The Incredible Human Journey (2 page)

As well as looking at the physical remains of our ancestors, palaeoanthropology also draws on the clues left behind – the traces of the material culture of past people, in other words
archaeology
. Palaeolithic archaeologists are, by necessity, experts in recognising and interpreting stone tool types. Some engage in
experimental archaeology, testing out methods of making and using ancient tools and other cultural items. The insights from
such practical work can be profound.

The earth itself contains ‘memories’ of past climate and geography held in sediments and layers of ice. Unlocking these secrets
has armed palaeoanthropologists with powerful tools for reconstructing the human family tree, and for understanding the environments
in which our ancestors lived.
Geologists
now join the fray, as people who understand how landscapes are formed, how sediments are laid down, how caves are made, and
dating experts often come from this field. The study of both fossils and archaeological remains has benefited hugely from
advances in dating techniques, meaning that we can now pin fairly precise ages on clues from the deep past. The study of
climate change in the past is called
palaeoclimatology.

As well as digging for physical remains in the ground, there are clues to our ancestry held in the DNA (deoxyribonucleic acid,
the stuff of life) of everyone alive today.
Geneticists
involved in palaeoanthropology often come from a background of medical genetics – where genes responsible for particular diseases
or conditions are tracked down. But differences in our genes can also be used to reconstruct past histories. An exciting new development is the possibility of obtaining ancient DNA from fossil bones – providing another way of approaching
the species question.

Linguists
have also tried to reconstruct human histories, by looking at language families. However, most linguists feel that languages
cannot be reliably traced back more than 10,000 years, although, as we shall see, there are some interesting insights emerging
from studies combining linguistics with genetics.

In my journey around the world I have visited many communities of indigenous people in different continents. Many of those
I have met have been given different names at different times by outsiders, some of which carry racist or, at the very least,
derogatory overtones. I have always tried to use terms to describe people that they themselves are happy with, which is why,
for example, in the first part of ‘African Origins’, I refer to the people of the Kalahari as ‘Bushmen’, a name they use in
English to refer to themselves. Similarly, people of mixed European and sub-Saharan African ancestry in South Africa refer
to themselves as ‘coloureds’; the Evenki of Siberia call themselves by that name, and the same goes for the Semang and Lanoh
tribes of Malaysia, the Native Americans of Canada and North America, and the Aboriginal Australians.

The Ice Age

This story of ancient human migrations across the world is set almost entirely within the later stages of what geologists
call the Pleistocene period, or the Ice Age. In its entirety, the Pleistocene lasted from 1.8 million years ago to 12,000
years before the present. Although our species appears only in the late Pleistocene, by the end of that period modern humans
had made their way into every continent (except Antarctica). In some chapters we will also dip our toes into the Holocene,
the period that followed the Pleistocene or Ice Age, and in which we’re still living today.

As we look deep into the past, over vast stretches of time, the apparent stability of geography and climate that we perceive
as individuals melts away and we see instead a picture of changing climate, with sea levels and whole ecosystems in flux.
The population expansions and migrations of our ancient ancestors were governed by climate change and its effect on the ancient
environment. Reconstructing past climates, or palaeoclimates, is an exciting field of science that draws on ancient clues
that have been ‘frozen in time’ as well as our understanding of the relationship between the earth and the sun.

The earth’s orbit is not a perfect circle, and so there are times (spanning thousands of years) when the earth is nearer the
sun, and warmer, and other times when it is further away, and consequently colder. These cycles last around 100,000 years.
As well as this, the tilt of the earth’s axis varies, on a 41,000-year cycle, affecting the degree of difference between the
seasons. The earth also wobbles a little around its axis, on a 23,000-year cycle. There are times when the factors affecting tilt and
orbit work together to create exceptional chilliness – a glacial period. At other times, the factors come together to produce
a very warm period, called an interglacial. This theory was developed by the Serbian mathematician Milutin Milankovitch in
the early twentieth century.
⁵
,
⁶

During the 1960s and 1970s, researchers were able to pin down ice ages with increasing levels of accuracy using deep-sea cores,
samples drilled from the seabed. Those cores contain the shells of tiny marine animals, called foraminifera, and the carbonate
in their shells contains different isotopes of oxygen. The two isotopes of relevance here are
¹⁶
O, the lighter, ‘normal’
kind, and
¹⁸
O, a heavier version. Both are present in the ocean, but water that evaporates from the oceans contains more of
the lighter kind. This means that water precipitating from the atmosphere – as rain, hail, snow or sleet – also contains more of the lighter
¹⁶
O than the seas. And it’s
that
water, falling on to land or ice caps, which becomes frozen into large ice sheets during an ice age. That means there’s more
of the heavier
¹⁸
O left behind in the seas, and more of it gets incorporated into those tiny shells, during an ice age.
⁷
So marine cores, which can be dated using uranium series dating and by looking at the way the earth’s magnetic pole has switched
in the past, hold an amazing record of past climate and ice ages.

Formations in limestone caves – in stalagmites, stalactites or flowstone, or in the useful, all-embracing jargon, ‘speleothem’
(from the Greek for cave deposit) – also contain a record of past climate, depending on the proportions of oxygen isotopes
that are present in the water that forms them. At any one time, the ratio of heavy and light oxygen isotopes in that water
depends on global temperatures – and how much water is locked up as ice, as well as on local air temperatures and the amount
of rainfall. While deep-sea cores are useful for looking at global climate, speleothem is very useful for investigating how
climate has varied in a specific locality. Another indicator of past climates is pollen: soil samples containing pollen can
be analysed to show the range of plants that were living in a particular area.

The Pleistocene was a period marked by repeated glaciations and ending with the last ice age. As ice sheets grew and then
shrank back, sea levels would fall and rise. With differences of up to 60 million km
³
in the amount of water locked up as
ice, sea levels fluctuated by up to 140m.
⁷
The oxygen isotopes trapped in deep-sea cores and speleothem can be used to draw up a series of alternating cold and warm
stages called ‘oxygen isotope stages’, often abbreviated to OIS. Just looking at the last 200,000 years, there have been three
major cold periods (corresponding with oxygen isotope stages or OIS 2, 4 and 6) interspersed with four warmer periods (OIS
1, 3, 5 and 7). But the Pleistocene really was one long, cold ice age.
Interglacials account for less than 10 per cent of the time.
⁷

At the moment we’re enjoying a nice, warm interglacial, oxygen isotope stage 1. The last full-glacial period, OIS 2, lasted
from 13,000 to 24,000 years ago. The peak of this most recent cold phase, around 18,000 to 19,000 years ago, is known as the
‘Last Glacial Maximum’ (or ‘LGM’).
OIS 3, from 24,000 to 59,000 years ago, was a bit warmer and more temperate, though still much colder than the present, and
is called an ‘interstadial’. OIS 4, from 59,000 to 74,000 years ago, was another full-glacial period, though nowhere near
as cold as OIS 2.
⁴
,
⁸
OIS 5, the last (sometimes called the ‘Eemian’ or ‘Ipswichian’) interglacial, was a warm, balmy period,
lasting from about 130,000 to 74,000 years ago. Before that, there was another glacial period, OIS 6, starting at about 190,000
years after the preceding interglacial, OIS 7.

This level of detail might seem a bit excessive, but our ancient ancestors were very much at the mercy of the climate (as
we still are today). For instance, there was a population expansion during the wet warmth of OIS 5, and a crash, or ‘bottleneck’,
during the cold dryness of OIS 4. And sea levels fluctuated according to how much water was locked up in ice: during cold,
dry periods, sea levels were significantly lower – by as much as 100m – than during warm, wet periods. Between 13,000 and
74,000 years ago (i.e. during OIS 2–4), the world was a drier, colder place than it is today. Although the map of the world
was generally very similar, there was more land exposed; many of today’s islands would have been joined to the mainland, and
in places where the coast slopes gently the shoreline would have been much further out than it is today. This is of particular significance to archaeologists looking for traces of our ancestors along those ancient coasts – which
are now submerged.

Stone Age Cultures

Archaeologists classify periods differently from geologists, depending on what humans were doing at the time. During the Stone
Age, humans (including
Homo sapiens
and their ancestors) were making stone tools.
This is before metals – copper, tin, iron – were discovered and used. In fact, in the scheme of things, metal-working is a
very recent invention.

The Stone Age is traditionally divided up into the
Palaeolithic
(old stone age – roughly corresponding with the Pleistocene period),
Mesolithic
(middle stone age) and
Neolithic
(new stone age). These stages happened at different times in different places, so it can become quite confusing.
The categories are also based on European prehistory, where much early archaeological work was carried out. But in terms of global archaeology, western Europe is a bit of a backwater, even a cul-de-sac
⁹
and so the terminology that has grown up there is sometimes rather unhelpful when we’re trying to understand what was happening
in the rest of the world. However, the categories at least provide us with a vocabulary and some kind of framework to help us think about the deep past.

Table
showing the relationship between geological periods, oxygen isotope stages and what humans were getting up to at the time.

Each stage is characterised by different styles and ways of making stone tools, but also by differences in the broader lifestyles
of people. Put very simply (really too simply, as we shall see later), the Palaeolithic lifestyle was that of a nomadic hunter-gatherer,
the Mesolithic saw a trend towards settling down, and the Neolithic saw the beginning of settled villages, cities, agriculture,
pottery and organised religion.

Throughout the Palaeolithic, and in the Mesolithic, too, our ancestors were nomadic. They left barely a trace of their passing
– no buildings, and very little in the way of possessions – and those material possessions that they did have were often made
of what we now think of as biodegradable materials, so they have long since disappeared. When we find stone tools, we are
often looking at something that was just a part of a more complex piece of equipment. Sometimes there are hints from polished
areas of the stone tool suggesting how it might have been tied to something. Very rarely are the conditions right for organic
materials – like pieces of wood or animal hide – to be preserved. When you consider the scarcity of the remains, it’s quite
amazing that we
can
find the occasional trace and, from this, reconstruct part of our collective (pre)history.

During the Palaeolithic period, there are changes in the types of stone tools people were making, and the period is divided
up into Lower, Middle and Upper Palaeolithic (or, in Africa, the Early, Middle and Later Stone Age). Stone tools start to
appear in the ground, in what is grandly termed the ‘archaeological record’, around 2.5 million years ago, made by early members
of our own genus,
Homo
. These are crude, pebble tools, and the toolkit or stone tool ‘technology’ is called
Oldowan
after the sites excavated by Mary Leakey in the Olduvai Gorge. These basic tools continued to be made for hundreds of thousands
of years. Our early ancestors were not great innovators! But we have to grant them some skill. In the wild, chimpanzees make
tools out of easily modified materials like sticks or grass stems, and use stones to crack nuts; chimpanzees in captivity
can be taught to
make
stone tools, but their products are still not as good as those Oldowan tools.
¹⁰