CHAPTER I
THE QUEEN’S ORANG-UTAN
In 1842 Queen Victoria went to London Zoo. She was
less than amused: ‘The Orang Outang is too wonderful . . . he is
frightfully, and painfully, and disagreeably human.’ The animal was
not a male but a female called Jenny and Charles Darwin had, some
years earlier, visited its mother. He too spotted the resemblance
between the apes on either side of the bars. The young biologist
scribbled in his notebook that ‘Man in his arrogance thinks himself
a great work. More humble and I believe true to consider him
created from animals.’ Seventeen years after Victoria’s visit, in
1859, he published the theory that proved the Queen’s kinship, and
his own, to Jenny, to every inmate of the Zoological Gardens and to
all the inhabitants of the Earth.
The Origin of Species caused uproar among
the Empress of India’s subjects. Her Chancellor, Benjamin Disraeli,
asked famously: ‘Is man an ape or an angel? My Lord, I am on the
side of the angels. I repudiate with indignation and abhorrence
these new fangled theories.’ Many of his fellow citizens agreed.
Even so, the notion at once entered public discourse (and
Punch devoted its 1861 Christmas annual to gorilla-like
humans and their opposites). In time, and with some reluctance, the
notion that every Briton, high or low, shared descent with the rest
of the world was accepted. A quarter of a century on, W. S. Gilbert
penned the deathless line that ‘Darwinian man, though well behaved,
at best is only a monkey shaved’ and the idea of Homo
sapiens as a depilated ape became part of popular culture,
where it belongs. Victoria herself congratulated one of her
daughters, the crown princess of Prussia, for turning to The
Origin: ‘How many interesting, difficult books you read. It
would and will please beloved Papa.’
As the Queen had noticed, the physical similarity
of men to apes is clear. In 1859, Charles Darwin came up with the
reason why. A certain caution was needed to promote the idea that
what had made animals had also produced men and women, and he
waited for twelve years before he expanded on the subject. The
Descent of Man describes how - and why - Homo sapiens
shares its nature with other primates. The book uses our own
species as an exemplar of evolution.
To the founder of modern biology, man obeyed the
same evolutionary rules as all his kin and shared much of his
physical being with them; as the book says, in its final paragraph,
he still bears ‘the indelible stamp of his lowly origin’. In moral
terms Homo sapiens was something more: ‘. . . of all the
differences between man and the lower animals, the moral sense or
conscience is by far the most important. This sense . . . is summed
up in that short but imperious word “ought,” so full of high
significance. It is the most noble of all the attributes of man,
leading him without a moment’s hesitation to risk his life for that
of a fellow-creature.’ No ape understands the meaning of ‘ought’, a
word pregnant with notions quite alien to every species apart from
one. Even so, despite that essential and uniquely human attribute,
every ape - and we are among them - is, like every other creature,
the product of a common biological mechanism.
The logic of evolution is simple. There exists,
within all plants and animals, variation passed from one generation
to the next. More individuals are born than can live or breed. As a
result, there develops a struggle to stay alive and to find a mate.
In that battle, those who bear certain variants prevail over others
less well endowed. Such inherited differences in the ability to
transmit genes - natural selection, as Darwin called it - mean that
the advantageous forms become more common as the generations
succeed each other. In time, as new versions accumulate, a lineage
may change so much that it can no longer exchange genes with those
that were once its kin. A new species is born.
Natural selection is a factory that makes almost
impossible things. It manufactures what seems like design with no
need for a designer. Evolution builds complicated organs like the
eye, the ear or the elbow by piecing together favoured variants as
they arise. Almost as an afterthought, it generates new forms of
life.
Its tale as told in The Origin of Species
turns on the efforts of farmers as they develop new breeds from
old, on changes in wild creatures exposed to the rigours of nature
and the demands of the opposite sex, on the tendency of isolated
places to evolve unique forms, and on the silent words of the
fossils that tell of a planet as it was before evolution moved on.
Its pages speak of the embryo as a key to the past and of how
structures no longer of value and others that appear almost too
perfect are each testimony of the power of natural selection. The
geography of life, on islands, continents and mountains, is also
evidence of the common descent of mushrooms, mice and men. Most of
all, life’s diversity can be arranged into a series of groups
arranged within groups, of ever-decreasing affinity, as a strong
hint that they split apart from each other longer and longer
ago.
The Descent of Man uses that logic to
disentangle the history of a single species. Unique as it might
think itself, Homo sapiens is animal like all others. The
book’s famous last sentence reads, in full: ‘I have given the
evidence to the best of my ability: and we must acknowledge, as it
seems to me, that man with all his noble qualities, with sympathy
which feels for the most debased, with benevolence which extends
not only to other men but to the humblest living creature, with his
god-like intellect which has penetrated into the movements and
constitution of the solar system - with all these exalted powers -
Man still bears in his bodily frame the indelible stamp of his
lowly origin.’
In 1871 - and even in 1971 - the evidence for that
final and provocative statement was weak indeed. Now, everything
has changed. The entire evolutionary case can be made in terms of
ourselves and our relatives; of apes and monkeys, of chimps and
gorillas, and of men and women. Our new ability to look at genes,
cells, tissues and organs in exquisite detail means that we know
more about the human past than about that of any other species.
Evolution is best viewed through our own eyes; and not just because
we are all interested in where we came from but because advances in
science mean that Homo sapiens has become the embodiment of
every evolutionary idea. Darwin’s theory has not altered much in
the century and a half since it was proposed. The technology used
to study it has, on the other hand, been transformed.
Technical as they have become, the tools used today
to examine the past would have been familiar in their nature, if
not in their details, to biologists of the nineteenth century.
Charles Darwin was, among his many talents, a proficient anatomist.
He used changes in the physical structure of pigeons, pigs and
people as evidence for his theory. The first chapter of The
Descent of Man is a somewhat ponderous account of the
differences between the bones and bodies of men and apes.
Dissection, once at the centre of biology (and biologists of a
certain age still flinch at the smell of formalin), not long ago
appeared antiquated, but now it looks very modern. Molecular
biology is no more than comparative anatomy plus a mountain of
cash. Its chemical scalpels cut up creatures into thousands of
millions of individual letters of DNA code. Those who wield them
have shown beyond all doubt the truth behind Queen Victoria’s fear
that the bodily frame of Jenny the orang-utan was proof of the
common ancestry of humans with apes and with far more.
The Human Genome Project - the scheme to read off
our own DNA sequence - set the seal on an enterprise which began in
the sixteenth century when Vesalius opened the heart and discovered
that it had four chambers rather than the three insisted on by the
Greeks. Its completion was announced in 2000 and again in 2003,
2006 and 2008 (and some parts of the double helix still remain
unread). A science that had been in its infancy a mere description
of bones and muscles became an adolescent when The Origin of
Species showed how shared structure was evidence of common
descent. It has at last matured. The anatomy of DNA has become the
key to the history of life.
In a glass-fronted cabinet at University College
London resides the stuffed body of the eighteenth-century
philosopher Jeremy Bentham, the ‘greatest good for the greatest
number’ man. His Auto-Icon, as he called it, was an attempt at a
memorial that would cost less than the showy shrines then
fashionable. Bentham was convinced that his idea would catch on.
Two centuries later, it did. James Watson - the surviving half of
the duo who unwound the double helix - was presented with his own
auto-icon, a compact disc of his entire DNA sequence, which he can,
if he wishes, display for public edification in a small plastic
case.
Watson’s essence is coded into a tangled mass of
intricate chemistry. The egg that made him contained two metres of
DNA and each of the billions of cells that descend from it as his
body grows and ages has a copy. Each of those molecular sentences
is written in three thousand two hundred million letters, the four
bases of the familiar genetic code. Twenty years ago, when the
scheme to read the whole lot off was proposed, it took months to
decipher the number of letters found in this paragraph. The
molecule was sliced into random bits, each was read from end to end
and the whole genome stitched together with a search for places
where the fragments overlap. Such methods are antique. Today’s
machines pick up flashes of light from molecules tagged with
fluorescent dyes, each base with its own colour, and squeezed one
at a time through tiny pores. It takes no more than a few hours to
read off a piece as long as this entire book, which itself contains
less than one part in several thousand of the whole content of the
human genome. Soon it will become possible to sequence single
molecules rather than multiple copies, as is now necessary, and
enthusiasts speak of machines that will read off a million DNA
bases a second.
The first human sequence cost up to a billion
dollars and Watson’s version was auctioned off for a million. In
2008 the Knome Corporation offered to read off the DNA of anybody
with a spare $350,000. In fact, the whole lot can now be done for a
fraction of that sum. Within five years the price will drop to a
few thousand dollars per genome and it will become possible to
decipher the DNA of any creature at nominal cost. The web of
kinship that binds life together will then be revealed in all its
details.
The raw material of evolution is, in its physical
structure as an intertwined helix, simple or even elegant, but in
its biology is entirely the opposite. In its details DNA is,
frankly, a mess, for natural selection has been forced to build
upon what it already has. Life did not emerge from engineering, but
from expedience. The Darwinian machine has no strategy and can
never look forward. Its tactics are based on the moment, and the
genomes it makes, like the creatures they code for, are the
products of a set of short-term fixes. James Watson’s molecule is
marked by redundancy, decay and the scars of battles long gone.
Genes - like cells, guts and brains - work, but only just.
Human DNA contains long stretches that appear to be
useless and numerous sections that are mirror-images of each other.
Repetition is everywhere: of particular genes into families that
carry out similar tasks and of multiplied lengths of material that
seems redundant. The remnants of viruses make up almost half the
total and the remainder is littered by the decayed hulks of ancient
and once functional structures. All but one part in fifty of the
genome was, as a result, once (mistakenly) dismissed as biological
garbage.
The genes themselves have become blurred and
ambiguous as we learn more. There are far fewer than expected when
the genome project was proposed - just over twenty thousand rather
than the multitude then assumed to be essential. Some overlap with
each other or say different things when read in opposite directions
or when active in different tissues. Many contain inserted
sequences of DNA that looks as if they have no function (although
some of the supposed junk does a useful job while other sections
cause disease should they wake up and shift position). Plenty of
questions remain. How important is the part - often a small part -
of each gene that codes for proteins compared with the on and off
switches, the accelerators and brakes, and the rest of the control
machinery? We do not know.
Even the size of the package makes little sense. A
chicken has slightly less DNA than does a Nobel laureate but half
its genes are identical, or almost so, to our own - evidence, given
that we last shared an ancestor three hundred million years ago, of
how conservative evolution can be. A tiny plant called
Arabidopsis, a relative of the Brussels sprout, has more
genes than either. All this says more about how hard it can be to
define what a gene actually is than about the talents of sprout
versus sentient being.
Eight decades passed between Vesalius’ dissection
of the heart and the discovery of the circulation of the blood. The
genome is now in that transitional period. DNA’s nuts and bolts
(and even some of its bells and whistles) have been dismantled, but
most of those who work on it still study structure without much
insight into function. William Harvey (the circulation man) saw the
heart as a mere pump, and understood nothing of its exquisite
system of control. Genes are much the same. Each is linked into a
network with others and responds to messages from both within and
outside the cell. The path from instruction to product is a
labyrinth, rather than a straight line. The proteins that pour from
the cell’s biological factories are not simple blocks that slot
together but are folded, spliced, cut, or fused into new mixtures
in a way that depends on local conditions almost as much as upon
their own structure. Diseases as different as diabetes and prostate
cancer may arise from damage in the same segment of DNA, while
others such as breast cancer emerge from errors in several
different genes. Most of the double helix is switched off the
majority of the time, African genes are, on average, more active
than are those of Europeans and life has begun to look far more
complicated than any molecular biologist had feared.
Evolutionists are not in the least surprised. They
were baffled at some of the decisions made by those who ran the
Genome Project. Like Vesalius, James Watson and his colleagues had
a Platonic view of existence. Every heart and every human was built
on the same plan and to understand one was to understand them all.
The first DNA sequencers outPlato-ed Plato for they assumed not
just that the essence of humankind could be found within a single
person, but that this Mr Average was, in the interests of political
correctness, best stitched together from bits of double helix taken
from random donors across the globe.
That was a big mistake. The Platonic approach
ignores the vital truth that evolution is a comparative science.
Natural selection depends on inherited differences. To understand
the past biology needs not just a single genome but many. To map
variation from person to person, from place to place, or from
species to species shows how, when and where evolution has been at
work. So central is diversity to the idea of descent with
modification that the first two chapters of The Origin are
devoted to the nature and extent of variability in the bodies and
habits of plants and animals. Now, genetics has begun to tell the
tale in the language of DNA.
James Watson’s auto-icon disclosed no more than
half his secrets for it contained just one of the two versions of
the double helix present in each cell. His rival in the race to
decipher the secrets of life, the biologist and businessman Craig
Venter, was less reticent. He read off both his copies, that
received from his father and that from his mother. Venter was happy
to reveal its contents: his father died young of a heart attack,
and he has himself been bequeathed a variant that predisposes to
the disease. He has also inherited genes supposed to increase the
wish to seek novelty, to be active in the evening rather than early
in the day and to have wet rather than dry ear wax.
Whatever Venter’s intimate chemistry says about his
personality, his bed-time or the exudations of his auditory canal,
it has a message for us all for it gave the first hint of the true
level of human diversity. Both his parents are white Europeans (and
hence represent just a small sample of mankind) but their DNA is
distinct at around one site in two hundred along the entire chain -
which adds up to tens of millions of differences between
them.
On the global scale, hundreds of millions of sites
in the inherited alphabet vary from person to person and the
‘Thousand Genomes Project’, now well under way, has set out to fund
out just how many there might be. Unlike its predecessors it will
search out rare variants, those carried by fewer than one person in
a hundred and present in vast abundance - and given the advances of
technology, the project may cost little more than fifty million
dollars. Already we know that each of the twenty-three human
chromosomes - the physical location of the genes - has millions of
single-letter changes aligned along it. The variable sites are so
tightly packed together that, over short lengths of the double
helix, they almost never separate when the molecule is cut, spliced
and reordered, as it always is when sperm or egg is formed. Such
long blocks represent sets of chemical letters that travel down the
generations together. Rather like surnames, they are excellent
clues of relatedness.
In addition to its single-letter changes, the
double helix is marked by duplications of certain pieces and
deletions of others. The order of its letters may also be reversed,
and great stretches can hop to a new place. A study of three
hundred whole genomes has already revealed a thousand and more such
differences in the numbers of particular DNA sequences. Some genes
are arranged in families - groups of similar structures that
descend from a common ancestor and have taken up a series of
related jobs. The biggest has eight hundred members. It helps build
the senses of taste and smell. Its elements vary in number from
person to person and some lucky individuals have fifty more copies
of a certain scent receptor than do others.
Most such changes involve fewer than ten letters,
but some are a million base-pairs from end to end. A few people
may, because of the gains and losses, have millions more DNA bases
and thousands more genes than do others and the potential variation
in dose from person to person represents more than the length of
the largest human chromosome. Even so, some of the repeated
segments have just the same structure in humans as in the
coelacanth, which split apart four hundred million years ago.
DNA is a labile and uncertain molecule. A
multiplied sequence often makes mistakes as egg or sperm are
formed, to produce longer or shorter versions of what went before.
Some bits move or multiply at a rate of one in a hundred each
generation rather than the one in a million once assumed to be
typical. Age changes us and the double helix is reordered,
duplicated and deleted as the years go by (which means that the
offspring of older parents inherit more mutations than do those of
young).
Variability beneath the skin is far more extensive
than Darwin had ever imagined. Biologists have long known that,
with the exception of identical twins, everyone in the world is
distinct from everyone else, and from all those who have ever
lived, or ever will. That claim is too modest. In fact, every sperm
and every egg ever made by all the billions of men and women who
have walked the Earth since our species began is unique; a figure
unimaginable before the days of molecular biology.
Such variety links individuals, families and
peoples into a shared network of descent. It shows how man is
related to chimpanzees, gorillas, orangs and macaques, and for that
matter to plants and to bacteria. Evolution - like astronomy - has
always looked at the past through the eyes of the present but its
new technology - like the star-gazers’ development of giant
telescopes - means that it can now see far further and deeper into
the universe of life than once it could.
Even so, biology is not like astronomy. The images
that flood from its machines are often blurred and ambivalent. Many
statements about ancestry are filled with unproven, and often
unstated, assumptions about the rate of change in DNA, the size of
ancient populations and the effect - or supposed lack of effect -
of mutations on the well-being of those who bear them. The
information in the genome is almost limitless, but at present its
language remains ambiguous.
Fortunately, the Earth has some better witnesses to
years gone by. Like the remnants of stellar rocks that sometimes
strike our planet, they are silent, shattered and few in number but
at least they give direct evidence of how the past unfolded. Darwin
was well aware of the importance of the fossil record to his case.
One page in six of The Origin is devoted to the relics of
the rocks, to the record’s imperfections and to the central role it
plays as proof of the fact of change. In 1871, no human fossils
(with the exception of a skull from Germany now known to come from
a Neanderthal) had been recognised. Things have much improved and
the primate record is far more complete than it was even a few
decades ago. The tale it tells is still fragmented and uncertain,
but what it says fits remarkably well with the history revealed by
the double helix.
In the Miocene epoch - from around twenty-three
million to five million years ago - the Earth was a true Planet of
the Apes. Primates were all over the place, with a hundred or more
distinct species of ape, in Africa, in Asia and in Europe. They
lived in woodlands, plains, forests and swamps. Some were no bigger
than a cat and others larger than a gorilla. For much of the time
their capital was in Europe and many of our predecessors have laid
their bones there. Then the animals moved on, to set up shop in
Africa. A ten-million-year-old fossil from Kenya may be the common
ancestor of men, chimps and gorillas. If so, it confirms Darwin’s
speculation that it was more probable ‘that our early progenitors
lived on the African continent than elsewhere’. He did not, of
course, know that continents had broken up and drifted across the
world, and that Africa itself did not exist in the earliest days of
the evolution of our line.
One day almost all the players in that ancient
drama left the stage. The apogee of the apes was over and their
long twilight - now fast turning into night - had begun. The sun
began to set on their family well before humans appeared, but, once
they did, their nemesis was assured.
Lucy, the famous fossil of Australopithecus
afarensis, was a creature quite human in appearance, lightly
built and little more than a metre tall, with relatively long legs
and small teeth. She belonged to a group who lived between three
and four million years before the present. Others among her kin
left footprints in Tanzanian volcanic ash as proof that they walked
upright at a time when their brains were but a third the size of
our own. The males were considerably larger than the females.
Homo habilis - ‘handy man’ - lived in South and East Africa
for about a million years from two and a half million years ago. It
had long arms, brow ridges and a larger brain than Lucy, and was
quite good at making tools. Similar individuals were found in
Africa, and perhaps in Georgia.
Homo erectus¸ the upright human, the next
fossil claimed as a direct (or almost direct) human ancestor,
emerged around 1.8 million years ago, and may have split into two
species in its homelands in Africa and Asia. Some individuals had
brains as large as our own and lived as far north as the South of
France. A rather younger European arrived around 1.2 million years
before the present, and left a few of his bones in the caves of the
Sierra de Atapuerca in northern Spain. That ancient Spaniard has
been christened Homo antecessor, and might be the common
ancestor of ourselves and the Neanderthals. A later European from
around half a million years ago, Heidelberg Man, may have been an
antecedent of the Neanderthals rather than ourselves. He too first
appeared in Africa. Many - perhaps too many - more supposed members
of our close family have been named as distinct species, and the
human pedigree has begun to look more like a bush than a tree. As a
result, direct lines of descent have become harder to trace than
once they were.
For most of history, our ancestors shared their
home with several related species that were much closer to
themselves than the chimpanzee is to us. Those days have gone, and
nearly all members of man’s ancient household have left no issue
today.
The Neanderthals were once our most immediate kin.
They lived in Europe and the Middle East from around a quarter of a
million years ago to about thirty thousand. They had bigger skulls
- and, perhaps, bigger brains - than modern humans (although they
were also beefier in general). They trapped animals in pits, and
may have been cannibals (although another view of the carved bones
of their fellows is that they represent a ritual burial).
Neanderthals lived in small groups in an icy Europe for far longer
than our own species has existed, and then disappeared. Like many
other apes, they went quickly. Perhaps a cold snap defeated them,
for a remnant hung on in the warmth of southern Spain until well
after the moderns arrived. The victors had better clothes, which
allowed the tropical ape that they were - and we are - to survive
in a climate that killed off an animal more used to bad weather but
less well clad. Perhaps Homo sapiens murdered the
Neanderthals or starved them out, but we do not know. Sex was not
on the agenda, for fossil DNA from a Croatian specimen shows that
they were quite distinct from our direct ancestors. In addition,
today’s Europeans and Middle Easterners retain no ancient lineages
that might have come from an extinct relative. DNA suggests that
the Neanderthals’ last common ancestor with modern humans lived in
Africa more than six hundred thousand years ago, long before
Homo sapiens emerged.
Soon after the loss of his cousin, that species
began to spread across the world. Modern humans filled the whole
habitable globe no more than a thousand or so years before the
present, when at last men and women reached New Zealand and Hawaii.
Their ancient journeys can still be read in DNA. The double helix
reveals a clear split between Africa and everywhere else, a legacy
of the small group of migrants who first stepped out of our native
continent into an uninhabited world, together with a second and
more ancient split within Africa that separates the Khoi-San - the
Bushmen - from all others. Other great genetic trends, such as
those across the New World and the Pacific, track the last
migrations into a deserted landscape.
Once, it seemed that modern Europe had a more
complicated history than did most of the globe, with several waves
of migration superimposed on each other. The genes of local
hunters, who arrived long ago, were - perhaps - diluted by those of
the first farmers who spread, just a few thousand years before the
present, from a population explosion in the Middle East. Some
variants do show a trend from south-east to north-west, in a
pattern that might indeed reflect a slow wave of inter-communal
sex. The archaeology of pots and seeds suggests in contrast that
agriculture was taken up at some speed, as soon as people learned
about it, with no need for weddings. In Britain, at the western
edge of the new technology, carbon dates taken from charred grains
suggest that around 4000 BC farming replaced hunting within just a
couple of centuries, too fast for any large-scale mixture of
populations. There is no real evidence of a flood of lascivious
rustics coming from the east. Instead, ancient Europe was more open
to ideas than it was to genes. The trends seen today are the
remnants of the first grand migration thirty thousand years before
the emergence of agriculture, as humans arrived in an empty
continent from the south and east. The mitochondrial DNA - the
female lineages - found in the remains of a hunter-gatherer group
in northern Spain look more or less the same as those of modern
Spaniards in the same place, with no sign of mass immigration.
Modern Europeans trace most of their heritage to the first wave of
hunters. Since then, they - and their DNA - have tended to stay at
home.
As men and women filled the world they killed off
many of their kin. The Neanderthals were the first to go, and human
habits have not changed since then. Today, just a few remnants of
our once extensive clan linger on. In a century or so we will be
the single large primate (and almost the only large mammal), to be
found outside farms or zoos. Almost all the apes will be gone, some
before they are studied by science. That fact is a tragedy both for
the creatures involved and for science itself, for each of them
says something about our own biological heritage. They contain
within their DNA the story of human evolution and, perhaps, more:
for some of our own inborn diseases are caused by genes identical
to some that function perfectly well in our relatives.
The physical similarity of primates and humans was
noticed by Queen Victoria and, after The Origin, was often
used by those anxious to judge the evolutionary status of their
fellow men. Charles Kingsley, author of The Water Babies,
wrote to his wife about an Irish visit that ‘I am haunted by the
human chimpanzees I saw . . . to see white chimpanzees is dreadful;
if they were black, one would not feel it so much.’ Chimpanzees
are, indeed, our closest relative. Darwin himself noted that, among
their many other affinities to humans, they ‘have a strong taste
for tea, coffee, and spirituous liquors: they will also, as I have
myself seen, smoke tobacco with pleasure’.
Whatever our shared vices, chimps are not like us
in many ways. They are hairy and bad-tempered and do not show the
whites of their eyes. The animals have rather small brains, no ear
lobes and cannot walk upright, float, or cry when upset. They give
birth with less pain than we do, and the young mature without any
obvious period of adolescence. Our kidneys keep salt better in the
body than do theirs, and we have more white blood cells.
Chimpanzees are in addition safe from the horrors of old age as
they tend to die young and even in zoos do not get Alzheimer’s
disease. When they are faced with diseases brought on by infection
or poor diet, their symptoms often differ from our own, which means
that they have not been as useful in medical research as might be
hoped.
Chimp sex life has a definite flavour of its own.
Men lack the penile bone found in male chimpanzees, but when it
comes to penis size, man stands alone. Women have outer labia,
absent in their closest relative. Chimpanzee males have larger
testes than we do in relation to their body size and, unlike
ourselves, seal up their mates with a sticky plug after sex.
Promiscuity is the rule. The creatures copulate with enthusiasm and
their close kin the pygmy chimps or bonobos are even more
energetic. The females show when they are fertile (unlike women,
who conceal all signs of that crucial moment) and the males then
indulge in a competitive frenzy to mate with them. Sperm from
rhesus macaques, a species known to be highly promiscuous, swim
faster and lash harder than those of gorillas, in which a single
male more or less monopolises the females. Chimpanzee sperm are
almost as energetic as those of the macaque while ours lag well
behind either. They do, on the other hand, beat the male cells of
the gorilla.
The chimpanzee genome was read off in 2005. Not
many of the single letters in the DNA code have changed since the
split from our own family line for, on that simple measure, humans
and their closest relative are almost 99 per cent the same. At the
protein level, too, we are close, with no more than about one amino
acid in a hundred having altered.
Such figures underrate the real divergence of the
two species. Changes in the number and position of inserted,
repeated or deleted segments mark both lines. There are three times
as many alterations of this kind as of single-base changes, which
puts the overall difference between men and chimps at around 4 per
cent. Primates go in for the gain and loss of genes more than do
other mammals and our own lineage is out in front with a rate of
change three times faster than average. Homo sapiens has
gained seven hundred gene copies since the split with chimps, and
the chimp has lost almost the same number. One chromosome has gone
even further. Women have two large X chromosomes, men an X matched
with a smaller Y. The human and chimp X have diverged by just half
a per cent in the single letters of the DNA alphabet while the Y
has shifted three times more, as proof that women, with two Xs, are
closer to chimpanzees than are men.
Many of the differences between the two primates
have built up because we can modify our environment in a way that
other primates cannot. As a result, we depend less on changes in
our DNA than once we did and so have lost many once-functional
genes. Mankind is feebler than it was. We became shaved monkeys
with just a single mutation or a few because a segment of DNA that
codes for the hair protein no longer works. It received its fatal
blow a quarter of a million years ago. Samson lost his strength
with his locks, and so did his ancestors, for the DNA behind
certain powerful muscles is out of action in humans compared with
their closest living relatives (which is why to wrestle with a
chimpanzee is a mistake). A shared déjeuner sur l’herbe is
also best avoided, for the animals have enzymes that break down
poisons fatal to ourselves. Darwin noted that ‘savages’ ate many
foods that were harmful unless cooked; and red kidney beans still
fall into that category. Chimpanzees need no kitchens, for they can
manage a variety of noxious plants (certain herbs used for medical
treatment included) that we cannot. They have also kept many of the
talents of taste and smell lost in humans, perhaps because they
need to be more careful in their choice of food before they chew
it. Many of our own gustatory sensors live on just as battered
remnants of once-useful structures.
As well as the differences between chimpanzees and
humans, each varies to some degree from place to place. The
chimpanzee is strongly subdivided at the DNA level. It has three
distinct ‘races’, in West, in Central and in Eastern Africa. The
central group is about three times as diverse as is the western.
The extent and pattern of diversity hints that the western and
central groups split half a million years ago, while the eastern
segment found an identity no more than fifty thousand years before
the present. Humans are in comparison tedious, with far less change
among the world’s populations than among the chimp races.
Sequencing machines are now hard at work on more of
our relatives. Rhesus macaques are small monkeys common in India,
Burma and elsewhere in the Far East, and widely used in medical
research. They share rather more than nine-tenths of their DNA with
humans. Many of the shifts involve - as in the chimpanzee - changes
in the order or numbers of copies of particular segments. The
animals eat lots of fruit, and genes that help digest sugar have
been multiplied compared with our own. Some of their genes are in a
form that in humans leads to disaster. The mutation for the rare
inborn disease known as phenylketonuria - a fatal inability to deal
with certain foods - is the standard version found in macaques.
Might some dietary change have rendered lethal to ourselves an
enzyme once useful in our ancestors? A group of genes that
predisposes to cancer in humans helps make sperm in macaques. Why
does a sexual helper in monkeys cause our cells to run out of
control? If we knew, we might have a new weapon against the
disease.
Men and chimps, and men and macaques, have changed
a lot since their paths parted. The fossils and the genes combine
to say when and how their evolutionary divergence, and others from
long before, took place. The daring assumption that DNA accumulates
error at a regular rate, combined with information on dates from
the scattered fossils of our distant ancestors, hints that the
first true mammals evolved around a hundred and twenty-five million
years ago. The double helix also shows that chimps, orangs, humans
and monkeys cluster together in a class that includes lemurs and
rabbits but does not admit horses, dogs, bats and many other hairy
creatures. The kinship of men, lemurs, rabbits and the rest is
revealed by a certain piece of mobile DNA that hops around the
genome. It has been inserted in the same place in all those
creatures, proof that they share a common ancestor distinct from
that of their furry fellows.
Genes, fossils and geography combine to suggest
that the primates as a group began around eighty-five million years
before the present. The monkeys and apes split not long after that
- which means that their true origin was on the vast continent of
Gondwana rather than on the fragments that we now recognise as
Africa, Madagascar and India. The macaque set off on its own
pathway around twenty-five million years before today. The split
between ourselves and our close relatives is, it appears, quite
recent. The limited genetic divergence between chimpanzees and
humans suggests that they separated five to seven million years
ago. Their common ancestor broke away from the gorilla line a
million years or more earlier, and that trio split from the
orang-utan branch about six million years before that.
There is more to evolution than the random
accumulation of mistakes. Darwin’s machine may not have a long-term
direction, but it can swerve around obstacles as they arise. At the
wheel is natural selection: inherited differences in the ability to
pass on genes. In its long and arduous journey, selection’s ability
to cope with whatever turns up has led to the physical differences
between men and chimps, men and macaques and, for that matter, men
and rabbits or bats. Each diverged from the same shared ancestor,
and each has faced its own challenges and, with the help of natural
selection, found its own unique set of solutions.
Not all of us leave descendants, but we all have
ancestors. To transmit its DNA to the present day, each of them had
to survive, find a mate and produce offspring. An infinity of their
contemporaries tripped at one or other of life’s hurdles and left
no posterity. The Descent of Man speculates about how
selection might have acted upon the human line and that of our
relatives but it offered little direct evidence of its action.
Sexual choice was, its author thought, important (and he began but
abandoned a project to discover whether blondes were less likely to
marry than were brunettes) but his case for its role was far weaker
than that for animals and plants presented in The Origin of
Species.
The evidence for lust as an engine of human
evolution is still patchy at best, but that for other forms of
natural selection is now compelling. The process has been - and
still is - at work in our own lineage. It leaves its footprints
upon the genome in many ways, some obvious and some less so.
Sometimes, natural selection can be seen in action. More often, the
evidence of its labours is indirect and gives no hint of how and
why it was busy.
Long-term trends such as the increase in human
brain size over millions of years show what selection can achieve,
given time. The grand patterns of genes across the globe are also
proof of its powers.
None are grander than the shifts in man’s physical
appearance from place to place, which are more marked than those in
any other large mammal. The story of how the trends in human hair
and skin colour evolved has emerged, albeit in several shades of
grey, as evidence of how selection causes change and of how subtle
and unexpected its actions can be.
Homo sapiens and his immediate ancestors
moved not long ago from white to black, and in some places back to
white again. Chimps have rather pale skins, although their faces
may become tanned. African skin is, in contrast, dusky, which means
that darkness is relatively new to the human line. In religious
art, Adam and Eve are always shown as light-skinned. Given the
looks of today’s Middle Easterners that was doubtful at best. The
first modern humans, a hundred thousand years and more ago, were
certainly black.
DNA hints that our new and swarthy appearance arose
about a million years before the present. At just that time, our
ancestors began to move from the forests to the sun-baked
savannahs. Long legs and arms and a distinct nose (not found in
chimps) also emerged, perhaps to cope with life in the sun. In
addition, we lost our hair - perhaps to cool down - and dark skin
was favoured as it protected against the harmful effects of
ultraviolet light. The colour of the skin turns on the amount of a
pigment called melanin.
The first hint about Eve’s complexion came not from
people but fish. The zebrafish is often used to study embryonic
development. A certain mutant lacks the dark stripes that give the
animal its name and is almost transparent. The gene responsible has
been tracked down in both its mutated and its normal version. A
search through our own DNA reveals an almost precise match; so
close, indeed, that the human gene will reinstate a zebrafish’s
stripes when injected into a mutant embryo. The enzyme it makes
shows a large shift in structure across the globe. A certain
building block - an amino acid - is present at one point along the
protein chain in 98 per cent of Africans, while in 99 per cent of
Europeans it is replaced by a different version. The form found in
Africa makes far more pigment than does the alternative. A large
part of the shift in appearance between the inhabitants of the two
continents hence emerges from a change in a single letter of the
genome. The length of DNA involved varies not at all in its
functional section throughout Africa, as a hint that dark skin was
strongly favoured when it first arose and that any later changes
have been removed by selection. Europeans are more diverse, with a
variety of forms of the crucial protein that give rise to black,
blonde or red hair and to dark or to almost translucent skin.
Fossil DNA shows that Neanderthals had their own, different,
mutation in that segment of the genome, so that they too were
probably white.
In a twist to the tale, the light skins of China
and Japan evolved in a different way. The gene that bleached the
Europeans played no part, for the locals bear the African, rather
than the European form. The people of the Far East paled in their
own fashion, and evolution picked up changes in quite a different
set of genes. A certain segment of DNA, when it goes wrong, causes
albinism - a loss of skin pigment - in Europeans. The loss of
melanin from Asian skin comes, in large part, from a mutation in a
different section of that gene. Several other parts of the melanin
factory differ in structure between Africa, Asia and Europe. Most
have small but noticeable effects on colour, which is why the
children of a marriage between an African and a European vary from
dark to light and do not resemble either of their parents
exactly.
The earliest modern Europeans and Asians of forty
or fifty thousand years ago were almost certainly black. Even the
French cave-painters at Lascaux may have had that complexion, for
their images of the aurochs, the giant oxen, are reddish, while
those of the men who hunt them are darker. The first Englishmen -
those who followed the ice as it melted - reached these islands
thirteen thousand years ago. They too may have retained their
African colour when they set foot on their new nation’s
shores.
Why does it pay to be black in Benin but fair in
Folkestone? Everything we know about melanin is positive, while
fair skins seem at first sight to do more harm than good. Melanin
protects against skin cancer - and fifty thousand people develop
that in Britain each year. Two thousand die. Light skin burns
easily. That may sound trivial, but sunburn makes it hard to sweat
and easy to overheat, which brings dangers of its own. In addition,
melanin reduces the destruction of vitamins in the blood as they
are exposed to the harsh rays of the sun. Fair-skinned women who
sunbathe have reduced levels of a vitamin called folic acid, and
their newborn children pay the price, for a shortage of the stuff
causes birth defects. Given the problems of pale skin, something
powerful must have changed us on the journey from the azure
firmament of the tropics to the gloom of British skies.
Another vitamin was to blame. Vitamin D helps build
bones. It controls the levels of calcium and phosphorus in the
blood for it helps the gut to absorb them and rescues quantities of
each element that would otherwise be lost in the urine. Oily fish,
eggs and mushrooms are rich in the stuff and many governments now
add it to milk or flour to promote their citizens’ health. Vitamin
D can, in addition, be made in the skin through the action of
ultraviolet light on a form of cholesterol.
To do the job, the light must get in and melanin
keeps it out. Africans have to spend several hours a day in bright
sunlight to make enough vitamin D to stay healthy, but northern
Europeans who expose their arms, head and shoulders for fifteen
minutes at a midsummer noon can make enough to meet their
needs.
A shortage of the stuff puts children in danger of
the soft-bone disease rickets, which leads to a curved spine or
legs and can cause severe disability. Sufferers may also experience
seizures and spasms - a side-effect of calcium shortage - which can
end in heart failure. Nine out of ten infants in Victoria’s smoky
and starved cities showed signs of the illness and rickets is still
the commonest non-infectious childhood disease in the world.
Most young black people in the United States have
low levels of the crucial vitamin and the condition is, as a
result, three times more common among black Americans than in their
white fellow citizens. As a youth the athlete O. J. Simpson
suffered from rickets and wore home-made leg braces. On this side
of the Atlantic, my own generation was saved by free cod-liver oil,
but the modern world is not so lucky. In Britain, soft bones are
back. A third of Asian and Afro-Caribbean children are short of
vitamin D (for the former the fact that they are not allowed to
uncover themselves is in part to blame). Severe deficiency is nine
times more frequent in that group than in Europeans and one in a
hundred of their children show signs of illness. Girls do worse,
which is bad news later on, for their pelvis narrows and they find
it harder to give birth. There have even been cases of shortage in
affluent white children allowed to play in the sunshine - but
protected from the dangers of ultraviolet with sunscreen.
The magic substance also helps to hold diabetes,
arthritis, muscular dystrophy and heart disease at bay and protects
against the spread of certain cancers, with a higher rate of lung
and bowel cancer in cloudy places. Any change in skin colour that
helped to generate more of the vitamin must have been most helpful
on mankind’s journey into the gloom. Natural selection noticed the
new mutations at once and in cloudy places fair skin soon took
over.
Selection has lead to many other upheavals in
human DNA. Many of them emerged from shifts in our habits as we
moved from ape to early human, and to modern man. Migration, shifts
in diet and the rise of towns and cities all led to genetic
change.
For nine-tenths of our history as a species, most
people saw fewer people in their lifetimes than an average
westerner now does on his way to work. Agriculture led to a
population explosion, and Homo sapiens is now ten thousand
times more abundant than is any other mammal of his size. In a
world of pathogens and parasites, abundance is an expensive luxury.
Epidemics have often cut our species down to size. They need large
populations to sustain themselves, and migrants to spread the
infection. The Plague of Justinian, which began in Constantinople
in AD 541, put paid to a quarter of the people of the Eastern
Mediterranean. The Black Death spread along the Silk Road from
China in the fourteenth century and returned again and again to the
teeming and filthy cities of the west. Two out of three Europeans
died. Sickness is potent fuel for selection and many genes respond
to it.
One illness shows its power better than any other.
A third of the world’s population is exposed to malaria, half a
billion are infected and the disease kills five people a minute.
The real attack began about ten thousand years ago, when men moved
into - and cut down - tropical forests at a time of warm, wet
weather. That helped mosquitoes to breed and the parasite to
spread.
In Kenyan families, poor conditions - a marshy
spot, too much rain, too many children - explain some of the
variation in individual risk of illness, but genetic differences
are behind at least a third of the overall chance of ending up in
hospital. Some variants have a large influence and are soon picked
up by evolution while others are more subtle. The most important
involve changes in the red blood pigment, haemoglobin. A quarter of
a billion people bear at least a single copy of a mutated version
of the molecule. The best known is sickle-cell, a simple change in
the DNA alphabet. The haemoglobin of those with two copies forms
long crystals in parts of the body low in oxygen. The red cells
take up a crescent shape that restricts circulation and causes
pain, heart disease and worse. Those with a single version of the
altered message are healthy, with half the risk of fever if
infected and a ten times lower chance of serious illness. A third
of all Africans are in that situation and the gene is common in
southern Europe, in the Middle East and in India. It has arisen on
at least four different occasions. Other such changes give a lesser
protection in countries such as Bangladesh, while deletions of long
or short sections of DNA do the same in the Middle East and
Oceania. Once again, those who carry two copies of a damaged gene
pay a severe price while people with just one are protected.
Many other genetic changes have been pressed into
service against that unpleasant illness. The parasite uses a
certain red-cell enzyme to fuel its machinery. Hundreds of millions
of people bear a defective version, but in return gain a defence. A
certain form of the parasite cannot get into cells that lack a
particular attachment site. Almost all West Africans have this
variant. Elsewhere, a change in the shape of the red cell baffles
the agent of infection, while the high salt and iron levels in
African blood also fend it off. Dozens of sections of the DNA are
implicated in the fight against malaria and many, no doubt, remain
to be discovered. Large or small, each has been picked up by the
selection, which, just as in the evolution of pale skins in Europe
and Asia, has cobbled together a response step by step.
Natural selection is always poised to deal with
enemies as they arise. Wherever it works, it leaves evidence, often
indirect, that it has passed by. Some changes in DNA alter the
structure of proteins while others do not. The ratio between the
two is a crude test of its actions, for useful sections of the
genome are more likely to accumulate change under the influence of
selection than are the non-functional parts. On that criterion, our
lineage has experienced rather less of its attentions than has that
of the chimpanzee.
Another clue to the action of Darwin’s agent comes
from the blocks of genetic variants packed close to each other
along each chromosome. As a favoured gene - a new anti-malaria
mutation, perhaps, or a change in skin colour - is picked up and
becomes more common, it will drag along sections of DNA on either
side. The stronger and more recent the selection, the longer the
segment that accompanies it. In Africa, both the gene for black
skin colour and that for sickle-cell sit in the middle of great
sections of double helix that vary scarcely at all from person to
person. That pattern hints that in each case the new mutation was
seized upon at once and spread fast.
In time such uniform blocks of DNA are broken up by
the random reshuffling of genes that takes place when sperm and egg
are formed, but the process can take a long time. A length of DNA
that is identical from person to person within the generally
diverse genome is hence evidence that selection is, or has been, at
work. The human and chimp genomes each have thousands of such
segments. One gene in sixty among the chimps bears that Darwinian
mark but only half as many in humans, as proof that we have coped
with new challenges in a manner that our close relative cannot.
Man’s ability to modify the environment to suit his needs has
weakened the hammer blows of nature. Anti-malaria drugs now do what
could be achieved only by expensive mutations. Thousands of years
ago, our skin responded fast to a shift in climate, with a genetic
change; but most people, black or white, now protect themselves
against the sun in quite a different way, with clothes.
The loss of our native nudity was an early hint of
the evolutionary talent that made us unique - the ability to
respond to a challenge not with bodies but with brains. Clothing
allowed us to spread across the world, for with its help we take
the tropics with us wherever we go.
Adam and Eve, in their sultry paradise, were
unashamed, but after the first (and least original) of all sins
they made aprons to hide their nether parts. When did they first
put them on? Lice hint at when garments were invented. Chimps and
gorillas have lots and spend many hours grooming as a result. When
humans emerged on to the sunny savannahs they lost their hair. The
lice had a hard time and evolved to live in the few patches of
habitat left. We now have three kinds, the head and the body louse,
plus the pubic louse. The body louse is the only one that hangs on
to clothing. The pubic version is closest to the lice found on
gorillas and may have joined us from there. DNA shows that the
other two evolved from a chimpanzee parasite which began its
intimate acquaintance with our own bodies six million years ago.
The body and head forms, in contrast, separated more recently -
perhaps no more than fifty thousand years before the present. That
may mark the moment when we first donned our vestments and gave a
resourceful louse a new place to live. Men, their parasites prove,
dressed themselves as they took their first steps towards the icy
north.
Since then we have learned to cope with external
parasites with insecticides, with cold with central heating and
with noxious foods with kitchens. Each talent is a product of the
contents of the skull, which are - like Adam’s underpants - unique.
Darwin noted that ‘There can be no doubt that the difference
between the mind of the lowest man and that of the highest animal
is immense’, and he was right. To understand human evolution we
need to know how and why our brain, the most human of organs, is so
different from that of any other primate and why and how our
behaviour is even more so.
The structure is three times as big, and the
cortex, the thoughtful bit, five times larger than that of the
chimpanzee and the modern skull is several times roomier than that
of three million years ago. Chimps are born with a brain almost as
big as that of an adult animal while babies, whose brains are
already larger than that of a chimpanzee, continue to invest in
grey matter until they are two. Genes active within the human
cranium have multiplied themselves when compared with those in
other primates and one such, which when it goes wrong leads to the
birth of infants with tiny heads, has evolved particularly fast.
The nerves within the human skull are more connected to each other,
and their junctions more sophisticated, than are those of the chimp
and the structure is also busier at the molecular level. Even so,
much of the DNA most active in that part of the body has changed no
more rapidly than that at work in liver, muscle or scrotum.
The brain is expensive, for by weight it uses about
sixteen times more energy than does muscle. That represents a
quarter of the entire budget of the body at rest and means that we
expend twice as much effort on the intellect as do chimpanzees. How
can we afford such a luxurious appendage? Humans eat no more than
other primates of comparable size but have a richer diet, with more
meat and fewer roots and leaves, than do our relatives. As a result
we need smaller intestines to soak it up. We also invest less in
muscle than other apes and the enzymes that burn food are more
efficient than theirs. All this began, like black skin, a million
and more years ago, when people moved from forests to savannahs,
travelled in larger groups and became better hunters with a meatier
diet. The way to man’s brain was through his guts.
Even so, today’s organ of thought is no bigger than
that of the Neanderthals. Fossils of their newborns show that they
were born with a brain as large as our own, which grew even faster
during infancy, but those creatures acted far more like apes than
we do. Something more than an extra dose of grey matter has made us
what we are. To quote Darwin: ‘of all the differences between man
and the lower animals, the moral sense or conscience is by far the
most important’. A glance at our relatives shows how right he
was.
Chimpanzees are nastier than many people like to
think. They kill monkeys and are pretty unpleasant to each other
too. Their sex lives would shock Queen Victoria and their ethical
universe, if they have such a thing, is far darker than our own.
They live in groups, but the groups break and reform as their
members quarrel. Terror makes the world go round. Set up a task in
which two chimps need to pull a rope to get a tray of food. They
will, but only if they are out of reach of each other. Otherwise,
the dominant animal attacks its subordinate even if neither then
gets anything. Anger and greed destroy the hope of reward. What
makes humans different is a loss of fear, odd as that sounds in a
world where that emotion seems to be everywhere. When anxiety goes,
society can emerge.
Our social skills begin early. A group of
two-year-olds asked to find a piece of food after they saw it moved
to a new place or turned to a new position or put in a box with a
beep were pretty good at each job - but no better than adult
chimpanzees, for both babies and chimps succeeded at about two
trials out of three. When it came to the need to learn from others
the babies won hands down. They became far better at each problem
when they saw someone else solve it, or when an adult pointed to or
gazed at where the food was hidden or made noises that told them
they were getting warm. Each response demands an insight into
another’s inner sentiments. We have a lot more of that talent than
do our relatives. The chimps took no notice of those who tried to
help.
Chimpanzees can learn, but do not teach: like all
apes, they ape but do not educate. In some places, adults fish for
insects with a stick or bash nuts with a stone, and the young
emulate them. Even so, the grown-ups make no effort to show the
infants how to do the job, do not change their ways when youngsters
are around and never check to see how well they are doing. Birds,
with their bird brains, can do what a chimp does, for a budgie will
pull out the stopper of a bottle of food if it sees another do the
job, and crows are even smarter.
Real education asks for more. A good pedagogue can
teach almost any subject as long as he keeps a few pages ahead of
his charges and they respond to his efforts. Teachers also have
insight into the mental lives of their pupils, into who understands
the lesson and who does not, and know how to encourage them without
their becoming bored.
The chimp’s negligence about the next generation is
a reminder that the minds of our hairy relatives are not much like
our own. A competent teacher needs to understand what his students
are thinking - and chimps do not: they have no more than a
rudimentary ‘theory of mind’, as psychologists put it. We have
lots, and it helps those on both sides of the lectern. Teenagers
might doubt the fact, but no ape could ever become a
schoolmaster.
The best way of reading a mind is to chat to it.
Thomas Love Peacock invented a character called Sir Oran Haut-Ton,
who learns to play the French horn but not to speak (he is elected
to Parliament, where his silence gives him an air of wisdom).
Homo sapiens is the eloquent ape. Even deaf children left in
groups babble with their hands. Speech is the scaffold upon which
society is built. No other primate can speak and all attempts to
persuade them to do so have failed (Noam Chomsky, the theoretician
of language, noted that it was ‘about as likely that an ape will
prove to have a language ability as there is an island somewhere
with flightless birds waiting for humans to teach them to
fly’).
The origin of language is a cause of endless
dispute which, given that just one creature can speak, may never be
resolved. Darwin thought that perhaps it began with imitation: that
‘some unusually wise ape-like animal should have thought of
imitating the growl of a beast of prey, so as to indicate to his
fellow monkeys the nature of the expected danger’. The Descent
of Man also suggests that it could have started with love
songs, and that speech was in part a side-effect of sexual
selection. Perhaps it was; or perhaps it grew instead from the
simple fact that we are social animals. Apes groom each other
because the constant pacification calms them all down and cuts down
the conflict that is never far from the surface. Big groups demand
too much scratching time but reassuring sounds can placate lots of
individuals at once. The savage breast might first have been
charmed in that way; possibly, indeed, with song - which could be
why some stutterers can sing a sentence when they cannot say
it.
However it began, language makes us what we are.
The ability to speak is coded for on the left side of the brain and
plenty of primates have a brain almost as lopsided as our own. Even
so, chimp tongues fill their mouths while ours are dainty in
comparison. The human tongue has retreated down the throat. The
language of Shakespeare is a complex set of sounds made as the
space above the larynx flexes and bends. The anatomical changes
leave evidence in the shape of the skull. Neanderthals had
chimp-like mouths and could do little more than grunt. The first
skull capable of speech emerged no more than fifty thousand years
ago - not long before the explosion of technology that led to the
modern world.
One British child in twenty has some form of speech
disorder. A certain rare inborn abnormality makes it impossible for
those who inherit it to cope with grammar. Baby mice with the same
damaged gene make fewer squeaks than usual when removed from their
mothers, and people with a version impaired in a different way are
at risk of schizophrenia; of, like Saint Joan, hearing voices that
are not there. The normal version found in humans differs in two of
its amino acids from that in all other primates. It is foolish to
speak of a gene for language but if the transition from animal to
human turned on speech it may have involved rather few molecular
changes. The situation is confused by the discovery that
Neanderthals have the human version of the gene, which must hence
date back to our inarticulate joint ancestor.
Wherever they came from, words are the raw material
of a new kind of genetics, in which information passes through
mouths and ears as well as through eggs and sperm. It moved us on
from our status as a rare East African ape to the most abundant of
all mammals. Ideas, not genes, make us what we are. Our DNA is not
very different from those of our kin, but what we do - or say -
with it has formed our fate.
Even so, the famous ‘indelible stamp’ is without
doubt imprinted into the human frame. Modern biology shows that
chimpanzees are even more like us than Charles Darwin imagined -
but in no more than the most literal way. The strengths and the
limitations of his ideas in deciphering what makes us human have
become ever clearer as knowledge advances. His theory is powerful
indeed but enthusiasts need to be reminded where its power comes to
an end.
In 1926, the Soviet government sent an expedition
to Africa. It was directed by Ilya Ivanovich Ivanov, famous for his
work on the hybridisation of horses and zebras by artificial
insemination. The Politburo hoped to do the same with men and apes,
for the experiment would be ‘a decisive blow to religious
teachings, and may be aptly used in our propaganda and in our
struggle for the liberation of working people from the power of the
Church’. In Guinea, Ivanov obtained sperm from an anonymous African
and inseminated three chimps - but none became pregnant. He then
planned to fertilise women with chimpanzee sperm, but was not
allowed to do so. Back in Russia he set out to do the same with a
male orang-utan and a woman who had written that ‘With my private
life in ruins, I don’t see any sense in my further existence . . .
But when I think that I could do a service for science, I feel
enough courage to contact you. I beg you, don’t refuse me . . . I
ask you to accept me for the experiment.’ The orang, alas, died
before its moment of glory and Ivanov was arrested and exiled to
Kazakhstan, where he, too, met a childless end.
Americans anxious to stop research in human
genetics once attempted to patent the idea of a human-chimp hybrid
in order to whip up protest. The application was denied on the
equivocal grounds that the US constitution does not allow the
ownership of human beings (whether the cross-breed would have that
status was not discussed). Artificial fertilisation of chimpanzee
egg with a man’s sperm may now be feasible (although claims to have
produced a ‘humanzee’ are fraudulent) but is universally seen as
beyond the pale. The problem is not one of biology, but of what it
means to be human. A hybrid between a chimp and Homo sapiens
makes too ready an equation between our apish bodies and our
immortal minds.
Charles Darwin was well aware of the limits of his
own theory. As he points out in the famous last sentence of The
Descent of Man, men and women possess noble qualities, sympathy
for the debased, benevolence to the humblest and an intellect which
penetrates the solar system. All that does not change the fact that
in our bodily frames, most of all when reduced to chemical
fragments, we bear the indestructible mark of our humble
ancestry.
Some people despise his science as a result,
because it appears to destroy man’s special place in nature, but
they fail to understand what evolution is all about. Biology, in
its proof of our kinship with chimpanzees, underlines its
irrelevance to ourselves. The double helix does not diminish
Homo sapiens but sets him apart on a mental and moral peak
of his own. The theory of evolution does not render us less human
than we were before. Instead the insight it provides into man’s
place in nature has made us far more so than we ever realised. A
century and a half after Queen Victoria’s disagreeable visit to
Jenny the orang-utan, I gave a talk at London Zoo which pointed
this out - and most of the apes agreed.