Inbreeding behind unique phenomenon, say scientists.
Boy was mauled to death, his sister managed to escape and raised alarm.
So what caused this abearation spotted by tourists in Kamchatka?
In earlier case, brown bear plundered graves and ate human remains.
New 'bear security rules' follow mailings of humans from hungry animal in remote towns and villages.
This spike of bear cannibalism is reported at the South-Kamchatka nature reserve in Kamchatka.
Moments later he is filmed running at top speed when the beast attacks.
Rangers in Yakutia are on a lookout after watching a video showing a failed rescue attempt.
One region has shot 58 ravaging brown bears this year because they intrude too close to settlements, destroying livestock.
The recording comes as several people get killed and wounded in recent 'worst-ever' bear attacks.