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Photo of Susan Carey Susan Carey as seen on
Animal Einsteins: Number Crunchers

Click on Susan's photo to read a brief bio.

q What is the difference between the new world monkeys and old world monkeys you mentioned in a previous answer? How would this affect their counting skills? Bob

A New world monkeys are those species that are found in the Americas and old world monkeys those species found in Africa and Asia. The New world monkeys, for the most part, are evolutionary more distant from humans than are old world monkeys (for the most part). That means that we have to go farther back in time before we find a common ancestor between tamarins and us than before we find common ancestor between rhesus and us. This doesn't necessarily mean that tamarins will be less like us in counting skills than are rhesus (that's one of the questions we want to know the answer to), but it seems that that is so. So, for example, in the choice experiment you saw on the show, rhesus succeed up to choices between three apples in one box vs. four in the other, but tamarins only succeed on one vs. two (and a few we've tested succeed regularly on two vs. three). q What made you start doing this type of research? And how old were you when you knew you wanted to be a scientist? (asked by several viewers)

A I didn't know I wanted to be a scientist until I was in college, but I was always most interested in science and math of all the subjects I studied in grade school and high school. What made me start doing this type of research is a long story. All my career (and I've been at this since 1971), I've been fascinated with the problem of where knowledge comes from. This has usually led me to study cognitive development (the development of knowledge) in children, including babies, but it has also led me to study the history of science.

Since babies don't have language, I had the idea that the methods we use to study what babies know could be used to study what other creatures who don't have language, like monkeys, know. Then we could study the problem of where knowledge comes from in evolution, as well as in the history of culture and in the development of each individual child. So the short answer to the question is this--it seemed that this line of research, if it was feasible, might help me gain another type of answer to the question that interests me most: where does human knowledge come from.
q How long have you been working with the monkeys on the island? Have you ever been attacked by the monkeys? Mrs. Jordan's Fifth Grade Science Class

A I have just started working with the monkeys on the island (I've been at it, on and off, for three years. But others have worked with them for years and years, almost 50. There used to be a very aggressive monkey who would jump on people's heads and then jump off, but he never really hurt anybody. He's now so old that he doesn't do that any more. Also, once somebody I was sitting next to (Marc Hauser, who was also on the program, the man who studies the Cotton-top tamarins) was eating a peach and a hungry monkey lunged at him to try to get the peach. But usually, the monkeys stay away from the people. We are much bigger than they are, and they're a little afraid of us. If one approaches, you can always pick up a rock and pretend to throw it at them, and they will back off. I never felt in the slightest bit of danger on the Island. They are mainly curious. (If they weren't, our experiments wouldn't work.) q How do you design your experiments? scooby-doo

A We start with a question. For example, "do monkeys notice the number of objects involved in the events unfolding before them?" We then figure out methods that -might- help us answer the question. Then we try them out. If a particular experiment does not work, we don't know what that means. It might mean that the monkeys don't have the knowledge needed to succeed at the task, or it might mean that the experiment just didn't capture their attention or they just didn't care. So then we try something else. And so it goes. If the experiment did seem to work, then we ask ourselves whether it could have worked for the wrong reason, because of some feature of the task we set the monkeys that was not what we were interested in. And then we think possible other reasons for success, and we design experiments that would test whether each one could have been what really led to the monkeys' behavior. So you see, it is a long process, step by step. Each answer we get leads to another question. Once you have a clear question, it isn't hard to think up experiments that might answer it. q Did you ever put the same number of apples in both boxes and see what happens? Shannon C., biology student at St. Bernard's Central Catholic High School, Fitchburg, MA

A Good question. No, we didn't, because we assume that the monkeys would just choose one or the other, randomly. What else could they do? We don't think they would even hesitate, weighing the choice, because they are trying to grab the apples as fast as they can (ever worried about other monkeys swooping in). But we have done a lot of other versions of the study not mentioned on the show--for example, one piece of apple in one box and a rock in the other (same number of objects). 100% of the monkeys choose the apple. This was actually the first study we did, to make sure that method would work, that they could see it was food from such a distance, and so on. Then to make sure they are actually counting the slices of apples, rather than choosing the box that had the most motion associated with it, we did three apple slices and a rock vs. four apple slices (same amount of motion, same number of objects). They go with the four apple slices. And finally, to make sure they are not just avoiding the rock (which they are afraid of), we did three apple slices and a rock vs. two apple slices. Now they go with three apple slices and the rock. So they are clearly enumerating the number of apple slices. q How are you certain that you do not test the same monkeys more than once? Mary S., biology student at St. Bernard's Central Catholic High School, Fitchburg, MA

A Good question. Each monkey is tattooed with a number and we write down their numbers. q Can monkeys have mental retardation since they are so similar to humans? Brooke

A Good question. I do not know the answer, but I would certainly place my bets with the answer: yes. Some mental retardation in humans is caused by genetic abnormalities which cause the brain not to develop normally; other is caused by damage to the developing brain due to accidents of one sort or another (including drug/alcohol use by the mother, or lack of oxygen due to birth complications, etc.) These types of causes would seem possible in monkeys, except drug/alcohol use, of course. But I would also guess that severely retarded monkeys would not survive into adulthood. Monkeys need their wits about them to survive. q My students enjoyed the real-life field experiments you conducted. They commented that animals in the wild seemed to be very different than the animals kept in the laboratory. They wondered who funded your experiments and approximately how much money do your experiments in the natural areas cost. Thank you for your time! Jackie Robertson

A Our experiments are funded by the National Science Foundation, one of the two major governmental sources of funding for scientific research (the other being the National Institutes of Health). As scientific research goes, this is not very expensive. We have to pay for me and an assistant to go down to Puerto Rico. (Air fare around $400-500 each). Once we get there, housing is very cheap. Then we have to pay a fee that is our part of maintaining the monkey colony on Cayo Santiago. Since we only go down a few weeks a year, this also is not very expensive, about $2000 a year. It is much, much more expensive to maintain a laboratory colony of monkeys. q How does the intelligence of wild monkeys differ from ones in captivity? Mrs. Jordan's Fifth Grade Science Class

A Good question. It depends upon how much of intelligence depends upon learning. Monkeys in captivity and monkeys in the wild are the same species of animal, but monkeys who live in laboratory settings have been trained in ways that monkeys in the wild have not. The clearest example of this difference involves chimpanzees, who are apes, not monkeys. Chimpanzees in captivity have been taught to use language-like symbols. Some researchers think that learning language-like symbols actually changes the intelligence of chimpanzees, but scientists do not consider that this question has been answered for sure.

q Do you feel that the monkeys taken to the island for behavioral studies have been sensitized or affected by long-term exposure to people studying them? By this I mean are their responses conditioned by their exposure to people? Laura

A Most research on the island concerns social interactions; human observers track individual monkeys, their coalitions, their dominance hierarchies, and so on. These researchers never interact with the monkeys as we do in these experiments. (That is, only we show monkeys magic tricks, give them food, and so on.) That the monkeys are used to people probably plays a big role in making our work possible, but I don't think that the monkeys have had any experience relevant to the actual questions we are asking about animal minds (e.g., number representations). Remember, each monkey is only tested once by us.

q According to what I saw in the "Number Crunchers" story, it seems the monkeys were not actually counting, it seemed they were recognizing volume. The apple chips (or whatever piece of fruit) were all approximately the same size. Did you test your subjects on, say, 2 really large pieces in one box and 3 significantly smaller pieces in the other? Perhaps that test would bring other factors into play, such as rational tendencies toward volume. It just seems that a natural tendency of an animal in the wild would be to see the biggest pile of shapes, and go forward with the hunt. All in all, I enjoyed the show and I applaud all efforts of the scientists and the crews! Deanna

A We are doing the experiments you suggest right now! We assume, as you do, that the monkeys are trying to maximize total amount of apple stuff. But remember, in these studies the monkeys see the apple pieces one at a time. So even if they are summing the individual volumes, they must keep track of the number of pieces. We assume (but the experiments you suggest will tell us the answer), that from 10-15 feet away, the monkeys can't actually see the volumes of the individual pieces well enough to accurately sum the volumes. Therefore, we assume that the monkeys themselves are making an equal-volume assumption and then using number to estimate total volume.

q What kind of monkeys did you use in your experiment? Why did you choose to work with this particular monkey in the wild, rather than on captive animals? (Asked by several viewers)

A We used rhesus macaques. The choice of species was mainly for convenience (because we were doing other experiments on Cayo already). We wanted a non-ape, old-world monkey, to compare (eventually) with an ape species and a new-world monkey like Marc Hauser's Cotton-top tamarins, a species more distant from us evolutionarily than are old-world monkeys. We are doing these experiments in the wild so we can test experimentally naive monkeys. In this research, we are interested in spontaneous representations of the world, because these may give us important insights into the conceptual representations that supported the evolution of language. Thus, it is important that we test each animal just once. A population of 1000 wild monkeys allows us to do that. These experiments can be done in the laboratory, of course, and we have explored some of the same issues in this context as well.


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