossil evidence at our disposal already suggests,
it’s likely that the australopithecines branched out,
relatively soon after they split off from the chimpanzee group,
into several different species, and that the hominid bush
kept on sending out new branches. Like many other mammalian
groups, the australopithecines seem to have traveled through
time in a cluster of species. Hartebeests, the grass-eating
antelopes whose remains are sometimes found in association
with those of hominids, exist in that kind of cluster. At
its center are the “true” hartebeests: Coke’s
hartebeest, Liechenstein’s hartebeest, Swayne’s
hartebeest, Jackson’s hartebeest, the tora hartebeest
and the red hartebeest. On its outer margins, are “near-hartebeests”:
Hunter’s antelope, the topi-tsessebe group, and the
blesboks.
The “true hartebeests” are very similar to each
other. Except for Liechenstein’s hartebeest which lives
in forested grassland, they are all open-savanna animals.
One of the reasons hartebeests seem to have radiated into
different species, is the simple fact that they are spread
right across Africa. The fact that Australopithecines were
also widely distributed through Africa, and that the wooded
savannas they occupied have been separated and fragmented
repeatedly by the wet-dry glacial cycles we'll speak about
in Chapter 23 of this book, probably means that they, too,
would have split into separate species or variants.
After about three million years ago – around at the
time, therefore, that Australopithecus afarensis
was fading from the scene and Australopithecus africanus
was making its first appearance – the australopithecine
cluster seems to have diverged into “gracile”
and “robust” groups.
The “robusts” evolved massively-built skulls,
designed to anchor big muscles that powered outsize jaws and
molar teeth. Those skulls were widened by enormous, protruding
cheekbones, and topped (in the males) with “saggital
crests” – ridges that run across the top of the
skull in the same position that a rooster wears its comb.
The possessors of this heavy-duty chewing apparatus do not,
however, seem to have had larger or more robust bodies than
those of the graciles. Some anthropologists place the robusts
in the genus Australopithecus, while others consider
them to be different enough to merit their own genus, which
they would call Paranthropus.
The graciles had what we would regard as normal-sized cheekbones.
Saggital crests were either reduced or absent among them.
Their skulls were thinner, and their jaws and teeth, smaller.
Still bigger than those of later humans, the cheek-teeth of
the graciles were smaller than those of the robusts. The powerful
chewing-apparatus of the robusts suggest that they were eating
a coarser, more fibrous diet than that of the graciles. The
graciles themselves ate what modern humans would consider
to be a forbiddingly high-fiber diet, but it’s thought
that they had started processing their food outside their
mouths to a greater degree than the robusts, cutting, scraping
and/or mashing it, perhaps, with crude tools before eating
it. We know that Dart was over-eager to identify horns and
bits of broken bone as australopithecine tools. Is it possible,
however that Australopithecus africanus and/or one
or more of its contemporaries did in fact use tools of one
kind or another to obtain and/or process their food? And could
they, more specifically, have fashioned stone tools for those
purposes? For years there was a gap between the latest australopithecans
to be found, (A. africanus, which made its last appearance
around 2.3 million years ago) and the earliest stone tools
(found in a 1.8-million-year-old layer at Olduvai in Northern
Tanzania.)
Stone tools of a relatively simple kind (cutting-flakes chipped
off apple-sized “core stones”) had been turning
up in that 1.8-million-year-old Olduvai layer for decades.
There was no clue, at first, as to the kind (or kinds) of
hominid that had produced them.
Then, in 1960, Jonathan Leakey discovered fragments of a
hominid skull in Olduvai’s 1.8-million-year-old, tool-bearing
layer. This skull, catalogued as OH 7, was found, after reconstruction,
to have a capacity of 650 c.c. (vs. the approximately 500
c.c. which typical of Australopithecus africanus). The
walls of OH 7’s skull were also somewhat thinner than
those of africanus, and its teeth, marginally smaller. A robust
australopithecine, named Zinjanthropus (now regarded
as Paranthropus) boisei, and been discovered
by Mary Leakey in a contemporaneous or near-contemporaneous
layer at Olduvai, a year before. Louis Leakey assumed, however,
that the species represented by OH 7, rather than Zinjanthropus,
was the maker of the tools which had been found elsewhere
in the 1.8 million-year-old layer. Because the tools in that
layer were, in 1960, the oldest ones yet discovered, and it
was further assumed that OH 7’s species had been the
first one to make stone tools.
On the strength of the latter assumption, Raymond Dart suggested
to Louis Leakey that OH 7 be called Homo habilis.
“The specific name,” Leakey, Tobias and Napier
explained in their announcement of the new species, “is
taken from the Latin meaning ‘able, handy, mentally
skillful, vigorous.’” Placing OH 7 in the genus
Homo was the daring kind of move that appealed to
iconoclasts like Dart and Leakey. It provoked what Richard
Leakey describes, in his Origins of Humankind, as
“a storm of objections.” Some scientists are still
urging that the species named on the basis of OH 7 should
be referred to Australopithecus habilis. A subsequent
find which included a substantial amount of “post cranial”
material, the so-called “dik-dik hominid” (OH
62) unearthed at Olduvai in 1986, confirmed that habilis
was, in fact, typically australopithecine as regards both
size and body proportions.
Leakey and Dart seem to have reasoned this way in placing
OH 7’s species in the genus Homo: even if the
changes in morphology or body-shape displayed by OH7 were
relatively small ones, the momentous new behavior which this
being seemed to have acquired – making stone tools –
was significant enough to warrant put it in a different genus,
and, moreover, into the human genus. Just as Eugène
Dubois probably wouldn’t have called his 1892 Trinil
find Pithecanthropus erectus if
he didn’t think that it represented the first, or one
of the first, human-related species to walk upright, Leakey
and Dart probably wouldn’t have named OH 7’s species
Homo habilis if they didn’t
think it was among the first of the hominid species to manufacture
stone tools.
That assumption has, however, begun to look like an unlikely
one. In the years following the discovery of OH 7, stone tools
fully three-quarters of a million years older than the 1.8
million year old Oldovai implements have been found at a number
of different sites in Northern Kenya and Ethiopia. (Although
the oldest of these newly-discovered tools date back to between
2.5 and 2.6 million years ago, all the Pliocene tools are
broadly similar to the 1.8 million year old tools found at
Olduvai, and are classified with them as products of the “Oldowan
Industrial Complex.)
The oldest fossil to be identified with Homo habilis
is a 2.3-million-year-old upper jaw from Hadar in Ethiopia.
Two other fragmentary finds – one from Sterkfontein
in South Africa (Sts 19), the other from a 2.4 million-year-old
layer at Chemeron in Kenya – lend credence to the idea
that habilis could have been around at the time when the 2.5
million-year-old tools were being made. Even if that were
so, however, habilis would not have been the only hominid
in existence at this time: Australopithecus africanus was
still in existence until about 2.3 million years ago, as was
the “robust” species Paranthropus aethiopicus.
In the April 23, 1999 edition of Nature, Berhane
Asfaw, Tim White and their colleagues announced the discovery
on the Bouri peninsula on the Middle Awash River in Ethiopia,
of yet another hominid living at the time the first tools
show up between 2.5 and 2.6 million years ago, which they
named Australopithecus garhi.
* * *
Because the two partial skulls attributed to garhi
display several points of similarity with A. afarenis,
Asfaw et al. concluded that garhi “is descended
from Australopithecus afarensis, and is a candidate
ancestor early Homo.” The word “garhi”
means “surprise” in the Afar language, and the
new hominid lives up to that name in several different ways.
To begin with, it has a very small cranial capacity for such
a late-appearing australopithecine: only about 450 c.c. Secondly,
its cheek teeth – especially its premolars – are
wide enough to blur the distinction between gracile and robust
australopithecines. If garhi’s cheek-teeth
are unexpectedly big, however, its canines are startlingly
so – bigger, in fact, than those of any other hominid.
Like the robusts, (and like afarensis) it had a saggital
crest to anchor some of the big muscles that powered those
teeth.
Post-cranial or “below the skull” bones (including
partial skeletons) were found elsewhere at Bouri, in the same
level as the skull or “cranial” material. If we
assume that those post-cranial remains represent the same
species as the partial crania, then garhi has a further
set of surprising features. In apes and australopithecines
the bones of the upper arms and the thighs are approximately
the same length. In hominids with “modern” body-proportions
however, such as Homo erectus and H. sapiens,
the femurs or thigh-bones are significantly longer than the
humeruses or upper-arm bones. Garhi’s thigh-bones
are modern in this respect, i.e. long in comparison with the
bones of its upper arms, but that “advanced” characteristic
stands in sharp contrast with “primitive” forearms
which are as long as those of a chimpanzee – or a typical
australopithecine.
* * *
Also in the Bouri area, and at the same 2.5-2.6 million-year-old
geological horizon in which Asfaw and his associates found
these hominid remains, the late Jean de Heinzelin capped a
long and productive career as a geologist and archeologist,
as part of a team who found the left lower jaw of a medium-sized
“alcelaphine” antelope, i.e. a member of the grass-eating
wildebeest/ hartebeest family. This alcelaphine jaw had been
modified in a remarkable way: on its “posteriomedial”
surface, i.e. on the back end of the inside of that jaw, are
three successive, curved scratch/cut marks, unmistakably made
by a stone tool. The position and direction of those “curvilinear
striations” tells us that they were probably made in
the process of removing the animal’s tongue. In the
same level at which this cutmarked jaw was found, and about
200 yards away, de Heinzelin’s team discovered a section
of a large bovid’s tibia which bears both cut- and chop
marks. Meat had clearly been sliced off that tibia before
it was smashed to extract its marrow.
Further excavation at this locality resulted in the discovery
of the fairly intact femur of a Hipparion or three-toed horse,
bearing marks showing that it had been disarticulated (i.e.
cut loose from the bones to which it had been connected),
and defleshed by a stone tool.
Interestingly enough, no stone tools were found in direct
association with any of these cutmarked bones, or with any
of the hominid remains. Stone tools were picked up at Bouri
at places where the layer containing the hominid remains and
the butchered bones had eroded to the surface, but only in
rare instances, involving one implement at a time. At Gona,
however, about 60 miles from Bouri, stone tools were made
and discarded in great abundance. This is so because Gona,
unlike Bouri, has a plentiful supply of fine-grained stone
suitable for tool-making. The material used to make the stone
tools used to butcher the antelopes and the three-toed horse
at Bouri, was brought, in fact, from Gona.
The only thing we can deduce for sure from these Bouri and
Gona finds on the Middle Awash River, is that hominids of
some kind were making and using stone tools 2.5 million
years ago. De Heinzelin and his colleagues were careful to
point out that it is merely likely, but by no means certain,
that the hominid identified by Asfaw, White et al as
garhi was that maker.
* * *
Under the loose definition I’ve been using for this
discussion – “little hominids” – all
members of the human family living before 2 million years
ago were australopithecines. At or near the Pliocene-Pleistocene
border, however, about 1.6 million years ago, a tall, long-limbed
hominid similar to, or identical with, the Pithecanthropus
erectus that Rene Dubois found next to the Solo river
in Java shows up in the Turkana region of Northern Kenya,
and at Swartkrans in South Africa. This new species –
which I’ll refer to as Homo erectus although
some anthropologists regard its African form as a separate
species which they call Homo ergaster – wasn’t
just a larger version of the australopithecines. Erectus’
arms had become proportionately shorter than those of the
australopithecines, its legs considerably longer, and its
shoulders, wider. The external appearance of its body was
now, in fact, very similar to that of Homo sapiens.
The only obvious difference between it and sapiens
lay in the shape of their heads: the capacity of erectus’
brain had only increased to about 850 c.c. – about halfway,
therefore, between the 500 c.c. australopithecine capacity
and the 1,375 c.c. of Homo sapiens.
Erectus is often presumed to a descendant of
habilis, probably because the cranial capacity of specimens
attributed to the latter taxon exceeds that of other australopithecines.
It’s not impossible, however, that more than one of
the australopithecine species might have been converging on
a larger-brained form toward the end of the Pliocene. The
long femurs attributed to A. garhi raise the possibility
that that species might have been on or near the line that
lead to the tall new hominid. We know very little about the
“bush” of hominid species which existed at the
start of the Pleistocene. Our attempts to classify the famous
KNM-ER 1470 skull illustrate this ignorance. This 1.9 million-year-old
cranium minus teeth or lower jaw, was unearthed at Koobi Fora
east of Lake Turkana (formerly Lake Rudolf) by Richard Leakey
in 1972. It had a brain capacity of 775 c.c. – larger,
therefore, than the 650 c.c. of the original find attributed
to Homo habilis, but smaller than the 800 c.c. which
is regarded as the lower limit for Homo erectus.
Leakey didn’t assign 1470 to a particular species,
describing it simply as “an early member of the genus
Homo.” In 1986, a Russian paleontologist, Valerii
Alexeev, labeled it Pithecanthropus rudolfensis.
The Pithecanthropus part didn’t take, but rudolfensis
did. As a result, many people started referring to 1470
(and the handful of other finds which resemble it) as Homo
rudolfensis. Recently, Maeve Leakey and her co-workers
pointed out what they see as striking similarities between
1470 and Kenyanthropus platyops, the 3.5-million-year-old
contemporary of Australopithecus afarensis we talked
about earlier in this chapter. They suggest, on the strength
of those similarities, that 1470 be re-assigned to the genus
Kenyanthropus.
It would be entertaining if Maeve Leakey’s suggestion
were adopted, and if it were shown, thereafter, that modern
humans are descended from Kenyanthropus rudolfensis rather
than from Homo habilis. How, one wonders, would paleontologists
re-arrange the taxonomic scheme to avoid having to call our
species Kenyanthropus sapiens? The possibility that
1470 is close to the line of human ancestry is not, moreover,
a remote one. According to Ralph Holloway, an anthropologist
at Columbia University, 1470’s skull is the earliest
found to date, whose interior surface contains a concavity
corresponding to Broca’s area – a brain region
which contributes to the ability of modern humans to speak.
Holloway’s analysis of this skull also revealed a noticeable
degree of “brain lateralization.” “Strong
brain lateralization” is a uniquely human characteristic.
It’s a state of affairs in which one of the hemispheres
of the brain – usually, but not always, the left one
– is significantly bigger than the other.
Strong lateralization is associated with the development
of the brain’s so-called “language areas.”
Broca’s area – the one that is thought to have
left its imprint on the inside of 1470’s skull –
was discovered in the 1860s. The French physician and anatomist
Pierre Paul Broca (1824-1880) performed an autopsy on the
brain of a man nicknamed “Tan” or “Tan-tan.”
This patient had been suffering from what Broca termed “aphemia”
and what we now call “aphasia,” – the inability
to communicate by using speech – and couldn’t
say anything but “tan.” The autopsy showed that
Tan’s aphasia was associated with a syphilitic lesion
of the hindmost, lower end of the frontal lobe of the brain’s
left hemisphere. Subsequent investigations by Broca confirmed
that disruption of this particular area by accident or disease
interferes with the ability to speak. Then, in 1874, Carl
Wernicke (1848 -1904) discovered that lesions of an area on
the posterior, upper section of the temporal lobe in the same
hemisphere also produce aphasia. Broca’s and Wernicke’s
aphasias present differently: when people suffering from the
former are able to speak, they do so in a halting, ungrammatical
way, but they are able to make sense – and they can
understand language. Those suffering from Wernicke’s
aphasia are unable, on the other hand, to understand what
is being said to them, and – even though they are often
able to utter words and phrases quite freely – their
speech makes no sense.
Broca’s and Wernicke’s areas appear, therefore,
to play different but complementary roles in the business
of producing and understanding speech. Connected by a thick
bundle of neurons called the “arcuate fasciculus,”
they are among the principal “islands” in an “archipelago”
of language-related areas scattered across the cortex of the
brain’s larger hemisphere (which is, as we’ve
seen, usually the left one). Parts of the right hemisphere
also make contributions to linguistic communication: prosody
– the rhythms, intonations and “melodies”
which add meaning to our speech – is composed and interpreted
there. The great majority of the brain’s language-related
functions are, however, performed in the “archipelago”
which includes Broca’s and Wernicke’s areas. That
archipelago constitutes a physically large system,
and this is at least part of the reason why the hemisphere
that contains it is significantly bigger than the other one.
The inside of 1470’s skull provides, as we’ve
seen, the first direct evidence of human-like lateralization,
but there’s convincing indirect evidence that
brain lateralization may already have been present at an even
earlier stage of hominid evolution. That evidence concerns
“handedness,” i.e. the preference for using one
hand over the other.
Like humans, apes prefer one hand over the other for the
performance of tasks requiring a relatively precise degree
of control. That preference is more-or-less evenly divided,
however, between left and right hands in ape populations.
Right- and left-handedness exist, in other words, in ape species,
but no ape species is dominated (as our species is) by right-handers
(or, for that matter, by left-handers). This more-or-less
even distribution between left- and right-handedness, is accompanied
by a relatively weak degree of brain lateralization. In our
species, on the other hand, 90% of whose members are right-handed,
the brain is strongly lateralized.
If we could show, therefore, that an early hominid species
consisted mainly of right-handed individuals, we’d have
reason to believe that the brains of that species would already
have approached the “strong lateralization” which
characterizes modern humans. Surprisingly, there is a way
of determining the ratio of right- to left-handers in early
hominid populations. Beginning with the work of Nick Toth,
several investigations have shown that stone flakes belonging
to the Oldowan Industrial Complex were, in the great majority
of cases, struck off their “cores” by right-handed
individuals.
We’re able to assume, therefore, with a fairly high
degree of confidence, that the brains of those Oldowan toolmakers
were already characterized by a degree of lateralization which
approached that of our species. The roots of language could
well extend, therefore, as Raymond Dart believed they did,
into the evolutionary history of the australopithecines.
CHAPTER 10–
Hominids
as meat-eaters
