Genetically modified organisms, or GMOs, remain controversial, but like so many other politically hot topics, the controversy is more cultural than scientific.

Scientific evidence more than a century ago settled on the consensus that life on earth is the product of organic evolution. Over the last several decades a scientific consensus has emerged that our planet is warming from man-made causes. Over that same time scientists agreed, based upon evidence, that vaccines do not cause autism. Yet all of these topics remain publically controversial.

Now, the science seems to be converging on the consensus that GMO crops are safe for the environment and human consumption. Those who have opposed GMO crops are not happy with the science.

A recent Gallup poll asked the following question:

“From what you know or have heard, do you believe that foods that have been produced using biotechnology pose a serious health hazard to consumers, or not?”

Of the respondents, 48% said yes, and 36% said no.

An ABC poll reports that 52% of those surveyed believe GMO foods are unsafe, 93% favor mandatory labeling, and 57% said they would use such labeling to avoid GMO food. (Although, California recently rejected a ballot to require such labeling.)

A disconnect between public opinion and scientific evidence is not uncommon, and represents a serious challenge to scientists, science communicators, and those involved in public policy. As is often the case, specific and important public policy decisions depend upon understanding the science.

Concerns about GMO stem from several premises. The most flimsy of which is nothing more than the naturalistic fallacy – that GMO are somehow unnatural and therefore hazardous. Humans have been altering plants and animals for their own use for thousands of years, however. Almost nothing that you eat is the product of evolution without extensive human tinkering.

The most legitimate basis for concern is the precautionary principle. Modifying plants and animals may be nothing new, but genetic technology makes such modification more rapid and powerful. We can now put genes from algae or bacteria into plants. The law of unintended consequences dictates that we should be very careful about introducing new organisms into the world, and into our bodies. There should be standards of scientific research and regulation – and there are.

A final source of concern is the politics and economics of allowing companies to essentially own organisms, and potentially have a strangle hold on our food production. This is a highly complex and political aspect of GMO that I won’t get into further here.

The scientific controversy has mostly focused on the second question – have we done sufficient research of high enough rigor to conclude that GMO crops are safe for people and the environment? Of course, “sufficient” is a judgment call without an objective demarcation, but we can at least determine the consensus of scientific opinion.

As with climate change and vaccines, the stakes here are fairly high. If we inadvertently introduce a dangerous organism or gene into the environment this could have dire consequences that would be difficult to contain. Meanwhile, there are opportunities to improve food production, make more efficient use of land, and improve nutrition.

The WHO estimates that 33% of preschool children are Vitamin A deficient, which is the leading preventable cause of blindness in children, affecting millions. GMO crops with added vitamin A could be a powerful solution to this health problem.

So – what does the scientific evidence say? A 2012 statement by the American Association for the Advancement of Science (AAAS) concluded: 

“As a result and contrary to popular misconceptions, GM crops are the most extensively tested crops ever added to our food supply. There are occasional claims that feeding GM foods to animals causes aberrations ranging from digestive disorders, to sterility, tumors and premature death. Although such claims are often sensationalized and receive a great deal of media attention, none have stood up to rigorous scientific scrutiny. Indeed, a recent review of a dozen well-designed long-term animal feeding studies comparing GM and non-GM potatoes, soy, rice, corn and triticale found that the GM and their non-GM counterparts are nutritionally equivalent.”

The National Academies of Science agrees: 

To date, no adverse health effects attributed to genetic engineering have been documented in the human population.”

The World Health Organization also agrees: 

“GM foods currently traded on the international market have passed risk assessments in several countries and are not likely, nor have been shown, to present risks for human health.”

As referred to by the AAAS, reviews of animal feed studies have concluded: 

“Results obtained from testing GM food and feed in rodents indicate that large (at least 100-fold) 'safety' margins exist between animal exposure levels without observed adverse effects and estimated human daily intake. Results of feeding studies with feed derived from GM plants with improved agronomic properties, carried out in a wide range of livestock species, are discussed. The studies did not show any biologically relevant differences in the parameters tested between control and test animals.”

Given the state of the evidence, there are two reasonable positions – either that there is sufficient evidence to establish the safety of existing GMO crops, or that current evidence supports a conclusion of safety bur further evidence is desirable. At present the evidence does not support a conclusion of any specific risk from GMO crops.

For those who are skeptical of GMO, therefore, more research and evidence can only be a good thing. Despite this, there have been reports of about 80 acts of vandalism against government or academic research projects on GMO crops. Such acts betray an irrational fear, rather than reasonable concern.


Genetic modification is a powerful technology. Our world is filling up with new powerful technologies. This is mostly a good thing, but such technologies are tools, and they can be used wisely or carelessly, and with good intent or ill.

It is perfectly reasonable to be suspicious of new powerful technologies, and of the companies who promote and desire to use them. The precautionary principle is valid, requiring rigorous scientific research and thoughtful government regulation, with the goal of allowing humanity to benefit from such technologies while minimizing the risks.

A risk vs benefit analysis is therefore most useful. No new technology is without risk, but sometimes opposing innovation has greater risks.

There appears to be a strengthening scientific consensus that GMO crops and animals are safe and useful. As the scientific community starts to more vociferously back such conclusions, political opposition to GMO is heating up. We seem to be heading for a confrontation. As always, we would be best served if the science wins out.


Steven Novella, M.D. is the JREF's Senior Fellow and Director of the JREF’s Science-Based Medicine project.