Natural History

There’s a common statement on various websites related to opossums. It goes something like this:

“Opossums are not as stupid as people think. A study (or studies or tests) show that opossums are better at learning and discrimination showed them to be higher ranked than dogs.”

Okay. I’m going to call bullshit on this one.

Wanna know why?

I can’t find the study or test or any kind of peer-reviewed paper that says this.

And if I were a researcher making comparisons between the cognitive abilities of certain animals and the opossum wound up besting the dog, then I’d have very real questions about my methodology.

Here are the reason for my skepticism:

First of all, opossums have very small, very primitive brains. They are primitive mammals that retain much of the basal mammalian body type. They look very similar to basal placental mammals like the Cuban solenodon. Primitive mammals are unlikely to have many of the sophisticated cognitive abilities of more derived species, especially those that evolved to hunt cooperatively, like wolves and domestic dogs.

Secondly, no ethologist has recognized any sophisticated behavior in opossums. Opossums have been commonly kept as pets and as research animals for a very long time. They have been studied very closely, but no one is writing any great pieces of research on how opossums are able to reach such cognitive heights with such primitive little brains.

Now, there are many, many researchers looking into the cognitive abilities of dogs.  Studies have shown that dogs have very sophisticated social cognition, which they may have evolved through domestication. Dogs recognize the importance of human gestures, and they also know that when a person closes his or her eyes, the person cannot sense what the dog is doing.  There are dogs that respond to hundreds of words, and dogs can think abstractly.

If it were suddenly discovered that opossums could best dogs at these skills, it would be shatter almost everything we know about cognition in vertebrates. It would also fundamentally shift how we understand brain physiology, for an opossum’s brain is far more primitive and less complex than that of a dog.

So here’s my question to every site and book I’ve seen that makes this claim:

Where is the study that shows the impressive learning and discrimination abilities of opossums?

What’s its citation?

My guess is this study either doesn’t exist, or it is a simple methodology error in a multi-species comparative cognition study that the authors attempt to account for in the work.

And one study does not change the entire body of knowledge about a subject. It’s only when a particular study has a superior methodology that one can say it is paradigm shifting.

If this study does exist, it didn’t change the scientific community’s understanding of opossum versus dog intelligence.

If it did, you’d be seeing researchers working with large numbers of opossums to see how their cognitive abilities work.

And that’s simply not the case.

The old saw that states that extraordinary claims require extraordinary evidence certainly applies here.

And as far as I can tell, this is nothing more than an internet rumor that somehow grew legs.