On Science Skeptics and Deniers

Do all climate change skeptics also question the theory of evolution? Do anti-vaccinationists also believe that GMO foods are unsafe? As we’ll see in this post, scientific skepticism and “science denial” are much more nuanced than most people think.


To begin with, scientific skeptics on hot-button issues such as climate change, vaccination and GMOs (genetically modified organisms) are often linked together as anti-science deniers. But the simplistic notion that skeptics and deniers are one and the same – the stance taken by the mainstream media – is mistaken. And the evidence shows that skeptics or deniers in one area of science aren’t necessarily so in other areas.

The split between outright deniers of the science and skeptics who merely question some of it varies markedly, surveys show, from approximately twice as many deniers as skeptics on evolution to about half as many deniers compared to skeptics on climate change.

In evolution, approximately 32% of the American public are creationists who deny Darwin’s theory of evolution entirely, while another 14% are skeptical of the theory. In climate change, the numbers are reversed with about 19% denying any human role in global warming, and a much larger 35% (averaged from here and here) accepting a human contribution but being skeptical about its magnitude. In GMOs, on the other hand, the percentages of skeptics and deniers are about the same.

The surveys also reveal that anti-science skepticism or denial don’t carry over from one issue to another. For example, only about 65% of evolutionary skeptics or deniers are also climate change skeptics or deniers: the remaining 35% who doubt or reject evolution believe in the climate change narrative of largely human-caused warming. So the two groups of skeptics or deniers don’t consist of the same individuals, although there is some overlap.

In the case of GMO foods, approximately equal percentages of the public reject the consensus among scientists that GMOs are safe to eat, and are skeptical about climate change. Once more, however, the two groups don’t consist of the same people. And, even though most U.S. farmers accept the consensus on the safety of GMO crops but are climate change skeptics, there are environmentalists who are GMO deniers or skeptics but accept the prevailing belief on climate change. Prince Charles is a well-known example of the latter.

Social scientists who study such surveys have identified two main influences on scientific skepticism and denial: religion and politics. As we might expect, opinions about evolution are strongly tied to religious identity, practice and belief. And, while Evangelicals are much more likely to be skeptical about climate change than those with no religious affiliation, climate skepticism overall seems to be driven more by politics – specifically, political conservatism – than by religion.

In the political sphere, U.S. Democrats are more inclined than Republicans to believe that human actions are the cause of global warming, that the theory of evolution is valid, and that GMO foods are safe to eat. However, other factors influence the perception of GMO food safety, such as corporate control of food production and any government intervention. Variables like demographics and education come into the picture too, in determining skeptical attitudes on all issues.

Lastly, a striking aspect of skepticism and denial in contemporary science is the gap in opinion between scientists and the general public. Although skepticism is an important element of the scientific method, a far larger percentage of the population in general question the prevailing wisdom on scientific issues than do scientists, with the possible exception of climate change. The precise reasons for this gap are complex according to a recent study, and include religious and political influences as well as differences in cognitive functioning and in education. While scientists may possess more knowledge of science, the public may exhibit more common sense.

Next week: Use and Misuse of the Law in Science

When No Evidence Is Evidence: GMO Food Safety

The twin hallmarks of genuine science are empirical evidence and logic. But in the case of foods containing GMOs (genetically modified organisms), it’s the absence of evidence to the contrary that provides the most convincing testament to the safety of GMO foods. Although almost 40% of the public in the U.S. and UK remain skeptical, there simply isn’t any evidence to date that GMOs are deadly or even unhealthy for humans.

Absence of evidence doesn’t prove that GMO foods are safe beyond all possible doubt, of course. Such proof is impossible in practice, as harmful effects from some as-yet unknown GMO plant can’t be categorically ruled out. But a committee of the U.S. NAS (National Academy of Sciences, Engineering and Medicine) undertook a study in 2016 to examine any negative effects as well as potential benefits of both currently commercialized and future GMO crops.


The study authors found no substantial evidence that the risk to human health was any different for current GMO crops on the market than for their traditionally crossbred counterparts. Crossbreeding or artificial hybridization refers to the conventional form of plant breeding, first developed in the 18th century and continually refined since then, which revolutionized agriculture before genetic engineering came on the scene in the 1970s. The evidence evaluated in the study included presentations by 80 people with diverse expertise on GMO crops; hundreds of comments and documents from individuals and organizations; and an extensive survey by the committee of published scientific papers.

The committee reexamined the results of several types of testing conducted in the past to evaluate genetically engineered crops and the foods derived from them. Although they found that many animal-feeding studies weren’t optimal, the large number of such experimental studies provided “reasonable evidence” that eating GMO foods didn’t harm animals (typically rodents). This conclusion was reinforced by long-term data on livestock health before and after GMO feed crops were introduced.

Two other informative tests involved analyzing the composition of GMO plants and testing for allergens. The NAS study found that while there were differences in the nutrient and chemical compositions of GMO plants compared to similar non-GMO varieties, the differences fell within the range of natural variation for non-GMO crops. 

In the case of specific health problems such as allergies or cancer possibly caused by eating genetically modified foods, the committee relied on epidemiological studies, since long-term randomized controlled trials have never been carried out. The results showed no difference between studies conducted in the U.S. and Canada, where the population has consumed GMO foods since the late 1990s, and similar studies in the UK and Europe, where very few GMO foods are eaten. The committee acknowledged, however, that biases may exist in the epidemiological data available on certain health problems.

The NAS report also recommended a tiered approach to future safety testing of GMOs. The recommendation was to use newly available DNA analysis technologies to evaluate the risks to human health or to the environment of a plant –  grown by either conventional hybridization or genetic engineering – and then to do safety testing only on those plant varieties that show signs of potential hazards.

While there is documentation that the NAS committee listened to both sides of the GMO debate and made an honest attempt to evaluate the available evidence fairly, this hasn’t always been so in other NAS studies. Just as politics have interfered in the debate over Roundup and cancer, as discussed in last week’s post, the NAS has been accused of substituting politics for science. Further accusations include insufficient attention to conflicts of interest among committee and panel members, and even turning a blind eye to scientific misconduct (including falsification of data). Misconduct is an issue I’ll return to in future posts.

Next week: What Intelligent Design Fails to Understand About Evolution

Politics Clashes with Science over Glyphosate and Cancer

Nothing exemplifies the attack on science more than its subversion to politics. The intrusion of political forces into the scientific sphere has distorted the debates over dietary fat, climate change, GMO crops and other controversial topics. Particularly contentious at present is the charge that the weedkiller glyphosate causes cancer, an allegation that’s behind thousands of U.S. lawsuits filed by cancer victims against glyphosate manufacturer Monsanto. The victims, who suffer from non-Hodgkin’s lymphoma, claim the cancer was caused by spraying the company’s glyphosate-based Roundup herbicide.


Best-seller Roundup has been used since 1974 to kill weeds in more than 100 food crops as well as greenhouses, aquatic areas, and residential parks and gardens. It became an especially profitable product for Monsanto in 1996 after the agricultural behemoth introduced Roundup Ready seeds, which are genetically engineered to make crop plants resistant to the herbicide; the revolutionary advance meant that farmers could now use Roundup to kill weeds while the crop was growing, instead of only before planting.

The carcinogenic potential of glyphosate has been evaluated several times in the U.S. by the EPA (Environmental Protection Agency), and in Europe by the EFSA (European Food Safety Authority) and the ECHA (European Chemicals Agency). While all these evaluations concluded that glyphosate was unlikely to be carcinogenic to humans, the IARC (International Agency for Research on Cancer) shocked the world in 2015 by classifying glyphosate as a potential carcinogen. It’s the IARC assessment that underpins the multimillion-dollar mass litigation against Monsanto.

So who’s right? The various government agencies in the U.S. and Europe that see no problem in continuing to use Roundup, or the WHO (World Health Organization)’s IARC? Both camps maintain that the scientific evidence is on their side.

The dispute is an all-too-common example of how politics is invading science. As reported by Reuters last year, the IARC made significant changes between the original draft of its 2015 monograph on glyphosate and the published version. Although it’s not unusual for a final agency report to differ from the draft, what stands out in this case is that the principal changes were the deletion of all statements and findings – and there were many – contrary to the IARC’s ultimate conclusion that glyphosate probably causes cancer.

The agency refuses to say who made the changes or why. If such secrecy alone were not enough to arouse suspicion, Reuters found 10 significant alterations to the draft chapter on animal studies – the very chapter that in the final report provided “sufficient evidence" that glyphosate causes cancer in animals. The draft chapter had reported the conclusions of multiple studies finding no link at all between glyphosate and cancer in laboratory animals. But the final report concluded exactly the opposite.

That the changes to the IARC report were politically rather than scientifically motivated is reinforced by the EPA’s finding that glyphosate poses no carcinogenic risk to humans. This conclusion was also reached by the EFSA, the ECHA and the UN’s FAO (Food and Agriculture Organization) – despite the EFSA and ECHA, like other European agencies, being more conservative and pro-environment than their U.S. counterparts. Not surprisingly, the environmentally activist organization Greenpeace has called the EFSA report faulting the IARC declaration “a whitewash.”

By far the greatest amount of scientific data on the possible human carcinogenicity of glyphosate comes from a 2005 study of 85,279 American farmers and their spouses. The so-called AHS (Agricultural Health Study) included epidemiological, animal carcinogenicity, and genotoxicity investigations to elucidate the carcinogenic potential of Roundup products.

Both the EPA and the IARC utilized the AHS data in their recent, conflicting evaluations of glyphosate. However, the IARC monograph also included a number of “low-quality” studies that the EPA elected to omit. Although this may seem arbitrary on the EPA’s part, the studies omitted by the EPA lacked, for example, information on glyphosate exposure of individual subjects. Such shortcomings are important in light of the current reproducibility crisis in the biomedical sciences: up to 90% of published findings in some areas of biomedicine can’t be replicated. The inclusion of scientifically inferior data by the IARC strongly suggests political interference in the scientific process.

Of six specific studies that investigated the association between glyphosate exposure and non-Hodgkin’s lymphoma – the possible linkage at issue in the mass lawsuits – the EPA stated that “a conclusion … cannot be determined based on the available data.” Nevertheless, for cancer overall, the EPA report found the strongest support for an assessment of glyphosate exposure as “not likely to be carcinogenic to humans,” which is the weakest of five EPA risk classifications on cancer.

Meanwhile, the jury in the first trial of the Roundup litigation ruled on August 10 that Monsanto’s weedkiller was a substantial contributing factor in causing non-Hodgkin’s lymphoma and ordered the company to pay $289 million in damages, a figure since reduced to $78 million on appeal. With further trials scheduled in 2019, only time will tell who is right about the science.

Next week: When No Evidence Is Evidence: GMO Food Safety