I know environment has a great effect on the boys, so does it mean that humans have the innate evil or they became evil under the influence of environment?
Being marooned on a lost island was a key factor in the boys' increasing tendency towards savagery. Without adult supervision and with no social norms other than what they had learned during their upbringing, the boys literally "ran wild" (with their comportement degenerating over time). The island did not cause the boys to be bad, but the circumstances of their being there, isolated from any other human contact, did indeed give ample opportunity for their primitive instincts to run full course.
See the following enotes reference on Coral Island, a similar story with common themes.
See the following enotes reference on Coral Island, a similar story with common themes.Sources: http://www.enotes.com/flies/coral-island-revisited
i think that environment is the basic reason behind the whole transition from civilised boys to savages, as you have already stated the boys are immature and due to the lack of civilization and responsible adults presence; the inner fears and the uncivilised part of humanbeings takes over.
I agree that environment has a great effect on the boys. I think it is the lack of structure (rules) in the environment that brings on the debate of whether humans are innately good or evil.
Humans have the ability to be good or evil no matter what their environment is but environmental influence can be used to support your claim that humans are innately evil (or innately good).