Origini e
definizione di Agricoltura
L'agricoltura è l'attività economica che
consiste nella coltivazione di specie
vegetali. La finalità principale
dell'agricoltura è di ottenere prodotti delle
piante da utilizzare a scopo alimentare o
non, ma sono possibili anche altre finalità che
non prevedano necessariamente l'asportazione dei
prodotti.
Tradizionalmente, nella cultura
italiana, l'agricoltura è popolarmente riferita allo
sfruttamento delle risorse vegetali a fini alimentari,
mentre lo sfruttamento delle corrispondenti risorse di
origine animale, l'allevamento, ne è quasi ritenuta
antitetica. A fini scientifici e giuridici, comunque,
entrambe le materie sono comunemente riunite nella più vasta
accezione di agricoltura, che abbraccia la coltivazione
delle piante (arboree,
erbacee),
l'allevamento degli animali e
lo sfruttamento delle foreste.
Storia e Origini
Si è scoperto che l'agricoltura sarebbe nata almeno 10.000
anni fa attraverso la
domesticazione. Non solo tale domesticazione sarebbe
avvenuta molto prima nell'area definita
Mezzaluna fertile, ma persino prima di ogni altra specie
vegetale, quali
frumento, e
legumi. La scoperta è avvenuta in un villaggio presso il
fiume
Giordano a 15 km a nord di
Gerico. È con l'introduzione delle pratiche agricole
che, in tempi remoti, i nomadi fondarono le prime
aggregazioni urbane.
L'economia dell'Egitto
era basata sull'agricoltura e fu tra le prime popolazioni a
utilizzare l'aratro
in legno, e
zappa; soprattutto nel bacino del medioriente e del
mediterraneo, l'uomo, abbandonata la vita nomade per
insediarsi stabilmente, cominciò ad addomesticare gli
animali.
L'allevamento garantiva una maggiore disponibilità di
carne e
latte, oltreché materie prime come
lana e
pelli e fino alla scoperta dei
motori a scoppio, fu la più importante forza di lavoro
come aiuto nell'aratura e nella fertilizzazione del terreno.
Il rapporto tra la proprietà della terra e ruolo sociale
divenne ben presto fondamentale.
Nel mondo classico e latino, il sistema agrario si basava
sulla divisione della terra in funzione all'esigenza della
città e sull'ager publicus[1] oltreché nella rotazione
biennale dove, in
autunno, circa metà della terra veniva seminata con
cereali e l'altra metà veniva lasciata a riposo (maggese).
Il secondo anno s'invertivano le due porzioni. Nell'antica
Roma, le leggi agrarie prevedevano che il terreno di
patrimonio pubblico, frutto di conquiste militari, fosse
concesso in uso ai contadini. L'ager publicus sparì intorno
al II secolo d.C.
Nuove piante
Durante il Medioevo giunsero in Europa nuove piante portate
dagli
arabi:
riso,
cotone,
carrubo,
pistacchio,
spinacio,
agrumi. Dopo la scoperta dell'America giunsero il
mais, la
patata, la
zucca, il
fagiolo, l'arachide,
il
pomodoro, il
peperone, la
papaya.
La prima rivoluzione agricola
L'agricoltura basata sulla rotazione biennale e sul maggese
rimase predominante fino al XVII secolo. Il progressivo
sviluppo dei commerci, tuttavia, stimolò gradualmente
l'adozione di nuove tecniche produttive.
In particolare, nelle
Fiandre e nel
Brabante il terreno era poco fertile, ma il notevole
sviluppo del commercio marittimo fece aumentare notevolmente
la domanda di prodotti quali il lino per le tele, i
coloranti per il panno, l'orzo e il luppolo per la birra, la
canapa per le funi, il tabacco ecc. La densità della
popolazione, inoltre, favoriva lo sviluppo dell'orticoltura
e della frutticoltura. Si adottarono quindi nuove tecniche
basate sulla rotazione pluriennale e sulla sostituzione del
maggese con pascoli per il bestiame, anche per ottenerne
concime naturale.
Tali innovazioni vennero
studiate da esperti europei ed americani. L'inglese Richard
Weston visitò le province fiamminghe intorno al 1650 e
descrisse in una sua famosa opera, A discourse of husbandrie
used in Brabant and Flanders, il loro metodo basato sulla
rotazione delle colture (lino, rapa, avena, trifoglio).
I nuovi metodi dettero origine al cosiddetto sistema di
Norfolk, generalmente considerato il prototipo di una
nuova agricoltura che, grazie alla rotazione e ad altri
aspetti (recinzioni,
grandi aziende, lunghe affittanze,
aratro in metallo tirato da cavalli ecc.), consentì
all'Inghilterra di esportare grandi quantità di grano e
farine nel periodo 1700-1770.
Secondo
Paul Bairoch, il notevole sviluppo dell'agricoltura
stimolò la successiva
rivoluzione industriale grazie alla domanda di aratri e
altri attrezzi in metallo.
Altri paesi seguirono l'esempio
dell'Inghilterra. Ad esempio, in Francia, in cui le tecniche
agricole medioevali dominarono fino al 1750, la scuola
fisiocratica di
François Quesnay propose espressamente fin dal 1756
(data dell'articolo Fittavoli che Quesnay scrisse per l'Encyclopédie)
l'adozione del modello inglese.
La seconda rivoluzione agricola
La rivoluzione industriale chiamò a sé dalle campagne
numerosi braccianti che si riversarono verso altri
continenti e/o nelle grandi città. In Italia la
migrazione fu dal sud verso il triangolo
Piemonte/Veneto/Emilia
e per contrastarla furono previsti dei piani governativi
ossia piani di bonifica delle terre governative che venivano
destinate all'agricoltura.
Nel corso del XIX secolo
migliori strumenti aratori e sistemi di semina, acquisizione
sul mercato di nuove sementi e di nuove piante con elevata
produttività (mais),
la comparsa delle macchine agricole e dei
concimi chimici, attuarono una profonda ristrutturazione
rurale che stimolò ancora la costruzione di nuove
attrezzature e macchine per tutte le esigenze lavorative
agrarie. L'attività agricola divenne ben presto di tipo
industriale nei
Paesi economicamente avvantaggiati, mentre nell'Europa
dell'Est, Sud America, Asia e Africa rimasero grandi
terreni non coltivati, anche se coltivabili.
Agricoltura contemporanea
Nei secoli, e sino a tempi recenti anche nel Mondo
Occidentale, l'agricoltura ha avuto sempre primaria
importanza per lo sviluppo dei popoli e degli Imperi. Oggi è
spesso degnata di un'attenzione superficiale nelle economie
moderne, mentre resta fonte primaria di sussistenza e perno
dello sviluppo economico dei paesi più poveri ed arretrati.
L'importanza di questa pratica è dimostrata dal fatto di
essere a tutti gli effetti una scienza e di essere ormai al
confine con numerose altre scienze come la
genetica e la
biologia sia animale che vegetale.
I governi dei
paesi industrializzati tra il 1960 e fine anni novanta
hanno indotto la cosiddetta
rivoluzione verde, ossia hanno investito in maniera
consistente nella ricerca agricola, direttamente sui campi
degli agricoltori, cercando altri sistemi per incrementare
la produzione alimentare con lo sviluppo di prodotti
pesticidi e fertilizzanti, incoraggiandoli ad utilizzare
queste nuove tecnologie e rivoluzionando le tradizionali
pratiche agrarie con l'abbandono e l'estinzione di molte
varietà locali e tradizionali.
L'agricoltura contemporanea si
basa sempre più sull'immissione di energia esterna al
sistema sotto forma di
fitofarmaci, meccanizzazione,
fertilizzanti,
ingegneria genetica,
tecnologia; si parla quindi di
agricoltura intensiva, che rovinano i terreni e
producono cibi tossici ed insalubri, in antagonismo
all'agricoltura estensiva.
Ferme restando le implicazioni
negative di una pratica agricola intensiva troppo spinta, la
continua crescita dei fabbisogni alimentari mondiali, la
necessità di mantenere bassi i prezzi degli alimenti, la
riduzione della superficie coltivabile, l'esigenza di
coltivare anche in zone nettamente sfavorevoli (talvolta
anche per inquinamento) e di poter ottenere prodotti di
qualità nutrizionale elevata, pongono gli operatori davanti
ad una limitata rosa di scelte.
Le pratiche tradizionali usate
prima della rivoluzione verde avevano il difetto di non
essere in grado di fornire prodotti in larga quantità ed
economici, attraenti per i consumatori, ma soprattutto
coerenti con gli standard qualitativi e di sicurezza imposti
dalla legge nonché adatti ai processi di trasformazione
industriale. Una parte di questa agricoltura tradizionale
prende oggi il nome di
agricoltura biologica, che costituisce comunque una
nicchia di mercato di una certa rilevanza e presenta prezzi
medio-alti.
D'altra parte l'agricoltura
intensiva presenta evidenti problemi di sostenibilità e per
questo di anno in anno cresce l'esigenza di tecnologia di
settore sempre più attenta alle problematiche ambientali.
Tra le soluzioni tecnologiche,
si è avuto da un lato l'adozione di approcci di lotta
integrata, dall'altro il miglioramento dei composti chimici
(meno tossici e persistenti) e delle varietà impiegate. In
questa ottica si collocano anche gli O.G.M.,
Organismi geneticamente
modificati.
Sviluppo italiano
Anche se la meccanizzazione ha uno stampo anglosassone, le
primissime macchine agricole del
XVII secolo, sono il frutto dell'ingegno italiano:
Giuseppe Locatelli, costruì la prima semplice
seminatrice, composta da un cassetto contenente i semi
applicato all'aratro. Procedendo, l'aratro faceva ruotare un
distributore a cucchiaio inserito nel cassetto ed il seme
cadeva a terra.
Giovanni Cavallina, costruì la prima macchina seminatrice
meccanica, con un sistema di ripiani a fori e dei piccoli
tubi, deponeva i semi nei solchi appena tracciati
dall'aratro.
Nel XIX secolo Lambruschini e i fratelli Ridolfi,
costruirono un rovesciatore di tipo elicoidale per
sminuzzare le zolle più grosse.
La prima forza motrice di tipo meccanico fu la
macchina a vapore, utilizzata per far funzionare le
prime trebbiatrici per cereali e le presse per paglia e
fieno.
Negli Stati Uniti si costruì il
primo trattore, la macchina motrice per eccellenza. Erano
però macchine pesantissime e difficili da maneggiare. Dopo
vent'anni di prove, le industrie Ford fornirono agli
agricoltori americani trattori più leggeri, facili da
riparare, semplici nella manutenzione, a prezzi accessibili.
Nel 1930, le industrie
Landini costruirono il primo trattore con motore testa
calda, ben utilizzato nelle grandi opere di bonifica e
dissodamento.
Agricoltura, agronomia e raccolta
I fattori naturali della produzione vegetale sono i
seguenti:
- Fattori biologici-mutrofici intrinseci: sono tali le basi
genetiche che influenzano l'anatomia,
la
morfologia (biologia) e la
fisiologia delle singole specie agrarie e le
caratteristiche specifiche dei loro prodotti.
- Fattori biologici estrinseci: sono tali le relazioni
ecologiche che si instaurano fra le specie agrarie e gli
altri organismi viventi (piante, animali, microrganismi) che
popolano l'ecosistema naturale, con interazioni di
competizione,
predazione,
parassitismo,
simbiosi,
neutralismo, ecc.
- Fattori climatici: sono tali i fenomeni dovuti
all'interazione dell'atmosfera
e del
sole con la superficie terrestre nelle sue diverse
componenti (litosfera,
idrosfera,
biosfera). I principali fattori climatici che
influenzano la produzione vegetale sono la
radiazione solare, la
temperatura, le
precipitazioni o idrometeore, il
vento, l'umidità
atmosferica, l'evapotraspirazione,
la composizione chimica dell'aria.
Di minore rilevanza diretta è invece la
pressione atmosferica.
- Fattori pedologici: sono tali i fenomeni dovuti
all'interazione del
terreno con l'idrosfera, l'atmosfera, il sole,
l'idrosfera e la biosfera. Il terreno è un ambiente
complesso, derivato dalla
pedogenesi, generato dall'equilibrio fra la litosfera e
gli altri elementi che interagiscono sulla superficie
terrestre. Sono fattori pedologici le
proprietà fisiche del terreno, le
proprietà chimiche, le
proprietà biologiche, che nel complesso concorrono a
determinarne la
fertilità.
La vita quotidiana di
agricoltori all'opera su una terrazza delle
Cinque Terre (particolare di un
murale a
Riomaggiore)
A differenza della semplice
raccolta dei prodotti naturali della
terra, l'agricoltura è una tecnica che interviene
modificando i fattori naturali della produzione vegetale
allo scopo di incrementare, in qualità e quantità, il
prodotto. La raccolta, infatti, sfrutta la produzione
naturale del tutto subordinata alle esigenze specifiche
delle piante e alle dinamiche dell'ecosistema
senza alcun intervento dell'uomo. L'agricoltura prevede
invece l'intervento dell'uomo nel correggere, a suo favore,
le condizioni intrinseche ed estrinseche che determinano la
produzione vegetale.
Gli interventi dell'uomo che concorrono a delineare
un'attività agricola, distinguendola da quella della
semplice raccolta, sono ad esempio i seguenti:
- Interventi sui fattori biologici intrinseci: sono tali ad
esempio:
selezione, il
miglioramento genetico (?), le
biotecnologie
(?), l'ibridazione,
la
potatura, l'innesto,
la densità di piantagione. Nel complesso questi interventi
concorrono a indirizzare la naturale tendenza produttiva
delle singole specie agrarie verso specifiche esigenze
dell'uomo.
- Interventi sui fattori biologici estrinseci: sono tali ad
esempio il
diserbo, la
fitoiatria e la difesa dei
vegetali in senso lato, che mirano a contenere i
fenomeni di antagonismo biologico, altri come la
consociazione o forme più o meno avanzate di biotecnologia (micorizzazione,
batterizzazione e altre forme di inoculo di organismi
simbionti), mirano a promuovere fenomeni di sinergia
biologica. Altri ancora, come l'avvicendamento
colturale, hanno un ruolo complesso nel determinare
l'equilibrio fra antagonismi e sinergie.
- Interventi sui fattori climatici: sono tali ad esempio gli
apprestamenti protettivi mirati a ridurre l'influenza
negativa del
clima o potenziarne quella positiva fino a correggere
drasticamente uno o più fattori. Sono interventi sui fattori
climatici l'allestimento di
frangiventi, di opere di protezione dal freddo (serra,
tunnel,
pacciamatura, ecc.), l'irrigazione.
Meno palese è il ruolo svolto da altre pratiche agricole in
quanto si tratta di forme di adattamento a condizioni
climatiche esistenti: sono tali la scelta dell'epoca di
semina, il
trapianto, la scelta
varietale, la densità di piantagione, l'orientamento dei
filari, alcune
lavorazioni del terreno, ecc.
- Interventi sui fattori pedologici: sono i più complessi
perché trattasi di azioni che possono modificare
contemporaneamente differenti proprietà del terreno. Sono
tali le lavorazioni del terreno, che influenzano
principalmente (ma non solo) le proprietà fisiche, la
fertilizzazione, che influenzano principalmente le
proprietà chimiche ma hanno un ruolo non secondario anche su
quelle fisiche e biologiche, l'irrigazione, che influenza le
proprietà fisiche, chimiche e biologiche, ecc.
L'agronomia
è una scienza applicata che studia il ruolo dei singoli
fattori della produzione vegetale e le interazioni
reciproche, elabora le tecniche agricole con il
coordinamento dei fattori a differenti livelli, al fine di
ottimizzare la produzione ai fini economici. Per estensione
agronomia e agricoltura sono talvolta usati come sinonimi,
tuttavia, a rigore l'agronomia è una scienza applicata
collegata alle altre scienze (biologia,
chimica,
fisica,
geologia, ecc.), il cui ambito principale d'applicazione
è l'agricoltura. L'agricoltura è invece un insieme di
tecniche che riassumono le conoscenze
empiriche tramandate di generazione in generazione in
una pratica millenaria e quelle tecniche fornite dalla
ricerca scientifica in campo agronomico. Le varie forme di
agricoltura derivano dal ruolo ponderale che hanno, da un
lato, l'agronomia e, dall'altro, la tradizione.
Bibliografia
- Babel W. Congiunture agrarie e crisi agrarie Einaudi,
Torino, 1976
- Bairoch P., Rivoluzione industriale e sottosviluppo,
Einaudi, Torino, 1967
- Bloch Marc, Les caractères originaux de l'histoire rurale
française, A. Colin, Paris, 1952
- Daclon C.M., Agricoltura e riforme mondiali, in
Agricoltura, Rivista del Ministero Politiche Agricole e
Forestali, n. 300, 2000
- Daclon C.M., Biotecnologie e agricoltura, in Agricoltura,
Rivista del Ministero Politiche Agricole e Forestali, n.
302, 2000
- Saltini A., Storia delle scienze agrarie, 4 voll., Bologna
1984-89,
ISBN 88-206-2412-5,
ISBN 88-206-2413-3,
ISBN 88-206-2414-1,
ISBN 88-206-2414-X
- Saltini A. Processo all'agricoltura, Prefazione di
Giovanni Marcora, Bologna, 1979
- Sereni E.Storia del paesaggio agrario italiano Laterza,
1989
- Slicher van Bath Bernard H., Storia agraria dell'Europa
occidentale (500-1850), Einaudi, Torino, 1972 (traduzione
italiana dall'edizione inglese The Agrarian History of
Western Europe, A. D. 500 – 1850, E. Arnold, London, 1963,
curata dallo stesso autore; edizione originale: De
agrarische geschiedenis van West-Europa (500-1850), Het
Spectrum, Utrecht-Antwerpen, 1962)
- Vignoli G., Profili giuridici della produzione agricola,
Giuffrè, Milano, 1991.
- Vignoli G. Aspetti giuridici delle attività genetiche in
agricoltura, Giuffrè, Milano, 1986.
- Vignoli G. I territori italofoni non appartenenti alla
Repubblica Italiana - Agraristica, Giuffrè, Milano, 1995.
Tratto da it.wikipedia.org
http://www.eticamente.net/40442/guida-per-lorto-sinergico-come-realizzare-lorto-piu-naturale-assoluto.html
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Published
in Australian Biologist 6: 96 – 105, June 1993
By Greg
Wadley & Angus Martin
-
Department
of Zoology, University of Melbourne
Introduction
What might head a list of the defining characteristics
of the human species ? While our view of ourselves could hardly avoid
highlighting our accomplishments in engineering, art, medicine, space
travel and the like, in a more dispassionate assessment agriculture would
probably displace all other contenders for top billing. Most of the other
achievements of humankind have followed from this one. Almost without
exception, all people on earth today are sustained by agriculture.
With a
minute number of exceptions, no other species is a farmer. Essentially all
of the arable land in the world is under cultivation. Yet agriculture
began just a few thousand years ago, long after the appearance of
anatomically modern humans.
Given the rate and the scope of this revolution in
human biology, it is quite extraordinary that there is no generally
accepted model accounting for the origin of agriculture. Indeed, an
increasing array of arguments over recent years has suggested that
agriculture, far from being a natural and upward step, in fact led
commonly to a lower quality of life. Hunter-gatherers typically do less
work for the same amount of food, are healthier, and are less prone to
famine than primitive farmers (Lee & DeVore 1968, Cohen 1977, 1989). A
biological assessment of what has been called the puzzle of agriculture
might phrase it in simple ethological terms: why was this behaviour (agriculture)
reinforced (and hence selected for) if it was not offering adaptive
rewards surpassing those accruing to hunter-gathering or foraging
economies?
This paradox is responsible for a profusion of models
of the origin of agriculture. 'Few topics in prehistory', noted Hayden
(1990) 'have engendered as much discussion and resulted in so few
satisfying answers as the attempt to explain why hunter/gatherers began to
cultivate plants and raise animals. Climatic change, population pressure,
sedentism, resource concentration from desertification, girls' hormones,
land ownership, geniuses, rituals, scheduling conflicts, random genetic
kicks, natural selection, broad spectrum adaptation and multicausal
retreats from explanation have all been proffered to explain domestication.
All have major flaws ... the data do not accord well with any one of these
models. '
Recent discoveries of potentially psychoactive
substances in certain agricultural products - cereals and milk - suggest
an additional perspective on the adoption of agriculture and the
behavioural changes ('civilisation') that followed it. In this paper we
review the evidence for the drug-like properties of these foods, and then
show how they can help to solve the biological puzzle just described .
The emergence of agriculture and civilisation in the
Neolithic
The transition to agriculture
From about 10,000 years ago, groups of people in
several areas around the world began to abandon the foraging lifestyle
that had been successful, universal and largely unchanged for millennia (Lee
& DeVore 1968). They began to gather, then cultivate and settle around,
patches of cereal grasses and to domesticate animals for meat, labour,
skins and other materials, and milk.
Farming, based predominantly on wheat and
barley, first
appeared in the Middle East, and spread quickly to western Asia, Egypt and
Europe. The earliest civilisations all relied primarily on cereal
agriculture. Cultivation of fruit trees began three thousand years later,
again in the MiddleEast, and vegetables and other crops followed (Zohari
1986). Cultivation of rice began in Asia about 7000 years ago (Stark
1986).
To this day, for most people, two-thirds of protein and
calorie intake is cereal-derived. (In the west, in the twentieth century,
cereal consumption has decreased slightly in favour of meat, sugar, fats
and so on.) The respective contributions of each cereal to current total
world production are: wheat (28 per cent), corn/maize (27 per cent), rice
(25 per cent), barley (10 per cent), others (10 per cent) (Pedersen et al.
1989).
The change in the diet due to agriculture
The modern human diet is very different from that of
closely related primates and, almost certainly, early hominids (Gordon
1987). Though there is controversy over what humans ate before the
development of agriculture, the diet certainly did not include cereals and
milk in appreciable quantities. The storage pits and processing tools
necessary for significant consumption of cereals did not appear until the
Neolithic (Washburn & Lancaster 1968). Dairy products were not
available in quantity before the domestication of animals.
The early hominid diet (from about four million years
ago), evolving as it did from that of primate ancestors, consisted
primarily of fruits, nuts and other vegetable matter, and some meat -
items that could be foraged for and eaten with little or no processing.
Comparisons of primate and fossil-hominid anatomy, and of the types and
distribution of plants eaten raw by modern chimpanzees, baboons and humans
(Peters & O'Brien 1981, Kay 1985), as well as microscope analysis of
wear patterns on fossil teeth (Walker 1981, Peuch et al.1983) suggest that
australopithecines were 'mainly frugivorous omnivores with a dietary
pattern similar to that of modern chimpanzees' (Susman 1987:171).
The diet of pre-agricultural but anatomically modern
humans (from 30,000 years ago) diversified somewhat, but still consisted
of meat, fruits, nuts, legumes, edible roots and tubers, with consumption
of cereal seeds only increasing towards the end of the Pleistocene (e.g.
Constantini 1989 and subsequent chapters in Harris and Hillman 1989).
The rise of civilisation
Within a few thousand years of the adoption of cereal
agriculture, the old hunter-gatherer style of social organisation began to
decline. Large, hierarchically organised societies appeared, centred
around villages and then cities. With the rise of civilisation and the
state came socioeconomic classes, job specialisation, governments and
armies.
The size of populations living as coordinated units
rose dramatically above pre-agricultural norms. While hunter-gatherers
lived in egalitarian, autonomous bands of about 20 closely related persons,
with at most a tribal level of organisation above that, early agricultural
villages had 50 to 200 inhabitants, and early cities 10,000 or more.
People 'had to learn to curb deep-rooted forces which worked for
increasing conflict and violence in large groups' (Pfeiffer 1977:438).
Agriculture and civilisation meant the end of foraging
- a subsistence method with shortterm goals and rewards - and the
beginning (for most) of regular arduous work, oriented to future payoffs
and the demands of superiors. 'With the coming of large communities,
families no longer cultivated the land for themselves and their immediate
needs alone, but for strangers and for the future. They worked all day
instead of a few hours a day, as hunter-gatherers had done. There were
schedules, quotas, overseers, and punishments for slacking off' (Pfeiffer
1977:21).
Explaining the origins of agriculture and civilisation
The phenomena of human agriculture and civilisation are
ethologically interesting, because (1) virtually no other species lives
this way, and (2) humans did not live this way until relatively recently.
Why was this way of life adopted, and why has it become dominant in the
human species?
Problems explaining agriculture
Until recent decades, the transition to farming was
seen as an inherently progressive one: people learnt that planting seeds
caused crops to grow, and this new improved food source led to larger
populations, sedentary farm and town life, more leisure time and so to
specialisation, writing, technological advances and civilisation. It is
now clear that agriculture was adopted despite certain disadvantages of
that lifestyle (e.g. Flannery 1973, Henry 1989). There is a substantial
literature (e.g. Reed 1977), not only on how agriculture began, but why.
Palaeopathological and comparative studies show that health deteriorated
in populations that adopted cereal agriculture, returning to
pre-agricultural levels only in modem times.
This is in part attributable
to the spread of infection in crowded cities, but is largely due to a
decline in dietary quality that accompanied intensive cereal farming (Cohen
1989). People in many parts of the world remained hunter-gatherers until
quite recently; though they were quite aware of the existence and methods
of agriculture, they declined to undertake it (Lee & DeVore 1968,
Harris 1977). Cohen (1977:141) summarised the problem by asking: 'If
agriculture provides neither better diet, nor greater dietary reliability,
nor greater ease, but conversely appears to provide a poorer diet, less
reliably, with greater labor costs, why does anyone become a farmer?'
Many explanations have been
offered, usually centred
around a particular factor that forced the adoption of agriculture, such
as environmental or population pressure (for reviews see Rindos 1984,
Pryor 1986, Redding 1988, Blumler & Byrne 1991). Each of these models
has been criticised extensively, and there is at this time no generally
accepted explanation of the origin of agriculture.
Problems explaining civilisation
A similar problem is posed by the post-agricultural
appearance, all over the world, of cities and states, and again there is a
large literature devoted to explaining it (e.g. Claessen & Skalnik
1978). The major behavioural changes made in adopting the civilised
lifestyle beg explanation. Bledsoe (1987:136) summarised the situation
thus:
'There has never been and there is not now agreement on
the nature and significance of the rise of civilisation.
The questions
posed by the problem are simple, yet fundamental. How did civilisation
come about? What animus impelled man to forego the independence,
intimacies, and invariability of tribal existence for the much larger and
more impersonal political complexity we call the state? What forces fused
to initiate the mutation that slowly transformed nomadic societies into
populous cities with ethnic mixtures, stratified societies, diversified
economies and unique cultural forms? Was the advent of civilisation the
inevitable result of social evolution and natural laws of progress or was
man the designer of his own destiny? Have technological innovations been
the motivating force or was it some intangible factor such as religion or
intellectual advancement?'
To a very good
approximation, every civilisation that
came into being had cereal agriculture as its subsistence base, and
wherever cereals were cultivated, civilisation appeared. Some hypotheses
have linked the two. For example, Wittfogel's (1957) 'hydraulic theory'
postulated that irrigation was needed for agriculture, and the state was
in turn needed to organise irrigation. But not all civilisations used
irrigation, and other possible factors (e.g. river valley placement,
warfare, trade, technology, religion, and ecological and population
pressure) have not led to a universally accepted model.
Pharmacological properties of cereals and milk
Recent research into the pharmacology of food presents
a new perspective on these problems.
Exorphins: opioid substances in food
Prompted by a possible link between diet and mental
illness, several researchers in the late 1970s began investigating the
occurrence of drug-like substances in some common foodstuffs.
Dohan (1966, 1984) and Dohan et al. (1973, 1983) found
that symptoms of schizophrenia were relieved somewhat when patients were
fed a diet free of cereals and milk. He also found that people with
coeliac disease - those who are unable to eat wheat gluten because of
higher than normal permeability of the gut - were statistically likely to
suffer also from schizophrenia. Research in some Pacific communities
showed that schizophrenia became prevalent in these populations only after
they became 'partially westernised and consumed wheat, barley beer, and
rice' (Dohan 1984).
Groups led by Zioudrou (1979) and Brantl (1979) found
opioid activity in wheat, maize and barley (exorphins), and bovine and
human milk (casomorphin), as well as stimulatory activity in these
proteins, and in oats, rye and soy. Cereal exorphin is much stronger than
bovine casomorphin, which in turn is stronger than human casomorphin. Mycroft et al. (1982, 1987) found an analogue
of MIF-1, a naturally occurring dopaminergic peptide, in wheat and milk.
It occurs in no other exogenous protein.
(In subsequent sections we use
the term exorphin to cover exorphins, casomorphin, and the MIF-1 analogue.
Though opioid and dopaminergic substances work in different ways, they are
both 'rewarding', and thus more or less equivalent for our purposes.)
Since then, researchers have measured the potency of
exorphins, showing them to be comparable to morphine and enkephalin (Heubner
et al. 1984), determined their amino acid sequences (Fukudome &Yoshikawa
1992), and shown that they are absorbed from the intestine (Svedburg et al.1985) and can produce effects such as analgesia and reduction of
anxiety which are usually associated with poppy-derived opioids (Greksch
et al.1981, Panksepp et al.1984). Mycroft et al. estimated that 150 mg of
the MIF-1 analogue could be produced by normal daily intake of cereals and
milk, noting that such quantities are orally active, and half this amount
'has induced mood alterations in clinically depressed subjects' (Mycroft
et al. 1982:895). (For detailed reviews see Gardner 1985 and Paroli 1988.)
Most common drugs of addiction are either opioid
(e.g
heroin and morphine) or dopaminergic (e.g. cocaine and amphetamine), and
work by activating reward centres in the brain. Hence we may ask, do these
findings mean that cereals and milk are chemically rewarding? Are humans
somehow 'addicted' to these foods?
Problems in interpreting these findings
Discussion of the possible behavioural effects of
exorphins, in normal dietary amounts, has been cautious. Interpretations
of their significance have been of two types:
- where a pathological effect is proposed
(usually
by cereal researchers, and related to Dohan's findings, though see also
Ramabadran & Bansinath 1988), and
- where a natural function is proposed
(by milk researchers, who suggest that casomorphin may help in mother-infant
bonding or otherwise regulate infant development).
We believe that there can be no natural function for
ingestion of exorphins by adult humans. It may be that a desire to find a
natural function has impeded interpretation (as well as causing attention
to focus on milk, where a natural function is more plausible) . It is
unlikely that humans are adapted to a large intake of cereal exorphin,
because the modern dominance of cereals in the diet is simply too new. If
exorphin is found in cow's milk, then it may have a natural function for
cows; similarly, exorphins in human milk may have a function for infants.
But whether this is so or not, adult humans do not naturally drink milk of
any kind, so any natural function could not apply to them.
Our sympathies therefore lie with the pathological
interpretation of exorphins, whereby substances found in cereals and milk
are seen as modern dietary abnormalities which may cause schizophrenia,
coeliac disease or whatever. But these are serious diseases found in a
minority. Can exorphins be having an effect on humankind at large?
Other evidence for 'drug-like' effects of these foods
Research into food allergy has shown that normal
quantities of some foods can have pharmacological, including behavioural,
effects. Many people develop intolerances to particular foods. Various
foods are implicated, and a variety of symptoms is produced. (The term 'intolerance'
rather than allergy is often used, as in many cases the immune system may
not be involved (Egger 1988:159). Some intolerance symptoms, such as
anxiety, depression, epilepsy, hyperactivity, and schizophrenic episodes
involve brain function (Egger 1988, Scadding & Brostoff 1988).
Radcliffe (1982, quoted in 1987:808) listed the foods
at fault, in descending order of frequency, in a trial involving 50
people: wheat (more than 70 per cent of subjects reacted in some way to it),
milk (60 per cent), egg (35 per cent), corn, cheese, potato, coffee, rice,
yeast, chocolate, tea, citrus, oats, pork, plaice, cane, and beef (10 per
cent). This is virtually a list of foods that have become common in the
diet following the adoption of agriculture, in order of prevalence. The
symptoms most commonly alleviated by treatment were mood change (>50
per cent) followed by headache, musculoskeletal and respiratory ailments.
One of the most striking phenomena in these studies is
that patients often exhibit cravings, addiction and withdrawal symptoms
with regard to these foods (Egger 1988:170, citing Randolph 1978; see also
Radcliffe 1987:808-10, 814, Kroker 1987:856, 864, Sprague & Milam
1987:949, 953, Wraith 1987:489, 491). Brostoff and Gamlin (1989:103)
estimated that 50 per cent of intolerance patients crave the foods that
cause them problems, and experience withdrawal symptoms when excluding
those foods from their diet. Withdrawal symptoms are similar to those
associated with drug addictions (Radcliffe 1987:808). The possibility that
exorphins are involved has been noted (Bell 1987:715), and Brostoff and
Gamlin conclude (1989:230):
'... the results so far suggest that they might
influence our mood. There is certainly no question of anyone getting
'high' on a glass of milk or a slice of bread - the amounts involved are
too small for that - but these foods might induce a sense of comfort and
wellbeing, as food-intolerant patients often say they do. There are also
other hormone-like peptides in partial digests of food, which might have
other effects on the body.'
There is no possibility that craving these foods has
anything to do with the popular notion of the body telling the brain what
it needs for nutritional purposes. These foods were not significant in the
human diet before agriculture, and large quantities of them cannot be
necessary for nutrition. In fact, the standard way to treat food
intolerance is to remove the offending items from the patient's diet.
A suggested interpretation of exorphin research
But what are the effects of these foods on normal
people? Though exorphins cannot have a naturally selected physiological
function in humans, this does not mean that they have no effect.
Food intolerance research suggests that cereals and milk, in normal
dietary quantities, are capable of affecting behaviour in many people. And
if severe behavioural effects in schizophrenics and coeliacs can be caused
by higher than normal absorption of peptides, then more subtle effects,
which may not even be regarded as abnormal, could be produced in people
generally.
The evidence presented so far suggests the following
interpretation.
The ingestion of cereals and milk, in normal modern
dietary amounts by normal humans, activates reward centres in the brain.
Foods that were common in the diet before agriculture (fruits and so on)
do not have this pharmacological property.
The effects of exorphins are
qualitatively the same as those produced by other opioid and / or
dopaminergic drugs, that is, reward, motivation, reduction of anxiety, a
sense of wellbeing, and perhaps even addiction. Though the effects of a
typical meal are quantitatively less than those of doses of those drugs,
most modern humans experience them several times a day, every day of their
adult lives.
Hypothesis: exorphins and the origin of agriculture and
civilisation
When this scenario of human dietary practices is viewed
in the light of the problem of the origin of agriculture described earlier,
it suggests an hypothesis that combines the results of these lines of
enquiry.
Exorphin researchers, perhaps lacking a long-term
historical perspective, have generally not investigated the possibility
that these foods really are drug-like, and have instead searched without
success for exorphin's natural function. The adoption of cereal
agriculture and the subsequent rise of civilisation have not been
satisfactorily explained, because the behavioural changes underlying them
have no obvious adaptive basis.
These unsolved and until-now unrelated problems may in
fact solve each other. The answer, we suggest, is this: cereals and dairy
foods are not natural human foods, but rather are preferred because they
contain exorphins. This chemical reward was the incentive for the adoption
of cereal agriculture in the Neolithic. Regular self-administration of
these substances facilitated the behavioural changes that led to the
subsequent appearance of civilisation.
This is the sequence of events that we
envisage.
Climatic change at the end of the last glacial period
led to an increase in the size and concentration of patches of wild
cereals in certain areas (Wright 1977). The large quantities of cereals
newly available provided an incentive to try to make a meal of them.
People who succeeded in eating sizeable amounts of cereal seeds discovered
the rewarding properties of the exorphins contained in them. Processing
methods such as grinding and cooking were developed to make cereals more
edible. The more palatable they could be made, the more they were consumed,
and the more important the exorphin reward became for more people.
At first, patches of wild cereals were protected and
harvested. Later, land was cleared and seeds were planted and tended, to
increase quantity and reliability of supply. Exorphins attracted people to
settle around cereal patches, abandoning their nomadic lifestyle, and
allowed them to display tolerance instead of aggression as population
densities rose in these new conditions.
Though it was, we suggest, the presence of exorphins
that caused cereals (and not an alternative already prevalent in the diet)
to be the major early cultigens, this does not mean that cereals are 'just
drugs'. They have been staples for thousands of years, and clearly have
nutritional value. However, treating cereals as 'just food' leads to
difficulties in explaining why anyone bothered to cultivate them. The fact
that overall health declined when they were incorporated into the diet
suggests that their rapid, almost total replacement of other foods was due
more to chemical reward than to nutritional reasons.
It is noteworthy that the extent to which early groups
became civilised correlates with the type of agriculture they practised.
That is, major civilisations (in south-west Asia, Europe, India, and east
and parts of South-East Asia; central and parts of north and south
America; Egypt, Ethiopia and parts of tropical and west Africa) stemmed
from groups which practised cereal, particularly wheat, agriculture (Bender
1975:12, Adams 1987:201, Thatcher 1987:212). (The rarer nomadic
civilisations were based on dairy farming.)
Groups which practised vegeculture (of
fruits, tubers etc.), or no agriculture (in tropical and south Africa, north and central
Asia, Australia, New Guinea and the Pacific, and much of north and south
America) did not become civilised to the same extent.
Thus major civilisations have in common that their
populations were frequent ingesters of exorphins. We propose that large,
hierarchical states were a natural consequence among such populations.
Civilisation arose because reliable, on-demand availability of dietary
opioids to individuals changed their behaviour, reducing aggression, and
allowed them to become tolerant of sedentary life in crowded groups, to
perform regular work, and to be more easily subjugated by rulers. Two
socioeconomic classes emerged where before there had been only one (Johnson
& Earle 1987:270), thus establishing a pattern which has been
prevalent since that time.
Discussion
The natural diet and genetic change
Some nutritionists deny the notion of a
pre-agricultural natural human diet on the basis that humans are
omnivorous, or have adapted to agricultural foods (e.g. Garn & Leonard
1989; for the contrary view see for example Eaton & Konner 1985) .
An omnivore, however, is simply an animal that eats both meat and plants: it
can still be quite specialised in its preferences (chimpanzees are an
appropriate example). A degree of omnivory in early humans might have
preadapted them to some of the nutrients contained in cereals, but not to
exorphins, which are unique to cereals.
The differential rates of lactase
deficiency, coeliac
disease and favism (the inability to metabolise fava beans) among modern
racial groups are usually explained as the result of varying genetic
adaptation to post-agricultural diets (Simopoulos 1990:27-9), and this
could be thought of as implying some adaptation to exorphins as well. We
argue that little or no such adaptation has occurred, for two reasons:
first, allergy research indicates that these foods still cause abnormal
reactions in many people, and that susceptibility is variable within as
well as between populations, indicating that differential adaptation is
not the only factor involved. Second, the function of the adaptations
mentioned is to enable humans to digest those foods, and if they are
adaptations, they arose because they conferred a survival advantage. But
would susceptibility to the rewarding effects of exorphins lead to lower,
or higher, reproductive success? One would expect in general that an
animal with a supply of drugs would behave less adaptively and so lower
its chances of survival. But our model shows how the widespread exorphin
ingestion in humans has led to increased population. And once civilisation
was the norm, non-susceptibility to exorphins would have meant not fitting
in with society. Thus, though there may be adaptation to the nutritional
content of cereals, there will be little or none to exorphins. In any
case, while contemporary humans may enjoy the benefits of some adaptation
to agricultural diets, those who actually made the change ten thousand
years ago did not.
Other 'non-nutritional' origins of agriculture models
We are not the first to suggest a non-nutritional
motive for early agriculture. Hayden (1990) argued that early cultigens
and trade items had more prestige value than utility, and suggested that
agriculture began because the powerful used its products for competitive
feasting and accrual of wealth. Braidwood et
al. (1953) and later Katz and Voigt
(1986) suggested that the incentive for cereal cultivation was the
production of alcoholic beer:
'Under what conditions would the consumption of a wild
plant resource be sufficiently important to lead to a change in behaviour
(experiments with cultivation) in order to ensure an adequate supply of
this resource? If wild cereals were in fact a minor part of the diet, any
argument based on caloric need is weakened. It is our contention that the
desire for alcohol would constitute a perceived psychological and social
need that might easily prompt changes in subsistence behaviour' (Katz
& Voigt 1986:33).
This view is clearly compatible with
ours. However
there may be problems with an alcohol hypothesis: beer may have appeared
after bread and other cereal products, and been consumed less widely or
less frequently (Braidwood et al. 1953). Unlike alcohol, exorphins are
present in all these products. This makes the case for chemical reward as
the motive for agriculture much stronger. Opium poppies, too, were an
early cultigen (Zohari 1986). Exorphin, alcohol, and opium are primarily
rewarding (as opposed to the typically hallucinogenic drugs used by some
hunter-gatherers) and it is the artificial reward which is necessary, we
claim, for civilisation. Perhaps all three were instrumental in causing
civilised behaviour to emerge.
Cereals have important qualities that differentiate
them from most other drugs. They are a food source as well as a drug, and
can be stored and transported easily. They are ingested in frequent small
doses (not occasional large ones), and do not impede work performance in
most people. A desire for the drug, even cravings or withdrawal, can be
confused with hunger. These features make cereals the ideal facilitator of
civilisation (and may also have contributed to the long delay in
recognising their pharmacological properties).
Compatibility, limitations, more data needed
Our hypothesis is not a refutation of existing accounts
of the origins of agriculture, but rather fits alongside them, explaining
why cereal agriculture was adopted despite its apparent disadvantages and
how it led to civilisation.
Gaps in our knowledge of exorphins limit the generality
and strength of our claims. We do not know whether rice, millet and
sorghum, nor grass species which were harvested by African and Australian
hunter-gatherers, contain exorphins.
We need to be sure that
preagricultural staples do not contain exorphins in amounts similar to
those in cereals.
We do not know whether domestication has affected
exorphin content or-potency. A test of our hypothesis by correlation of
diet and degree of civilisation in different populations will require
quantitative knowledge of the behavioural effects of all these foods.
We do not comment on the origin of noncereal
agriculture, nor why some groups used a combination of foraging and
farming, reverted from farming to foraging, or did not farm at all. Cereal
agriculture and civilisation have, during the past ten thousand years,
become virtually universal. The question, then, is not why they happened
here and not there, but why they took longer to become established in some
places than in others. At all times and places, chemical reward and the
influence of civilisations already using cereals weighed in favour of
adopting this lifestyle, the disadvantages of agriculture weighed against
it, and factors such as climate, geography, soil quality, and availability
of cultigens influenced the outcome. There is a recent trend to
multi-causal models of the origins of agriculture (e.g. Redding 1988,
Henry 1989), and exorphins can be thought of as simply another factor in
the list. Analysis of the relative importance of all the factors involved,
at all times and places, is beyond the scope of this paper.
Conclusion
'An animal is a survival machine for the genes that
built it. We too are animals, and we too are survival machines for our
genes. That is the theory. In practice it makes a lot of sense when we
look at wild animals.... It is very different when we look at ourselves.
We appear to be a serious exception to the Darwinian law.... It obviously
just isn't true that most of us spend our time working energetically for
the preservation of our genes' (Dawkins 1989:138).
Many ethologists have acknowledged difficulties in
explaining civilised human behaviour on evolutionary grounds, in some
cases suggesting that modern humans do not always behave adaptively . Yet
since agriculture began, the human population has risen by a factor of
1000: Irons (1990) notes that 'population growth is not the expected
effect of maladaptive behaviour'.
We have reviewed evidence from several areas of
research which shows that cereals and dairy foods have drug-like
properties, and shown how these properties may have been the incentive for
the initial adoption of agriculture. We suggested further that constant
exorphin intake facilitated the behavioural changes and subsequent
population growth of civilisation, by increasing people's tolerance of (a)
living in crowded sedentary conditions, (b) devoting effort to the benefit
of non-kin, and (c) playing a subservient role in a vast hierarchical
social structure.
Cereals are still staples, and methods of artificial
reward have diversified since that time, including today a wide range of
pharmacological and non-pharmacological cultural artfacts whose function,
ethologically speaking, is to provide reward without adaptive benefit. It
seems reasonable then to suggest that civilisation not only arose out of
self-administration of artificial reward, but is maintained in this way
among contemporary humans. Hence a step towards resolution of the problem
of explaining civilised human behaviour may be to incorporate into
ethological models this widespread distortion of behaviour by artificial
reward.
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