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February 11, 2009
Source:
The Global Crop Diversity
Trust
Oxford evolutionary biologist,
Richard Dawkins, makes the argument that were superior creatures
from a distant galaxy to visit earth – just getting here would
demonstrate that superiority – they would likely have little
more than passing interest in our music, culture, literature,
languages, economies, and history. Shakespeare, Freud, Marx,
Hollywood and the Pyramids might be no more than a curiosity.
Charles Darwin, however, would be another matter altogether.
Darwin’s explanation of how remarkably diverse and complicated
life forms on Earth resulted from “cumulative evolution by
non-random survival of random hereditary changes” might well
strike them as the most profound idea ever developed by one of
our species. And yet, at its heart, the insight is so simple. As
T.H. Huxley famously lamented to himself at the time, “How
extremely stupid not to have thought of that”.
This year we observe two major anniversaries: on 12 February,
the 200th anniversary of Charles Darwin’s birth, and in
November, the 150th anniversary of the publication of On the
Origin of Species.
Amateur plant and animal breeders have probably never had their
accomplishments so profoundly appreciated since the 1800s when a
quiet and modest man named Charles Darwin focused his curiosity
on them. His correspondence with pigeon and dog breeders was
extensive, his powers of observation extraordinary. Darwin was
keenly interested in the variability among individuals, whether
pigeons or peas. He discerned that differences were heritable.
Small, incremental improvements could be passed from generation
to generation and changes could be accumulated, leaving the
starting point far behind. This was nowhere more evident than
with agricultural crops and farm animal breeds. Little wonder
then, that the first chapter of his monumental On the Origin of
Species was entitled, “Variation under Domestication”.
Darwin also realized that flora and fauna alike produced more
offspring than could survive, and reasoned that the probability
of survival favored those most fit, and that the resulting
inheritance of qualities favoring fitness would produce gradual
changes in the population – i.e., evolution.
As Darwin came to understand, evolution was the product of
billions of tiny “experiments” in survival and fecundity, the
outcome of which decided which individuals, with which traits,
became parents to the next generation. Over time, the
statistical odds favor the retention and spread of these
adaptive differences and the loss of any that are
counterproductive – an albino deer, for example.
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In summary, the key ingredients in
Darwin’s schema were diversity, inheritance, selection, and
time. It was the interaction and the impact of the combination
of these (See Figure above) that Darwin was the first to unveil.
Responsibility
Sir Ronald Fisher, an early and prominent geneticist, contended
that the smaller the change, the more likely it would be
positive. He used a microscope analogy. A tiny movement in the
objective lens has a 50% chance of being in the right direction
and improving focus. A large movement in the lens, whether in
the right or wrong direction, is likely to worsen the focus.
So it is that dramatic changes in organisms from one generation
to the next, as a result of a major mutation, rarely succeed.
Huge random changes have the potential to take an organism in
countless directions, many, indeed most of them probably
unviable. The resulting organism simply is not adapted to the
environment in which it was born. Changes of a more limited
scope will be less dramatic, but will stand a better chance of
building on an existing success – that of the parents. As
Dawkins puts it, “However many ways there may be of being alive,
it is certain that there are vastly more ways of being dead”.
The small steps, not the giant leaps, are the most likely to
succeed.
And this brings us, finally, to the connection with crop
diversity. Unlike wild species, crops are domesticated. Their
fitness, their evolution is in our hands and as Sir Otto Frankel
put it, “we have acquired evolutionary responsibility”.
Darwin understood that populations that made appropriate and
successful adaptations survived and that those that didn’t
perished, and that agricultural crops were not exempt. He noted,
for example, that certain crop varieties “withstand certain
climates better than others” and in Origin, outlined a screening
and breeding experiment, suggesting that someone sow kidney
beans,
“…so early that a very
large proportion are destroyed by frost, and then collect
seed from the few survivors, with care to prevent accidental
crosses, and then again get seed from these seedlings, with
the same precautions…”
Modern genebanks and plant
breeders are essentially doing this today on a large scale and
with many crops. Drawing on the huge diversity stored in
genebanks, breeders expose samples to different conditions
(heat, drought, a new disease) to find the adaptive traits for
producing the new varieties that farmers will sow in the future.
But if this genetic diversity is not conserved, if we lose the
ability to make and accumulate those small changes so central to
evolution, we will have removed one of Darwin’s essential
pillars of evolution – variation – and will have rendered
selection impotent.
The diversity of our crops – what we have managed to save of it
– is what humans will have to fashion those small incremental
adaptive changes in crops necessary for their survival. Climate
change, and other pressures on agricultural systems and crops
intensify daily. Agriculture needs to respond, even now, with
crop varieties adapted and ready to meet these challenges. What
better way to commemorate Charles Darwin’s life and work than
guaranteeing that agriculture’s evolutionary process can
continue.
America’s new President, Barack Obama, said in his inaugural
address “What is required of us now is a new era of
responsibility… This is the price and promise of citizenship”.
For the world’s food supply, good global citizenship requires us
to embrace our “evolutionary responsibility”. It remains to be
seen whether we are prepared to pay its price.
To learn more about the topic
Darwin, Charles. On
the Origin of Species. 1859. (various publishers)
The Complete Work of Charles Darwin, online and searchable
at:
http://darwin-online.org.uk/
Dawkins, Richard. The Blind Watchmaker. Penguin.
1986.
Mayr, Ernst. One Long Argument: Charles Darwin and
the Genesis of Modern Evolutionary Thought. Harvard
University Press. 1991.
Mayr, Ernst. What Evolution Is. Basic Books. 2001.
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