Primatology.net

So the paper, I mentioned this morning, on chimpanzees hunting with spears has come out… and literally the entire blogosphere I know and track has reported on it. If that’s any indication that this is a remarkable finding to them, then so be it. By the way, Digg loves this news too.

To me this is an interesting finding, but nothing really new.

We have known for a long time chimpanzees use tools in one form or another. Chimpanzee tool use was documented by several primatologists in the field, such as stone tools to crack nuts and sticks used to fish ants and termites. The history, or rather prehistory, of chimpanzee tool use was supplemented with recent archaeological evidence that shows us chimpanzee tool use has been happening for thousands of years.

So what’s the big deal if chimps now also use ‘spears’ to hunt? To me it is just another tool used by a species of primate that has already been well documented as an intelligent organism.

The big deal is the authors of this Curent Biology paper, “Savanna Chimpanzees, Pan troglodytes verus, Hunt with Tools” are claiming the chimps are actually making the spears, and not just selecting for sticks that would be good spears. If this is the case, then this is a critical behavior that distinguishes this form of tool use, from nut cracking. In nut cracking, chimpanzees select for stones that would be more effective in cracking nuts. They don’t particularly make stones that would be good nut crackers. The abstract reflects what they found and I’ve bolded the statements that I feel are particularly outstanding:

“Although tool use is known to occur in species ranging from naked mole rats to owls, chimpanzees are the most accomplished tool users. The modification and use of tools during hunting, however, is still considered to be a uniquely human trait among primates. Here, we report the first account of habitual tool use during vertebrate hunting by nonhumans. At the Fongoli site in Senegal, we observed ten different chimpanzees use tools to hunt prosimian prey in 22 bouts. This includes immature chimpanzees and females, members of age-sex classes not normally characterized by extensive hunting behavior. Chimpanzees made 26 different tools, and we were able to recover and analyze 12 of these. Tool construction entailed up to five steps, including trimming the tool tip to a point. Tools were used in the manner of a spear, rather than a probe or rousing tool. This new information on chimpanzee tool use has important implications for the evolution of tool use and construction for hunting in the earliest hominids, especially given our observations that females and immature chimpanzees exhibited this behavior more frequently than adult males.”

So there you have it, chimps make spears. More over, more female chimps make them than males… I’m sure my physical anthropology professor Adrienne Zihlman would like to read that.

I’ve gathered a list of other blogs who have reported on this paper at the time of my writing of this post, you should have a read and see what other people find interesting.

• Chimpanzees make and use spears from Tetrapod Zoology.
• Woman the Hunter? from The Loom.
• Chimps With Spears from Mixing Memory.

And from National Geographic News, ‘Chimps Use “Spears” to Hunt Mammals, Study Says‘ as well as a video, ‘Chimps Make and Use “Spears” to Hunt.’ According to the National Geographic News, one of the author’s work, Jill Pruetz, with chimpanzees will be featured in an upcoming NOVA/National Geographic special on PBS but the air date is not yet announced.

What’s this? Chimps hunt using spears?

That’s what the authors, Jill Pruetz and Paco Bertolani, are reporting in a yet to be published paper in the journal Current Biology.

Since we don’t have the primary source, I’m relying on a news article published by the BBC News to share this with you. Here’s all I got so far:

“Chimpanzees in Senegal have been observed making and using wooden spears to hunt other primates… Researchers documented 22 cases of chimps fashioning tools to jab at smaller primates sheltering in cavities of hollow branches or tree trunks…. Chimps had not been previously observed hunting other animals with tools.”

This is an important finding, right on the coat tails of the report on the 4,300 year old stone tools used by chimps. I don’t know yet if this is a case where chimps fashioned spears or just selected for sticks that are effective spears (like the best stones that will be good anvils and hammers), but at the very minimum it expands our knowledge base on tool usage in non-human primates.

You can expect me to keep a diligent eye open for this publication. I’ll do my best to read it as soon as I get my grubby hands on it.

A big topic of conversation in zoos and other animal facilities is stress: Who suffers from it? What are the causes and repercussions? How can we identify it biologically? And what are the best ways to recognize the causes in hopes of alleviating the stress?

We have all seen stress in animals (including ourselves) appear in some form of aberrant behaviors and other various conditions: pacing, head tossing (with carnivores), hypergrooming, displaying (like throwing feces or vomit), losing sleep, breaking out into hives, and self mutilation, just to name a few. While these behaviors and conditions are visual, concern also lies in what we can’t easily see… chronic stress resulting in suppression of the immune system, high blood pressure, stress dwarfism, fibrosing cardiomyopathy, etc.

Robert Sapolsky of Stanford University has been researching the physiological effects of stress on health (with a nice set of publications including both scientific papers and popular books) for decades and recently presented at the American Association for the Advancement of Science in San Francisco on Feb 17^th, 2006 (which I’m sad to say I missed). ScienceDaily highlights his research asking “Why Do Humans And Primates Get More Stress-related Diseases Than Other Animals?”

The bottom line is that:

“Primates are super smart and organized just enough to devote their free time to being miserable to each other and stressing each other out. But if you get chronically, psychosocially stressed, you’re going to compromise your health. So, essentially, we’ve evolved to be smart enough to make ourselves sick.”

Sapolsky helps us to think of it in terms of real stress versus psychological stress:

“During real stress – for example, something is intent on eating you and you’re running for your life – versus what your body does when you’re turning on the same stress response for months on end for purely psychosocial reasons.”

By constantly stressing ourselves out we are forcing our bodies to run in ways that are only intended for short bursts of time. We are essentially breaking down our system and becoming vulnerable to severe health problems (like those previously mentioned).

The baboon studies Sapolsky spearheaded are hugely relevant to this situation:

“We’ve found that baboons have diseases that other social mammals generally don’t have. If you’re a gazelle, you don’t have a very complex emotional life, despite being a social species. But primates are just smart enough that they can think their bodies into working differently. It’s not until you get to primates that you get things that look like depression.

The reason baboons are such good models is, like us, they don’t have real stressors. If you live in a baboon troop in the Serengeti, you only have to work three hours a day for your calories, and predators don’t mess with you much. What that means is you’ve got nine hours of free time every day to devote to generating psychological stress toward other animals in your troop. So the baboon is a wonderful model for living well enough and long enough to pay the price for all the social-stressor nonsense that they create for each other. They’re just like us: They’re not getting done in by predators and famines, they’re getting done in by each other.”

Needless to say, it’s important to understand more of the neuroscience behind stress. Sapolsky highlights some of the new research:

“It’s becoming clear that in the hippocampus, the part of the brain most susceptible to stress hormones, you see atrophy in people with post-traumatic stress disorder and major depression. There’s a ton of very exciting, very contentious work as to whether stress is causing that part of the brain to atrophy, and if so, is it reversible. Or does having a small hippocampus make you more vulnerable to stress-related traumas?”

Also…

“There are now studies showing that chromosomal DNA aging accelerates in young, healthy humans who experience something incredibly psychologically stressful. That’s a huge finding.”

Animals respond differently to every situation and stress is no exception. Understanding these differences, according to Sapolsky, is one of the most important areas of neuroscience research:

“This gets you into the realm of why do some people see stressors that other people don’t, and why, in the face of something that is undeniably a stressor to everybody, do some people do so much worse than others?”

It will be interesting to see how this research unfolds. Will it result in solid methods to understand how stress works? Will it lead to non-invasive biological markers of stress? Currently some researchers are relying on cortisol as a hormonal marker of stress. I’ve been to many a lecture reviewing the pros and cons of using cortisol in behavioral research, each generally ending with the same thought: cortisol is an accurate marker telling us that something is happening, but whether that something is bad stress (versus good stress, like riding a roller coaster) is still unknown. Some may say that the captive situations we’re using in research are more likely to prompt bad stress which would mean that cortisol is a better marker of bad stress than we are giving it credit for, but until that separation is apparent, we’re kind of back to the drawing board.

Understanding the animals that we work with can sometimes be a challenging job. Hopefully with all of the research going on in this field, we will be able to formulate a better understanding of what stress is (for each individual animal) so that we can do our best to identify and eliminate the stressors (and consequently the health problems).