Take it easy Curious George… just put the stick down

23 02 2007

As if those darned chimpanzees hadn’t given creationists enough trouble with all their tool-use and intelligence, a new report in the journal Current Biology suggests that at least one group may have devised primitive “spears” (although from the way they use it it’s more like a probe/skewer) to get at bush babies slumbering in trees. I checked the journal’s website for the article but it does not appear to be available to non-subscribers as yet, although most news outlets are carrying the story. There is also some video from a forthcoming PBS NOVA documentary, although admittedly it does not illuminate much about the behavior.

Indeed, chimpanzees have featured in the news a number of times in the past few weeks, and here’s a quick rundown of the news in case anyone missed it;

February 10, 2007 – The American Museum of Natural History opens the Anne and Bernard Spitzer Hall of Human Origins to the public, featuring casts, reconstructions, and media-intensive displays to help educate people about hominid evolution. You can read my thoughts on the exhibit here.

February 12, 2007 – Oldest yet Chimpanzee tools found in Africa,
suggesting that chimpanzees have been using stone tools to crack open nuts for at least 4,000 years. We know from extant chimpanzees that youngsters are taught how to do this through observation, suggesting that this form of tool use has been taught for far longer than previously suspected (the oldest set of stone tools prior to this discovery were 100 years old). Have a look at the video below for a look at how it’s done.

It’s important to note that the piece of stone is not the only important part in the behavior; the nut must be held in place or else attempting to crack it will be fruitless. Usually another stone or piece of wood with a depression in it help keep the nut still so that full force of the stone can be exerted on it, an example of this on film seen in the BBC’s wonderful series, The Life of Mammals

February 23, 2007 – According to a new study published in PLoS Genetics, it is suggested that humans and chimpanzees split from their common ancestor about 4.1 million years ago. Bear in mind that the Laetoli footprints has been positively dated to 3.7 million years ago, so if these new figures for speciation times are correct, then the evolution from a common ancestor to Australopithecus must have been rather rapid in relative terms.

Anyway, back to the study that was produced yesterday about the “spears.” What seems to be the case is that immature and female chimps (individuals that usually don’t get much meat when hunting parties return and call first dibs on the pulverized monkeys) take a twig or stick and whittle the tip down to something of a point with their teeth, which they then “forcibly” stick the probe into holes in trees hoping to snag a snack, using enough power that if there is prey in their it would be impaled or injured by the motion according to the researchers. The chimps sniff and lick the probes upon retracting them, the behavior seeming reminiscent overall of chimp’s habit of “fishing” for termites or orangutans using sticks to get honey out of trees. Indeed, this seems to me almost like the modification of an already familiar behavior rather than something entirely new, although more study will certainly be needed to see if the chimpanzees are just probing to see what they get or they have an intent to stun or even potentially impale whatever is in the holes. Another scientist named Gilby said that Gombe chimpanzees will sometimes use a similar method to extract honey or birds from tree holes in this AP article, so again more research will need to be done to understand how “novel” this behavior is and all its details.

This also reminds me of some studies done of chimpanzees using sticks as weapons, the males wielding sticks to hurt females during some displays. I haven’t been able to find anything on the internet about this (the initial reference I found was in the book The Octopus and the Orangutan), but it appeared that as yet the males that did use the sticks had not extended them into use beyond beating up some of the females. A video I saw in my Behavioral Biology class last week also featured chimpanzees faced with a fake leopard, the chimpanzees attempting to use sticks to hurt the fake cat. From what the video showed, the chimpanzees had not figured out how to effectively use the sticks and branches to strike, throwing them about at odd angles that I’m sure would hurt, but certainly nothing like swinging a baseball bat. The fake leopard was decapitated by some means or another (it was not shown how), but again it seems that while some chimps may be using branches as offensive weapons they have not yet figured out how to use them efficiently enough for them to be useful.

Usage of tools for hunting, defense, or even offense is interesting as chimps seem to be quite proficient in using tools that could be used for weapons (rocks and sharp sticks) but have not extended the use of those tools as yet. I wonder what led to the first “weapons” or hunting tools, and I think to fully understand the answer we need to look at the paleoecology of where hominids arose. When the line that would lead to hominids split from the line leading to today’s extant apes, there were far more predators around, especially on the savanna that Australopithecenes and others would likely call home. In addition to big cats like we have today (leopards, lions, cheetahs), there were giant hyenas and saber-toothed cats and various horned and tusked herbivores, Africa being a pretty dangerous place to live at the time. If you were going to live on the plains, where there are few trees and you can’t run fast enough to escape, natural selection would certainly favor those who could protect themselves and use weapons most efficiently, pressures that are highly relaxed today. While I’m sure tool use among extant chimpanzees can help us gain insight into our own history,we must remember that we need to get the big picture of ecology, behavior, and morphology during the time hominids arose in order to successfully figure out what happened; evolution does not work in a vacuum.




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