Lone Survivors (6 page)

The Neanderthals are advanced humans and thus share features with both
heidelbergensis
and with us. Yet there are also some retained primitive traits and those that betoken a separate evolutionary pathway. They have an elongated superior pubic ramus like
erectus
and
heidelbergensis
; rounder femora like
erectus
and
heidelbergensis
; a large brain volume like ours; a high and arched temporal bone like ours; reduced interorbital breadth; reduced total facial projection; a lightly built tympanic; in many Neanderthals, simplification and shrinkage of tooth crowns as in
sapiens
; weak or absent iliac pillar.

Then there are the features that seem to distinguish the Neanderthals as an evolutionary lineage. Some of these are concerned with a distinctive body shape, rib cage, and limb proportions, but the clearest ones are on the skull: a double-arched brow ridge with central sinuses; a double-arched but small occipital torus with a central pit (the suprainiac fossa); a spherical vault shape in rear view; distinctive shape of the semicircular canals of the inner ear (see chapter 3); strong midfacial projection and cheekbones that are inflated and retreat at the sides; a high, wide, and projecting nose; large and nearly circular orbits; a high but relatively narrow face; and enlarged front teeth (incisors), which are hollowed (shoveled) on the inside surfaces of the upper centrals.

(
Clockwise from top left
) Skulls of
erectus
(Sangiran, Java),
heidelbergensis
(Broken Hill, Zambia),
sapiens
(Indonesia), and
neanderthalensis
(La Ferrassie, France).

The feature that stands out (literally) in these comparisons of modern and archaic species is the strong brow ridge of the latter, and its absence in the former. The anatomist Hermann Schaaffhausen, one of the first describers of the original Neanderthal skull, called its strong brows “a most remarkable peculiarity,” and although there have been many scientific hypotheses to explain their presence or absence, none really convince me. The fact that many of the huge brow ridges in fossils are hollowed inside, with large sinuses (air spaces), suggests that they are not there to bear or transmit physical forces from blows to the head or heavy chewing. The eccentric anthropologist Grover Krantz even strapped on a replica brow ridge from a
Homo erectus
skull for six months to investigate its possible benefits, finding that it shaded his eyes from the sun, kept his long hair from his eyes when he was running, and also scared people out of their wits on dark nights. For me, that last clue might be significant, and like the paleontologist Björn Kurtén I think it may even have had a signaling effect in ancient humans, accentuating aggressive stares, especially in men. Thus its large size could have been sexually selected through the generations, a bit like antlers in deer. But if that is so, why don't we have large brows like our predecessors? Well, I think the rest of this book will show that modern humans have developed so many other ways to impress each other, from weapons to bling, that perhaps the selective benefits of large brows wore off in the last 200,000 years.

(
Clockwise from top left
) Side view of skulls of
erectus
(Sangiran, Java),
heidelbergensis
(Broken Hill, Zambia),
sapiens
(Indonesia), and
neanderthalensis
(La Ferrassie, France).

If there were, in fact, different human species in the past, could they have interbred? In my view, RAO has never precluded interbreeding between modern and archaic people during the dispersal phase of modern humans from Africa. This is undoubtedly one of the main areas of confusion in studies of modern human origins: how to recognize species in the fossil record, and what this signifies. Some researchers argue that many distinct morphological groups in the fossil record warrant specific recognition, with the existence of at least ten such species of the genus
Homo
during the last 2 million years (that is,
Homo ergaster, erectus, georgicus, antecessor, heidelbergensis, rhodesiensis, helmei, floresiensis, neanderthalensis, sapiens
).

At the other extreme, some multiregionalists argue that only one species warrants recognition over that period:
Homo sapiens
. An additional complication is that different species concepts may become confused; for example, some multiregionalists have applied what is called the
Biological Species Concept
(
BSC
) to the fossil record to justify their belief that
H. neanderthalensis
and
H. sapiens
must have belonged to the same species and would have been fully interfertile. This concept, developed from the study of living organisms, argues that a species consists of the largest community of a group of plants or animals that breeds among itself, but not with any other community. Thus it is “reproductively isolated” with reference to other species, but its own varieties can interbreed with each other. Living
Homo sapiens
would be a good example of this, since people from all over the world are potentially able to mate and have fertile children, but we are apparently reproductively quite distinct from our ape cousins. I say “apparently” because there are persistent rumors that in the 1940s and 1950s scientists in the United States and/or the Soviet Union conducted unethical experiments impregnating female chimpanzees with human sperm—the results of which, so the rumors go, have been suppressed.

And what if we could still meet a Neanderthal—could modern humans interbreed with one? First this brings up the potential conflict between the BSC (which relates to living species) and the completely different concepts that I just used to recognize species in the fossil record, such as the degree of variation in the skeleton. Using the latter measure (a morphological species concept based on what is preserved in the fossil record), I and many other anthropologists recognize the Neanderthals as specifically distinct from
Homo sapiens
. But there is a conflict at the heart of the BSC: the fact that many closely related mammal species can hybridize and may even produce fertile offspring. Examples are wolves and coyotes, bison and cows, chimps and bonobos, and many species of monkey. So we have to recognize that species concepts are humanly produced categories which may or may not always work when compared with the reality of nature. So in my view, even if there was Neanderthal-modern hybridization (and I will discuss that thorny question in chapter 7), it would not necessarily mean that Neanderthals belonged to the same species as us—it would depend on the scale and impact of the interbreeding.

Fossils—the relics of ancient species—sparked my interest in the distant past when I began collecting them as a boy, and they still fascinate me. But on their own they are just mineralized and inert bones and teeth. In the next two chapters I will show how a range of exciting new techniques are helping us return these inanimate fossils to their ancient environments and bring them back to life.

2

Unlocking the Past

Just down the corridor from my room at the museum, locked in their own special cabinet, are some of the most notorious relics in the story of human evolution, mentioned already in chapter 1—Piltdown Man. They were found and announced, to an unsuspecting world, about a hundred years ago, and they provide a sobering reminder to all scientists to beware of something that seems too good to be true—because it may well not be true! British paleoanthropologists of the time had seen German, Dutch, and French scientists discover fossils of possible ancient ancestors, but Britain had nothing to compare with these. Moreover some of these British experts were, as we have seen, supporters of the view that our species had a deep and separate evolution from people like Java Man and Neanderthal Man. Imagine their delight, then, when a “missing link” was apparently discovered in their own backyard, in the county of Sussex. It seemed to have an apelike jawbone and a very human braincase, and these were combined to make the ape-man called “
Eoanthropus dawsoni
.” Of course we now know that its “ape” jaw and “human” skull were exactly that—two completely different and relatively recent specimens maliciously combined to create a misleading transitional fossil. But the hoaxer or hoaxers were knowledgeable enough to not just rely on anatomy to fool the experts—they knew enough about how fossils were dated in 1912 to also misuse that knowledge, to make a case that the Piltdown assemblage of bones and stone tools were as ancient as the remains of Java Man. They were able to get away with it because none of the physical dating techniques that I will discuss in this chapter (such as radiocarbon dating) were known a hundred years ago, and, instead, human fossils could really only be
relatively
dated—that is, dated in relation to the material found alongside them. The hoaxer(s) planted genuine fossils of primitive mammals from other sites alongside the remains of Piltdown Man, so they would look suitably ancient. In 1953 the whole sorry story began to unfold, and when radiocarbon dating was finally applied to show the ape and human remains were both less than a thousand years old, it was the ultimate nail in Piltdown Man's coffin!

So, in this chapter, I will show how new dating techniques have revolutionized our view of human evolution in each of the main regions and time periods in which they have been applied, and I will use a variety of examples to look at the way the records of past climates and environments are influencing the story of our evolutionary origins. We now think that Neanderthals and modern humans evolved along parallel paths, the former lineage north of the Mediterranean and the latter south of it, in Africa. After several false starts, modern humans finally emerged from Africa and spread along Asian coastlines toward China and Australia. But Europe, perhaps the last bastion of the Neanderthals, seems to have remained beyond modern reach until about 45,000 years ago. We have only recently dated some of the most important human fossils, work that has revolutionized the time scale of our evolution. Fascinating new environmental and archaeological evidence also shows the complexity of the process of our evolution, and of the extinction of our close relatives the Neanderthals.

There are two main categories of dating:
relative
and
physical
(that is, based on the laws of physics, sometimes also called
radiometric
or
absolute
)
dating
. The first relates an object or layer to another object or layer in time; one may be younger than the other, or (within the limits of the method) they may be about the same age. The geologic law of superposition supposes that, unless there has been major disturbance, a layer in a geologic sequence is always younger than the layer below it; this is the main principle at work in relative dating. More rarely, a geologic event such as a tsunami or a volcanic eruption can be traced across a region, and fossils or artifacts associated with that event can be assumed to be contemporary with it, and thus with each other. But such relative dating cannot tell us how old the materials in question actually are; it can only place them in relation to each other—that is, show they are relatively older, younger, or correlated (similar) in age. Thus if I dug in my garden and found Roman pottery that looked similar to pottery found at, say, Fishbourne Roman Palace in Sussex, I could assume that my finds were about the same age as those at Fishbourne; but without independent evidence of how old Fishbourne Palace was, or the pottery was, that would be as far as I could go. I could get more detailed relative dating by, say, researching the age of Roman coins found at Fishbourne, or I could attempt a physical determination by asking a specialist in luminescence dating (see discussion later in this chapter) to use physical signals within the clay of my pottery to tell me how long ago it had been fired.