Hugh
D. Wilson
Professor of Biology
Texas A&M University
Genetic modification of flowering plant lineages that provide Homo sapiens with food and fiber began 15 – 20 thousands years ago with our initial selections from the wild flora and experiments with cultivation of selected taxa. This initial impact on crop genomes, later refined by more focused human selection and accelerated during the agricultural revolution, is evident today as commercial plant products on display in markets throughout the world. The current debate on ‘genetically modified’ foods does not center on agricultural traditions that have served our species well for thousands of years. Scientific concern is focused on new technologies that offer the opportunity to modify crop plant genomes in a radical manner and, more importantly, application of these technologies via review procedures that maximize corporate profit and thereby minimize assessment of long-term impact. I feel that massive global economic investment in biotechnology, and associated corruption of governmental regulatory organizations, has focused attention on potential benefits of biotech crop ‘improvement’ and shifted attention away from potential risks. The ‘spin’ of the current debate has involved polarization to the point that those critical of the biotechnology enterprise are cast as ‘non-scientific’. With this unfortunate political dynamic in mind, those considering the various arguments involved in this debate must take a close look at the source of arguments being presented, i.e., who is being paid by commercial, biotech sources – either directly or through research ‘grants’, and who is not? My full academic background and history of research funding is available on line.
‘Agent Orange’, ‘DDT’, ‘Thalidomide’, ‘Asbestos’, and ‘Chernobyl’ are terms that signal a simple and fairly conspicuous fact of human history; we do not always know what we are doing or, if we do, informed sources are often ignored. Our best science can move too quickly from a base that carries significant ignorance to produce negative results that only become evident over the long term. The lure of new technologies has, in the past, stimulated rapid implementation to achieve a ‘quick fix’ or expanded corporate cash flow. We tend to isolate ourselves from our natural base and, as a result, often fail to appreciate the complexity of biotic systems that make up our operating environment. We then are forced to respond to unanticipated results by cleaning up the mess created when our new technologies interact with nature and, often, forgetting those that argued against initial implementation, repeat the same type of mistake. Not a pretty picture, but it reflects a pattern that is well documented in modern times and further suggested by massive human population crashes evident in the archaeological record.
Much of the current concern and debate on biotech-mediated agriculture relates to possible negative impacts from human consumption of transgenic artifacts in food, or the environmental-ecological consequences that might result when these artifacts are released into nature. These, in my view, represent traditional ‘pollution’ problems that, while the topic of legitimate concern, can be corrected when they become apparent. My primary personal concern, detailed below, is focused on a potential negative impact of ‘released’ transgenic artifacts that will be - unintentionally - incorporated into extant genomes and thereby produce negative consequences that could include biotic extinction events. This is a biological process that will be difficult to detect at initiation and impossible to correct if extinction is an end result.
Much of my professional life has focused on tracking the ‘family tree’ of specific domesticated plant species to better define points of origin, patterns of differentiation, and paths of subsequent dispersal. Assessment of my position in this matter requires, first of all, awareness of the simple fact that our domesticated plant species are the products of evolution via mechanisms initially defined by Darwin in 1859 and later refined by modern science. If current polls are to be believed, most Americans do not believe in evolution, much less appreciate or understand the underlying genetic/genomic mechanisms of phyletic, selective change through time. Thus, as opposed to the standard ‘pollution’ problem posed by transgenic artifacts as food or environmental contaminants, the potential problem that I see as most significant over the long term – which I will call ‘lineage pollution’ – is apparently a difficult concept for the public mind to grasp. Also, other scientists working in the general field of crop plant evolution will question the basic premise of my concern, i.e., that ‘companion weeds’ of crop plant species have evolved with the crop as active players, with human participants, in the long term evolutionary process that has produced the crop. I feel that, in most cases, free-living (wild, weedy) types that are able to exchange genetic material with a given domesticated type have been involved with reciprocal gene exchange over the phyletic history of the crop, i.e., both crop and companion weed represent the same lineage and the same genome. Finally, another personal premise that remains as a matter of scientific debate; I feel that this history of sporadic but continuous crop/weed gene exchange is a fundamental element of crop plant evolution. I think that data available on the genomic/genetic structure of weed/crop systems fully support, in most cases, the presence of ‘weed crop hybridization differentiation cycles’, as defined by Harlan (Harlan, J. R. 1975. Crops and Man. American Society of Agronomy, Madison), as an active component of the complex process of crop plant evolution.
If these phyletic notions are even partially accepted, it follows that retention of extant biodiversity representing crop plant genomes is of critical importance for human survival in the future. Our ability to manipulate crop plant evolution to either enhance production or accommodate change, as has been done in the past, will depend on the extent of genetic diversity available in the world's flora, i.e., cultivars, traditional land races, and free-living forms that share a common gene pool with domesticated kin. Modern, mechanized agriculture has functioned to diminish this diversity and genetic diversity represented by governmental or private germplasm collections is a minimal resource compared to that available in nature. Movement of mechanized, monocultural agricultural systems from developed to developing counties is displacing crop plant biodiversity at a rapid rate and this problem is not being addressed by the scientific/governmental community, which seems to find tropical wet forests more important, in terms of biodiversity conservation, than fields and weeds. Thus, possible negative consequences of ‘lineage pollution’ described below could exacerbate a problem that is quite serious right now.
I was drawn into this issue as a result of prior work on the origin and evolution of domesticated squash (Cucurbita pepo) and assessments of genetic structure/gene flow between domesticated squash and a free-living form known as the ‘Texas Gourd’. My published work in this particular area positioned me to provide expert opinion on a corporate petition to the U.S.D.A. for the commercial release of a transgenic squash. My report to the U.S.D.A. (Free-living Cucurbita pepo in the United States Viral Resistance, Gene Flow, and Risk Assessment) is in the public domain and supplemented by personal comments (Prologue/Epilogue). The reader can consult this document for detail on the nature of my concerns regarding transgenes as a component of crop lineage pollution. Given the caveats outlined above, this problem represents a relatively simple dynamic that I will try to define below using another example, the carrot.
The carrot (Daucus carota of the flowering plant family Apiaceae or Umbelliferae) is a well known crop with distinctive structural features of the root that most recognize as a commercial product. A common weed of fields and roadsides throughout temperate North America and Europe, known as ‘Queen Ann’s Lace’, is also distinctive and recognized by those with even a passing interest in the local flora. Queen Ann’s Lace is also known as ‘Wild Carrot’ and it is – indeed – a wild carrot, i.e., it is the conspecific companion weed of the domesticated carrot. While quite different from the domesticated carrot in terms of structure and ecological amplitude, it is very much a part of the carrot genome in that gene exchange occurs, has occurred in the past, and will occur in the future. Both types, fully domesticated carrots inhabiting fields and markets and free-living plants of vacant lots and pastures, are different structural expressions of the same genome. They are classified as the same species. They have evolved through time and space along the same path. So, the carrot - Daucus carota - represents a biological reality that is a bit more complex than the casual observer (and many scientists) might expect, and there is yet more involved.
The common presence of companion weeds for a given domesticated type represents an observation that stimulated the notion that crop evolution has proceeded, in most instances, by a process that has featured sporadic genetic exchange between domesticated and free-living forms via natural hybridization. Supporting this idea is the obvious genetic ‘downside’ of strong directional human selection, which involves problems associated in inbreeding and creation of a narrow genetic base, and the equally obvious genetic ‘upside’ of genomic hybridization, which includes hybrid vigor and increased genetic diversity. Available data on the genetic structure of crop/weed lineages tend to reveal, however, an interesting pattern. Crop types tend to be unusually uniform, relative to kin species not involved with human selection, for molecular markers used in the analysis and, in those cases where companion weeds are included in the study, the companion weed shares this lack of detectable genetic variation with the domesticated associate. These results suggest that, despite injections of variation via sporadic crop/weed hybridization events, selective forces acting on the system, both human and natural, are focused and strong. This shared lack of genetic variation between both domesticated and free-living elements also signals a very important point with regard to this discussion, i.e., domesticated and free-living elements share a common genome that has evolved, as an independent entity, through both space and time for, in most cases, thousands of years. Thus, crop/weed lineages present in today’s ethnoflora are biological entities that have moved away, in terms of both space, time, and genomic structure, from their points of origin. Modern companion weeds of a given crop are as far removed from the point of lineage origin as the crop form. All crop/weed lineages have a point of origin and, in most cases, this is a center of genetic diversity that includes true progenitor types (wild kin closest to the plants that were originally sampled by early foragers and farmers) and ancient ‘landrace’ domesticated types. It is this third component of a given crop lineage that is the most critical element, in terms of useful genetic diversity, of most modern crop lineages. For Daucus carota, this genomic nexus is centered somewhere in highlands of Afghanistan.
So, with this overview in mind, what is the problem with modern genetic engineering? Well, lets assume that Monsanto has tucked a Bt gene into a carrot cultivar. This gene, derived from a bacterial source, makes its home plant toxic to common consumers of plant tissue, insect larvae (caterpillars). A gardener buys the seed from Monsanto and creates a dense population of fully domesticated Daucus carota that will eventfully produce lots of good food and, after the food is produced via shunting the products of photosynthesis to the root, the Bt-equipped plants will do what all living things are designed to do; reproduce. Populations of any domesticated type under cultivation represented a concentrated and dense source of pollen. This pollen, sometimes mediated by insects, sometimes by the wind, will move among cultivated individuals and also move beyond the garden. If the companion weed, Queen Ann’s Lace, is in the area, its flowers will receive this pollen – and the Bt gene it carries. This event – gene flow - represents movement into the realm of nature and a move that takes the situation beyond the control or the gardener or Monsanto (see Blowin' in the Wind for an example). Subsequent fertilization will produce next years cohort of Queen Ann’s Lace and a few individuals of the Queen Ann’s Lace class of 2001 will carry something quite new, caterpillar resistance. The few plants that carry Monsanto’s Bt gene in 2001 will be more ‘fit’ that those that do not, i.e., their chances of survival to produce the class of 2002 are greater than those with no assistance from Monsanto. Thus, it is reasonable to assume that the genetic base of the class of 2002 would be dominated by progeny from these few ‘founder’ plants and, as a result, it will be narrowed relative to the situation that would be present if Bt had not been introduced into the game. If this scenario were to be played out in North America or Europe the genetic impact on the carrot lineage would probably be minimal in that the ‘founder’ populations of Queen Ann’s Lace in these areas do not carry the ‘nexus’ content of genetic diversity for the lineage. If, however, the gardener described above lived in Afghanistan, a transgene-mediated founder event could create a wave of population displacement or extinction that would be both profound and permanent.
This overview represents a simplified picture. The nature and magnitude of the ‘lineage pollution’ problem depends on the bioengineered taxon, the nature of the transgene, and the presence or absence of engineered devices that might work against gene flow from crop to weed. However, the evolutionary history of essentially all major crop plants is comparable to that described for the carrot and, to my knowledge, those responsible for reviewing commercial release of transgenic plant products in the U.S. Federal Government have, to this date, approved all requests. Thus, if even a portion of the scenario described above is true, it is happening right now.
See this page for additional information on this aspect of the debate as updated, when time permits, by this writer.