A lesson in formal logic

Recently, a paper published by Claudio Tennie, Josep Call and Michael Tomasello from the Leipzig Max Planck claimed to show that humans are unique because human culture “has the distinctive characteristic that it accumulates modifications over time.” They say that this is largely because, compared to the cultural learning of other animals, human cultural learning is “more oriented towards process than product.” This may very well be true. Unfortunately, there is no way to reach this conclusion based on the research described in their paper, despite what the authors would have you believe. This is because the authors rely on negative evidence as the foundation of their claim.

They compared apes to human children in their ability to learn a task (tying a loop from string in order to retrieve a reward) by watching a human model the behavior. The authors’ sketch drawing of the task is shown here:

The children were able to perform the task after watching the model; the apes were not. The authors then conclude that since no evidence had been produced to disprove their convictions, their initial claim must be correct: humans are uniquely oriented toward learning the process of solutions. In essence, the authors are making an argument of the form: the ability of apes to socially learn processes has not been proven true; therefore it is false. This is a logical fallacy, and excludes the possibility – very real in the case of negative evidence — that the test wasn’t testing what it was supposed to. For example, the children are dealing with their own species and the apes are asked to imitate another species, so the set up is inherently biased against the apes. See another blog on this website on the issue of fair comparison. Previous experiments at Yerkes Field Station have shown that chimpanzees perform better at a social learning task when another chimpanzee, instead of a human, models the task.

Another example of the problems inherent in this (faulty) logic is illustrated by the creationist website answersingenesis, which currently features the Tennie paper in its News to Note blog as evidence that, not only are we distinct from other animal species in our mechanisms of social learning, but that the very theory of evolution is itself, false. After summarizing the paper, the site observes, “If man and ape are closely related, then one might expect more adeptness in apes’ problem-solving techniques… As creationists, we know that the anatomical similarities between man and ape are the result not of a common ancestor, but of a common Creator.” It appears that using scientific papers to create a God-of-the-gaps argument is a growing trend amongst the creationist community, as an article in Nature by Johan Bolhuis and Clive Wynne received a similar response (see a reply to creationists by the authors in SEED Magazine). I do not know the personal beliefs of Tennie or his co-authors, nor do I have any interest in discussing religious beliefs here, but I have to think that even the authors can see the problem –not to mention irony- in their own logic when it is being used by a religious fundamentalist group to educate against one of science’s most stalwart theories.

-Ian Longacre


5 thoughts on “A lesson in formal logic

  1. I am one of the authors of this study. Let me not waste many words on the Creationists' issue here. These people have basically lost their sanity, and so it has become more or less fruitless to argue with them. As for our study and your "lesson in formal logic": in fact, contrary to your claim, we did not solely rely on negative evidence when presenting our view. We reviewed the available literature and thus did take into account the available positive evidence (most importantly direct evidence for our proposed "latent solutions", like, e.g., leaf swallowing and nettle-feeding). Moreover, our study's outcome followed our predictions, and thus is additional evidence for our view.


  2. I hope that, in the course of your PhD project, you will receive some more lessons in formal logic. That is, I fail to see the logic in your last statement: '(..) I have to think that even the authors can see the problem –not to mention irony- in their own logic when it is being used by a religious fundamentalist group to educate against one of science’s most stalwart theories.'. This is a very silly argument. You refer to our essay in Nature – yes, creationists and ID-ots have exploited it (and that's a little embarrassing), but that doesn't mean that the original essay was wrong. This is where your logic breaks down. You are trying to argue against us and Tennie et al. by putting us in the same category as misguided creationists. This is not science, nor is it logical. [Some ad hominems removed by moderator]-Johan Bolhuis


  3. In reply to both Drs. Tennie and Bolhuis:First, let me say that I was not trying to put anyone in the same category as literal creationists. To do so would indeed lend far too much credibility to the creationists. In fact, I was trying to make a very general point, although, apparently I didn’t make it very clearly, and for that I apologize. I was simply trying to show that inferences drawn from negative evidence often seem harmless when couched in scientific terms, but that when taken to extremes –as in the case of literal creationists- the risks of this logic become much more salient. Dr. Tennie, you are absolutely correct to point out my oversimplification of your argument. You did, in fact, review available literature, which included instances of positive evidence (which is one of several reasons why your paper is a good example of the scientific approach). Still, several potential explanations exist for why apes failed at the task you presented them with, such as the disadvantage to apes of a human model or a need for more exposure to the task. These explanations allow for the possibility that the mechanisms allowing for cultural transmission in apes differ in degree, not nature, from our own. If these possibilities were exhausted then one would be more inclined to agree with your conclusion. When negative evidence is used to drive a wedge between human and animal behavior it plays into the hands of creationists, so all the more reason to be careful with quick conclusions. So, although I have no interest in name-calling of creationists, the paper by Dr. Bolhuis was referenced in my blog to further illuminate the way in which negative evidence is used on a daily basis without much notice. -Ian Longacre


  4. Me again. Thank you for clearing this up. I think together with your last comment I can actually accept the general criticism of yours – even though I personally do not share the same general negative attitude towards negative data. In sum, I think we can actually both agree that more studies are needed. I fully subscribe to that. For example, the paper by Whiten et al. (in the same issue as ours) has a different take on ape social learning skills – and their view is also consistent with the literature. So, I guess this is what it boils down to: we simply need more literature (i.e., data).


  5. I am glad our dialogue could have an agreeable outcome. Your distillation of my long-winded writing is spot on- we just need more literature, and we probably agree on far more than we disagree. Thank you for your comments Dr. Tennie.Ian


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