转基因作物：真实、虚假与未知

    In the pitched debate over genetically modified (GM) foods and crops, it can be hard to see where scientific evidence ends and dogma and speculation begin. In the nearly 20 years since they were first commercialized, GM crop technologies have seen dramatic uptake. Advocates say that they have increased agricultural production by more than US$98 billion and saved an estimated 473 million kilograms of pesticides from being sprayed. But critics question their environmental, social and economic impacts.

 在有关转基因食品与作物的激烈争论中，很难判定哪些说法是具有科学根据的，哪些说法没有证据而只是凭空猜测的。自从转基因食品首次实施商业化运作将近20年以来，转基因作物的种植技术有了显著的提高。提倡者们说，转基因作物使农业生产值增加了980多亿美元，而且据估计所喷洒的杀虫剂减少了4.73亿公斤。但是，批评者们却对转基因作物所带来的环境、社会和经济影响持有怀疑态度。

    Researchers, farmers, activists and GM seed companies all stridently promote their views, but the scientific data are often inconclusive or contradictory. Complicated truths have long been obscured by the fierce rhetoric. “I find it frustrating that the debate has not moved on,” says Dominic Glover, an agricultural socioeconomist at Wageningen University and Research Centre in the Netherlands. “The two sides speak different languages and have different opinions on what evidence and issues matter,” he says.

 研究人员、农民、活动家以及转基因种子公司都在高调地提倡自己的观点，但是科学数据通常并非决定性的，或者甚至跟他们的观点是互相矛盾的。长期以来，复杂的真相已经被激烈的言辞所掩盖。“有关的争论没有取得进展，对此我感到很失望，”荷兰瓦赫宁恩大学研究中心的农业社会经济学家多米尼克·格洛弗说，“至于哪些是关键的证据，哪些是重要的问题，双方讲的语言不同，观点也不一致。”

    Here, Nature takes a look at three pressing questions: are GM crops fuelling the rise of herbicide resistant ‘superweeds’? Are they driving farmers in India to suicide? And are the foreign transgenes in GM crops spreading into other plants? These controversial case studies show how blame shifts, myths are spread and cultural insensitivities can inflame debate.

 在这里，《自然》杂志要审视三个亟待解决问题：1. 转基因作物催生了对除草剂具有抗性的“超级杂草”吗？2. 转基因作物正在促使印度的农民自杀吗？3. 转基因作物中的外来转基因是否会传播到其他植物中？这些富有争议的案例研究表明了责怪是如何转移的，假话是如何散播的，文化上的不敏感性又是如何促使争论激烈起来的。

  GM CROPS HAVE BRED SUPERWEEDS: TRUE

 1. 转基因作物引起了超级杂草的丛生——真实。

    Jay Holder, a farming consultant in Ashburn, Georgia, first noticed Palmer amaranth (Amaranthus palmeri) in a client’s transgenic cotton fields about five years ago. Palmer amaranth is a particular pain for farmers in the southeastern United States, where it outcompetes cotton for moisture, light and soil nutrients and can quickly take over fields.

 大约五年前，佐治亚州的农业顾问杰伊·霍尔德在一个客户的转基因棉田里首先注意到长芒苋（Amaranthus palmeri）。对于美国东南部的农民来说，长芒苋是特别令人头痛的植物，在吸收水分、光线和土壤养分方面能够超过棉花，很快在田野上取得主导地位。

    Since the late 1990s, US farmers had widely adopted GM cotton engineered to tolerate the herbicide glyphosate, which is marketed as Roundup by Monsanto in St Louis, Missouri. The herbicide–crop combination worked spectacularly well — until it didn’t. In 2004, herbicide-resistant amaranth was found in one county in Georgia; by 2011, it had spread to 76. “It got to the point where some farmers were losing half their cotton fields to the weed,” says Holder.

 自从20世纪90年代后期，美国农民开始大范围种植转基因棉，这种棉花经过生物工程处理，目的是要对抗除草剂——草甘膦（glyphosate）。草甘膦的市场名称为农达（Roundup），由密苏里州圣路易斯市的孟山都公司生产。利用这种除草剂与作物结合的办法很有效，直到2004年。那一年，在佐治亚州的一个县发现了抗除草剂的长芒苋。到2011年，抗除草剂的长芒苋扩展到76个县。“当时，已经达到如此地步：一些农民有一半棉田被这种杂草占去，”霍尔德说。

    Some scientists and anti-GM groups warned that GM crops, by encouraging liberal use of glyphosate, were spurring the evolution of herbicide resistance in many weeds. Twenty-four glyphosate-resistant weed species have been identified since Roundup-tolerant crops were introduced in 1996. But herbicide resistance is a problem for farmers regardless of whether they plant GM crops. Some 64 weed species are resistant to the herbicide atrazine, for example, and no crops have been genetically modified to withstand it (see ‘The rise of superweeds’).

 一些科学家以及一些反对转基因作物的组织警告说：种植转基因作物，鼓励大量使用草甘膦，正在促使许多杂草朝着抗除草剂的方向进化。自从1996年引进抗农达的作物以来，发现了24个对草甘膦具有抗性的杂草物种。然而，不管是否种植转基因作物，杂草对除草剂的抗性对于农民来说总是一个难题。例如，大约有64个杂草物种对除草剂莠去津（atrazine）具有抗性，而且尚无转基因作物能够对抗该除草剂。

    Still, glyphosate-tolerant plants could be considered victims of their own success. Farmers had historically used multiple herbicides, which slowed the development of resistance. They also controlled weeds through ploughing and tilling — practices that deplete topsoil and release carbon dioxide, but do not encourage resistance. The GM crops allowed growers to rely almost entirely on glyphosate, which is less toxic than many other chemicals and kills a broad range of weeds without ploughing. Farmers planted them year after year without rotating crop types or varying chemicals to deter resistance.

 然而，可以将抗草甘膦的作物看做是自身成功的牺牲品。从历史上来看，农民利用多种除草剂，延缓了抗性的产生。此外，农民们还通过耕耘土地来控制杂草的生长，这种做法会损耗表层土，释放二氧化碳，但不会促进杂草抗性的产生。这些转基因作物使得种植者几乎完全依靠草甘膦，这种除草剂的毒性比许多其他化学药品都要低，在不用犁地的情况下可以杀死多种杂草。农民们年复一年地种植转基因作物，不变换作物品种，也不改用其它除草剂来制止抗性的产生。

    This strategy was supported by claims from Monsanto that glyphosate resistance was unlikely to develop naturally in weeds when the herbicide was used properly. As late as 2004, the company was publicizing a multi-year study suggesting that rotating crops and chemicals does not help to avert resistance. When applied at Monsanto’s recommended doses, glyphosate killed weeds effectively, and “we know that dead weeds will not become resistant”, said Rick Cole, now Monsanto’s technical lead of weed management, in a trade-journal advertisement at the time. The study, published in 2007 (ref. ¹), was criticized by scientists for using plots so small that the chances of resistance developing were very low, no matter what the practice.

 这种耕作方法得到孟山都公司的支持，该公司声称：在正确施用草甘膦的情况下，杂草是不可能自行产生抗性的。直到2004年，孟山都公司公布了一项历时多年的研究，研究表明轮换种植作物、改变除草药品无助于避免抗性的产生。在使用孟山都公司建议的剂量时，草甘膦能够有效地杀死杂草。时任公司除草部技术主任的里克·科尔在一家行业杂志的广告中称：“我们知道，死掉的杂草是不会产生抗性的！”该研究成果发表在2007年，由于试种的范围太小而受到科学家们的批评，原因是无论耕作方法如何，种植面积太小就会使得产生抗性的机会很少。

    Glyphosate-resistant weeds have now been found in 18 countries worldwide, with significant impacts in Brazil, Australia, Argentina and Paraguay, says Ian Heap, director of the International Survey of Herbicide Resistant Weeds, based in Corvallis, Oregon. And Monsanto has changed its stance on glyphosate use, now recommending that farmers use a mix of chemical products and ploughing. But the company stops short of acknowledging a role in creating the problem. “Over-confidence in the system combined with economic drivers led to reduced diversity in herbicide use,” Cole tells Nature.

 俄勒冈州科瓦利斯市国际抗除草剂杂草调查团团长伊恩·希普称：现在，全世界有18个国家发现了抗除草剂的杂草，其中遭受重大影响的国家有巴西、澳大利亚、阿根廷和巴拉圭。而孟山都公司目前在草甘膦使用上改变了立场，建议农民利用混合的化学除草剂产品，而且建议犁地。但是，孟山都公司决不承认在导致杂草抗性方面起到了一定的作用。“对耕作方法的过分自信，外加经济利益的驱使，导致了在除草剂的使用上趋于单一化，”科尔告诉《自然》杂志的记者说。

    On balance, herbicide-resistant GM crops are less damaging to the environment than conventional crops grown at industrial scale. A study by PG Economics, a consulting firm in Dorchester, UK, found that the introduction of herbicide-tolerant cotton saved 15.5 million kilograms of herbicide between 1996 and 2011, a 6.1% reduction from what would have been used on conventional cotton². And GM crop technology delivered an 8.9% improvement to the environmental impact quotient — a measure that considers factors such as pesticide toxicity to wildlife — says Graham Brookes, co-director of PG Economics and a co-author of the industry-funded study, which many scientists consider to be among the field’s most extensive and authoritative assessments of environmental impacts.

 总而言之，相对于以产业规模种植的传统作物，抗除草剂的转基因作物对环境所造成的破坏是较小的。英国多尔切斯特市一家咨询公司——PG经济学公司（PG Economics）进行的一项研究发现：在1996年至2011年期间，抗除草剂棉花的引进为农民节省了1550万公斤除草剂，比种植传统棉花少用6.1%的除草剂。PG经济学公司的副总裁、研究论文的合作者格雷厄姆·布鲁克斯说：转基因作物使环境影响指数改善了8.9个百分点。环境影响指数是一种把杀虫剂毒性对野生动植物的影响等因素都考虑在内的测量方法。许多科学家们认为，在对环境影响的评估方面，这项由企业资助的研究是该领域规模最大、最具权威性的研究之一。

    The question is how much longer those benefits will last. So far, farmers have dealt with the proliferation of resistant weeds by using more glyphosate, supplementing it with other herbicides and ploughing. A study by David Mortensen, a plant ecologist at Pennsylvania State University in University Park, predicts that total herbicide use in the United States will rise from around 1.5 kilograms per hectare in 2013 to more than 3.5 kilograms per hectare in 2025 as a direct result of GM crop use³.

 问题在于，这些益处还会持续多久呢？目前，农民们通过使用更多的草甘膦、搭配使用其他除草剂和犁地来对付抗性杂草的增殖扩散。宾夕法尼亚州立大学帕克分校植物生态学家大卫·莫滕森进行的一项研究预测到：转基因作物会直接导致美国除草剂使用总量的上升，2013年每公顷的除草剂使用量大约为1.5公斤，到2025年每公顷的使用量将会达到3.5公斤以上。

    To offer farmers new weed-control strategies, Monsanto and other biotechnology companies, such as Dow AgroSciences, based in Indianapolis, Indiana, are developing new herbicide-resistant crops that work with different chemicals, which they expect to commercialize within a few years.

 为了给农民提供控制杂草的新方法，孟山都公司和其他生物技术公司（如：印第安纳州的陶氏益农公司）正在开发对多种不同化学除草剂具有抗性的新一代作物，这种作物可望在几年之内实现商业化种植。

    Mortensen says that the new technologies will lose their effectiveness as well. But abandoning chemical herbicides completely is not a viable solution, says Jonathan Gressel, a weed scientist at the Weizmann Institute of Science in Rehovot, Israel. Using chemicals to control weeds is still more efficient than ploughing and tilling the soil, and is less environmentally damaging. “When farmers start to use more sustainable farming practices together with mixtures of herbicides they will have fewer problems,” he says.

 莫滕森称，这些新技术也将失去其效果。然而，以色列魏兹曼科学研究所研究杂草的科学家乔纳森·格雷塞尔说：完全放弃化学除草剂是不切实际的方案。利用化学除草剂来控制杂草仍然比耕耘土地更加有效，而且对环境的破坏程度较低。“一旦农民们开始采用更加可持续性的耕作方法，同时混合使用除草剂，他们就会遇到较少的困难，”格雷塞尔说。

 GM COTTON HAS DRIVEN FARMERS TO SUICIDE: FALSE

 2. 转基因棉促使了农民自杀——虚假。

    During an interview in March, Vandana Shiva, an environmental and feminist activist from India, repeated an alarming statistic: “270,000 Indian farmers have committed suicide since Monsanto entered the Indian seed market,” she said. “It’s a genocide.”

 在三月份的一次采访中，印度的环保活动家兼女权主义活动家凡达纳·施瓦一再重复一项惊人的统计数据：“自从孟山都公司的产品进入了印度种子市场之后，有27万印度农民自杀了，”她说，“这是种族灭绝的行径！”

    The claim, based on an increase in total suicide rates across the country in the late 1990s, has become an oft-repeated story of corporate exploitation since Monsanto began selling GM seed in India in 2002.

 在20世纪90年代后期，印度全国的总自杀率已经有所上升。因此，自从孟山都公司于2002年开始在印度销售转基因种子以来，种族灭绝的断言实际上就是多次出现的企业剥削情况。

    Bt cotton, which contains a gene from the bacterium Bacillus thuringiensis to ward off certain insects, had a rough start. Seeds initially cost five times more than local hybrid varieties, spurring local traders to sell packets containing a mix of Bt and conventional cotton at lower prices. The sham seeds and misinformation about how to use the product resulted in crop and financial losses. This no doubt added strain to rural farmers, who had long been under the pressures of a tight credit system that forced them to borrow from local lenders.

 Bt转基因棉含有来自苏云金杆菌（Bacillus thur?ingiensis）的一种基因，能够抵抗某些害虫。起初，这种基因棉在印度的推广并不顺利。开始时，Bt转基因棉的种子比当地的杂交品种贵五倍，促使当地的经销商以较低的价格销售一批Bt转基因棉与传统棉的混合棉种。假种子的销售以及有关产品使用的信息误导造成了作物收成上的减少和经济上的损失，这无疑增加了农民的负担。长期以来，农民们一直承受来自信贷紧缩体制的压力，使他们不得不向地方放贷者借款。

    But, says Glover, “it is nonsense to attribute farmer suicides solely to Bt cotton”. Although financial hardship is a driving factor in suicide among Indian farmers, there has been essentially no change in the suicide rate for farmers since the introduction of Bt cotton.

 然而，格洛弗说：“将农民自杀完全归因于Bt转基因棉是没有道理的。”在印度农民中，尽管经济困难是致使他们自杀的一个因素，但是从根本上来讲，在引进Bt转基因棉之后，农民的自杀率没有变化。

    That was shown by researchers at the International Food Policy Research Institute in Washington DC, who scoured government data, academic articles and media reports about Bt cotton and suicide in India. Their findings, published in 2008 (ref. ⁴) and updated in 2011 (ref. ⁵), show that the total number of suicides per year in the Indian population rose from just under 100,000 in 1997 to more than 120,000 in 2007. But the number of suicides among farmers hovered at around 20,000 per year over the same period.

 华盛顿哥伦比亚特区国际粮食政策研究所的研究人员证实了这一点。关于Bt转基因棉的种植和印度农民自杀的情况，他们搜集了政府数据、学术论文和媒体报道。研究人员所发现的情况发表于2008年，在2011年进行过更新。他们的发现表明：印度人口中每年自杀的总人数在1997年为刚刚不到10万，在2007年为12万多，但是在这十年中农民每年自杀的人数一直徘徊在两万左右。

    And since its rocky beginnings, Bt cotton has benefited farmers, says Matin Qaim, an agricultural economist at Georg August University in Gttingen, Germany, who has been studying the social and financial impacts of Bt cotton in India for the past 10 years. In a study of 533 cotton-farming households in central and southern India, Qaim found that yields grew by 24% per acre between 2002 and 2008, owing to reduced losses from pest attacks⁶. Farmers’ profits rose by an average of 50% over the same period, owing mainly to yield gains (see ‘A steady rate of tragedy’). Given the profits, Qaim says, it is not surprising that more than 90% of the cotton now grown in India is transgenic.

 在过去的十年中，德国哥廷根大学农业经济学家马丁·凯姆一直在研究印度Bt转基因棉所造成的社会和财政影响。他说：尽管开始推广时障碍重重，但是Bt转基因棉使农民们受到益处。在一项针对印度中部和南部533个棉农家庭进行的研究中，凯姆发现：在2002年至2008年之间，由于遭受虫害的损失减少，每英亩的产量增加了24%；在同一阶段，农民的利润平均增加了50%，原因主要是产量增加了。凯姆称：目前，印度种植的棉花中有90%以上是转基因棉，考虑到利润因素，这是不足为奇的。

    Glenn Stone, an environmental anthropologist at Washington University in St Louis, says that the empirical evidence for yield increases with Bt cotton is lacking. He has conducted original field studies⁷ and analysed the research literature⁸ on Bt cotton yields in India, and says that most peer-reviewed studies reporting yield increases with Bt cotton have focused on short time periods, often in the early years after the technology came online. This, he says, introduced biases: farmers who adopted the technology first tended to be wealthier and more educated, and their farms were already producing higher-than-average yields of conventional cotton. They achieved high yields of Bt cotton partly because they lavished the expensive GM seeds with care and attention. The problem now is that there are hardly any conventional cotton farms left in India to compare GM yields and profits against, says Stone. Qaim agrees that many studies showing financial gains focus on short-term impacts, but his study, published in 2012, controlled for these biases and still found continued benefits.

 华盛顿大学环境人类学家格伦·斯通说：根据实验，Bt转基因棉产量增加的证据是不足的。他进行了原始的现场研究，并分析了有关印度Bt转基因棉产量的研究文献。斯通说：在报道Bt转基因棉产量增加的研究中，多数经过同行评议的研究关注了短期的增产情况，通常是在这项新技术上线后最初几年的增产情况。他说，这样就产生了偏差：首先采用该技术的往往是比较富有而且文化程度较高的农民，况且他们在农场上所种植的已经是高于平均产量的传统棉了。他们的Bt转基因棉获得了高产量，部分原因是他们认真专注地播散这种昂贵的转基因棉种。斯通说：目前的问题是，印度几乎没有任何传统棉农场了，无法跟转基因棉形成产量和利润上的比较。凯姆承认，许多表明经济收益有所增加的研究注重了短期的成效，但是他发表于2012年的一项研究控制了这些偏差，仍然发现种植Bt转基因棉具有持续性的收益。

    Bt cotton did not cause suicide rates to spike, says Glover, but neither is it the sole reason for the yield improvements. “Blanket conclusions that the technology is a success or failure lack the right level of nuance,” he says. “It’s an evolving story in India, and we have not yet reached a definitive conclusion.”

 格洛弗表示，Bt转基因棉并没有引起自杀率的上升，但它也不是导致增产的唯一因素。“一概而论地说这项技术是成功的或是失败的，都是有失精当的，”他说，“在印度，这是一种不断发展的情况，我们还没有得出明确的结论。”

TRANSGENES SPREAD TO WILD CROPS IN MEXICO: UNKNOWN

 3. 转基因传播到墨西哥的野生作物中——未知。

    In 2000, some rural farmers in the mountains of Oaxaca, Mexico, wanted to gain organic certification for the maize (corn) they grew and sold in the hope of generating extra income. David Quist, then a microbial ecologist at the University of California, Berkeley, agreed to help in exchange for access to their lands for a research project. But Quist’s genetic analyses uncovered a surprise: the locally produced maize contained a segment of the DNA used to spur expression of transgenes in Monsanto’s glyphosate-tolerant and insect-resistant maize⁹.

 2000年，墨西哥瓦哈卡山区的一些农民想为自己种植销售的玉米办理有机产品认证，以期增加收入。当时，加州大学伯克利分校的细菌生态学家大卫·奎斯特同意为他们提供帮助，交换条件是准许在他们的玉米田里做一个研究项目。然而，奎斯特进行的基因分析揭示了一个令人吃惊的情况：在当地生产的玉米中，含有孟山都公司抗草甘膦兼抗虫害玉米中用来刺激转基因表达的DNA片段。

    GM crops are not approved for commercial production in Mexico. So the transgenes probably came from GM crops imported from the United States for consumption and planted by local farmers who probably didn’t know that the seeds were transgenic. Quist speculated at the time that the local maize probably cross-bred with these GM varieties, thereby picking up the transgenic DNA.

 在墨西哥，不允许转基因作物的商业化种植。因此，这种转基因可能来自进口于美国的、以消费为目的的转基因作物，当地农民很可能在不知道存在转基因的情况下进行了种植。奎斯特当时推测，当地的玉米很可能与转基因品种进行了杂交，因而获取了转基因DNA。

    When the discovery was published in Nature, a media and political circus descended on Oaxaca. Many vilified Monsanto for contaminating maize at its historic origin — a place where the crop was considered sacred. And Quist’s study came under fire for technical deficiencies, including problems with the methods used to detect the transgenes and the authors’ conclusion that transgenes can fragment and scatter throughout the genome¹⁰. Nature eventually withdrew support for the paper but stopped short of retracting it. “The evidence available is not sufficient to justify the publication of the original paper,” read an editorial footnote to a critique¹⁰ of the research published in 2002.

 当这项发现发表于《自然》杂志之后，一个由媒体界人士和政治界人士组成的团体来到瓦哈卡。许多人责骂孟山都公司，说该公司污染了在历史上占有重要地位的玉米发源地的玉米，而那里的人们认为玉米是神圣的。然而，由于技术上的不足，奎斯特的研究受到了严厉的批评，出现的问题包括检测转基因所利用的方法以及论文作者们得出的结论——转基因可以产生破裂并分散到整个基因组。《自然》杂志对论文的观点不再予以支持，但是决定不会撤销该论文的发表。2002年，在针对该研究发表的一篇评论文章中，杂志社使用脚注说明：“所获取的证据不足以证明原论文中所发布的观点是合理的。”

    Since then, few rigorous studies of transgene flow into Mexican maize have been published, owing mainly to a dearth of research funding, and they show mixed results. In 2003–04, Allison Snow, a plant ecologist at Ohio State University in Columbus, sampled 870 plants taken from 125 fields in Oaxaca and found no transgenic sequences in maize seeds¹¹.

 自从那时以后，主要由于缺乏研究资金，关于转基因流入墨西哥玉米的情况，几乎没有公开发表过缜密的研究，而且极个别的研究显示出含混不清的结果。2003年4月，俄亥俄州立大学哥伦布分校的植物生态学家阿利森·斯诺，从瓦哈卡125块玉米田中搜集了870个植物样品，发现玉米的种子里不存在转基因序列。

    But in 2009, a study¹² led by Elena Alvarez-Buylla, a molecular ecologist at the National Autonomous University of Mexico in Mexico City, and Alma Pieyro-Nelson, a plant molecular geneticist now at the University of California, Berkeley, found the same transgenes as Quist in three samples taken from 23 sites in Oaxaca in 2001, and in two samples taken from those sites in 2004. In another study, Alvarez-Buylla and her co-authors found evidence of transgenes in a small percentage of seeds from 1,765 households across Mexico¹³. Other studies conducted within local communities have found transgenes more consistently, but few have been published¹⁴.

 但是在2009年，墨西哥国立自治大学的分子生态学家埃琳娜·阿尔瓦雷茨-布伊拉和加州大学伯克利分校的植物分子遗传学家阿尔玛·派尼若-纳尔逊共同主持了一项研究，所发现的转基因跟奎斯特在2001年从瓦哈卡23个地点搜集到的三个样品，以及跟他在2004年从那些地点搜集到的两个样品中所发现的转基因相同。在另外的一项研究中，阿尔瓦雷茨-布伊拉及同事在来自遍及墨西哥1765个家庭的种子里发现了存在少量转基因的证据。其他在当地社区内进行的研究，也都更加一致地发现了转基因，但是很少有研究成果发表。

    Snow and Alvarez-Buylla agree that differences in sampling methods can lead to discrepancies in transgene detection. “We sampled different fields,” says Snow. “They found them but we didn’t.”

 斯诺和阿尔瓦雷茨-布伊拉承认，采样方法的不同可能会导致转基因检测上的差异。“我们也是在不同的田地上采样的，”斯诺说，“她们发现了转基因，我们却没有发现。”

    The scientific community remains split on whether transgenes have infiltrated maize populations in Mexico, even as the country grapples with whether to approve commercialization of Bt maize.

 尽管墨西哥正要决定是否批准Bt转基因玉米的商业化种植，但是至于转基因是否已经渗透到墨西哥的玉米品种中，科学界仍然存在着分歧。

    “It seems inevitable that there will be a movement of transgenes into local maize crops,” says Snow. “There is some proof that it is happening, but it is very difficult to say how common it is or what are the consequences.” Alvarez-Buylla argues that the spread of transgenes will harm the health of Mexican maize and change characteristics, such as a variety’s look and taste, that are important to rural farmers. Once the transgenes are present, it will be very difficult, if not impossible, to get rid of them, she says. Critics speculate that GM traits that accumulate in the genomes of local maize populations over time could eventually affect plant fitness by using up energy and resources or by disrupting metabolic processes, for example.

 “转基因将要扩散到当地的玉米作物中，这好像是不可避免的，”斯诺说，“有些证据表明，转基因扩散的情况正在发生，但是很难说这种情况有多么普遍，也很难说后果会如何。”阿尔瓦雷茨-布伊拉认为，转基因扩散将会有损于墨西哥玉米的健康生长，将会改变一种玉米的外观和味道等特性，而这些特性对于那里的农民来说是很重要的。她说，一旦转基因出现了，要想将它们剔除的话，即使并非不可能，也将会是极为困难的。例如，批评家们推测：随着时间的推移，转基因特性在基因组中逐渐积累，可能会通过耗尽能量和资源，或者通过扰乱代谢过程，最终影响到作物的适应性。

    Snow says that there is no evidence so far for negative effects. And she expects that if the transgenes now in use drift to other plants, they will have neutral or beneficial effects on plant growth. In 2003, Snow and her colleagues showed that when Bt sunflowers (Helianthus annuus) were bred with their wild counterparts, transgenic offspring still required the same kind of close care as its cultivated parent but were less vulnerable to insects and produced more seeds than non-transgenic plants¹⁵. Few similar studies have been conducted, says Snow, because the companies that own the rights to the technology are generally unwilling to let academic researchers perform the experiments.

 斯诺称：到目前为止，没有证据表明转基因会带来负面影响。她预计，如果现用的转基因流传到其他植物中，那么对于植物的生长将会造成中性的或有益的影响。2003年，斯诺及同事证明，当Bt转基因向日葵（Helianthus annuus）跟野生向日葵杂交之后，转基因后代仍然像栽培的上一代那样需要细心照料，但是不像上一代那样容易遭受害虫的攻击，而且比非转基因向日葵长出的籽粒更多。斯诺称，几乎没有进行过类似的研究，因为获得这项技术拥有权的公司通常不愿意让学术研究人员进行这种实验。

    In Mexico, the story goes beyond potential environmental impacts. Kevin Pixley, a crop scientist and the director of the genetic resources programme at the International Maize and Wheat Improvement Centre in El Batan, Mexico, says that scientists arguing on behalf of GM technologies in the country have missed a crucial point. “Most of the scientific community doesn’t understand the depth of the emotional and cultural affiliation maize has for the Mexican population,” he says.

 在墨西哥，相关的争论不止于对环境所造成的潜在影响。农作物科学家兼墨西哥国际玉米和小麦改良中心基因资源项目部主任凯文·皮克斯利称：在墨西哥，代表转基因技术参与争辩的科学家们忽略了至关重要的一点。“多数科学界的人士并不了解，玉米对于墨西哥人来说，在感情上和文化上具有深切的归属感，”他说。

    Tidy stories, in favour of or against GM crops, will always miss the bigger picture, which is nuanced, equivocal and undeniably messy. Transgenic crops will not solve all the agricultural challenges facing the developing or developed world, says Qaim: “It is not a silver bullet.” But vilification is not appropriate either. The truth is somewhere in the middle.

 对于转基因作物，不管是赞成还是反对，大量的报道总会忽略更加全面的情况，这一情况很微妙、很模糊，也必定很难处理。转基因作物不会解决发展中国家和发达国家所面临的一切农业方面的挑战，凯姆说：“转基因作物不是锦囊妙计。”但是，对其进行污蔑也是不应当的。真理存在于两者之间的某个位置上。