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Teenage chimps with spears and hammers

Two related papers this week: “Savanna chimpanzees, Pan troglodytes verus, hunt with tools� by Jill Preutz and Paco Bertolani, published in Current Biology (17:1-6), and “4,300-year-old chimpanzee sites and the origins of percussive stone technology� by Julio Mercader et al., published in Proceedings of the National Academy of Science (104:3043-3048).

Preutz and Bertolani report field observations of chimpanzees in Senegal making simple wooden spears and using them to kill bushbabies (sleeping in hollow trees) for food. Several individuals were seen making and using the spears, although apparently they only saw one successful “hunt.�

Some press reports have said that most of the chimps making and using spears were female, but what the abstract of the paper actually says is “females and immature chimpanzees exhibited this behavior more frequently than adult males.� Table 1 shows one adult male, one adult female, and eight immatures (four male and four female) making and/or using spears. So it might have been more informative to say that “immature chimpanzees exhibited this behavior more frequently than adults.� But apparently they wanted to contrast hunting with spears with “chimpanzee hunting in general, a predominantly [adult?] male activity.�

What can we conclude about tool use in human ancestors? Both humans and chimps are separated from our last common ancestor by a few million years of genetic and cultural evolution. Because other chimps have not been seen making spears, maybe “spear culture� arose in this particular chimp lineage some time after it diverged from our own. Is it possible that the first chimp to make a spear was copying a human spear-maker?

Mercado et al. found stones at three nearby sites in Cote d’Ivoire that had apparently been used by chimps to crack nuts thousands of years ago. Experts classifying the stones by their appearance as having been used for pounding. To avoid bias, these tests were done "blind" (experts weren't told which stones were which), with natural stones included as controls, including some with “natural modification that gives them the appearance of artifacts.� (The Far Side cartoon “Cow Tools� illustrates the problem.) Starch grains on some of the stones were identified as coming from nuts eaten mainly or exclusively by chimps and not by (modern?) humans. Carbon-14 dating of charcoal from forest fires showed that the layer where the stones were found was 4300 years old. This “predates the advent of settled farming villages in this part of the African rainforest�, making it less likely (though still possible) that the first chimps to use stones as “hammers� were imitating humans. Maybe the last common ancestor of humans and chimps used stone hammers and passed this cultural trait on to both lineages, or maybe the two species invented hammers independently.

Preutz and Bertolani endorse an earlier suggestion that “the earliest tool technology likely consisted of pounding or throwing rocks and hitting and jabbing sticks at about 6 million years ago.� Both of these studies, and other reports of chimps using sticks to collect termites, etc., show that animals with chimp-size brains can make and use rudimentary tools. If the last common ancestor of chimps and humans was using sharpened sticks as spears and stones as hammers several million years ago, humans have certainly made a lot more technological progress than chimps have. Maybe technologically innovative adolescent chimp nerds had more trouble finding mates?

Comments

Came over from Pharyngula. I read and enjoyed all of your posts. My bio background is (grimace) quite in my past, but you made the posts very understandable. I'll check back weekly.

i want pictures of these findings becuase i cant believe that a chimpanzee will have the intellectual compacity to even use this primitive technology, and if they did why dont we see it more often today than in the past 4000 years that apparently we found these artifacts

There are pictures in both articles, but the best evidence for chimp intellectual ability -- the best evidence for anything in science -- is independent investigators finding the same result. This criterion is met for chimp tool use in general -- there are lots of published field observations of chimps using/modifying sticks and stones as simple tools -- but these specific observations are brand new and therefore not yet replicated. A really interesting book on mental differences between humans and other apes is Folk Physics for Apes.

Interesting blog!
I'll have it bookmarked.

Off-topic comment (misreading of a different paper about chimps, unrelated to tool use) deleted here.

Ford,

"twebber" is a notorious young earth creationist troll, who frequents many a messageboard. I have been mentioning your blog elsewhere and he has picked up on it and will unfortunately now most probably plague your posts with his inane drivel.

It is my policy to ignore this individual and I strongly recommend others do the same, lest they be drawn into a never ending spiral of idiocy.

Many apologies for this and best wishes with the blog, it is an excellent idea. Indeed, by way of apology, can I make a hopefully useful suggestion for a future blog post. The following interesting paper in PNAS caught my attention:

http://www.pnas.org/cgi/content/abstract/104/10/3907

I tried submitting my trackbacks to this site, in case anyone wanted to see videos of chimpanzees hunting with a spear, using stones to crack nuts and the actual artifacts themselves. But I guess the trackbacks didn't go thru, so here's a list of posts, specifically for dustin and anyone interested:


Video of chimp hunting with a spear
Video of nut cracking behavior of Chimpanzees
Chimpanzee Archaeology - stone tools used by chimps from 4,300 years ago

Hey, thanks for the great info. I saw this in national geographic, too. I'll be linking you on my blog right alongside Pharyngula.

Interestingly, Darwin made comment on tool use in The Descent of Man:

It has often been said that no animal uses any tool; but the chimpanzee in a state of nature cracks a native fruit, somewhat like a walnut, with a stone.23 Rengger24 easily taught an American monkey thus to break open hard palm-nuts, and afterwards of its own accord it used stones to open other kinds of nuts, as well as boxes. It thus also removed the soft rind of fruit that had a disagreeable flavour. Another monkey was taught to open the lid of a large box with a stick, and afterwards it used the stick as a lever to move heavy bodies; and I have myself seen a young orang put a stick into a crevice, slip his hand to the other end, and use it in the proper manner as a lever. In the cases just mentioned stones and sticks were employed as implements; but they are likewise used as weapons. Brehm25 states, on the authority of the well-known traveller Schimper, that in Abyssinia when the baboons belonging to one species (C. gelada) descend in troops from the mountains to plunder the fields, they sometimes encounter troops of another species (C. hamadryas), and then a fight ensues. The Geladas roll down great stones, which the Hamadryas try to avoid, and then both species, making a great uproar, rush furiously against each other. Brehm, when accompanying the Duke of Coburg-Gotha, aided in an attack with fire-arms on a troop of baboons in the pass of Mensa in Abyssinia. The baboons in return rolled so many stones down the mountain, some as large as a man's head, that the attackers had to beat a hasty retreat; and the pass was actually for a time closed against the caravan. It deserves notice that these baboons thus acted in concert. Mr. Wallace26 on three occasions saw female orangs, accompanied by their young, "breaking off branches and the great spiny fruit of the Durian tree, with every appearance of rage; causing such a shower of missiles as effectually kept us from approaching too near the tree."

http://johnhawks.net/weblog/reviews/behavior/darwin_primate_tool_use_2007.html

SteveF:
Thanks for the quote. It would be nice to have independent verification of these stories, in case one or two of them might have been made up to sell a travel book or something, but it certainly shows the literature on ape tool use is older than I realized.

I had not heard anything at all about chimpanzees in Senegal making simple wooden spears and using them to kill bushbabies (sleeping in hollow trees) for food.

Yikes, soon we will be hearing about them building drones.

Thanks for the post.


Rick
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