Siempre Arica

PERSPECTIVES
formance. But other methods were in the
process of development.

TIMELINE

Biotechnology in the 1930s:
the development of hybrid maize
Donald N. Duvick
Hybrid maize was one of the first examples of
genetic theory successfully applied to food
production. When first introduced, it seemed
almost miraculous; sturdy hybrids convinced
sceptical farmers that ‘the professors’and
their arcane science could do them some
good. Strangely, the genetic basis of heterosis
(hybrid vigour) was and still is unknown. But to
this day, newer hybrids continue to outyield
their predecessors; they do so because they
are tougher and healthier.

manipulate genetic materials. Genetic transformation, also called genetic engineering, is
one kind of biotechnology.)
Why were similarconcerns not expressed
70 years ago when maize hybrids were bred
and released rapidly and on a large scale in the
heart of the United States ‘Corn Belt’? I will
consider these questions in the light of the
following account of the origins and development of hybrid maize.
Darwin, maize and hybrid vigour

Hybrid maize (Zea mays) is not new, but the
biological and sociological bases onwhich it
was built are now considered as new — and
disturbing — by some segments of the public.
When hybrid maize was invented and
presented to US farmers in the first decades
of the twentieth century, it was based on
two new operations, one biological and the
other socio-economic. First, strange manipulations (forced inbreeding and controlled
hybridization) produced biological products thathad never before existed in nature.
Second, farmers gave up their time-honoured practice of saving their own varieties
of seed in favour of annual purchases of
hybrid maize seed.
These two actions are deplored today by
some elements of society as the undesired and
potentially dangerous consequences of the
application of biotechnology (especially, of
genetic transformation) to plantbreeding1,2.
(The term ‘biotechnology’ has many definitions, but is used here to refer to the branch of
molecular biology that uses recombinant
DNA technology to study, categorize and

Charles Darwin did many experiments to
test his theory on the origin of species3. One
of them involved a comparison of inbred and
cross-pollinated maize. He noted that the
progeny of cross-pollinated maize plantswere 25% taller than the progeny of self-pollinated plants and had greater tolerance to
cooler growing conditions. From these
experiments, he concluded in 1876 that, as a
general rule, cross-pollinated (hybrid) plants
have “greater height, weight, and fertility” as
compared with their self-pollinated counterparts because of their “greater innate constitutional vigour”4.
In the United States,William Beal at
Michigan State College was encouraged by
Darwin’s observations on hybrid vigour and
hybridized pairs of open-pollinated varieties
of maize. Beal observed increased vigour and
grain yield in the hybrids of different varieties
and, in 1880, he encouraged the use of this
method5–7. However, because the results of
further experiments were unpredictable5,
hybridization seemedto have no future as a
way to improve maize yields and general per-

NATURE REVIEWS | GENETICS

New breeding methods

Improved varieties. Around the turn of the
twentieth century, farmers in the United
States began to look harder than before for
ways to increase maize yields. Urban populations were increasing rapidly with a concomitant increase in the demand for meat,
which in turnincreased demand for feed
grains. As new lands were no longer available for exploitation, increased production
needed to come from higher yields. The use
of plant breeding to produce new and/or
improved, higher-yielding varieties of maize
looked like a promising option. Those farmers and scientists who selected new breeding
varieties rose to the challenge.
Disappointingly, the use of...