A few days ago a colleague asked me if I'd seen an essay called "Dogs Don't Remember," published by Dr. Ira Hyman. I hadn't, and then, as I was doing an interview, a similar question about mental time travel by animals came up so I decided to pen a few comments about Dr. Hyman's claims that "Dogs don't remember what happened yesterday and don't plan for tomorrow" and "Even if they can't describe their memories, chimps may engage in mental time travel. My dogs, however, are stuck in an eternal present."
In his essay, Dr. Hyman also writes, "If I walk into the backyard, the dogs are overjoyed to see me and act like they haven't seen me for days. If I stay in the backyard, they quickly become bored with me. If I go inside and return after 10-15 minutes, my dogs are overjoyed to see me and act like they haven't seen me in days. They don't remember that I was in the backyard just a few minutes ago."
I don't see that dogs or other nonhuman animals (animals) greeting a friend(s) after a short absence says much about whether or not they remember that an individual(s) had just been there. Many animals engage in repeated and effusive greeting ceremonies when first seeing a friend and shortly thereafter. So too do humans.
What about future planning?
Given his interests in mental time travel, Dr. Hyman also writes, "Dogs don't plan for particular future events although they have a general expectation of when dinner will appear." He may be correct here. I don't know of any studies that show that dogs "plan for particular future events" but, for example, I have seen dogs and wild coyotes very cautiously approach an area where unfriendly individuals live and often have felt they were planning for possible combat. Nonetheless, I'll grant for now that it is difficult to differentiate planning for a particular event and having a general expectation that something might occur. However, I wouldn't be so sure that dogs don't do both until the proper studies are conducted.
Studies on nonhuman primates, birds, and other animals show, in fact, that they do remember the past and plan for the future. In an essay I wrote called "What Makes Us Uniquely Human?" that was concerned with mental time travel, I noted that the prominent primatologists Christophe and Hedwige Boesch-Ackerman wrote in their book The Chimpanzees of the Tai Forest that "A hunting chimpanzee 'not only has to anticipate the direction in which the prey will flee (recorded as a half anticipation), but also the speed of the prey so as to synchronize his movements to reach the correct height in the tree before the prey enters it (recorded as a full anticipation) . ... We also recorded a double anticipation when a hunter not only anticipates the actions of the prey, but also the effect the action of other chimpanzees will have on the future movements of the colobus, that is he does not anticipate what he sees (the escaping colobus), but how a future chimpanzee tactic will further influence the escaping monkeys." And, even birds remember the past and plan for the future (see, for example, "Can animals recall the past and plan for the future?" and for numerous examples of more recent research on a wide variety of animals please see).
There's no evidence that dogs are stuck in "an eternal present"
So, all in all, unless others and I are missing something, dogs do remember yesterday. If Dr. Hyman literally means by "yesterday" the preceding day--24 hours ago--perhaps he's correct. To the best of my knowledge, no animals other than humans look at or wear watches or use calendars. However, it doesn't seem that Dr. Hyman literally means yesterday, but rather, more generally, "the past," given the example he uses about dogs greeting him repeatedly even if he's only been absent for a short while.
There are many examples of dogs and other animals "remembering yesterday." Think of dogs and other animals who have been severely abused and who suffer from severe fear or depression for years on end, and also, for example, think of dogs who remember where they and others peed and pooped, dogs who remember where their friends and foes live, dogs who change their behavior based on what they learned in various sorts of learning experiments, and dogs who remember where they're fed and where they've cached food and other objects. The list goes on and on.
From an evolutionary point of view it would be somewhat odd and exceptional if mammals such as dogs and many other animals didn't remember yesterday and plan accordingly. Mental time travel truly is a very exciting field of research and I look forward to more studies that speak to the questions of how past experiences inform future behavior. And, as I mentioned above, there already are many detailed studies that show that mental time travel back to the past and ahead toward the future is not uniquely human.
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