حمله شمپانزه به شمپانزه در جنگل بسیار رایج است، به خصوص میان گروه های کوچکی از نرهای در حال گشت زنی. اما انگیزه این خشونت کاری تاکنون دانسته نبود. اکنون پژوهشگران می گویند که به نظر می آید شمپانزه ها هم مانند انسان برای تصرف قلمرو همسایگان خود اقدام به این نوع حمله ها و قتل ها می کنند.
برای فهم این خشونت، پژوهشگران گروه بزرگی از شمپانزه ها را که در پارک ملی نگونو در اوگاندا زندگی می کنند مورد مطالعه قرار دادند. پس از یک دهه زیرنظر داشتن این گروه، دانشمندان 21 قتل شمپانزه به دست شمپانزه را شمارش کردند.
از میان آنها، دانشمندان به گونه ای مستقیم شاهد 18 فقره قتل بودند، و در سه مورد دیگر هم به نتیجه استقرایی رسیدند. آنها فکر می کنند که تا 13 فقره از قربانیان این قتل ها به تنها یک گروه همسایه تعلق داشتند.
جان میتانی از دانشگاه میشیگان می گوید: "غنیمت گیری روشن و ساده است." او می افزاید: "شمپانزه ها همدیگر را می کشند. آنها همسایه های خود را می کشند. تا این زمان، ما نمی دانستیم چرا. مشاهده های ما حکایت از آن دارد که که آنها برای بسط قلمرو خود و به بهای جان قربانیان خود این کار را می کنند."
پس از آن که بعضی از این همسایگان رقیب از میدان به در شدند، پژوهشگران مشاهده کردند که شمپانزه های نگونو شروع به استفاده از سرزمین جدید در شمال شرقی محدوده قلمرو سابق خود کردند. این مدرک به پژوهشگران امکان داد تا برای قتل ها و انگیزه ی تصاحب سرزمین جدید ارتباط برقرار نمایند.
دانشمندان فکر می کنند که تصاحب زمین جدید امکان دسترسی بیشتری به غذا و احتمالا شمپانزه های ماده را فراهم می کند. ...
Discover Magazine via CBS News | June 21, 2010
What Drives a Chimp to Murder?
Experts Say Chimps Will Murder Each Other for Access to Land
(Discover) Between 1998 and 2009, John Mitani witnessed 18 murders firsthand, and found
circumstantial evidence for three more. But no police were ever called, for these killers were all chimpanzees, from the Ngogo community in Uganda’s Kibale National Park.
Chimpanzees are highly intelligent animals, capable of great acts of empathy, technological sophistication, culture and cooperation. But they can also be murderers. Groups of chimps, mostly male, will mount lengthy aggressive campaigns against individuals from other groups, attacking them en masse and beating them to death. Their reasons for such killings have long been a source of debate among zoologists, but the aftermath of the Ngogo murders reveals an important clue. After the chimps picked off their neighbours, they eventually took over their territory. It seems that chimps kill for land.
The vast majority of these murders were carried out by groups of Ngogo males on patrol. These patrols are stern, single-file affairs. Males march along the borders of their territories, scanning for other chimps and neither feeding nor socialising. They monitor the northeastern part of their territory with particular fervour and indeed, 13 of their 21 kills took place here.
Of these victims, 4 were adult males and 9 were youngsters. That may seem like a small number, but for chimps, these are severe losses. At the hands of the Ngogo attackers, the northeastern community was experiencing death rates that were 23 to 75 times higher than those observed in other groups of chimps. They were even higher (by around 5 to 17 times) than the death rates due to violence between groups of human hunter-gatherers.
It’s clear that the Ngogo chimps are skilled at waging war against their neighbours and the exceptionally large males in their number probably contribute to their aptitude for violence. And because of their aggressive tactics, they have increased the size of their territory by some 22%, expanding into the northeast area that their neighbours once called home. With murder came new real estate to colonise.
Mitani’s observations back up other anecdotal evidence from other parts of Africa. In Gombe National Park, the Kasekala community of chimps took over the territory of the neighbouring Kahama clan after a series of fatal attacks. But the former community actually splintered off from the latter some time previously. Elsewhere in the Mahale Mountains, one group of chimps annexed the territory of another. All the males in the latter group mysteriously disappeared, but no murders were ever directly witnessed.
In contrast, Mitani found clear and direct evidence that the Ngogo chimps killed off their rivals and commandeered their land. These observations don’t rule out the alternative ideas that the attacks were motivated by a desire for more mates. After all, more acreage could attract more females into the group or improves the chances of existing members. But Mitani’s observations do rule out at least one idea behind chimp aggression - that it’s a side effect of humans. Some zoologists had suggested that by providing food to wild chimps, we were instigating conflict between them, but that’s clearly not the case in Ngogo.
Much of this behaviour might seem familiar, for it has poignant echoes of human warfare. After all, we also kill each other over resource. Richard Wrangham, a primatologist from Harvard University, has suggested that understanding the reasons behind chimp violence could help us to understand and address “the roots of violence in our own species”. Even so, Mitani is very careful about drawing an analogy between chimp and human aggression, given the myriad of reasons that humans have for waging war.
Chimp expert Frans de Waal appreciates his caution. He says, “There have been claims made in the past that since chimps wage war and we do as well it must be a characteristic that goes back 6 million years, and that we have always waged war, and always will.
“There are many problems with this idea, not the least of which is that firm archaeological evidence for human warfare goes back only about 10-15 thousand years. And apart from chimpanzees, we have an equally close relative, the bonobo, that is remarkably peaceful. The recent discovery of Ardipithecus also adds to the picture, as the suggestion has been that Ardi was relatively peaceful too. The present study provides us with a very critical piece of information of what chimpanzees may gain from attacking neighbours. How this connects with human warfare is a different story.”
By Ed Yong
Reprinted with permission from Discover
Chimpanzee Gangs Fight and Kill For Land, New Research Suggests
Chimpanzee gangs commit these crimes to gain territory.
By Clara Moskowitz, LiveScience Senior Writer / June 21, 2010
Chimp-on-chimp attacks in the wild are very common, especially among small packs of males on patrol. Now research suggests the motive for these crimes is to gain territory.
To understand this violence, researchers studied a large group of chimpanzees living in Ngogo, Kibale National Park in Uganda. After monitoring the group for over a decade, scientists counted 21 chimp-on-chimp murders.
Of those crimes, the researchers witnessed 18 directly, and deduced three from circumstantial evidence. They think as many as 13 of the victims belonged to a single neighboring group.
"The take-home is clear and simple," said researcher John Mitani of the University of Michigan. "Chimpanzees kill each other. They kill their neighbors. Up until now, we have not known why. Our observations indicate that they do so to expand their territories at the expense of their victims."
After some of these neighboring competitors were dispatched with, the researchers observed the Ngogo chimpanzees beginning to use a large portion of new territory to the northeast of their previous range. That piece of evidence allowed the researchers to link the murders with a motive – that of gaining new ground.
The scientists think the new land offers greater access to food, and potentially to females.
The attacks seem to be triggered when bands of chimpanzees go out patrolling into the territory of a neighboring chimpanzee group.
"Patrollers are quiet and move with stealth," Mitani said. "They pause frequently to scan the environment as they search for other chimpanzees. Attacks are typically made only when patrolling chimpanzees have overwhelming numerical superiority over their adversaries."
This tends to happen often for the Ngogo chimpanzees, who have a particularly large group of more than 150 individuals — about three times the number found in chimp communities studied elsewhere. That advantage may explain the surprisingly high level of violence observed, the researchers said.
Mitani and colleagues described the research in the June 22 issue of the journal Current Biology.
Chimps Kill Neighbors to Expand Territory
ANI Tuesday, June 22, 2010 12:09 IST
Washington, DC: It has long been known that chimpanzees kill their neighbouring groups, but a motive has largely escaped researchers, until now.
A new study has, however, found that chimps, and especially small packs of males on patrol, kill one another to gain territory.
"The take-home is clear and simple. Chimpanzees kill each other. They kill their neighbours. Up until now, we have not known why. Our observations indicate that they do so to expand their territories at the expense of their victims," said John Mitani of the University of Michigan.
The findings were made in a large group of chimpanzees living in Ngogo, Kibale National Park, Uganda. Those chimpanzees have been the subject of close observation by researchers over the course of a decade.
During that time, the team directed by Mitani and David Watts of Yale University saw the Ngogo chimps kill 21 individuals from other groups. (Eighteen of those killings were observed directly, while the remaining three were deduced from circumstantial evidence.)
The researchers believe that as many as 13 of the victims belonged to a single neighbouring group, representing an "extremely high" rate of mortality due to inter-group violence.
With some of their competitors out of the way, the Ngogo chimpanzees began to use a large portion of new territory to the northeast of their previous range.
"Because the newly acquired territory corresponds to the area once occupied by many of the victims, we suggest that a causal link exists between the prior acts of lethal inter-group aggression and the subsequent territorial expansion," Mitani said.
Mitani and his colleagues think the new territory most likely benefits the chimps by affording them with greater access to food. It's also possible that the larger territory will ultimately mean greater access to females, but it is still too early to tell.
It's clear that the attacks are triggered when bands of chimpanzees go out 'on patrol' into the territory of a neighbouring chimpanzee community.
"Patrollers are quiet and move with stealth. They pause frequently to scan the environment as they search for other chimpanzees. Attacks are typically made only when patrolling chimpanzees have overwhelming numerical superiority over their adversaries," Mitani said.
The Ngogo chimpanzees may be at an unusual advantage over their neighbours due to the impressive size of their community, which may explain the surprisingly high level of violence observed, the researchers say.
The study has been reported in the June 22 issue of Current Biology, a Cell Press publication.