From the book, it is clear that mankind is naturally inclined to succumb to immoral behavior, even under the most civilized circumstances. Golding explores this idea in the story of a group of British boys who are stranded alone on an island, and with no guiding authority, quickly devolve into savagery. The boys, acting on their natural instincts and desires, gradually begin to lose their sense of morality and embrace evil.
At the start of their sojourn on the island, the kids put together a rough set of rules, hoping to ensure that no one breaks them. However, as life on the island develops, uncomfortable truths begin to become clear. Golding explains that one of the boys, Roger, takes pleasure in sadistically tormenting other kids, and that "there was a little boy waiting in the wings, capacities of delight and nastiness mixed up." This highlights the idea that mankind is naturally driven to evil, despite society's best efforts.
Another telling example of inherent evil found in the book is Jack, who starts off as an innocent-seeming choir leader. But as the novel goes on, Jack spirals further and further away from morality, succumbing to his own inner urge to dominate. Jack even admits this himself at one point, saying "I cut the pig's throat. I—I liked doing it. I'm going off by myself. See? I'm scared of you." From this, it is clear that Jack, who starts off as seemingly innocent, can still easily give into his primal desires and become evil if the situation allows it.
In Lord of the Flies, Golding provides a grim image of humanity and its potential for evil. The characters in the novel showcase the idea that without any social structure, people are easily capable of acting on their most immoral desires. It is therefore clear that mankind is inherently evil, a conclusion that creates an oddly dark message about human nature.