[Paleopsych] New Scientist: Life's top 10 greatest inventions
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Thu Apr 14 14:34:53 UTC 2005
Life's top 10 greatest inventions
PONDER this one in the bath. Chances are you've just scrubbed your
back with a choice example of one of evolution's greatest inventions.
Or at least, a good plastic copy.
Sponges are a key example of multicellular life, an innovation that
transformed living things from solitary cells into fantastically
complex bodies. It was such a great move, it evolved at least 16
different times. Animals, land plants, fungi and algae all joined in.
Cells have been joining forces for billions of years. Even bacteria
can do it, forming complex colonies with a three-dimensional structure
and some division of labour. But hundreds of millions of years ago,
eukaryotes - more complex cells that package up their DNA in a nucleus
- took things to a new level. They formed permanent colonies in which
certain cells dedicated themselves to different tasks, such as
nutrition or excretion, and whose behaviour was well coordinated.
Eukaryotes could make this leap because they had already evolved many
of the necessary attributes for other purposes. Many single-celled
eukaryotes can specialise or "differentiate" into cell types,
dedicated to specific tasks such as mating with another cell. They
sense their environment with chemical signalling systems, some of
which are similar to those multicellular organisms use to coordinate
their cells' behaviour. And they may detect and capture their prey
with the same kind of sticky surface molecules that hold cells
together in animals and other multicellular organisms.
So what started it? One idea is that clumping together helped cells
avoid being eaten by making them too much of a mouthful for
single-celled predators. Another is that single cells are often
constrained in what they can do - for example, most cannot grow
flagella to move and also divide at the same time. But a colony can
both move and contain dividing cells if each cell in it takes its
Researchers are now trying to reconstruct the biology of the first
multicellular creatures by studying the genomes of their nearest
living relatives. "We're trying to peer back hundreds of millions of
years," says Nicole King, a molecular biologist at the University of
California, Berkeley. She and her team are studying single-celled
protozoans called choanoflagellates to understand how animals came to
evolve from them some 600 million years ago. Choanoflagellates and
sponges - the only surviving witnesses to this step - share a common
ancestor and King has found that choanoflagellates have a surprising
number of equivalents to the signalling and cell-adhesion molecules
unique to animals.
Yet bigger and more complex isn't necessarily better. As King points
out, unicellular life still vastly outnumbers multicellular life in
terms of both biomass and species numbers. "So you could say
unicellular life is the most successful, but that multicellular life
is the most beautiful and dramatic."
THEY appeared in an evolutionary blink and changed the rules of life
forever. Before eyes, life was gentler and tamer, dominated by
sluggish soft-bodied worms lolling around in the sea. The invention of
the eye ushered in a more brutal and competitive world. Vision made it
possible for animals to become active hunters, and sparked an
evolutionary arms race that transformed the planet.
The first eyes appeared about 543 million years ago - the very
beginning of the Cambrian period - in a group of trilobites called the
Redlichia. Their eyes were compound, similar to those of modern
insects, and probably evolved from light-sensitive pits. And their
appearance in the fossil record is strikingly sudden - trilobite
ancestors from 544 million years ago don't have eyes.
So what happened in that magic million years? Surely eyes are just too
complex to appear all of a sudden? Not so, according to Dan-Eric
Nilsson of Lund University in Sweden. He has calculated that it would
take only half a million years for a patch of light-sensitive cells to
evolve into a compound eye.
"Eyes sparked an evolutionary arms race that transformed the planet"
That's not to say the difference was trivial. Patches of
photosensitive cells were probably common long before the Cambrian,
allowing early animals to detect light and sense what direction it was
coming from. Such rudimentary sense organs are still used by
jellyfish, flatworms and other obscure and primitive groups, and are
clearly better than nothing. But they are not eyes. A true eye needs
something extra - a lens that can focus light to form an image. "If
you suddenly obtain a lens, the effectiveness goes from about 1 per
cent to 100 per cent," says Andrew Parker, a zoologist at the
University of Oxford.
Trilobites weren't the only animals to stumble across this invention.
Biologists believe that eyes could have evolved independently on many
occasions, though genetic evidence suggests one ancestor for all eyes.
But either way, trilobites were the first.
And what a difference it made. In the sightless world of the early
Cambrian, vision was tantamount to a super-power. Trilobites' eyes
allowed them to become the first active predators, able to seek out
and chase down food like no animal before them. And, unsurprisingly,
their prey counter-evolved. Just a few million years later, eyes were
commonplace and animals were more active, bristling with defensive
armour. This burst of evolutionary innovation is what we now know as
the Cambrian explosion.
However, sight is not universal. Of 37 phyla of multicellular animals,
only six have evolved it, so it might not look like such a great
invention after all - until you stop to think. The six phyla that have
vision (including our own, chordates, plus arthropods and molluscs)
are the most abundant, widespread and successful animals on the
BRAINS are often seen as a crowning achievement of evolution -
bestowing the ultimate human traits such as language, intelligence and
consciousness. But before all that, the evolution of brains did
something just as striking: it lifted life beyond vegetation. Brains
provided, for the first time, a way for organisms to deal with
environmental change on a timescale shorter than generations.
A nervous system allows two extremely useful things to happen:
movement and memory. If you're a plant and your food source
disappears, that's just tough. But if you have a nervous system that
can control muscles, then you can actually move around and seek out
food, sex and shelter.
The simplest nervous systems are just ring-like circuits in cnidarians
- the jellyfish, urchins and anemones. These might not be terribly
smart, but they can still find the things they need and interact with
the world in a far more sophisticated way than plants manage.
The next evolutionary step, which probably happened in flatworms in
the Cambrian, was to add some sort of control system to give the
movements more purpose. This sort of primitive brain is simply a bit
of extra wiring that helps organise the networks.
Armed with this, finding food would have been the top priority the
earliest water-dwelling creatures. Organisms need to sort out
nutritious from toxic food, and the brain helps them do that. Sure
enough, look at any animal and you will find the brain is always near
the mouth. In some of the most primitive invertebrates, the oesophagus
actually passes right through the brain.
With brains come senses, to detect whether the world is good or bad,
and a memory. Together, these let the animal monitor in real time
whether things are getting better or worse. This in turn allows a
simple system of prediction and reward. Even animals with really
simple brains - insects, slugs or flatworms - can use their
experiences to predict what might be the best thing to do or eat next,
and have a system of reward that reinforces good choices.
The more complex functions of the human brain - social interaction,
decision-making and empathy, for example - seem to have evolved from
these basic systems controlling food intake. The sensations that
control what we decide to eat became the intuitive decisions we call
gut instincts. The most highly developed parts of the human frontal
cortex that deal with decisions and social interactions are right next
to the parts that control taste and smell and movements of the mouth,
tongue and gut. There is a reason we kiss potential mates - it's the
most primitive way we know to check something out.
AS FAR as humans are concerned, language has got to be the ultimate
evolutionary innovation. It is central to most of what makes us
special, from consciousness, empathy and mental time travel to
symbolism, spirituality and morality. Language may be a defining
factor of our species, but just how important is it in the
evolutionary scheme of things?
A decade ago, John Maynard Smith, then emeritus professor of biology
at the University of Sussex, UK, and Eors Szathmary from the Institute
of Advanced Study in Budapest, Hungary, published The Major
Transitions in Evolution, their description of life's great leaps
forward. They identified these crucial steps as innovations in the way
information was organised and transmitted from one generation to the
next - starting with the origin of life itself and ending with
Exactly how our ancestors took this leap is possibly the hardest
problem in science, Szathmary says. He points out that complex
language - language with syntax and grammar, which builds up meaning
through a hierarchical arrangement of subordinate clauses - evolved
just once. Only human brains are able to produce language, and,
contrary to popular belief, this ability is not confined to
specialised regions in the brain such as Broca's and Wernicke's areas.
If these are damaged others can take over. Szathmary likens language
to an amoeba, and the human brain to the habitat in which it can
thrive. "A surprisingly large part of our brain can sustain language,"
But that raises the question of why this language amoeba doesn't
colonise the brains of other animals, especially primates. Szathmary
is convinced the answer lies in neural networks unique to humans that
allow us to perform the complex hierarchical processing required for
grammatical language. These networks are shaped both by our genes and
by experience. The first gene associated with language, FOXP2, was
identified in 2001, and others will surely follow.
So why don't our close evolutionary relatives, chimps and other
primates, have similar abilities? The answer, recent analysis seems to
suggest, lies in the fact that while humans and chimps have many genes
in common, the versions expressed in human brains are more active than
those in chimps. What's more, the brains of newborn humans are far
less developed than those of newborn chimps, which means that our
neural networks are shaped over many years of development immersed in
a linguistic environment.
In a sense, language is the last word in biological evolution. That's
because this particular evolutionary innovation allows those who
possess it to move beyond the realms of the purely biological. With
language, our ancestors were able to create their own environment - we
now call it culture - and adapt to it without the need for genetic
FEW innovations have had such profound consequences for life as the
ability to capture energy from sunlight. Photosynthesis has literally
altered the planet's face, transforming the atmosphere and cocooning
Earth in a protective shield against lethal radiation.
Without photosynthesis, there would be little oxygen in the
atmosphere, and no plants or animals - just microbes scratching a
meagre existence from a primordial soup of minerals and carbon
dioxide. It freed life from these constraints and the oxygen it
generated set the stage for the emergence of complex life.
Before photosynthesis, life consisted of single-celled microbes whose
sources of energy were chemicals such as sulphur, iron and methane.
Then, around 3.5 billion years ago, or perhaps earlier, a group of
microbes developed the ability to capture energy from sunlight to help
make the carbohydrates they needed for growth and fuel. It is unclear
how they achieved this feat, but genetic studies suggest that the
light-harvesting apparatus evolved from a protein with the job of
transferring energy between molecules. Photosynthesis had arrived.
But this early version of the process didn't make oxygen. It used
hydrogen sulphide and carbon dioxide as its starting ingredients,
generating carbohydrates and sulphur as end products. Some time later
- just when is uncertain - a new type of photosynthesis evolved that
used a different resource, water, generating oxygen as a by-product.
In those early days, oxygen was poisonous to life. But it built up in
the atmosphere until some microbes evolved mechanisms to tolerate it,
and eventually hit on ways to use it as an energy source. That was a
pretty important discovery too: using oxygen to burn carbohydrates for
energy is 18 times as efficient as doing it without oxygen.
Life on Earth became high-powered at this point, setting the scene for
the development of complex, multicellular life forms - including
plants, which "borrowed" their photosynthetic apparatus from
photosynthetic bacteria called cyanobacteria. Today, directly or
indirectly, photosynthesis produces virtually all of the energy used
by life on Earth.
As well as providing an efficient means to burn fuel, oxygen made by
photosynthesis helps protect life. Earth is under constant bombardment
from lethal UV radiation streaming out from the sun. A by-product of
our oxygenated atmosphere is a layer of ozone extending 20 to 60
kilometres above Earth's surface, which filters out most of the
harmful UV. This protective umbrella allowed life to escape from the
sanctuary of the ocean and colonise dry land.
"It has altered the atmosphere and cocooned Earth in a protective
Now, virtually every biochemical process on the planet is ultimately
dependent on an input of solar energy. Take a deep breath and thank
those primordial oxygen-hating microbes for their biochemical
BIRDS do it, bees do it - for the vast majority of species, sexual
reproduction is the only option. And it is responsible for some of the
most impressive biological spectacles on the planet, from mass
spawnings of coral so vast that they are visible from space, to
elaborate sexual displays such as the dance of the bower bird, the
antlers of a stag and - according to some biologists - poetry, music
and art. Sex may even be responsible for keeping life itself going:
species that give it up almost always go extinct within a few hundred
Important as sex is, however, biologists are still arguing over how it
evolved - and why it hasn't un-evolved. That's because, on the face of
it, sex looks like a losing strategy.
Evolution ought to favour asexual reproduction for two reasons. First,
in the battle for resources, asexual species should be able to
outcompete sexual ones hands down. And secondly, because sperm and
eggs contain only half of each parent's set of genes, an organism that
uses sexual reproduction only gets 50 per cent of its genes into the
next generation. Asexuals are guaranteed to pass on 100 per cent.
Clearly, though, there is something wrong with this line of reasoning.
It's true that many species, including insects, lizards and plants, do
fine without sex, at least for a while. But they are vastly
outnumbered by sexual ones.
The enduring success of sex is usually put down to the fact that it
shuffles the genetic pack, introducing variation and allowing harmful
mutations to be purged (mutations are what eventually snuffs out most
asexual species). Variation is important because it allows life to
respond to changing environments, including interactions with
predators, prey and - particularly - parasites. Reproducing asexually
is sometimes compared to buying 100 tickets in a raffle, all with the
same number. Far better to have only 50 tickets, each with a different
However useful sex may be now that we've got it, that doesn't tell us
anything about how it got started. It could have been something as
mundane as DNA repair. Single-celled, asexual organisms may have
developed the habit of periodically doubling up their genetic
material, then halving it again. This would have allowed them to
repair any DNA damage by switching in the spare set. A similar
exchange of DNA still happens during the production of eggs and sperm.
Parasites are also in the frame. Parasitic lengths of DNA known as
transposons reproduce by inserting copies of themselves into the
cell's normal genetic material. Imagine a transposon within a
single-celled organism acquiring a mutation that happens to cause its
host cell to periodically fuse with other cells before dividing again.
The transposon for this primitive form of sex would be able to spread
horizontally between many different cells. Once it arose in a
population, parasitic sex would catch on pretty quickly.
COULD evolution have brought the Grim Reaper into being? Yes, indeed.
Not in all his guises, of course - living things have always died
because of mishaps such as starvation or injury. But there's another
sort of death in which cells - and perhaps, controversially, even
whole organisms - choose annihilation because of the benefits it
brings to some greater whole. In other words, death is an evolutionary
This is most obvious in the many varieties of programmed cell death or
apoptosis, a self-destruct mechanism found in every multicellular
organism. Your hand has five fingers because the cells that used to
live between them died when you were an embryo. Embryos as tiny as 8
to 16 cells - just 3 or 4 cell divisions after the fertilised egg -
depend on cell death: block apoptosis and development goes awry. Were
it not for death, we would not even be born.
Even as adults we could not live without death. Without apoptosis we
would all be overrun by cancer. Your cells are constantly racking up
mutations that threaten to make your tightly controlled cell division
run amok. But surveillance systems - such as the one involving the p53
protein, called the "guardian of the genome" (New Scientist, 18
December 2004, p 38) - detect almost all such errors and direct the
affected cells to commit suicide.
Programmed cell death plays a central role in everyday life too. It
ensures a constant turnover of cells in the gut lining and generates
our skin's protective outer layer of dead cells. When the immune
system has finished wiping out an infection, the now-redundant white
blood cells commit suicide in an orderly fashion to allow the
inflammation to wind down. And plants use cell death as part of a
scorched-earth defence against pathogens, walling off the infected
area and then killing off all the cells within.
It is easy to see how an organism can benefit from sacrificing a few
cells. But evolution may also have had a hand in shaping the death of
whole organisms. The cells of all higher organisms begin to age, or
senesce, after just a few dozen cell divisions, ultimately leading to
the death of the organism itself. In part that is one more protection
against uncontrolled growth. But one controversial theory suggests
this is part of an inbuilt genetic ageing program that sets an upper
limit on all our lifespans (New Scientist, 19 April 2004, p 26).
Most evolutionary biologists reject the idea of an innate "death
program". After all, they point out, animals die of old age in many
different ways, not by one single route as apoptotic cells do.
Instead, they view senescence as a sort of evolutionary junkyard:
natural selection has little reason to get rid of flaws that appear
late in life, since few individuals are lucky enough to make it to old
age. But now that people routinely survive well past reproductive age,
we suffer the invention evolution never meant us to find: death by old
THE name is synonymous with stealing, cheating and stealthy evil. But
the age-old battle between parasites and their hosts is one of the
most powerful driving forces in evolution. Without its plunderers and
freeloaders, life would simply not be the same.
From viruses to tapeworms, barnacles to birds, parasites are among the
most successful organisms on the planet, taking merciless advantage of
every known creature. Take the tapeworm. This streamlined parasite is
little more than gonads and a head full of hooks, having dispensed
with a gut in favour of bathing in the nutrient-rich depths of its
host's digestive system. In its average 18-year lifespan, a human
tapeworm can generate 10 billion eggs.
Many parasites, such as the small liver fluke, have also mastered the
art of manipulating their host's behaviour. Ants whose brains are
infected with a juvenile fluke feel compelled to climb to the tops of
grass blades, where they are more likely to be eaten by the fluke's
ultimate host, a sheep.
"They are really disgusting, but man, are they good at what they do,"
says Daniel Simberloff, an ecologist at the University of Tennessee
and translator of the popular French text The Art of Being a Parasite.
"Evolution is in large part probably driven by parasites. It is the
main hypothesis for the continuation of sexual reproduction. How much
more important can you get?"
The parasites that have had arguably the biggest effect on evolution
are the smallest. Bacteria, protozoans and viruses can shape the
evolution of their hosts because only the hardiest will survive
infection. And humans are no exception: the genes for several
inherited conditions protect against infectious disease when inherited
in a single dose. For example, one copy of the gene for sickle cell
anaemia protects against malaria. And it is still happening today. HIV
and TB, for instance, are driving evolutionary change in parts of our
genome, such as the immune-system genes (New Scientist, 22 November
2003, p 44).
Hosts can influence the evolution of their parasites too. For example,
diseases which require human-to-human contact for transmission often
evolve to be less deadly, ensuring a person will at least live long
enough to pass it on.
Parasites can also drive the evolution at a more basic level.
Parasitic lengths of DNA called transposons, which can cut and paste
themselves all over the genome, can be transformed into new genes or
encourage the mutation and shuffling of DNA that fuels genetic
variation. They have even been implicated in the origins of sex, as
they may have driven selection for cell fusion and gamete formation
LARGE numbers of individuals living together in harmony, achieving a
better life by dividing their workload and sharing the fruits of their
labours. We call this blissful state utopia, and have been striving to
achieve it for at least as long as recorded history. Alas, our efforts
so far have been in vain. Evolution, however, has made a rather better
job of it.
Take the Portuguese man-of-war. It may look like just another
jellyfish blob floating on the high seas, but zoom in with a
microscope and you see that what seemed like one tentacled individual
is in fact a colony of single-celled organisms. These "siphanophores"
have got division of labour down to a fine art. Some are specialised
for locomotion, some for feeding, some for distributing nutrients.
This communal existence brings major advantages. It allows the
constituent organisms, which would otherwise be rooted to the sea
floor, to swim free. And together they are better able to defend
themselves against predators, cope with environmental stress, and
colonise new territory. Portuguese man-of-war jellyfish are truly
With benefits like these on offer, it should come as no surprise that
colonial living has evolved many times. Except that it does come with
one big drawback, as the case of the slime bacteria, or myxobacteria,
illustrates. These microbes are perhaps the simplest colonial
organisms. Under normal circumstances individual bacteria glide along
on lonely slime trails. Only when certain amino acids are lacking in
their environment do individuals start to aggregate. The resulting
superorganism consists of a stalk topped by a fruiting body containing
spores. But since only the bacteria forming the spores will get the
chance of dispersal and a new life, why should the others play along?
How this kind of cooperation evolved, and how cheats are prevented
from taking advantage of it remains unclear for some types of colonial
But in one group of animals, the colonial insects, we do know what the
trick is - and it's an ingenious one. Females develop from fertilised
eggs, while males develop from unfertilised ones. This way of
determining sex, called haplodiploidy, ensures that sisters are more
closely related to each other than to their own offspring. And this
means that the best chance they can give their own genes of surviving
is to look after each other rather than lay eggs of their own. This is
what provides the stability at the heart of the beehive and termite
mound, and in many other insect colonies where haplodiploidy has
evolved at least a dozen times.
True sociality, or eusociality as it is technically known, is found in
all ants and termites, in the most highly organised bees and wasps,
and in some other species, not all of which employ haplodiploidy. And
although these mini societies need careful policing to keep cheats at
bay, this is probably the closest thing on Earth to utopia.
CROCODILES with gleaming gums, coral reefs, orchids, fish with
glow-in-the-dark lures, ants that farm, new directions for evolution.
All that from swapping food - for cleaning services, for transport,
for sunscreen, for shelter, and of course for other food.
Symbiosis has many definitions, but we'll take it to mean two species
engaging in physically intimate, mutually beneficial dependency,
almost invariably involving food. Symbiosis has triggered seismic
shifts in evolution, and evolution in turn continually spawns new
Perhaps the most pivotal couplings were the ones that turbocharged
complex, or eukaryotic, cells. Eukaryotes use specialised organelles
such as mitochondria and chloroplasts to extract energy from food or
sunlight. These organelles were originally simpler, prokaryotic cells
that the eukaryotes engulfed in an eternal symbiotic embrace. Without
them life's key developments, such as increasing complexity and
multicellular plants and animals, would not have happened. "There are
only two things that matter in this world: respiration and
photosynthesis. Eukaryotes didn't figure out either by themselves,
they borrowed them from prokaryotes through symbiosis," says Geoff
McFadden of the University of Melbourne, Australia.
Symbiosis has popped up so frequently during evolution that it is safe
to say it's the rule, not the exception. Angler fish in the deep ocean
host bioluminescent bacteria in appendages that dangle over their
mouths. Smaller fish lured by the light are easy prey. At the ocean
surface, coral polyps provide homes for photosynthetic algae, and swap
inorganic waste products for organic carbon compounds - one reason why
nutrient-poor tropical waters can support so much life. The algae also
produce a chemical that absorbs ultraviolet light and protects the
More than 90 per cent of plant species are thought to engage in
symbiotic couplings. Orchid seeds are little more than dust,
containing next to no nutrients. To germinate and grow, they digest a
fungus that infects the seed. "Birds and animals and insects that are
adapted to pollination and seed disposal, these are some of the
greatest symbioses. Without them we wouldn't have most of our
flowering plants," says Ursula Munro, an ecologist at the University
of Technology in Sydney, Australia.
"Without symbiosis we wouldn't have most of our flowering plants"
Plovers pick leeches from crocodiles' teeth, offering dental hygiene
in return for food. Leafcutter ants use chopped-up leaves as a
fertiliser for the fungus they grow in underground chambers. The ants
cannot digest the leaves but the fungus that feeds on them produces a
tasty meal of sugars and starch while breaking down the toxins in the
leaves. And there is not an animal out there, including us, that can
survive without the bacteria that live in its gut, digesting food and
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