Las t week, I wrote a post on the hierarchy of scientific evidence which included the figure to the right. In that post, I explained why some types of scientific papers produced more robust results than others. Some people, however, took issue with that and accused me of committing a genetic fallacy because I was attacking the source of their information rather than the information itself. They were specifically unhappy about my claim that personal anecdotes, gut feelings, counter-factual websites, etc. did not constitute scientific evidence. After all, how dare I assert that their opinions weren’t as valuable as a carefully controlled study (note the immense sarcasm). In reality, of course, my argument was not fallacious, and they were simply misunderstanding how the genetic fallacy works. This misunderstanding is, however, quite common and somewhat understandable. The genetic fallacy can admittedly be very confusing. Therefore, I want to briefly explain what this fallacy is, how to spot it, and when it is and is not acceptable to criticize the source of an argument/piece of information.

If you’re a regular reader of this blog, then much of this may sound very familiar. That is because I have already covered a lot of the key points in a previous post on ad hominem fallacies. The ad hominem fallacy is generally considered to be a type of genetic fallacy; therefore, the same general rules apply.

Note: in this post, I am going to specifically deal with this fallacy as it pertains to scientific issues.

What is the genetic fallacy?

As it’s name suggests, the genetic fallacy results from attacking the source or origin of information, rather than the information itself. If you think about that for a second, the reason for the confusion becomes clear. On the one hand, the reason that genetic fallacies don’t work is obvious: the truth of a claim is not dependent on the one who is making the claim. Even someone who is wrong 99.9% of the time will occasionally be right. On the other hand, however, the source of the information is clearly important. It’s intuitively obvious that not all sources are equal, and some sources are more authoritative than others. Imagine, for example, that during a trial, the prosecution brought in some random guy off of the street and asked him to testify about the forensic evidence of the case. The defense would very correctly attack the source of that information by arguing that this person was not a credentialed expert and, therefore, his testimony should not be trusted. There is obviously nothing fallacious about that, and the prosecution clearly couldn’t respond by accusing the defense of a genetic fallacy (they also couldn’t respond by saying “well he watched some Youtube videos on crime scene investigations and he’s read some blogs and done thousands of hours of research”).

So how do we resolve this apparent dilemma? The answer is that attacking the source of a claim is only fallacious if the source is irrelevant to veracity and trustworthiness of that claim. The Internet Encyclopedia of Philosophy defines it like this (my emphasis):

A critic uses the Genetic Fallacy if the critic attempts to discredit or support a claim or an argument because of its origin (genesis) when such an appeal to origins is irrelevant.

In other words, there is nothing wrong with attacking a source, if the source of the information is actually germane to whether or not you should trust the information. So, if someone cites questionable sources like Youtube videos or personal anecdotes, there is nothing wrong with you saying that we shouldn’t trust that information, because the sources actually are unreliable. That’s no different from not trusting some random guy off the street as an expert witness in a courtroom. Remember, that the burden of proof is always on the person making the claim, so it is their responsibility to provide you with evidence from a trustworthy source. As a result, if they make a claim like, “vaccines are dangerous” and their “evidence” is an Info Wars article, you are under no obligation to discredit that article. Rather, it is their obligation to provide you with evidence from a reliable source.

It’s important to note, however, that you can only use attacks against a source to show that the information cannot be trusted. You cannot use them to say that the information is false. For example, if someone presents you with “evidence” from a Natural News article, there is nothing wrong with saying, “Natural News is not a reliable source, therefore we should not trust that information.” It would, however, be fallacious to say, “Natural News is not a reliable source, therefore that information is wrong” (technically that would be a special case of the fallacy fallacy). Even an extremely unreliable source may be right every once in a while.

In addition to assaults on the source of the information, the genetic fallacy can also occur when you attack the reason for a person holding a particular view. For example, I frequently see creationists attack their opponents by saying, “you only accept evolution because you are an atheist who doesn’t want to believe in God.” Even if that premise was true (which it often isn’t), it’s irrelevant. It has no bearing on whether or not evolution is true, and is, therefore, a genetic fallacy.

Finally, it’s important to realize that for an argument to be a genetic fallacy the assault on the source has to actually be the argument. For example, if you show me a scientific study, and I respond by saying, “well the authors of that study are just ugly idiots so I don’t need to listen to them,” then I would have committed a genetic fallacy (specifically, an ad hominem fallacy). If, however, I explained at length why the study was flawed, then concluded with a Trump-like jab at the authors appearance/intelligence, I would not have committed a fallacy. It would be uncouth and inappropriate for me to do that, but it wouldn’t actually be a fallacy because the attack on the source was tangential to my argument.

Addendum (19-Jan-16): The genetic fallacy also occurs if you assert that something is true because of its source (i.e., the appeal to authority fallacy is actually a type of genetic fallacy), but in this post, my focus was on attacking sources, rather than using them as proof of a position.

The genetic fallacy vs. the hierarchy of scientific evidence

Now that you understand what this fallacy is, let’s bring it to bear on the topic that inspired this post: the hierarchy of scientific evidence. It should by now be clear that using the hierarchy of evidence to assess the validity of a scientific claim is not the same thing as committing a genetic fallacy. Nevertheless, let’s look closer.

First, let’s look at my assertion that personal opinions, anecdotes, anti-science websites, etc. do not count as scientific evidence. It’s worth noting, that I didn’t actually say that they aren’t trustworthy. Rather, I simply said that they aren’t scientific evidence, and that claim is demonstrably true because those sources do not produce evidence via the standards and methodologies of science. Therefore, they are, by definition, not scientific evidence. If I ask someone to give me scientific evidence for a position, then I am asking for actual original research. I want to see the peer-reviewed paper that found the result that they are reporting, not the Youtube video they watched.

Nevertheless, although I didn’t claim that non-scientific sources are untrustworthy in the original post, I clearly think that they are. People often take issue with this, but if you stop and think about it for a second, the claim is self-evident. All that I am saying is that for scientific topics, we have to use scientific evidence, which necessarily comes from the peer-reviewed literature. Websites, Youtube videos, etc. are inherently second hand information, which may or may not be reliable. The scientific literature, on the other hand, is primary information. When you read a scientific paper, you can see the actual results of an experiment rather than simply reading someone’s biased explanation of those results. Further, to publish a peer-reviewed paper takes a tremendous amount of work. You have to pass a rigorous peer-review process during which numerous other scientists will evaluate your work to ensure that it was done correctly. In contrast, any idiot with a computer and internet connection can make a website/Youtube video with absolutely no assurance of quality control. To be clear, that doesn’t automatically mean that the information contained in second-hand sources is wrong, but it does mean that you don’t have any reason to trust that information, which is why they aren’t valid sources for scientific topics. Further, websites like Natural News, Info Wars, Answers in Genesis, etc. are notorious for containing inaccurate information, which gives you an extremely strong, relevant, and legitimate reason not to trust them.

Even within the scientific literature, however, you should be looking critically at the sources. Some experimental designs are simply more powerful than others and produce more reliable results. For example, if you have a meta-analysis of randomized controlled trials vs. a cross sectional analysis, it would not be a genetic fallacy to say that the cross sectional analysis is less reliable than the meta-analysis. From a strictly mathematical point of view, cross sectional studies are weak. They simply cannot make causal conclusions. In contrast, randomized controlled trials are very powerful and can make causal conclusions, and meta-analyses are even better because they combine multiple data sets, thus greatly increasing the sample size and reducing the chance of reaching a faulty conclusion. It’s a simple mathematical fact that meta-analyses are better than cross sectional analyses. Therefore, the type of study (i.e., the source of the information) is extremely relevant to the trustworthiness of a study, and using that information in a debate does not constitute a genetic fallacy.

Conclusion

Genetic fallacies occur when you make an irrelevant attack on the source of information rather than the information itself. That does not mean, however, that it is always fallacious to attack the source of information. Some sources clearly are better than others, and the burden of proof is always on the person making the claim. Thus, it is their responsibility to provide high quality sources, and you are not responsible for disproving the information from extremely low quality sources. Nevertheless, determining when attacks on sources are fallacious can admittedly be confusing. Therefore, I have constructed the flowchart on the right to help you determine when you can and cannot attack a source.

Note: Just to be clear, arbitrarily accusing someone of being a shill without providing actual evidence that they are being paid off does not constitute a legitimate, relevant concern.

More posts on logical fallacies: