Does imagination make us human?

Do you take your coffee with milk? Would you like a slice of pizza? Oh hold on, that pizza will have to wait—someone is calling on the plastic phone on the kitchen wall. Who? Obviously my best friend Phoebe from down the street. Uh oh, now the coffee is cold. I’ll put on a fresh pot! Would you like some mustard on that pizza?

I used to spend hours upon hours in my Little Tikes Party Kitchen™, over-caffeinating anyone who stopped by with one fresh pot of coffee after another. And while I eventually grew out of my Party Kitchen, I did not stop playing. Many years later, you could find me in my room with a friend, building an elaborate Barbie house floor plan out of propped up books. When it was finally time for bed, I’d squeeze into the very small open spot in my double bed—the rest was covered with stuffed animals and beanie babies. What choice did I have? If any of them had to sleep on the floor, they would be sad and uncomfortable!  

Why do we play?

Screen Shot 2018-06-13 at 9.51.20 PM copy

One of the new adorable tiger cubs at the San Diego zoo!  

Humans are certainly not the only species to engage in playful behavior–there is a plethora of youtube videos of painfully adorable young animals at play (ha, and you thought you were going to get work done today!). However, humans are quite unique among other species in the number of years we spend as immature—dependent on adults to deal with real life troubles while we are free to spend large portions of time in the imaginary world of play. Why? Why would we have evolved to have such a long period of immaturity in which we suck up an incredible amount of our caretakers’ time and resources.



As with most ideas about how and why we evolved certain uniquely human traits, it’s difficult to prove anything. However, at a recent CARTA symposium on Imagination and Human Origins, Dr. Caren Walker, a psychology professor at UCSD, presented a hypothesis for why we evolved to play for a longer period of time than other species. She outlined a theory that a longer protected period for exploratory learning gave our ancestors an enhanced ability to grasp the forces of causation in their environments. This capacity for making causal inferences could have helped them make more sophisticated tools (by understanding cause and effect in a physical sense) and could have boosted their social intelligence (by understanding cause and effect in an emotional and interpersonal sense) [1]. This idea is already supported by data showing that levels of intelligence across primate species positively correlates with the age of weaning. In other words, the more time a primate species spends helpless early on, the more intelligent the adults animals are [2]. Humans are way off the charts, both in terms of intelligence and in terms of time spent dependent on an adult.

brain size

A figure showing the relationship between the intelligence and weaning time of primate genera. The numbers in the parentheses denote the number of species analyzed. Image from Piantadosi and Kidd, PNAS 2016 [2] 



Of course, this correlation cannot entirely be pinned on spending more time at the Party Kitchen. A longer childhood involves multiple factors beyond more time spent playing. But pretend play may indeed play an important role in developing cognitive abilities. In particular, Dr. Walker highlighted the potential link between pretend play and counterfactual thinking.

Practicing counterfactual thinking

Animals we see playing in the wild are often practicing skills that will later be needed for fighting, hunting, or food-gathering. But, in my case, I can assure you that the stove in my Party Kitchen did not work quite like a real-life stove, and I certainly did not develop a thorough understanding of how to make a pot of coffee. So what was the point? In her talk, Dr. Walker put forth the theory that one of the key advantages of play is learning counterfactual thinking.

A counterfactual is a statement that describes cause and effect in a particular way. In the situation “If A, then B,” the counterfactual would be “In the absence of A, not B”. Counterfactual thinking is particularly useful in distinguishing between different causal models. Imagine eating an ice cream cone on a hot day and ending up with sticky hands. These three factors could be connected in three ways: the hot day could cause the melting and the stickiness independently of one another, the hot day could cause sticky hands which make the ice cream start to drip, or the hot day melts the ice cream which leads to sticky hands. These three options are called causal models–models of cause and effect. A young child might first think that her hands were sticky because of the heat. But then perhaps the next day is just as hot, but she does not have an ice cream cone and her hands don’t get sticky. She could take this evidence into account and update her causal model to reflect that if there is no melting ice cream then there are no sticky hands, even on a hot day.

causal models


In the mid 90s, a group of researchers in the UK directly tested whether young children (age 3-5) were capable of counterfactual thinking. They found that even at this young age, children could accurately answer questions about a hypothetical situation (If A had not occurred, then B or not B?). They could also apply counterfactual thinking to a story (the protagonist got black ink all over her hands because he did not use a pencil) [3].

Some, including Dr. Walker, theorize that pretend play gives children practice in making these types of causal assumptions and maintaining a pretense through multiple actions [4]. For example, I might imagine that I am pouring cups of coffee for my family from my Party Kitchen. If I knock over one of the cups, I must then realize and react to the fact that the coffee has spilled all over the counter. Practicing cause and effect in this way hones a child’s understanding of a world.

Taking the theory further, this extended period of immaturity compared to other species gives us more protected time in which to experiment and explore these causal models. Practicing cause and effect gives us incredible depth of understanding of both the physical principles at work in the environment as well as the social ramifications of our actions. In this sense, it’s plausible that our tendency and capacity for imaginative play helped us to develop some of the very skills that define us as a species.

Kids are scientists!

These theories connecting play and counterfactual reasoning are of course interesting tokid-scientists-01 think about in the context of evolution, but as a graduate student who spends her days in the lab, when I think about causal models I can’t help but consider how they relate to science research as well. Counterfactuals form the basis of many scientific research experiments. To show that A is necessary to cause B, you must convincingly show that if you remove A, you no longer get B. For instance, in my own research, I am trying to determine whether a particular molecule causes blood-brain barrier dysfunction in disease. I am testing whether mice lacking this molecule have better clinical outcomes in a mouse model of multiple sclerosis. This is not just specific to my own work–you could pick up a journal article describing almost any basic science research experiment and you would see that classic pattern: if not A, then not B. So really, pretend play may be a medium through which kids practice being good scientists! Thanks, Mom and Dad, for sitting through endless meals at my Party Kitchen.


And because photos don’t suffice…

A video of me at my Party Kitchen  🙂


  1. Buchsbaum D, Bridgers S, Skolnick Weisberg D, Gopnik A. The power of
    possibility: causal learning, counterfactual reasoning, and pretend play. Philos
    Trans R Soc Lond B Biol Sci. 2012 Aug 5;367(1599):2202-12. doi:
    10.1098/rstb.2012.0122. PubMed PMID: 22734063; PubMed Central PMCID: PMC3385687.
  2. Piantadosi ST, Kidd C. Extraordinary intelligence and the care of infants. Proc Natl Acad Sci U S A. 2016 Jun 21;113(25):6874-9. dos: 10.1073/pnas.1506752113. Epub 2016 May 23. PubMed PMID: 27217560; PubMed Central PMCID: PMC4922193.
  3. Harris PL, German T, Mills P. Children’s use of counterfactual thinking in causal reasoning. Cognition. 1996 Dec;61(3):233-59. PubMed PMID: 8990973.
  4. Walker CM, Gopnik A. Pretense and possibility–a theoretical proposal about the effects of pretend play on development: comment on Lillard et al. (2013). Psychol Bull. 2013 Jan;139(1):40-4. doi: 10.1037/a0030151. PubMed PMID: 23294089.


Tiger cub:

Spilled milk:

Kid scientists: