Sunday, August 9, 2009
Tool use and cognition, Part 1: Thumbs not required
In my Anth 200 class, I have my students read an article by Craig Stanford entitled "Got Culture." It's from his book Significant Others (2001) so after 8 years, obviously there's been a lot more research that's come out on culture and tool use among animals. But he brings up one question:
"If tool use and other cultural innovations can be so valuable to chimpanzees, why have they not arisen more widely among primates and other big-brained animals?" He later concludes, "So to be a cultural animal, it is not enough to be big-brained. You must have the anatomical prerequisites for tool cultures to develop. Even if these are in place, there is no guarantee that a species will generate a subsistence culture in the form of tools."
I would disagree. As I caution my students, since this article was written, a lot more reports of tool use have come about, in a variety of animals. Furthermore, a lot of them lack the anatomical prerequisites (dexterous fingers, grasping hands, opposable thumbs). Tool use has been observed in elephants (which do have a dexterous trunk, with finger-like appendages), crows (which use their beaks to hold tools), dolphins (who once again, use their "beaks"), and spider monkeys (who have a reduced thumb that is pretty much just a little stub).
So why don't we see tool use more often among other large-brained animals? I suspect that first, it has a lot to do with a) observation time, and b) what we're looking for. Chimpanzees are incredibly well-studied in the wild, as compared to a lot of other species. Furthermore, observations of tool use among orangutans, bonobos, and gorillas were not made until well-after long-term studies had been initiated. Thus, it might take a lot of time to catch these observations, particularly if it's rare behavior. Additionally, if you're not looking for and expecting tool use, you might miss it. In the first field study conducted on spider monkeys back in the 1930s, Carpenter (1935) observed that spider monkeys engaged in directed branch-dropping at observers. This does fulfill the classic definition later articulated by Beck (1980):
‘‘the external employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself when the user holds or carries the tool during or just prior to use and is responsible for the proper and effective orientation of the tool."
However, this behavior has gone overlooked, and there's some debate whether it counts as tool use. The question is whether it is intentional and directed: personally, given my own experiences nearly being concussed by a branch dropped/thrown by a spider monkey (thanks to one of my field school students last summer, I was warned just in time), I suspect it is--but conclusively demonstrating intentionality and directedness is tough to do. Furthermore, there is even one paper in which an author argues that when capuchins branch-drop, it is directed and intentional, but when spider monkeys or howler monkeys do it, it's not. But clearly, that sounds like a very capuchin-centric double-standard. Furthermore, behaviors like fur-rubbing don't seem to even be included in reports of tool use, even though they also fit that definition (and once again, could be subject to debate).
I think this is because, if a chimpanzee does something with an unattached object, it's more likely to be accepted as tool use. If another animal uses it (especially if it's not an ape or capuchin), it's likely to be questioned--is that really tool use? or should it be classified as object use, or substrate manipulation? Is it really intentional and directed? Do they understand what they are doing? Does it count if they use a tool to modify an aspect of themselves, other individuals, or an "object" such as "water" or "vocalizations?" While all of these are important questions, it's important that we apply the same criteria to evaluating if a behavior meets the definition of tool use. And I think, if researchers studying animals were looking for, or at least considering, that certain behaviors may be tool use, or cultural traditions, they may be more likely to actually take note of them and document them as such. While we still need to be exploring whether the behavior is intentional and directed, and whether the animals understand the properties of what they are using, that doesn't mean we should discount such observations, or reclassify them under another definition (unless, of course, they don't meet the standard criteria).
Anyway, I will write more on this subject later on. But for now, here's a few links and references:
Orangutans use leaves as a tool to modify their vocalizations
Cultural transmission of tool use in bottlenose dolphins
And of course, our recent paper on tool use in spider monkeys . . . You can read the media interpretation here, or read the paper itself:
Lindshield, SL, Rodrigues, MA. 2009. Tool use in wild spider monkeys (Ateles geoffroyi). Primates 50(3): 269-272.