The evolution of plants

The evolution of plants has resulted in a wide range of complexity, from the earliest algal mats,
through multicellular marine and freshwater green algae, terrestrial bryophytes, lycopods and
ferns, to the complex gymnosperms and angiosperms of today. While many of the earliest groups
continue to thrive, as exemplified by red and green algae in marine environments, more recently
derived groups have displaced previously ecologically dominant ones, e.g. the ascendance of
flowering plants over gymnosperms in terrestrial environments.

There is evidence that cyanobacteria and multicellular photosynthetic eukaryotes lived in

freshwater communities on land as early as 1 billion years ago, and that communities of
complex, multicellular photosynthesizing organisms existed on land in the late Precambrian,
around 850 million years ago.[8]

Evidence of the emergence of embryophyte land plants first occurs in the mid-Ordovician
(~470 million years ago), and by the middle of the Devonian (~390 million years ago), many of
the features recognised in land plants today were present, including roots and leaves. By Late
Devonian (~370 million years ago) some free-sporing plants such as Archaeopteris had
secondary vascular tissue that produced wood and had formed forests of tall trees. Also by late
Devonian, Elkinsia, an early seed fern, had evolved seeds.[9] Evolutionary innovation continued
throughout the rest of the Phanerozoic eon and still continues today. Most plant groups were
relatively unscathed by the Permo-Triassic extinction event, although the structures of
communities changed. This may have set the scene for the appearance of the flowering plants in
the Triassic (~200 million years ago), and their later diversification in the Cretaceous and
Paleogene. The latest major group of plants to evolve were the grasses, which became important
in the mid-Paleogene, from around 40 million years ago. The grasses, as well as many other
groups, evolved new mechanisms of metabolism to survive the low CO
2 and warm, dry conditions of the tropics over the last 10 million years.

Colonization of land
Land plants evolved from a group of green algae, perhaps as early as 850 mya,[8] but algae-like
plants might have evolved as early as 1 billion years ago. [7] The closest living relatives of land
plants are the charophytes, specifically Charales; assuming that the habit of the Charales has
changed little since the divergence of lineages, this means that the land plants evolved from a
branched, filamentous alga dwelling in shallow fresh water, [10] perhaps at the edge of seasonally
desiccating pools.[11] However, some recent evidence suggests that land plants might have
originated from unicellular terrestrial charophytes similar to extant Klebsormidiophyceae.[12] The
alga would have had a haplontic life cycle. It would only very briefly have had paired
chromosomes (the diploid condition) when the egg and sperm first fused to form a zygote that
would have immediately divided by meiosis to produce cells with half the number of unpaired
chromosomes (the haploid condition). Co-operative interactions with fungi may have helped
early plants adapt to the stresses of the terrestrial realm.[13]

The Devonian marks the beginning of extensive land colonization by plants, which – through
their effects on erosion and sedimentation – brought about significant climatic change.
Cladogram of plant evolution

Plants were not the first photosynthesisers on land. Weathering rates suggest that organisms
capable of photosynthesis were already living on the land 1,200 million years ago,[11] and
microbial fossils have been found in freshwater lake deposits from 1,000 million years ago,[14]
but the carbon isotope record suggests that they were too scarce to impact the atmospheric
composition until around 850 million years ago.[8] These organisms, although phylogenetically
diverse,[15] were probably small and simple, forming little more than an algal scum.[11]

Evidence of the earliest land plants occurs much later at about 470Ma, in lower middle
Ordovician rocks from Saudi Arabia[16] and Gondwana[17] in the form of spores with decay-
resistant walls. These spores, known as cryptospores, were produced either singly (monads), in
pairs (dyads) or groups of four (tetrads), and their microstructure resembles that of modern
liverwort spores, suggesting they share an equivalent grade of organisation.[18] Their walls
contain sporopollenin – further evidence of an embryophytic affinity. [19] It could be that
atmospheric 'poisoning' prevented eukaryotes from colonising the land prior to this, [20] or it could
simply have taken a great time for the necessary complexity to evolve.[21]

Trilete spores similar to those of vascular plants appear soon afterwards, in Upper Ordovician
rocks about 455 million years ago.[22][23] Depending exactly when the tetrad splits, each of the
four spores may bear a "trilete mark", a Y-shape, reflecting the points at which each cell
squashed up against its neighbours.[24] However, this requires that the spore walls be sturdy and
resistant at an early stage. This resistance is closely associated with having a desiccation-resistant
outer wall—a trait only of use when spores must survive out of water. Indeed, even those
embryophytes that have returned to the water lack a resistant wall, thus don't bear trilete marks.
[24]
A close examination of algal spores shows that none have trilete spores, either because their
walls are not resistant enough, or in those rare cases where it is, the spores disperse before they
are squashed enough to develop the mark, or don't fit into a tetrahedral tetrad.[24]

The earliest megafossils of land plants were thalloid organisms, which dwelt in fluvial wetlands
and are found to have covered most of an early Silurian flood plain. They could only survive
when the land was waterlogged.[25] There were also microbial mats.[26]

Once plants had reached the land, there were two approaches to dealing with desiccation.
Modern bryophytes either avoid it or give in to it, restricting their ranges to moist settings, or
drying out and putting their metabolism "on hold" until more water arrives, as in the liverwort
genus Targionia. Tracheophytes resist desiccation, by controlling the rate of water loss. They all
bear a waterproof outer cuticle layer wherever they are exposed to air (as do some bryophytes),
to reduce water loss, but since a total covering would cut them off from CO
2 in the atmosphere tracheophytes use variable openings, the stomata, to regulate the rate of gas
exchange. Tracheophytes also developed vascular tissue to aid in the movement of water within
the organisms (see below), and moved away from a gametophyte dominated life cycle (see
below). Vascular tissue ultimately also facilitated upright growth without the support of water
and paved the way for the evolution of larger plants on land.

A snowball earth, from around 850-630 mya, is believed to have been caused by early
photosynthetic organisms, which reduced the concentration of carbon dioxide and increased the
amount of oxygen in the atmosphere.[27] The establishment of a land-based flora increased the
rate of accumulation of oxygen in the atmosphere, as the land plants produced oxygen as a waste
product. When this concentration rose above 13%, [when?] wildfires became possible, evident from
charcoal in the fossil record.[28] Apart from a controversial gap in the Late Devonian, charcoal is
present ever since.

Charcoalification is an important taphonomic mode. Wildfire or burial in hot volcanic ash drives
off the volatile compounds, leaving only a residue of pure carbon. This is not a viable food
source for fungi, herbivores or detritovores, so is prone to preservation. It is also robust, so can
withstand pressure and display exquisite, sometimes sub-cellular, detail.

Evolution of life cycles

Further information: Alternation of generations

All multicellular plants have a life cycle comprising two generations or phases. The gametophyte
phase has a single set of chromosomes (denoted 1n), and produces gametes (sperm and eggs).
The sporophyte phase has paired chromosomes (denoted 2n), and produces spores. The
gametophyte and sporophyte phases may be homomorphic, appearing identical in some algae,
such as Ulva lactuca, but are very different in all modern land plants, a condition known as
heteromorphy.

The pattern in plant evolution has been a shift from homomorphy to heteromorphy. The algal
ancestors of land plants were almost certainly haplobiontic, being haploid for all their life cycles,
with a unicellular zygote providing the 2N stage. All land plants (i.e. embryophytes) are
diplobiontic – that is, both the haploid and diploid stages are multicellular. [6] Two trends are
apparent: bryophytes (liverworts, mosses and hornworts) have developed the gametophyte as the
dominant phase of the life cycle, with the sporophyte becoming almost entirely dependent on it;
vascular plants have developed the sporophyte as the dominant phase, with the gametophytes
being particularly reduced in the seed plants.

It has been proposed that the basis for the emergence of the diploid phase of the life cycle as the
dominant phase, is that diploidy allows masking of the expression of deleterious mutations
through genetic complementation.[29][30] Thus if one of the parental genomes in the diploid cells
contains mutations leading to defects in one or more gene products, these deficiencies could be
compensated for by the other parental genome (which nevertheless may have its own defects in
other genes). As the diploid phase was becoming predominant, the masking effect likely allowed
genome size, and hence information content, to increase without the constraint of having to
improve accuracy of replication. The opportunity to increase information content at low cost is
advantageous because it permits new adaptations to be encoded. This view has been challenged,
with evidence showing that selection is no more effective in the haploid than in the diploid
phases of the lifecycle of mosses and angiosperms.[31]

There are two competing theories to explain the appearance of a diplobiontic lifecycle.

The interpolation theory (also known as the antithetic or intercalary theory)[32] holds that the
interpolation of a multicellular sporophyte phase between two successive gametophyte
generations was an innovation caused by preceding meiosis in a freshly germinated zygote with
one or more rounds of mitotic division, thereby producing some diploid multicellular tissue
before finally meiosis produced spores. This theory implies that the first sporophytes bore a very
different and simpler morphology to the gametophyte they depended on.[32] This seems to fit well
with what is known of the bryophytes, in which a vegetative thalloid gametophyte nurtures a
simple sporophyte, which consists of little more than an unbranched sporangium on a stalk.
Increasing complexity of the ancestrally simple sporophyte, including the eventual acquisition of
photosynthetic cells, would free it from its dependence on a gametophyte, as seen in some
hornworts (Anthoceros), and eventually result in the sporophyte developing organs and vascular
tissue, and becoming the dominant phase, as in the tracheophytes (vascular plants). [6] This theory
may be supported by observations that smaller Cooksonia individuals must have been supported
by a gametophyte generation. The observed appearance of larger axial sizes, with room for
photosynthetic tissue and thus self-sustainability, provides a possible route for the development
of a self-sufficient sporophyte phase.[32]

The alternative hypothesis, called the transformation theory (or homologous theory), posits
that the sporophyte might have appeared suddenly by delaying the occurrence of meiosis until a
fully developed multicellular sporophyte had formed. Since the same genetic material would be
employed by both the haploid and diploid phases they would look the same. This explains the
behaviour of some algae, such as Ulva lactuca, which produce alternating phases of identical
sporophytes and gametophytes. Subsequent adaption to the desiccating land environment, which
makes sexual reproduction difficult, might have resulted in the simplification of the sexually
active gametophyte, and elaboration of the sporophyte phase to better disperse the waterproof
spores.[6] The tissue of sporophytes and gametophytes of vascular plants such as Rhynia
preserved in the Rhynie chert is of similar complexity, which is taken to support this hypothesis.
[32][33][34]
By contrast, with the exception of Psilotum modern vascular plants have heteromorphic
sporophytes and gametophytes in which the gametophytes rarely have any vascular tissue.[35]
  Animal origin
 Evolutionary origin
 Further information: Urmetazoan

 Dickinsonia costata from the Ediacaran biota (c. 635–542 MYA) is one of the earliest
animal species known.[77]
 The first fossils that might represent animals appear in the 665-million-year-old rocks of
the Trezona Formation of South Australia. These fossils are interpreted as most probably
being early sponges.[78]
 The oldest animals are found in the Ediacaran biota, towards the end of the Precambrian,
around 610 million years ago. It had long been doubtful whether these included animals,
[79][80][81]
but the discovery of the animal lipid cholesterol in fossils of Dickinsonia
establishes that these were indeed animals. [77] Animals are thought to have originated
under low-oxygen conditions, suggesting that they were capable of living entirely by
anaerobic respiration, but as they became specialized for aerobic metabolism they
became fully dependent on oxygen in their environments.[82]

 Anomalocaris canadensis is one of the many animal species that emerged in the
Cambrian explosion, starting some 542 million years ago, and found in the fossil beds of
the Burgess shale.
 Many animal phyla first appear in the fossil record during the Cambrian explosion,
starting about 542 million years ago, in beds such as the Burgess shale. Extant phyla in
these rocks include molluscs, brachiopods, onychophorans, tardigrades, arthropods,
echinoderms and hemichordates, along with numerous now-extinct forms such as the
predatory Anomalocaris. The apparent suddenness of the event may however be an
artefact of the fossil record, rather than showing that all these animals appeared
simultaneously.[83][84][85][86]
 Some palaeontologists have suggested that animals appeared much earlier than the
Cambrian explosion, possibly as early as 1 billion years ago. [87] Trace fossils such as
tracks and burrows found in the Tonian period may indicate the presence of triploblastic
worm-like animals, roughly as large (about 5 mm wide) and complex as earthworms.[88]
However, similar tracks are produced today by the giant single-celled protist Gromia
sphaerica, so the Tonian trace fossils may not indicate early animal evolution. [89][90]
Around the same time, the layered mats of microorganisms called stromatolites decreased
in diversity, perhaps due to grazing by newly evolved animals.[91]

 March 14, 2011

Lurking in the blood of tropical snails is a single-celled creature called Capsaspora owczarzaki.
This tentacled, amoebalike species is so obscure that no one even noticed it until 2002. And yet,
in just a few years it has moved from anonymity to the scientific spotlight. It turns out to be one
of the closest relatives to animals. As improbable as it might seem, our ancestors a billion years
ago probably were a lot like Capsaspora.
The origin of animals was one of the most astonishing and important transformations in the
history of life. From single-celled ancestors, they evolved into a riot of complexity and diversity.
An estimated seven million species of animals live on earth today, ranging from tubeworms at
the bottom of the ocean to elephants lumbering across the African savanna. Their bodies can
total trillions of cells, which can develop into muscles, bones and hundreds of other kinds of
tissues and cell types.

The dawn of the animal kingdom about 800 million years ago was also an ecological revolution.

Animals devoured the microbial mats that had dominated the oceans for more than two billion
years and created their own habitats, like coral reefs.

The origin of animals is also one of the more mysterious episodes in the history of life. Changing
from a single-celled organism to a trillion-cell collective demands a huge genetic overhaul. The
intermediate species that might show how that transition took place have become extinct.

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“We’re just missing the intervening steps,” said Nicole King, an evolutionary biologist at the
University of California, Berkeley.

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To understand how animals took on this peculiar way of life, scientists are gathering many lines
of evidence. Some use rock hammers to push back the fossil record of animals by tens of
millions of years. Others are finding chemical signatures of animals in ancient rocks. Still others
are peering into the genomes of animals and their relatives like Capsaspora, to reconstruct the
evolutionary tree of animals and their closest relatives. Surprisingly, they’ve found that a lot of
the genetic equipment for building an animal was in place long before the animal kingdom even
existed.

It was only in the past few years that scientists got a firm notion of what the closest relatives to
animals actually are. In 2007, the National Human Genome Research Institute started an
international project to compare DNA from different species and draw a family tree. The cousins
of animals turn out to be a motley crew. Along with the snail-dwelling Capsaspora, our close
relatives include choanoflagellates, amoebalike creatures that dwell in fresh water, where they
hunt for bacteria.

Now scientists are trying to figure out how a single-celled organism like Capsaspora or
choanoflagellates became a multicellular animal. Fortunately, they can get some hints from other
cases in which microbes made the same transition. Plants and fungi evolved from single-celled
ancestors, as well as dozens of other less familiar lineages, from brown algae seaweed to slime
molds.
Image

Credit...Andrew Parkinson/Getty Images

Primitive multicellularity may have been fairly easy to evolve. “All that has to happen is that the
products of cell division stick together,” said Richard E. Michod of the University of Arizona.
Once single-celled organisms shifted permanently to colonies, they could start specializing on
different tasks. This division of labor made the colonies more efficient. They could grow faster
than less specialized colonies.

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Eventually, this division of labor could have led many cells in proto-animals to give up their
ability to reproduce. Only a small group of cells still made the proteins required to produce
offspring. The cells in the rest of the body could then focus on tasks like gathering food and
fighting off disease.

“It’s not a hurdle,” said Bernd Schierwater of the University of Veterinary Medicine in Hanover,
Germany. “It’s a very good way to be very efficient.”

Yet multicellularity also threw some new challenges at the ancestors of animals.

“When cells die in a group, they can poison each other,” said Dr. Michod. In animals, cells die in
an orderly fashion, so that they release relatively few poisons. Instead, the dying cells can be
recycled by their living brethren.

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Another danger posed by multicellularity is the ability for a single cell to grow at the expense of
others. Today that danger still looms large: cancer is the result of some cells refusing to play by
the same rules as the other cells in our body.

Even simple multicellular organisms have evolved defenses to these cheaters. A group of green
algae called volvox have evolved a limit to the number of times any cell can divide. “That helps
reduce the potential for cells to become renegades,” said Dr. Michod.

To figure out the solutions that animals evolved, researchers are now sequencing the genomes of
their single-celled relatives. They’re discovering a wealth of genes that were once thought to
exist only in animals. Iñaki Ruiz-Trillo of the University of Barcelona and his colleagues
searched Capsaspora’s genome for an important group of genes that encode proteins called
transcription factors. Transcription factors switch other genes on and off, and some of them are
vital for turning a fertilized egg into a complex animal body.
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In the current issue of Molecular Biology and Evolution, Dr. Ruiz-Trillo and his colleagues
report that Capsaspora shares a number of transcription factors that were once thought to be
unique to animals. For example, they found a gene in Capsaspora that’s nearly identical to the
animal gene brachyury. In humans and many other animal species, brachyury is essential for
embryos to develop, marking a layer of cells that will become the skeleton and muscles.

Dr. Ruiz-Trillo and his colleagues have no idea what Capsaspora is doing with a brachyury gene.
They’re now doing experiments to find out; in the meantime, Dr. Ruiz-Trillo speculates that
single-celled relatives of animals use the brachyury gene, along with other transcription factors,
to switch genes on for other tasks.

Image

Credit...Anna Topuriya

“They have to check out their environment,” said Dr. Ruiz-Trillo. “They have to mate with other
organisms. They have to eat prey.”

Studies by other scientists point to the same conclusion: a lot of the genes once thought to be
unique to the animal kingdom were present in the single-celled ancestors of animals. “The origin
of animals depended on genes that were already in place,” Dr. King said.

In the transition to full-blown animals, Dr. King argues, these genes were co-opted for
controlling a multicellular body. Old genes began to take on new functions, like producing the
glue for sticking cells together and guarding against runaway cells that could become tumors.

Paleontologists have searched for decades for the fossils that chronicle this transition to the
earliest animals.

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Last year, Adam Maloof of Princeton and his colleagues published details of what they suggest
are the oldest animal fossils yet found. The remains, found in Australia, date back 650 million
years. They contain networks of pores inside of them, similar to the channels inside living
sponges.
Sponges may have also left behind other ancient traces. Gordon Love of the University of
California, Riverside, and his colleagues have drilled down into deposits of oil in Australia
dating back at least 635 million years. In the stew of hydrocarbons they’ve brought up, they have
found cholesterol-like molecules that are produced today only by one group of sponges.

The fact that sponges show up so early in the fossil record is probably no coincidence. Recent
studies on animal genomes indicate that sponges are among the oldest lineages of living animals
— if not the oldest. Sponges are also relatively simple compared with most other animals. They
have no brains, stomachs or blood vessels.

Despite their seeming simplicity, sponges are card-carrying members of the animal kingdom.
Like other animals, sponges can produce eggs and sperm, which can then produce embryos.
Sponge larvae swim through the water to find their way to a good spot where they can settle
down for a sedentary life and grow into adults. Their development is an exquisitely sophisticated
process, with stem cells giving rise to several different cell types.

The first sponge genome was only published in August. It offered scientists an opportunity to
compare the DNA of sponges to that of other animals as well as to Capsaspora and other single-
celled relatives. The researchers looked at each gene in the sponge genome and tried to match it
to related groups of genes in other species, known as gene families. All told, they were able to
find 1,268 gene families shared by all animals — including sponges — but not by other species.

Credit...Gjon Mili//Time Life Pictures-Getty Images

Those genes were presumably passed down to living animals from a common ancestor that lived
800 million years ago. And by surveying this catalog, scientists can infer some things about what
that ancestor was like.

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“It wasn’t just an amorphous blob of cells,” said Bernard M. Degnan of the University of
Queensland. Instead, it was already setting aside eggs and sperm. It could produce embryos, and
it could lay down complicated patterns in its body.

Animals didn’t just evolve multicellular bodies, however. They also appear to have evolved new
ways of generating different kinds of bodies. Animals are more prone to mutations that shuffle
sections of their proteins into new arrangements, a process called domain shuffling. “Domain
shuffling seems to be a critical thing,” Dr. Degnan said.

Dr. Degnan and his colleagues have found another source of innovation in animals in a molecule
called microRNA. When cells produce proteins from genes, they first make a copy of the gene in
a molecule called RNA. But animal cells also make microRNAs that can attack RNA molecules
and destroy them before they have a chance to make proteins. Thus they can act as another kind
of switch to control gene activity.
MicroRNAs don’t seem to exist in single-celled relatives of animals. Sponges have eight
microRNAs. Animals with more cell types that evolved later also evolved more microRNAs.
Humans have 677, for example.

MicroRNAs and domain shuffling gave animals a powerful new source of versatility. They had
the means to evolve new ways of reshaping their embryos to produce a wide range of forms —
from big predators to burrowing mud-feeders.

That versatility may have allowed early animals to take advantage of changes that were
unfolding all around them. About 700 million years ago, Earth emerged from the grips of a
worldwide ice age. Noah Planavsky of the University of California, Riverside, and his colleagues
have found evidence in rocks of that age for a sudden influx of phosphorus into the oceans at the
same time. They speculate that as glaciers melted, phosphorus was washed from the exposed
land into the sea.

The phosphorus may have acted as a pulse of fertilizer, stimulating algae growth. That may have
been responsible for the rapid rise of oxygen in the ocean at the same time. Animals may have
been prepared to use the extra oxygen to fuel large bodies and to use those bodies to devour other
species.

“It was a niche to be occupied,” said Dr. Ruiz-Trillo, “and it was occupied as soon as the
molecular machinery was in place.”

A version of this article appears in print on March 15, 2011, Section D, Page 3 of the New York edition
with the headline: From Single Cells, A Vast Kingdom Arose. Order Reprints | Today’s Paper | Subscribe
History of technology
WRITTEN BY
Robert Angus Buchanan
Professor of the History of Technology; Director, Centre for the History of Technology, Science,
and Society, University of Bath, England. Author of The Power of the Machine.
See Article History

History of technology, the development over time of systematic techniques for making and
doing things. The term technology, a combination of the Greek technē, “art, craft,” with logos,
“word, speech,” meant in Greece a discourse on the arts, both fine and applied. When it first
appeared in English in the 17th century, it was used to mean a discussion of the applied arts only,
and gradually these “arts” themselves came to be the object of the designation. By the early 20th
century the term embraced a growing range of means, processes, and ideas in addition to tools
and machines. By mid-century technology was defined by such phrases as “the means or activity
by which man seeks to change or manipulate his environment.” Even such broad definitions have
been criticized by observers who point out the increasing difficulty of distinguishing between
scientific inquiry and technological activity.
International Space Station
The International Space Station (ISS) photographed from the space shuttle Discovery, which
docked with the ISS on July 28, 2005.
NASA

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A highly compressed account of the history of technology such as this one must adopt a rigorous
methodological pattern if it is to do justice to the subject without grossly distorting it one way or
another. The plan followed in the present article is primarily chronological, tracing the
development of technology through phases that succeed each other in time. Obviously, the
division between phases is to a large extent arbitrary. One factor in the weighting has been the
enormous acceleration of Western technological development in recent centuries; Eastern
technology is considered in this article in the main only as it relates to the development of
modern technology.

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Within each chronological phase a standard method has been adopted for surveying the
technological experience and innovations. This begins with a brief review of the general social
conditions of the period under discussion, and then goes on to consider the dominant materials
and sources of power of the period, and their application to food production, manufacturing
industry, building construction, transport and communications, military technology, and medical
technology. In a final section the sociocultural consequences of technological change in the
period are examined. This framework is modified according to the particular requirements of
every period— discussions of new materials, for instance, occupy a substantial place in the
accounts of earlier phases when new metals were being introduced but are comparatively
unimportant in descriptions of some of the later phases—but the general pattern is retained
throughout. One key factor that does not fit easily into this pattern is that of the development of
tools. It has seemed most convenient to relate these to the study of materials, rather than to any
particular application, but it has not been possible to be completely consistent in this treatment.
Further discussion of specific areas of technological development is provided in a variety of
other articles: for example, seeelectronics; exploration; information processing.
General considerations
Essentially, techniques are methods of creating new tools and products of tools, and the capacity
for constructing such artifacts is a determining characteristic of humanlike species. Other species
make artifacts: bees build elaborate hives to deposit their honey, birds make nests, and beavers
build dams. But these attributes are the result of patterns of instinctive behaviour and cannot be
varied to suit rapidly changing circumstances. Human beings, in contrast to other species, do not
possess highly developed instinctive reactions but do have the capacity to think systematically
and creatively about techniques. Humans can thus innovate and consciously modify the
environment in a way no other species has achieved. An ape may on occasion use a stick to beat
bananas from a tree, but a person can fashion the stick into a cutting tool and remove a whole
bunch of bananas. Somewhere in the transition between the two, the hominid, the first humanlike
species, emerges. By virtue of humanity’s nature as a toolmaker, humans have therefore been
technologists from the beginning, and the history of technology encompasses the whole
evolution of humankind.

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In using rational faculties to devise techniques and modify the environment, humankind has
attacked problems other than those of survival and the production of wealth with which the term
technology is usually associated today. The technique of language, for example, involves the
manipulation of sounds and symbols in a meaningful way, and similarly the techniques of artistic
and ritual creativity represent other aspects of the technological incentive. This article does not
deal with these cultural and religious techniques, but it is valuable to establish their relationship
at the outset because the history of technology reveals a profound interaction between the
incentives and opportunities of technological innovation on the one hand and the sociocultural
conditions of the human group within which they occur on the other.

Social involvement in technological advances

An awareness of this interaction is important in surveying the development of technology
through successive civilizations. To simplify the relationship as much as possible, there are three
points at which there must be some social involvement in technological innovation: social need,
social resources, and a sympathetic social ethos. In default of any of these factors it is unlikely
that a technological innovation will be widely adopted or be successful.

The sense of social need must be strongly felt, or people will not be prepared to devote resources
to a technological innovation. The thing needed may be a more efficient cutting tool, a more
powerful lifting device, a labour-saving machine, or a means of using new fuels or a new source
of energy. Or, because military needs have always provided a stimulus to technological
innovation, it may take the form of a requirement for better weapons. In modern societies, needs
have been generated by advertising. Whatever the source of social need, it is essential that
enough people be conscious of it to provide a market for an artifact or commodity that can meet
the need.

Social resources are similarly an indispensable prerequisite to a successful innovation. Many

inventions have foundered because the social resources vital for their realization—the capital,
materials, and skilled personnel—were not available. The notebooks of Leonardo da Vinci are
full of ideas for helicopters, submarines, and airplanes, but few of these reached even the model
stage because resources of one sort or another were lacking. The resource of capital involves the
existence of surplus productivity and an organization capable of directing the available wealth
into channels in which the inventor can use it. The resource of materials involves the availability
of appropriate metallurgical, ceramic, plastic, or textile substances that can perform whatever
functions a new invention requires of them. The resource of skilled personnel implies the
presence of technicians capable of constructing new artifacts and devising novel processes. A
society, in short, has to be well primed with suitable resources in order to sustain technological
innovation.

Leonardo da Vinci: ornithopter

Leonardo da Vinci's plans for an ornithopter, a flying machine kept aloft by the beating of its
wings, c. 1490.
SuperStock

A sympathetic social ethos implies an environment receptive to new ideas, one in which the
dominant social groups are prepared to consider innovation seriously. Such receptivity may be
limited to specific fields of innovation—for example, improvements in weapons or in
navigational techniques—or it may take the form of a more generalized attitude of inquiry, as
was the case among the industrial middle classes in Britain during the 18th century, who were
willing to cultivate new ideas and inventors, the breeders of such ideas. Whatever the
psychological basis of inventive genius, there can be no doubt that the existence of socially
important groups willing to encourage inventors and to use their ideas has been a crucial factor in
the history of technology.

Social conditions are thus of the utmost importance in the development of new techniques, some
of which will be considered below in more detail. It is worthwhile, however, to register another
explanatory note. This concerns the rationality of technology. It has already been observed that
technology involves the application of reason to techniques, and in the 20th century it came to be
regarded as almost axiomatic that technology is a rational activity stemming from the traditions
of modern science. Nevertheless, it should be observed that technology, in the sense in which the
term is being used here, is much older than science, and also that techniques have tended to
ossify over centuries of practice or to become diverted into such para-rational exercises as
alchemy. Some techniques became so complex, often depending upon processes of chemical
change that were not understood even when they were widely practiced, that technology
sometimes became itself a “mystery” or cult into which an apprentice had to be initiated like a
priest into holy orders, and in which it was more important to copy an ancient formula than to
innovate. The modern philosophy of progress cannot be read back into the history of technology;
for most of its long existence technology has been virtually stagnant, mysterious, and even
irrational. It is not fanciful to see some lingering fragments of this powerful technological
tradition in the modern world, and there is more than an element of irrationality in the
contemporary dilemma of a highly technological society contemplating the likelihood that it will
use its sophisticated techniques in order to accomplish its own destruction. It is thus necessary to
beware of overfacile identification of technology with the “progressive” forces in contemporary
civilization.

On the other hand it is impossible to deny that there is a progressive element in technology, as it
is clear from the most elementary survey that the acquisition of techniques is a cumulative
matter, in which each generation inherits a stock of techniques on which it can build if it chooses
and if social conditions permit. Over a long period of time the history of technology inevitably
highlights the moments of innovation that show this cumulative quality as some societies
advance, stage by stage, from comparatively primitive to more sophisticated techniques. But
although this development has occurred and is still going on, it is not intrinsic to the nature of
technology that such a process of accumulation should occur, and it has certainly not been an
inevitable development. The fact that many societies have remained stagnant for long periods of
time, even at quite developed stages of technological evolution, and that some have actually
regressed and lost the accumulated techniques passed on to them, demonstrates the ambiguous
nature of technology and the critical importance of its relationship with other social factors.

Modes of technological transmission

Another aspect of the cumulative character of technology that will require further investigation is
the manner of transmission of technological innovations. This is an elusive problem, and it is
necessary to accept the phenomenon of simultaneous or parallel invention in cases in which there
is insufficient evidence to show the transmission of ideas in one direction or another. The
mechanics of their transmission have been enormously improved in recent centuries by the
printing press and other means of communication and also by the increased facility with which
travelers visit the sources of innovation and carry ideas back to their own homes. Traditionally,
however, the major mode of transmission has been the movement of artifacts and craftsmen.
Trade in artifacts has ensured their widespread distribution and encouraged imitation. Even more
important, the migration of craftsmen—whether the itinerant metalworkers of early civilizations
or the German rocket engineers whose expert knowledge was acquired by both the Soviet Union
and the United States after World War II—has promoted the spread of new technologies.

Wernher von Braun after surrendering to U.S. forces

German rocket engineer Wernher von Braun (with arm in cast) and his brother Magnus (second
from right) after surrendering to U.S. forces, May 2, 1945.
MSFC/NASA

The evidence for such processes of technological transmission is a reminder that the material for
the study of the history of technology comes from a variety of sources. Much of it relies, like any
historical examination, on documentary matter, although this is sparse for the early civilizations
because of the general lack of interest in technology on the part of scribes and chroniclers. For
these societies, therefore, and for the many millennia of earlier unrecorded history in which slow
but substantial technological advances were made, it is necessary to rely heavily upon
archaeological evidence. Even in connection with the recent past, the historical understanding of
the processes of rapid industrialization can be made deeper and more vivid by the study of
“industrial archaeology.” Much valuable material of this nature has been accumulated in
museums, and even more remains in the place of its use for the observation of the field worker.
The historian of technology must be prepared to use all these sources, and to call upon the skills
of the archaeologist, the engineer, the architect, and other specialists as appropriate.

History of technology
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