"When on board H.M.S.
Beagle, as naturalist, I was much struck with certain facts in the distribution
of the organic beings inhabiting South America, and in the geological relations
of the present to the past inhabitants of that continent. These facts,
as will be seen in the latter chapters of this volume, seemed to throw
some light on the origin of species - that mystery of mysteries,
as it has been called by one of our greatest philosophers."
- Charles Darwin, "The Origin of Species"
"In North America the
black bear was seen by Hearne swimming for hours with widely open mouth,
thus catching, almost like a whale, insects in the water. As we sometimes
see individuals following habits different from those proper to their species
and to the other species of the same genus, we might expect that such individuals
would occasionally give rise to new species, having anomalous habits, and
with their structure either slightly or considerably modified from that
of their type."
- Charles Darwin, "The Origin of Species"
"But with regard to
the material world, we can at least go so far as this - we can perceive
that events are brought about not by insulated interpositions of Divine
power, exerted in each particular case, but by the establishment of general
- Whewell, "Bridgewater Treatise".
"If a man will begin
in certainties, he shall end in doubts; but if he will be content to begin
with doubts, he shall end with certainties."
- Bacon, "Advancement of Learning"
~ Variation Under Domestication
~ Variation Under Nature
~ The Struggle For Existence
~ Laws Of Variation
~ Difficulties On Theory
~ Imperfection Of The Geological Record
~ Geographical Distribution
~ Mutual Affinities of Organic Beings
~ Interlude : Almost Like A Whale
~ Recapitulation & Conclusion
# AN HISTORICAL SKETCH
"I will here give a
brief sketch of the progress of opinion on the Origin of Species. Until
recently the great majority of naturalists believed that species were immutable
productions, and had been separately created. This view has been
ably maintained by many authors. Some few naturalists, on the other
hand, have believed that species undergo modification, and that the existing
forms of life are the descendants by true generation of pre-existing forms."
- Charles Darwin, "The Origin of Species"
'The Origin of Species' is, without doubt, the book of the millenium.
Milton, some say, was the last man to know everything (or to know enough about most things to discuss them with authority). Darwin was the last biologist who could claim that. Nobody could do that now. So great is today's knowledge that there are no Milton's of biology. To understand evolution involved interests so disparate that it is impossible to embrace them all. That is the joy - and the tragedy - of modern science.
There had been ideas about evolution before Darwin's time, but he was the first to provide not just a mechanism but the proof that it worked.
Every AIDS patient
is a monument to the theory of evolution. Natural selection alters the
identity of the virus as the disease progresses. The human immunodeficiency
virus contains in its brief history the entire argument of 'The Origin
of Species': variation, a struggle for existence, and natural selection
that in time leads to new forms of life.
Much of the story of AIDS is evolution on a human scale. Our lives are too short to understand the evolution of other beings in such detail.
To deny the truth of
evolution on grounds of faith alone debases both science and religion.
The point was made by Galileo himself. Summoned to explain his views and
their conflict with Scripture, he argued that the Church had no choice
but to agree with the discoveries of science. It would, he said, 'be a
terrible detriment for the souls if people found themselves convinced by
proof of something that it was made a sin to believe'. Creationists have
not yet faced that fact.
No biologist can work withut the theory of evolution. Like Galileo's notion of a solar system with the sun at the centre, Darwin's long argument makes sense of their subject.
# VARIATION UNDER DOMESTICATION
"When we compare the
individuals of the same variety or sub-variety of our older cultivated
plants and animals, one of the first points which strikes us is, that they
generally differ more from each other than do the individuals of any one
species or variety in a state of nature. And if we reflect on the
vast diversity of the plants and animals which have been cultivated, and
which have varied during all ages under the most different climates and
treatment, we are driven to conclude that this great variability is due
to our domestic productions having been raised under conditions of life
not so uniform as, and somewhat different from, those to which the parent
species had been exposed under nature."
- Charles Darwin, "The Origin of Species"
Many people turn to 'The Origin' in a search for a philosophy of life. Most are disappointed to find that the first chapter is mainly about pigeons.
Pigeons alone have dozens of breeds. The transformation of what was once a plain and unambiguous bird tells an evoluntionary story. It shows that species are not set in stone, but are always in flux.
Pigeons have been succeeded
in Cockney affections by dogs. The city's dogs are beasts very different
from a timber wolf. All are a product of selection. A dog show is evolution
chalked out for all to behold.
Speechless though they remain, dogs are, because of the evolutionary pressures imposed by their owners, silent witnesses to the malleability of nature.
Dogs, though, retain
a past much older than their alliance with our species. Each is a barely
evolved wolf, a descendant of a dangerous animal. That is part of their
But the dog has disappeared (as a distinct species), victim of evolution. Two centuries after it gained its scientific name (Canis familiaris), the International Commission on Zoological Nomenclature has stripped it of its identity. Their action accepts the transition between breed and species.
Dogs as an entity were doomed because, once out of its owner's sight, any dog is happy to have sex with any other - and even, given the chance, with a wolf. As 'Canis lupus familiaris' it joins the American wolf 'Canis lupus occidentalis' and the European wolf, 'Canis lupus lupus'; each so much alike as to be ranked as mere varieties of the same animal.
A zoological garden bears the unwelcome message that because of man's inadvertent selection, any animal taken from the walk becomes domestic, a travesty of its natural self. Evolution is hard at work on caged animals as on those born free. In time they will emerge as beings quite different from what they were. Those who conserve animals in the hope of returning their descendants to Nature may be disappointed by what they let loose.
Zookeepers suffer from
other kinds of unwanted evolution. As wild animals are hard to breed in
captivity, their guardians tend to choose those best able to cope with
their new circumstances. That means change - toward tameness and, as in
the foxes kept for fur, toward other things as well.
Although the animals' saviours hope to keep wild animals safe, what they may do is evolve new ones.
Evolution on the farm is a small-scale version of that in Nature. Variation under domestication - in fields, in zoos and in living rooms - is still powerful evidence for Darwin's theory.
# VARIATION UNDER NATURE
"It may be doubted
whether sudden and considerable deviations of structure,
such as we occasionally see in our domestic productions, more especially with plants, are ever permanently propagated in a state of nature. Almost every part of every organic being is so beautifully related to its complex conditions of life that it seems as improbable that any part should have been suddenly produced perfect, as that a complex machine should have been
invented by man in a perfect state."
- Charles Darwin, "The Origin of Species"
Species and nations
have a lot in common. What, for example, is a German? The tribe has
a shared and guttural means of communication that interrupts intercourse
of most kinds, but the attribute is equivocal, for Austrians speak the
same language. Since 1913, the country has defined its own citizens by
descent, by German blood (whatever that might be). It includes within
the realm the remnants of the Saxon diaspora (many of whom - Romanians
included - cannot speak German at all) but cuts out children born in Berlin
of Turkish parents.
Until the fall of the Berlin Wall, a geographical barrier made many of the nation's citizens more alien to one another than Westerners or Easterners were to the French or the Poles. A century ago German identity meant little, as there were only Prussians, Bavarians and Rhinelanders, political entities of their own, each now reduced to variants within some greater Teutonic whole. When will Germans be seen as Europeans, as Prussians have become German?
Species can, in the new world of the molecules, no longer be seen as absolutes. They are not units, but groups of individuals, each with a biological personality of its own.
Nobody knows how many
different species there might be, even in a taxonomy based on external
appearance. Molecular varaiation under nature reveals divisions invisible
to the most skilled taxonomist. To journey into the rainforest or garden
will uncover new kinds of being, but to sequence the DNA of those we know
may reveal many more.
Genes ask old questions about species in new ways, often to the discomfiture of those who classify the world.
In 1990, the American Fish and Wildlife Service gave up the anti-Darwinian struggle. It no longer placed hybrids outside the law. The federal government is now reduced to the preservation of 'evolutionary significant units', whatever those might be. The dignity of the law has met the volatility of Nature and has been forced to retreat.
Whatever species may
be (and they are not what governments hope), they are not fixed. Instead,
their boundaries change before our eyes. What is mere variety to some is
granted its own identity by others. Quite often, animals that are similar
on the surface differ in their genes. All this is grist for evolution,
for the transition between variation within a single kind and the origin
of a new one.
The biggest difficulty about species is to decide what they are. The problem is time - to describe in the two dimensions of today something that evolved in three. For classifiers, what matters most is the future. To taxonomy, their essence lies in years to come. Museums assume (and it seems fair) that cats and dogs are separate because there will never be an animal that traces a shared descent from dogs and cats.
# STRUGGLE FOR EXISTENCE
"It has been seen in
the last chapter that among organic beings in a state of nature there is
some individual variability: indeed I am not aware that this has
ever been disputed. It is immaterial for us whether a multitude of
doubtful forms be called species or sub-species or varieties; what rank,
for instance, the two or three hundred doubtful forms of British
plants are entitled to hold, if the existence of any well-marked varieties be admitted. But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life and of one organic being to another being, been perfected?"
"If under changing
conditions of life organic beings present individual differences in almost
every part of their structure, and this cannot be disputed; if there be,
owing to their geometrical rate of increase, a severe struggle for life
at some age, season or year, and this certainly cannot be disputed; then,
considering the infinite complexity of the relations of all organic beings
to each other and to their conditions of life, causing an infinite diversity
in structure, constitution, and habits, to be advantageous to them, it
would be a most extraordinary fact if no variations had ever occurred useful
to each being's own welfare, in the same manner as so many variations have
occurred useful to man. But if variations useful to any organic being
ever do occur, assuredly individuals thus characterised will have the best
chance of being preserved in the struggle for life; and from the strong
principle of inheritance, these will tend to produce offspring similarly
characterised. This principle of
preservation, or the survival of the fittest, I have called natural selection. It leads to the improvement of each creature in relation to its organic and inorganic conditions of life; and consequently, in most cases, to what must be regarded as an advance in organisation. Nevertheless, low and simple forms will long endure if well fitted for their simple
conditions of life."
"Natural selection, on the principle of qualities being inherited at corresponding ages, can modify the egg, seed, or young as easily as the adult. Among many animals sexual selection will have given its aid to ordinary selection by assuring to the most vigorous and best adapted males the greatest number of offspring. Sexual selection will also give characters useful to the males alone in their struggles or rivalry with other males; and these characters will be transmitted to one sex or to both sexes, according to the form of inheritance which prevails."
"As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications."
- Charles Darwin, "The Origin of Species"
The existence of any creature is a constant struggle against relentless forces.
What seems a primeval
forest is in truth an interval between catastrophes. Battle within battle
must be ever recurring with varying success; and yet in the long run the
forces are so nicely balanced that the face of Nature remains uniform for
long periods of time.
The forest is a cathedral, but it often burns down. Lightning strikes the earth 200 million times a year and sparks off innumerable fires. 5000 years ago the jungles of South America were reduced by fire to copses encircled by grassland. Much earlier even Ireland was covered by tropical forest. Its rocks are filled with ancient charcoal, the remnant of a forgotten firestorm.
Much of the struggle
for existence - on land as much as in the sea - is for a share of the sun's
energy. The sunnier a place, the more kinds of animals and plants it contains.
The energy flows upward, but does not go far. Most food chains have four
or five steps from bottom - the plankton in the ocean or grass of an African
savanna - to top, be it lion, eagle or killer whale.
Too many links in the chain leave too little for those at the top. It becomes impossible to add another and to evolve a beast that preys on blue whales, or on lions. Most of the islands of the Outer Hebrides have no eagles as they are not big enough to provide enough food. A bird that ate eagles would need most of Scotland to support itself.
Every plant or animal descends from ancestors tried by a struggle for existence for three and a half billion years before cities come on the scene. Man selects only for his own good. Nature only for that of the being which she tends. The Industrial Revolution was a test of the theory of evolution. Its results were often unexpected, sometimes unwelcome and always unplanned. So familiar is the testimony of natural selection that we do not recognize the best proof of its power: the fit of life to where it lives.
Evolution is an examination
with two papers. To succeed demands a pass in both. The first involves
staying alive long enough to have a chance to breed, while the mark in
the second depends on the number of progeny.
The dropouts from the first part of the ecological exam are easy to identify as they are, after all, dead. Variation in sexual success is more difficult to measure, particularly for the male candidates (who tend to disappear before their papers are ready for marking). The battle is of male against male, of female against female, and of either sex against the selfish interests of the other.
Malthus assumed that sex was so attractive that, given the chance, all would indulge as much as they could and that birth rates would always be near their maximum. Death was what counted. He was wrong. Until the 18th century the English married late - at 25 for women and even older for men. The rapid growth in numbers at the beginning of the Industrial Revolution came not from a decline in the power, but from an emancipation of the national libido.
Males have small sex cells, females large. The difference (the true definition of what the sexes actually are) results from an ancient conflict. Long ago (and in some simple organisms today), sex cells were all the same size and fused to make an embryo, well provided with food. Then self-interest made an appearance and one partner moved to making smaller but more abundant cells. He (for such was, from that moment, his gender) might have hungry young but there were more of them.
do prefer the frog with the deepest croak, the bowerbird with the most
decorated nest, the plant with the mosy symmetrical flower, and so - endlessly
It may be a matter of marketing. An extravagant signal could be a general statement of a male's ability to cope. A peacock able to manage his accessory must, no doubt, be quite a lusty specimen and could make an excellent father. As soap-makers know, advertisements are expensive. That is part of their point, for if a company can afford lavish publicity it must be a solid concern.
For a sunfish or a
supermarket, the best game to play depends on what everybody else is up
to. It pays to be different and to do what others do not. If a strategy
becomes rare it gains an advantage - but that it lost as soon as it becomes
That explains why most animals have equal numbers of each sex. After all, males and females are themselves no more than alternative solutions to the problem of handing on genes. If a single male can fertilize dozens of partners, why the spares? The reason is simple: the rarer caste is always better off. If so few males exist that each always finds lots of mates, then it pays a parent to have sons. A shortage of females puts an equivalent premium on daughters.
The pattern of less sex in cold places in found in many creatures. It hints at one reason why sex might maintain itself: faced with the predictable enemies of frost and starvation it is better to evolve a single set of hardy genes that are never broken up by admixture with others. In the steamier parts of the world the adversaries come from biology rather than the weather; they are other animals (parasites included). These can evolve themselves, and a constant production of new genetic combinations through sex is essential if their victims are to have a chance.
Bacteria are bound
to win their war against medicine. Nowhere does the evolutionary battle
take place in an arena where, in effect, one player holds all the cards.
Bacteria show what natural selection needs and what it can do when it gets
Penicillin was first used in the 1940s. Its history is an object lesson in natural selection. The first resistant strain was found within a year of its use and soon spread. The more the drugs are used, the more resistance spreads.
Bighorn sheep in the Rockies have been studied for almost a century; in that time all groups of 50 or fewer animals became extinct, while nearly all those with more than a hundred survived. When gambling with Nature, it pays to have a strong hand.
At any moment, a hundred thousand people are suspended over the Atlantic. Some smuggle alien plants and animals, but many more have seeds, insects and more in their turn-ups or their baggage.
Nature, though, starts in a different place and uses materials quite unlike those available to man. It cannot smelt copper or make crosses, but, with what it has, it works miracles. Man, his machines, and Darwin's idea may - given a few million years - do almost as well.
# LAWS OF VARIATION
"Our ignorance of the
laws of variation is profound. Not in one case out of a hundred can
we pretend to assign any reason why this or that part has varied.
But whenever we have the means of instituting a comparison, the same laws
appear to have acted in producing the lesser differences between varieties
of the same species, and the greater differences between species of the
same genus... Whatever the cause may be of each slight difference between
the offspring and their parents - and a cause for each must exist - we
have reason to believe that it is the steady accumulation of beneficial
differences which has given rise to all the more important modifications
of structure in relation to the habits of each species."
- Charles Darwin, "The Origin of Species"
Sex and confusion have long been bedfellows. For 10,000 years of success for plant and animal breeders, its practice was quite divorced from its theory. The laws of inheritance were quite unknown, and notions now seen as absurd were believed by everyone.
Genetics is the science of difference. Mutation is the fuel rather than the engine of biological advance.
Much of the genetic
damage lies at the feet of age and sex. Men are defined by their ownership
of a single gene. Any new mutations in a man are likely to bear more heavily
not upon his sons (who receive only his Y) but upon his daughters, who
get one of their two X chromosomes from him.
Therein lay the first clue about sex and age. Among European royalty, the daughters of old fathers die earlier than do those with younger sires. The difference is as much as two years for a fifty-year-old compared to a thirty-year-old father. For sons, parental age made no difference.
Males, it seems, are not mere conduits for genes between females. Indeed, they are responsible for most mutations.
Filled with complexities and exceptions as it is, genetics remains the rock upon which the edifice of evolution rests.
# DIFFICULTIES ON THEORY
"I will devote this chapter to the consideration of various miscellaneous objections which have been advanced against my views, as some of the previous discussions may thus be made clearer; but it would be useless to discuss all of them, as many have been made by writers who have not taken the trouble to understand the subject."
"To suppose that the
eye with all its inimitable contrivances for adjusting the focus to different
distances, for admitting different amounts of light, and for the correction
of spherical and chromatic aberration, could have been formed by natural
selection, seems, I freely confess, absurd in the highest degree.
When it was first said that the sun stood still and the world turned round,
the common sense of mankind declared the doctrine false; but the old saying
of Vox populi, vox Dei, as every philosopher knows, cannot be trusted in
science. Reason tells me, that if numerous gradations from a simple
and imperfect eye to one complex and perfect can be shown to exist, each
grade being useful to its possessor, as is certainly the case; if further,
the eye ever varies and the variations be inherited, as is likewise certainly
the case; and if such variations should be useful to any animal under changing
conditions of life, then the difficulty of believing that a perfect and
complex eye could be formed by natural selection, though insuperable by
our imagination, should not be
considered as subversive of the theory. "
"Natural selection will never produce in a being any structure more injurious than beneficial to that being, for natural selection acts solely by and for the good of each. If a fair balance be struck between the good and evil caused by each part, each will be found on the whole advantageous. After the lapse of time, under changing conditions of life, if any part comes to be injurious, it will be modified; or if it be not so, the being will become extinct, as myriads have become extinct."
"Natural selection tends only to make each organic being as perfect as, or slightly more perfect than the other inhabitants of the same country with which it comes into competition. And we see that this is the standard of perfection attained under nature. The endemic productions of New Zealand, for instance, are perfect, one compared with another; but they are now rapidly yielding before the advancing legions of plants and animals introduced from Europe. Natural selection will not produce absolute perfection, nor do we always meet, as far as we can judge, with this high standard under nature."
"Although we have no
good evidence of the existence in organic beings of an innate tendency
towards progressive development, yet this necessarily follows, as I have
attempted to show in the fourth chapter, through the continued action of
natural selection. For the best definition which has ever been given
of a high standard of organisation, is the degree to which
the parts have been specialised or differentiated; and natural selection tends towards this end, inasmuch as the parts are thus enabled to perform their functions more efficiently.
- Charles Darwin, "The Origin of Species"
"I will not attempt any definition of instinct. It would be easy to show that several distinct mental actions are commonly embraced by this term; but every one understands what is meant, when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other birds' nests. An action, which we ourselves require experience to enable us to perform, when performed by an animal, more especially by a very young one, without experience, and when performed by many individuals in the same way, without their knowing for what purpose it is performed, is usually said to be instinctive."
"Thus, as I believe,
the most wonderful of all known instincts, that of the hive-bee, can be
explained by natural selection having taken advantage of numerous, successive,
slight modifications of simpler instincts; natural selection having, by
slow degrees, more and more perfectly led the bees to sweep equal spheres
at a given distance from each other in a double layer, and to build up
and excavate the wax along the planes of intersection. The
bees, of course, no more knowing that they swept their spheres at one particular distance from each other, than they know what are the several angles of the hexagonal prisms and of the basal rhombic plates; the motive power of the process of natural selection having been the construction of cells of due strength and of the proper size and shape for the larvae, this being effected with the greatest possible economy of labour and wax; that individual swarm which thus made the best cells with least labour, and least waste of honey in the secretion of wax, having succeeded best, and having transmitted their newly-acquired economical instincts to new swarms, which in their turn will have had the best chance of succeeding in the struggle for existence."
"I have endeavoured
in this chapter briefly to show that the mental qualities of our domestic
animals vary, and that the variations are inherited. Still more briefly
I have attempted to show that instincts vary slightly in a state of nature.
No one will dispute that instincts are of
the highest importance to each animal. Therefore, there is no real difficulty, under changing conditions of life, in natural selection accumulating to any extent slight modifications of instinct which are in any way useful... Finally, it may not be a logical deduction, but to my imagination it is far more satisfactory to look at such instincts as the young cuckoo
ejecting its foster-brothers, ants making slaves, the larvae of ichneumonidae feeding within the live bodies of caterpillars, not as specially endowed or created instincts, but as small consequences of one general law leading to the advancement of all organic beings - namely, multiply, vary, let the strongest live and the weakest die."
- Charles Darwin, "The Origin of Species"
Breeds differ in how highly strung they are, how much they snap at children and in their fondness for barking. Everyone knows that terriers are excitable, that pit bulls bite and that all pups urinate on the carpet. Temperament, like size or shape, is in the genes.
If behaviour varies and is inherited, it has no choice but to evolve. In the end, every action of every creature is a product of genes, however much the environment determines what those genes might do. Genes make brains; and brains make behaviour. Thus is instinct transmitted across the generations.
The culture of birds and apes comes from their history and their ability to learn. How they behave is built upon what evolution has provided. In humans, biology grants even more, but the same laws apply. If Mozart, instead of playing the pianoforte at three years old with wonderfully little practice, had played a tune with no practice at all, be might truly be said to have done so instinctively. Of course, he did not. His ability to learn the piano came from his ancestors. He played as he did because he was Mozart. Genes set the limit even to genius.
Individuals are just
part of the evolutionary equation. As all in the end die, the fate of the
genes is detached from those who transmit them. Natural selection acts
through the medium of DNA, rather than on the flesh of those who bear it.
It is interested in kinship.
Kin selection explains behaviour as strange - and more - as that of the beehive. Kinship can pay an individual to reduce its own chances if it improves the prospects of other members of its family. It can lead to the evolution of animals that cannot reproduce, and to other that kill their own kind. Generosity or selfishness emerge from natural selection. Once attention is directed to the genes as well as to their bearers, such eccentric behaviour makes perfect sense.
The laws of the animal world are ruthless. Plenty of parents kill their children, and plenty of children murder their siblings. For them, the economic part of the argument looms large and selfishness pays: if only one can survive, shared genes do not matter.
In their first year, marsupial mouse mothers kill all their daughters except one, to give their well brought-up and aggressive sons a chance. In their second try at reproduction, though, mothers destroy not daughters but sons, who, because they are so feeble compared to their competitors, do a worse job at handing on her genes than do her newborn and relatively healthy female offspring.
Within a beehive all
is not sweetness and light. Not only is there sterility but murder and
cannibalism. And cannibalism puts paid to the comfortable idea that Nature
is not really red in tooth and claw.
Many animals assess the genetic cost of a slaughter of the innocents. Often, males kill and eat the young of any unprotected female. A pregnant female mouse faced with a new male makes the best of a bad job - the imminent death of her pups - with a preemptive strike. She reabsorbs her foetuses, in a prenatal feast that gives the meal to her, rather than to the hopeful male.
"The view commonly
entertained by naturalists is that species, when intercrossed, have been
specially endowed with sterility, in order to prevent their confusion.
This view certainly seems at first highly probable, for species living
together could hardly have been kept distinct had they been capable of
freely crossing. The subject is in many ways important for us, more
especially as the sterility of species when first crossed, and that of
their hybrid offspring, cannot have been acquired, as I shall show, by
the preservation of successive profitable degrees of sterility. It
is an incidental result of differences in the reproductive
systems of the parent-species."
- Charles Darwin, "The Origin of Species"
# IMPERFECTION OF THE GEOLOGICAL RECORD
A murder victim becomes
an ecosystem in his own right. Within hours after a body is dumped in an
English woodland, blowflies lay eggs around its eyes and mouth. Soon, they
are joined by flesh flies, which drop larvae on to the skin. Three months
after death, 500 kinds of insects may feast upon the corpse. They are of
interest to the police, as they make it possible to work out the date of
death, and forensic entomology has solved many murders.
An infant is reduced to skeleton in a mere six summer days, while an adult takes three weeks. The bones themselves can last much longer but, a few years later, the chances are that not many will be left. For murder victims, the return to dust is swift. The same is true for all corpses, human or not. As a result, most of what evolution has made has mouldered away.
The lost armies of the dead have a moral for evolution. They are a reminder that the geological record is a history of the world imperfectly kept. The history of ancient Egypt, of the present century - and of the existence of our own species - will soon be gone forever: but what fragments remain may allow some future historian to guess ay the forgotten struggles that built his own world.
Much of the argument about whether the fossil record shows slow or rapid change depends on what those terms signify. What is gradual, and what is instantaneous? Those who peer into the depths find it hard to see things in proportion. When one referee in nature's race is used to a stopwatch and the other to Big Ben, disputes are to be expected. An instant to a palaeontologist may appear an infinity to those who study life today. In the fossils of the Turkana Basin in East Africa the 'intermediates' last for just a tiny part of the duration of their ancestor or descendant forms. As a result, they seem a classic case of an evolutionary leap in the snail pedigree. However, that moment represents, for different lineages, between 5,000 and 50,000 years.
The evolutionary play
has had such a long run that some changes in its scenery are inevitable.
500 million years ago the air had twenty times as much carbon dioxide as
it contains now. This led to a natural 'greenhouse effect' which was reversed
200 million years later when the level of the gas dropped. Oxygen too,
has swung between extremes. Twice as much of the gas as today allowed the
growth of enormous plants, of spiders the size of a book, and of scorpions
a foot long. A later burst led to the development of aerial reptiles such
as Quetzalcoatlus, with wings forty feet across. Oxygen's abundance allowed
many animals to burn energy at a rate great enough to persuade them into
the air. In today's attenuated atmosphere, nothing so large could carry
the burden of gravity.
Even the days of the Earth have changed. As the moon saps its neighbour's rotational energy, the globe slows its spin. Coral growth rings from 400 million years ago show that there were then 400 days a year.
# GEOGRAPHICAL DISTRIBUTION
"In considering the
distribution of organic beings over the face of the globe, the first great
fact which strikes us is, that neither the similarity nor the dissimilarity
of the inhabitants of various regions can be wholly accounted for by climatal
and other physical conditions. Of
late, almost every author who has studied the subject has come to this conclusion. The case of America alone would almost suffice to prove its truth; for if we exclude the arctic and northern temperate parts, all authors agree that one of the most fundamental divisions in geographical distribution is that between the New and Old Worlds; yet if we travel over
the vast American continent, from the central parts of the United States to its extreme southern point, we meet with the most diversified conditions; humid districts, arid deserts, lofty mountains, grassy plains, forests, marshes, lakes and great rivers, under almost every temperature. There is hardly a climate or condition in the Old World which cannot be paralleled in the New - at least so closely as the same species generally require. No doubt small areas can be pointed out in the Old World hotter than any in the New World; but these are not inhabited by a fauna different from that of the surrounding districts; for it is rare to find a group of organisms confined to a small area, of which the conditions are peculiar in only a slight degree. Notwithstanding this general parallelism in the conditions of Old and New Worlds, how widely different are their living productions!"
"If the difficulties
be not insuperable in admitting that in the long course of time all the
individuals of the same species, and likewise of the several species belonging
to the same genus, have proceeded from some one source; then all the grand
leading facts of geographical distribution are explicable on the theory
of migration, together with subsequent
modification and the multiplication of new forms. We can thus understand the high importance of barriers, whether of land or water, in not only separating but in apparently forming the several zoological and botanical provinces. We can thus understand the concentration of related species within the same areas; and how it is that under different latitudes, for instance, in South America, the inhabitants of the plains and mountains, of
the forests, marshes, and deserts, are linked together in so mysterious a manner, and are likewise linked to the extinct beings which formerly inhabited the same continent. Bearing in mind that the mutual relation of organism to organism is of the highest importance, we can see why two areas, having nearly the same physical conditions, should often be
inhabited by very different forms of life; for according to the length of time which has elapsed since the colonists entered one of the regions, or both; according to the nature of the communication which allowed certain forms and not others to enter, either in greater or lesser numbers; according or not as those which entered happened to come into more or less
direct competition with each other and with the aborigines; and according as the immigrants were capable of varying more or less rapidly, there would ensue in the to or more regions, independently of their physical conditions, infinitely diversified conditions of life; there would be an almost endless amount of organic action and reaction, and we should find some groups of beings greatly, and some only slightly modified; some developed in great force, some existing in scanty numbers - and this we do find in the several great geographical provinces of the world."
"On these same principles
we can understand, as I have endeavoured to show, why oceanic islands should
have few inhabitants, but that of these, a large proportion should be endemic
or peculiar; and why, in relation to the means of migration, one group
of beings should have all its species peculiar, and another group, even
within the same class, should have all its species the same with those
in an adjoining quarter of the world. We can see why whole groups
of organisms, as batrachians and terrestrial mammals, should be absent
from oceanic islands, whilst the most isolated islands should possess their
own peculiar species of aerial mammals or bats. We can see why, in
islands, there should be some relation between the presence of
mammals, in a more or less modified condition, and the depth of the sea between such islands and the mainland. We can clearly see why all the inhabitants of an archipelago, though specifically distinct on the several islets, should be closely related to each other, and should likewise be related, but less closely, to those of the nearest continent, or other source whence immigrants might have been derived. We can see why, if there exist very closely allied or representative species in two areas, however distant from each other, some identical species will almost always there be found."
- Charles Darwin, "The Origin of Species"
Iceland has the misfortune to sit astride a lava factory, the mid-Atlantic ridge itself. The country gets bigger by the day. Most of the island is less than 20,000 years old.
On the morning of 27 August 1883 a gigantic explosion shook the world. The bang was heard from Sri Lanka to central Australia. Its blast travelled four times around the globe, and the tidal wave reached Dover. Krakatau had exploded, with the force of 10,000 Hiroshima bombs.
And what of the future? If the continents continue to move at their present rate, in 50 million years America will be close to Asia as the Atlantic broadens and the Pacific gets narrower. Australia will rush northword to collide with Japan, and the eastern part of Africa will declare independence as the Rift Valley becomes a sea. The Straits of Gibraltar will soon close, and the Mediterranean may again dry into a salty plain before it disappears forever.
Land bridges, Altantises, and all the other myths dreamed up to explain the distribution of plants and animals are less remarkable than the truth: that the world has evolved as have its inhabitants.
# MUTUAL AFFINITIES OF ORGANIC BEINGS
"From the most remote period in the history of the world organic beings have been found to resemble each other in descending degrees, so that they can be classed in groups under groups. This classification is not arbitrary like the grouping of the stars in constellations. The existence of groups would have been of simple significance, if one group had been exclusively fitted to inhabit the land, and another the water; one to feed on flesh, another on vegetable matter, and so on; but the case is widely different, for it is notorious how commonly members of even the same subgroup have different habits."
- Charles Darwin, "The Origin of Species"
Man is a classifying animal. His world is so full of objects that he must reduce their number by arranging them in groups. The patterns seen by biologists as they arrange their world are, unlike those of tenth-century China, evidence for a system outside the mind of the classifier.
Embryology is based
on a search for resemblances among young animals that may be lost later
in development. Now at last the embryo is revealed as a picture, more or
less obscured, of the common parent form of each great class of animals.
It uncovers hidden patterns of relatedness because an embryo, sheltered
as it is from the need to adapt to the world outside, may retain more of
its past than does an adult. An embryonic elephant has kidneys rather like
those of a manatee, adapted to life in water.
The case is different when an animal during any part of its embryonic career is active, and has to provide for itself. Then, natural selection acts to modify even the youngest, and their history is lost.
One ancient gene has spawned a long lasting dynasty of power. The descendants of the first Duke of Habsburg found themselves, over seven centuries, in control of Austria, Spain and Hungary, and of parts of Germany, Italy and even of Mexico.
The Mass is a Christian eternal. Wherever he might be, a believer finds himself at home - and except for the language differences that emerged with the abandonment of Latin - part of a universal ceremony. Not so in Ethiopia. The Ethiopian Church was cut off for a thousand years, safe from the reforms that seized the rest of Christendom. As its rite passed down the generations, the errors grew until whole sections made no sense even to those who celebrated it.
Chickens have become animated machines to turn food into flesh, with lighter bones, weaker muscles and smaller brains than jungle fowl.
The bones of reduced elephants in Cyprus gave Jonathon Swift the idea for Lilliput, a land of insular dwarfs.
# INTERLUDE: ALMOST LIKE A WHALE?
"Light will be thrown
on the origin of man and his history."
- Charles Darwin, "The Origin of Species"
Most of humanity's diversity separates one person from the next. Some, though, reflects differences among populations. The centre of variety is in Africa, with trends of decrease through Europe and Asia to the small islands of the Pacific and the New World. Within Africa live peoples as distinct as the Zairean pygmies and the tall Nilotics. Europe, by contrast, can do no better than Greeks and Swedes. Between people and between places, Africa is different. Two Africans are, on the average, more dissimilar than two Europeans, and two African villages a few miles apart can be as distinct as whole nations elsewhere.
The most remarkable thing about humankind is how uniform it is. Eight tenths of all our variation is among individuals within a population, a tenth or so from the undoubted differences that exist among populations on the same continent - the Greeks and the Irish, or the Kenyans and Nigerians - about the same small proportion from the divergence between Europe, Asia, the Americas, Australia and Africa.
Man is also amazingly common. He has released himself from the struggle for existence. The abundance of any creature is related to its size, with fewer whales than mice. The fit is consistent, and almost all mammals from mouse to whale sit on the same line. Civilization has removed the constraints that limit all other animals, and man is ten thousands times more plentiful than expected from his size.
There has never been
a rest from natural selection. In the Western world only one baby in a
hundred died from an inherited disease and given a survival rate of 98%
to the age of thirty it might seem that natural selection has little raw
material left to play with. However, genes were involved in far more deaths
a century ago. And nineteen out of every twenty deaths of children are
in the Third World, compared to half the mortality at seventy.
Two people out of three die for reasons connected to the genes they carry, most of them because their inheritance is less able to cope with the environment - tobacco, alcohol, salt, sugar or stress - which they face.
Malaria kills two million
people a year. Its agent is a single-celled parasite passed on by mosquitoes.
All the parties - man, mosquito and parasite - have responded to natural
Man has done a lot of evolving in the face of malaria. The genes involved protext those who inherit a single copy, but they also cause the commonest inherited diseases in the world, because in double dose they damage the carriers. One person in fifteen, worldwide, has a copy of the altered haemoglobin gene and tens of millions suffer as they pay the price for the advantage that such genes give to their kin.
Those with two copies of the altered gene suffer from sickle-cell anaemia. But the gene maintains itself because children who inherit just one copy resist malaria and are otherwise well.
Millions of Africans trace their descent from the single individual within whom the mutation happened a long time ago.
This book began with makind's latest challenge, an attack by a virus that came from an ape. We have evolved in response to AIDS through the most familiar kind of natural selection. Some HIV+ people survive for decads, for good evolutionary reasons. One person in six inherits a gene which delays the onset of symptoms for years. About one in twenty is lucky enough to have two copies of this altered gene. This shuts out the virus altogether.
# RECAPITULATION & CONCLUSION
"As this whole volume is one long argument, it may be convenient to the reader to have the leading facts and inferences briefly recapitulated.
"That many and serious
objections may be advanced against the theory of descent with modification
through variation and natural selection, I do not deny. I have endeavoured
to give to them their full force. Nothing at first can appear more
difficult to believe than that the more complex organs and instincts have
been perfected, not by means superior to, though analogous with, human
reason, but by the accumulation of innumerable slight
variations, each good for the individual possessor. Nevertheless, this difficulty, though appearing to our imagination insuperably great, cannot be considered real if we admit the following propositions, namely, that all parts of the organisation and instincts offer, at least individual differences - that there is a struggle for existence leading to the preservation of profitable deviations of structure or instinct - and, lastly, that gradations in the state of perfection of each organ may have existed, each good of its kind. The truth of these propositions cannot, I think, be disputed.
It is, no doubt, extremely difficult even to conjecture by what gradations many structures have been perfected, more especially among broken and failing groups of organic beings, which have suffered much extinction; but we see so many strange gradations in nature, that we ought to be extremely cautious in saying that any organ or instinct, or any whole structure, could not have arrived at its present state by many graduated steps."
"Variability is governed
by many complex laws, by correlated growth, compensation, the increased
use and disuse of parts, and the definite action of the surrounding conditions.
There is much difficulty in ascertaining how largely our domestic productions
modified; but we may safely infer that the amount has been large, and that modifications can be inherited for long periods. As long as the conditions of life remain the same, we have reason to believe that a modification, which has already been inherited for many generations, may continue to be inherited for an almost infinite number of generations. On the other hand
we have evidence that variability, when it has once come into play, does not cease under domestication for a very long period; nor do we know that it ever ceases, for new varieties are still occasionally produced by our oldest domesticated productions.
Variability is not
actually caused by man; he only unintentionally exposes organic beings
to new conditions of life and then nature acts on the organisation and
causes it to vary. But man can and does select the variations given
to him by nature, and thus accumulates them in any desired manner.
He thus adapts animals and plants for his own benefit or pleasure.
He may do this methodically, or he may do it unconsciously by preserving the individuals most useful or pleasing to him without any intention of altering the breed. It is certain that he can largely influence the character of a breed by selecting, in each successive generation,
individual differences so slight as to be inappreciable except by an educated eye. This unconscious process of selection has been the great agency in the formation of the most distinct and useful domestic breeds. That many breeds produced by man have to a large extent the character of natural species, is shown by the inextricable doubts whether many of them are varieties or aboriginally distinct species."
"There is no reason
why the principles which have acted so efficiently under domestication
should not have acted under nature. In the survival of favoured individuals
and races, during the constantly recurrent Struggle for Existence, we see
a powerful and ever-acting form of Selection. The struggle for existence
inevitably follows from the high geometrical ratio
of increase which is common to all organic beings. This high rate of increase is proved by calculation--by the rapid increase of many animals and plants during a succession of peculiar seasons, and when naturalised in new countries. More individuals are born than can possibly survive. A grain in the balance may determine which individuals shall live and which shall die - which variety or species shall increase in number, and which shall decrease, or finally become extinct. As the individuals of the same species come in all respects into the closest competition with each other, the struggle will generally be most severe between them; it will be almost equally severe between the varieties of the same species, and next in severity between the species of the same genus. On the other hand the struggle will often be severe between beings remote in the scale of nature. The slightest advantage in certain individuals, at any age or during any season, over those with which they come into competition, or better
adaptation in however slight a degree to the surrounding physical conditions, will, in the long run, turn the balance.
With animals having separated sexes, there will be in most cases a struggle between the males for the possession of the females. The most vigorous males, or those which have most successfully struggled with their conditions of life, will generally leave most progeny. But success will often depend on the males having special weapons or means of defence or
charms; and a slight advantage will lead to victory."
"On this view of migration, with subsequent modification, we see why oceanic islands are inhabited by only few species, but of these, why many are peculiar or endemic forms. We clearly see why species belonging to those groups of animals which cannot cross wide spaces of the ocean, as frogs and terrestrial mammals, do not inhabit oceanic islands; and why, on the other hand, new and peculiar species of bats, animals which can traverse the ocean, are often found on islands far distant from any continent. Such cases as the presence of peculiar species of bats on oceanic islands and the absence of all other terrestrial mammals, are facts utterly inexplicable on the theory of independent acts of creation."
"When we no longer
look at an organic being as a savage looks at a ship, as something wholly
beyond his comprehension; when we regard every production of nature as
one which has had a long history; when we contemplate every complex structure
and instinct as the summing up
of many contrivances, each useful to the possessor, in the same way as any great mechanical invention is the summing up of the labour, the experience, the reason, and even the blunders of numerous workmen; when we thus view each organic being, how far more interesting - I speak from experience - does the study of natural history become!"
"In the future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Much light will be thrown on the origin of man and his history."
"It is interesting
to contemplate a tangled bank, clothed with many plants of many kinds,
with birds singing on the bushes, with various insects flitting about,
and with worms crawling through the damp earth, and to reflect that these
elaborately constructed forms, so different from each other, and dependent
upon each other in so complex a manner, have all been produced by laws
acting around us. These laws, taken in the largest sense, being Growth
with reproduction; Inheritance which is almost implied by reproduction;
Variability from the indirect and direct action of the conditions of life,
and from use and disuse; a Ratio of Increase so high as to lead to a Struggle
for Life, and as a consequence to Natural Selection, entailing Divergence
of Character and the Extinction of less improved forms. Thus, from
the war of nature, from famine and death, the most exalted object which
we are capable of conceiving, namely, the production of the higher animals,
directly follows. There is grandeur in this view of life, with its
several powers, having been originally breathed by the
Creator into a few forms or into one; and that, whilst this planet has gone circling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being evolved."
- Charles Darwin, "The Origin of Species"
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