为何不证明“转基因是安全的”的逻辑推导

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显然，没有绝对安全的事物。我们将要做一个测试和试着证明水在健康方面是安全的。

人们经常问，是否有文献支持并证明转基因作物是安全的。安全是一个相对的术语，一般被认为是否存在风险或者有害。同样地，问食物的安全与否，其实是问它是否存在风险。对于风险的评价有很多限定因素，但并不与绝对的安全相违背。对于风险的评估主要是检查手头上现有的证据，设计相关的试验来验证它对于身体健康和环境等的影响。最终，人们对这些数据进行评估，来确定它是否可以引起某些危害。

我们首先要提出一个虚拟的假设，反驳这个假设属于科研工作者的责任，通过实验来说明它们之间是不同的或者存在一个影响。例如，如果你想找出经常看电视的小孩会有暴力倾向，你的虚拟假设应当为“看电视并不会使小孩具有攻击性”。因此，我们的假设就会是“喝水不会诱发癌症”。

我们需要对这个假定进行更加具体的条件限制和说明。对于我们的研究，我们将会考虑我们的问题为“与全国的平均水平相比，居住在旧金山港湾区10-20年并且每天喝2-4杯自来水的居民，患乳腺癌的机率并没有增加”。

如果居住在旧金山港湾区的人患乳腺癌的几率与全国平均水平相同，那我们就证明那的水是“安全”的吗？并非如此。我们所得到的全部证据只能表明喝水并不能诱发癌症，还有就是水是可以放心饮用的。就像以前提到的，没有任何东西被证明是绝对安全的，其中也包括水。饮用太多或太少的水都可以对人体造成巨大的伤害，更不要说它没有经过合理的净化系统。因此，水也可以被认为是危险的：在世界范围内，由水所诱发的疾病是一个非常重要的致死方式；水还可以引发洪水，破坏人们的家园。但是，同时，我们需要水来维持正常的生命活动，饮用适量的水还可以改善人们的身体状况。科学也帮助我们对水的危害作出解释：水在某些情况下确实可以对引发某些伤害，但是我们可以确保这些伤害降低到最低。

让我们接着进行延伸分析：

广义论题：MMR疫苗（麻疹、腮腺炎和风疹的混合疫苗）不会引起孤独症。

具体论题：与没有接种过默克公司的MMR疫苗的白人小孩相比，接种过疫苗的小孩患孤独症的概率并没有提高。广义论题：转基因食物并不会伤害人们的内脏。

具体论题：与食用普通的饲料相比，食用含有30%转基因成分（转Bt基因的玉米）的食物30天后，猪肠道内的菌群并没有发生改变。

这就一定意味着你已经证明了接种MMR疫苗不能诱发孤独症吗？其实并不是。你是否已经证明转基因食物没有影响肠道内的细菌种类？其实也不是。你所做的只是增加了一些证据，它们表明MMR疫苗没有引发孤独症和转基因作物没有对人们产生伤害。你已经证明了在一些特定的检测领域内，试验组（转基因作物）和对照组（传统作物）对安全的风险性是非常低的。

直到有人提出了一个研究课题，表明A事件引起了B事件的发生。然后，我们的假设就为：A事件并不能导致B事件的发生。否则，你可以提出任何可能的假设，人们将不得不一一证明这些假设是错误的。你可以说虚拟的巨龙一起跳动可以引起地震的发生，并且要求我们来证明这个假设并不是真的。或者由于手表具有一定的辐射性，因此经常戴手表的人，非常可能患有腕管综合症。亦或者电脑可以释放危险的毒素，从而诱发脑瘤。直到你证明他们是假的，人们才会相信：巨龙并不会引发地震，而且计算机也不会诱发脑瘤。这个责任应当由提出这个论断的人来做，证明确实这个事情是存在的。

因此，如果你宣称地震是由巨龙所引起的，那么请你拿出足够的证据来支撑你的诊断，而并非由我来证明你是错误的。一个相同的论断，众所周知的罗素的茶壶，是由哲学家伯特兰·罗素的杜撰出来的。罗素说：如果我想说，在火星和太阳之间的轨道内，有一个茶壶正在运行，但是它非常的小，以致于用望远镜都无法观察得到。但是却没有人能驳倒我的论断。既然我的假设不能被驳倒，那么它就不应该受到人们的怀疑。但是如果我不断重复宣讲，会被人们认为是胡说八道。这个例子强调了，证明某些人的假设是非常的不可能。因此，举证的责任应当由提出假设的人来承担。

无论何时，人们提出一个不能证伪的假设，那么举证的责任应当由他来承担。通过了几十年的研究，一直宣称转基因作物可以诱发孤独症和癌症的人们，应当拿出足够的证据来证明他们的论断。正如卡尔·萨根所说，非凡的论断，需要非凡的证据。宣称我没有足够的知情权并不是一个经得起检验的证据，这也不能推导出转基因作物是有危害性的，这仅仅是一个无意义的推测。

缺乏足够的文献支持转基因作物是安全的，这经常引起人们的怀疑和恐惧。不可能证明它不具有危害性这一点，经常被反转基因人士来进行大肆地宣传（最近由一个医师发表在纽约每日邮报上的文章就是一个完美的例子）：我们是否知道转基因食物不会诱发癌症？我们是否知道转基因食物不会引发男性不育吗？等等。。好，这些已经足够了，我们都不知道。但是，许多饲喂实验都推导出，没有证据证明它们可以引发癌症，也没有理论依据说明它们可以发生。

我们是否知道吃石榴不会引发男性秃发吗？我们是否知道在键盘上打字可以传播性病吗？不知道，我们真的不知道。我不认为有人曾做过这方面的研究。但是，非常奇怪的是，没有人曾提议一个法案来限制键盘的作用，亦或有人声称我应该将我后院的石榴树砍掉。请记住这一点，没有任何人可以证明安全是绝对存在的，我们仅仅可以证明它具有非常少的危险性，以回应那些持有怀疑态度的人们。这些假设允许我们从科学的数据中清除那些迷信的说法。一些别有用心的人马上就可能得出结论，埃博拉病毒是人造的或者艾兹病并不是由HIV病毒所引起的。通过表明“给我证据表明埃博拉病毒是人造的”或者“足够的证据证明艾兹病是由HIV病毒所引起的”，我们可以站出来反对这些有害的理论。

当你问“转基因食物安全的证据”或者是否有文献支持时，事实上，这是一个抱有偏见的想法，无论他是否意识到这一点。不幸的是，我不能提供给你如此的证据，因为我并没有读过任何设计、执行和可重复性非常好的文献，来证明转基因对身体有负面的影响。

这就是为什么科学家非常重视并对转基因作物进行了大量的研究，这也是为什么科学家非常强调关于转基因作物的声明应由权威性的科研机构所发布。这也是为什么荟萃分析和文献综述是非常重要的。因为并不仅仅是一个报道证明其安全性，而是有大量的研究、充足的数据，非常多的调查表明目前市场上的转基因食物与传统育种的食物一样安全。通过对数据本身的验证，科学家得出了一个共识：在这个领域内的绝大多数科学家们都停止了争论，因为越来越多的数据使这个论断越来越清晰和明了。尽管，在这个转基因作物的问题上，并没有出现一个非常清晰的共识，但是他们都认为，目前市场上的转基因食物并没有比传统育种的食物有更大的危险性。

我最后的论点是：申请基金是非常困难的，科研单位需要看到具体的申请细节（编者注：申请不到这样不符合科研规律的项目，是没有人去证明“转基因是安全的”重要原因）：

1、如果一个科研工作者想确定是否一种物质可以诱发伤害，然后批准部门将会想知道伤害在何种情况下才会发生。在我们关于水是否安全的例子中，除非我们描述出一种生物学依据来表明水可以诱发乳腺癌，否则我们决不可能在这个课题上得到资助。

2、在目前的科研体系下，对于一个科研工作者来说，负面的数据或者不能驳倒你的假设不能真正的成为一个研究方向，或者他不能使批准部门使这项工作得以开展。设想你正在进行一个项目上，你不希望得到它们之间有差异，那么你不仅浪费了纳税人的钱，还浪费了你的时间。

但这是科研工作者不得不做的。在一个他们都不想有新颖结果的课题上，科研工作者不想浪费他们的时间和宝贵的资源。然而，与意识到这个简单的解释相反，许多人选择相信科学家们是视而不见的或者是被贿赂了。几乎没有相关领域的科学家认为，长期的饲喂转基因作物可以产生伤害，然而许多反转活跃分子将会认为那些跨国公司控制了他们。

但是如果你对安全的定义是5年内的研究，来研究1000只老鼠是否对Bt玉米和面筋过敏方面的问题。那么就意味着，你将会花费10年的时间，并且获得学校最低水平的工资；同时，你还要试着寻找一个批准单位来资助你的项目。

作者介绍：Layla Parker-Katiraee holds a PhD in Molecular Genetics from the University of Toronto and a Bachelors degree in biochemistry from the University of Western Ontario. She is currently a Senior Scientist in Product Development at a California human genetics biotech company. All views and opinions expressed are her own. 

翻页查看本文英文原文

英文原文：http://www.biofortified.org/2015/05/prove-gmos-are-safe/

（UP主注：原文链接下方有英文评论区，文章作者还对一些网友提出的问题做了现场解答，英文好可以自行翻看，无需科学上网。） 

Why no one will ever “prove that GMOs are safe”

When discussing transgenic crops, I regularly get asked to provide a paper that “proves” that GMOs are safe. Whether you want proof that biotech crops, organic bananas, or conventional peaches are safe, I cannot provide you with such a paper. Safety is a relative term and is generally defined as the absence of risk or harm. As such, asking for proof of safety is, in essence, asking someone for proof of the absence of risk. The risk of what ever is being evaluated is measured in relation to other options, not against a theoretic idea of “perfectly safe”. Relative risk is scientifically determined by examining the evidence at hand: experiments are performed to determine the impact of a substance on health, environment, etc and the data from these experiments are assessed to determine if the substance causes harm.

Scientifically, nothing is truly 100% safe. To explain why, we’re going to do an exercise and try to prove that water is safe. The first thing to keep in mind is that there are many aspects to water safety: impact on health, water transportation, water treatment, proper water storage, etc. For our example, we’re going to select “impact on health”.

Then, we have to come up with a null hypothesis. It may seem counter-intuitive and the double-negatives in the explanation below suck, however the baseline for much of research is that there’s no impact or no difference. It’s the researcher’s responsibility to disprove that hypothesis, ie. to show that there is a difference or that there is an impact. For example, if you want to find out if kids who watch TV are more prone to hitting, your null hypothesis could be “watching TV does not increase aggression”. So for our exercise, our hypothesis will be “Drinking water does not cause cancer”.

Next, we narrow down the hypothesis to a question that we can actually test. For example, “children aged 2-4 who watch 1-2 hours of TV a day do not hit their parents more frequently than children who do not watch any TV.” For our study, we’ll consider our question to be “Individuals who have lived in the San Francisco Bay Area for 10-20 years and drink 2-4 cups of tap water daily do not have a greater incidence of breast cancer than the national average”. We conduct our study and gather data which will probably take a few years. Then we apply the proper statistics. If our study finds a difference, then we’ve disproven our null hypothesis, much hoopla will be made, and our findings will be published in the “Journal of Awesome Research”. If there’s no difference, then our null hypothesis still stands and our study will likely be published in the “Journal of Flibbity-Flooba”.

If we find no difference in the incidence of breast cancer in our study, have we “proven” that water is “safe”? No. All we’ve done is add data to the body of evidence that suggests that drinking water does not cause cancer and that it’s safe to drink it. As previously mentioned, nothing can be truly proven safe, even water; too much or too little of it can kill us, let alone if it is improperly purified. Yes, water can be considered dangerous: water-borne illnesses are one of the leading causes of death worldwide, water causes floods, and it can damage homes. But at the same time, we need water to survive and its intake in the proper amounts promotes health. Science has helped us define the harm that water can cause and the proper steps that we can take to ensure that harm is minimized.

Let’s go beyond our water analogy: here are a few other hypotheses along with a more narrow question of what will be tested:

Broad: The MMR vaccine does not cause autism. Narrow: There is no significant difference in the incidence of autism in caucasian children who have received Merck’s MMR vaccine in the San Jose Bay Area and children who are not vaccinated.

Broad: Eating transgenic crops does not harm the gut. Narrow: There is no significant difference in the relative abundance of bacterial species in the intestinal flora of pigs fed a diet consisting of 30% genetically modified Bt-corn for 30 days compared to a control diet.

Again, let’s say that you are unable to disprove your null hypothesis. Does that mean that you’ve proven that the MMR vaccine doesn’t cause autism? No. Have you proven that GMOs do not impact the bacteria in the gut? No. What you’ve done is add data to a body of evidence that suggests that the MMR vaccine doesn’t cause autism and that crops developed through biotechnology don’t cause harm. You’ve been able to demonstrate a relative lack of risk between the substance (the genetically engineered crop) and a control (the conventional crop) in the specific area examined.

Until someone comes up with a study showing that A causes B, then the null hypothesis is what we turn to: A does not cause B. Otherwise you could come up with any crazy hypothesis and people would have to “prove you wrong”. You could state that that earthquakes are caused by invisible dragons jumping at the same time and demand evidence showing that it’s not true. Or that wearing a watch causes carpal tunnel syndrome due to the radiation emitted by the watch. Or that computers leach dangerous toxins that cause brain tumors. That’s not the way it works. Dragons don’t cause earthquakes and computers don’t cause brain tumors, until you can prove otherwise. The onus is on the person making a claim to provide evidence supporting its existence. Therefore, if you claim that invisible dragons cause earthquakes, it is not my responsibility to “prove you wrong”. Rather, it is your responsibility to provide evidence demonstrating that these beings caused the earthquake. A similar analogy, known as Russell’s Teapot, was coined by the philosopher Bertrand Russell. To illustrate where the burden of proof rightfully belongs when someone makes an unfalsifiable claim, Russell laid out this example: “If I were to suggest that there is a teapot, too small to be detected by a telescope, orbiting around the Sun somewhere between the Earth and Mars, nobody would be able to disprove my assertion. But if I were to go on to say that, since my assertion cannot be disproven it should not be doubted either, then I should rightly be thought to be talking nonsense.” This example highlights how impossible it would be to “prove him wrong”; therefore, the burden of proof would lie with him, as he is the one making the claim.

Whenever someone makes an unfalsifiable claim, the burden of proof lies with the person making the claim. Without a credible hypothesis for harm, and after decades of study, the burden of proof for the people claiming that biotech crops could be causing autism or cancer, lies with those making these claims.  As Carl Sagan said: “Extraordinary claims, require extraordinary evidence.” Claiming that “we just don’t know enough” is a not hypothesis that can be tested and is not in itself evidence of harm: it’s just idle speculation.

The absence of single papers demonstrating safety is often used to invoke fear and doubt, and impossibility of proving a negative is often capitalized in anti-GMO rhetoric (this recent article by a medical doctor in the New York Daily Mail is a perfect example of such arguments): “Do we know that GMOs don’t cause cancer? Do we know that they don’t cause male infertility? etc.” Well, no… We don’t… But in the many feeding studies that have been conducted, there’s absolutely no evidence to suggest that it DOES cause cancer, there’s no logical mechanism proposed by which this might occur, and the null hypothesis still stands. You could virtually make the same argument about anything. “Do we know that eating pomegranates doesn’t case male pattern baldness? Do we know that typing on a keyboard doesn’t cause STDs?” No… We don’t… I don’t think anyone has ever done those studies. But strangely enough, no one has proposed a ban the use of keyboards until someone proves that typing on one doesn’t cause herpes, nor has anyone suggested that I should uproot the pomegranate tree in my backyard. Remembering that safety can never be proven and that we can only demonstrate a lack of relative risk can allow us to view such claims with skepticism. The null hypothesis also allows us to weed out superstitious nonsense from cohesive scientific arguments. Some of the conspiracy theories circulating right now include the idea that the ebola virus is man-made and that AIDS is not caused by HIV. We can stand against such harmful ideas by stating “show me the evidence suggesting that ebola IS man-made” or “here’s a plethora of data indicating that AIDS IS caused by HIV”.

When you ask for “proof that GMOs are safe” or ask for a paper that has this evidence, that is absolutely the wrong request. In fact, it’s a loaded question, whether the person asking realizes or not, the “proof” is impossible to provide, no matter the subject. Ask a specific question and then try to find the data showing that it DOES cause harm. Unfortunately, I can’t provide you with such data because I haven’t read a well-designed, well-executed, reproducible study demonstrating that GMOs have a negative health impact.

THIS is why scientists stress the number of studies that have examined genetically engineered crops. THIS is why scientists stress the statements made by reputable scientific institutions about GMOs. THIS is why meta-analyses and literature reviews are important. Because no single study proves safety: its the sum of the studies, the body of data, the totality of research that’s been done which suggests that the current GMOs on the market are safe relative to their conventionally bred counter-parts. By examining the body of data, scientists develop a consensus: the overwhelming majority of mainstream working scientists in the relevant field stop debating an issue because the direction that the evidence points has become clear. Although there are many matters on which a clear consensus has not yet emerged, on the topic of genetically engineered crops the consensus is that the current crops on the market place pose no greater risk to health than their non-GMO counterparts.

My last point is this: receiving funding for a study is very difficult, and the institutions that fund these grants want to see proposals that

1）have a logical mechanism: in the context of this article, if a researcher wants to determine if a substance can cause harm, then the granting agency will want to know how that harm could potentially occur. In our exercise regarding the safety of water, we’d never get the money for our study unless we could outline a biological mechanism by which water could cause breast cancer.

2）have a high likelihood of generating positive results or disproving the null hypothesis. Negative data or being unable to disprove your hypothesis doesn’t really build a career for a research scientist in the current academic system, nor does it validate the work of the granting agency. As a consequence, many researchers will not pursue a path where they don’t see fruitful results nor will granting agencies fund such research. Imagine working on a project where you don’t expect to make a difference, waste tax-payers’ money, and burn away your time. Why on earth would you start such a project? While it is possible that this approach will miss some harms that we did not understand, in a resource constrained world, it’s counter-productive to pursue every speculation whether it makes “sense” or not. It’s far more productive to pursue the ideas that make sense before worrying about things that don’t make sense.

Whether or not you agree with the system, this is what scientists in the public arena have to work with. Scientists do not want to waste their time and valuable resources on a study where they don’t expect to demonstrate anything new. Instead of recognizing this simple explanation, many chose to believe that research is being silenced or that scientists are being paid off. Very nearly none of the scientists working in the relevant fields think that there is any reason that long term feeding trials of transgenic crops will produce a demonstration of harm, yet many anti-GMO activists would choose to believe that such research is not being conducted because “Big-Ag” drives funding at academic institutions. Rather than acknowledging that the absence of studies examining a link between Round-Up Ready corn and Alzheimer’s is a result of the fact that experts in the field cannot envision a credible mechanism for such harm based on the evidence at hand, many would prefer to believe that it’s because “Big-Ag” is suppressing the data or that Monsanto will break scientists’ kneecaps if they publish results suggesting that GMOs can cause harm.

But if your definition of “safety” is a 5 year longitudinal study on 1000 rats examining a link between Bt-corn and gluten sensitivity, by all means: spend 10 years of your life in school earning less than minimum wage, and then try to find a granting agency that will fund your study based on whatever evidence and reasoning you have. Best of luck in your future career path!