The New Scientist reports that elephants appear to be attacking human settlements as vengeance for years of abuse by people.

In Uganda, for example, elephant numbers have never been lower or food more plentiful, yet there are reports of the creatures blocking roads and trampling through villages, apparently without cause or motivation.

Scientists suspect that poaching during the 1970s and 1980s marked many of the animals with the effects of stress, perhaps caused by being orphaned or witnessing the death of family members - and produced the equivalent of post- traumatic stress disorder.

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Many herds lost their matriarch and had to make do with inexperienced "teenage mothers."

Combined with a lack of older bulls, this appears to have created a generation of "teenage delinquent" elephants.

Dr Joyce Poole, the research director at the Amboseli Elephant Research Project in Kenya, who has co-authored a paper on elephant behavior, said: "They are certainly intelligent enough and have good enough memories to take revenge.

"Wildlife managers may feel that it is easier to just shoot so-called `problem' elephants than face people's wrath.

"So an elephant is shot without people realizing the possible consequences on the remaining family members and the very real possibility of stimulating a cycle of violence."

Poole's study showed that a lack of older bulls to lead by example has created gangs of hyper-aggressive young males with a penchant for violence towards each other and other species.

For instance, in Pilanesburg National Park in South Africa, young bulls have been attacking rhinos since 1992. And in Addo Elephant National Park, also in South Africa, 90 percent of male elephants are killed by another male - which is 15 times the "normal" figure.

Richard Lair, a researcher specializing in Asian elephants at the National Elephant Institute based in Thailand, said that there are similar problems in India where villagers - particularly in West Bengal - live in fear of male elephants, which the villagers claim attack the village for only one reason - to kill humans.

"In wilderness areas where wild elephants have no contact with human beings they are, by and large, fairly tolerant," he said.

"The more human beings they see, the less tolerant they become."

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