Gibbings thinks that the point of which the group descend into savagery, is when Jack splits from Ralph and Piggy. This is because it signals the start of a more prominent divide, suggesting a contrast in civilizations is being projected from this point on. For example, Jack has regressed into becoming a savage as in the pre-historic times. When reading the book, you do not notice the descendance untill simon is killed. This is because throughout the descent there are still occasional moments of civilization on Ralphs behalf, which disguises the descent into savagery.
Re: What point did the boys begin to descend into savagery?
The first sign of savagery is when the boys begin to get the idea of hunting and the first kill is made. Jack seems to be the first that lets this hunt go to his head and uses the thrill of the hunt to enpower him. I agree with Gibbings in that the real 'descent' into savagery is when the group of boys splits and ralph becomes isolated and piggy and simon are dead. At this point there seems to be no one left to ensure civilisation remains on the island. Roger is another main character in the way of savagery, it seems his natural way and how he gets his 'kicks' on the island. Roger seems to be able to influence Jack in the later stages, and seems more of an authority figure when put up against him.