Rome, Italy
May 4, 2007
Source:
The Global Diversity Trust
- Analysis and Reflections no. 8/2007
How Great the Loss?
Adams' apple is extinct. And his beans are gone too. Both apple
and bean varieties bearing the name of an early president of the
United States have vanished. In fact, of the 7100 named
varieties of apples growing in the U.S. in the 1800s, some 6800
are probably now extinct. Ninety-five percent of almost 600
garden bean varieties, 95% of more than 500 cabbage varieties,
and 81% of 400 tomato varieties have also disappeared.
Simply to say that they have disappeared fails to convey the
finality of the situation. "Death is one thing; an end to birth
is something else," as biologists Soule and Wilcox once pointed
out. For the Ansault pear, described by the leading fruit expert
of the early 20th century as having flesh more "buttery" than
any other pear and possessing a "rich sweet flavor, and a
distinct but delicate perfume," there is no more birth. It's
extinct.
Given the business the Trust is in, we are used to fielding one
very natural but difficult question, "How much diversity has
been lost?"
Percentages such as those just provided cannot give an accurate
portrayal of the loss of crop diversity, or the loss of
potentially important traits. The Adams apple may be extinct,
but it was not the only red apple in the world. Red didn't
disappear. Many - theoretically even all - the individual genes
found in Adams apple could still exist, spread amongst the
still-surviving varieties.
All plants are biologically related. Rice, wheat, and maize, for
example, are grasses and as such are closely related. Darwin
explained such connections with his theory of "common descent".
We're all cousins. Indeed, chickens, as we just discovered, are
related to the long-gone Tyrannosaurus rex. And you and I share
genes with rice, wheat and the potted plant by the window.
Perhaps as many as 50%. If this estimate is roughly accurate,
then 50% of the genetic diversity of a crop will continue to
exist no matter how many varieties are lost, as long as you and
I are still alive.
So there's one admittedly mischievous answer to the question. No
one seriously fears losing the ubiquitous genes shared by
cabbages and kings, however. Losing genes associated with unique
and potentially important characteristics in crops is an
entirely different matter. This is the diversity that will
enable crops to adapt to the challenges already present as well
as to new and unknown threats that will inevitably arise.
In the 1900s, the commercialization and increasing globalization
of agriculture, as well as the marketing and distribution of
seeds by commercial and government agencies, combined to produce
motive and method for the replacement of numerous diverse crop
varieties with a smaller number of more genetically homogeneous,
scientifically-bred varieties. Garrison Wilkes likened the
process to "taking stones from the foundation in order to repair
the roof." The new varieties unintentionally undermined the
biological basis upon which they were built. Production leapt
forward, but much crop diversity was lost, as noted by ample
anecdotal accounts. But "because no one can say exactly how much
diversity once existed, no one can say exactly how much has been
lost historically," as FAO's first global assessment of the
state of crop diversity pointed out,
Likewise we cannot say with precision how much has been saved.
Three independent surveys of scientists undertaken in the 1980s
and 1990s each concluded, however, that a high percentage of
existing diversity of major crops has been collected and is in
genebanks - as much as 95% for wheat, rice, maize and potato.
Other crops are less well represented. Perhaps a fifth of
sorghum diversity and up to half of sweet potato diversity
remains to be collected and formally conserved.
Genebanks contain thousands of varieties that can no longer be
found on anyone's farm. The social and environmental conditions
that gave rise to them in the first place are quickly
disappearing and are unlikely to reappear. It is fortunate that
many varieties were collected and placed in managed collections,
otherwise the extent of genetic erosion would have been far, far
greater.
For the same reasons that so much diversity was lost in the last
century, the remaining diversity found on farms today and not in
genebanks would have to be considered seriously endangered. Only
now, there is a new threat: climate change.
The Intergovernmental Panel on Climate Change paints a gloomy
picture where up to 30% of earth's species will be at an
increased risk of extinction as global temperatures rise.
Profound climatic shifts will unavoidably exert pressure on the
remaining crop diversity not yet safeguarded in genebanks,
including the "wild relatives" of domesticated crops that have
been an important source of disease and pest resistance and have
even salvaged a number of our major crops.
The time has come to acknowledge both the old and familiar
threats to crop diversity as well as the new challenges, collect
samples of the remaining diversity, safeguard all of it in
genebanks, and guard those banks.
Lost and Found
The honest answer to the question of how much diversity has been
lost is "we just don't know". There was never a complete
inventory of what there was "in the first place". The word
"gene" has only been around since 1900; clearly we have no
quantitative measures of the genetic diversity that existed
before that.
We live in a world of wounds, as the ecologist Aldo Leopold once
remarked. Both Adams apple and Tyrannosaurus rex have departed.
But apple varieties are not the same as dinosaurs and therein
lies a distinction worth pondering. The diversity of apples and
other crops can be saved in a secure and lasting manner. The
global system the Trust is helping develop will do just that,
protecting the diversity that will enable crops to adapt to and
survive future changes in the environment. Dinosaurs didn't have
such a system, and they didn't stand a chance.
The important question is therefore not how much crop diversity
has been lost - we'll never know - but how much still exists and
what we are going to do about it. We can decide to get serious
about conserving what's left, or follow the lead of T. rex and
take our chances.
FAO. The State of the World's Plant Genetic Resources for Food
and Agriculture. Rome: 1998.
http://www.fao.org/ag/AGP/AGPS/Pgrfa/pdf/swrfull.pdf
Guarino, Luigi. Approaches to Measuring Genetic Erosion.
Bioversity International
http://apps3.fao.org/wiews/Prague/Paper3.jsp
The Global Diversity Trust is
an independent international organization whose mission is to
ensure the long term conservation of crop diversity, the
biological foundation for agriculture and food security. |
|
