Lord of the Flies is such a fabulous read! The two most obvious themes are loss of innocence and nature/human instinct vs. societal norms. While stranded on the island, the young boys go from functioning members of society (i.e. well-behaved, polite, considerate) to cruel savages. During this drastic change, the boys lose their innocence by retreating to basic animalistic instincts (survival mode) and foregoing everything that they have been taught about how they “should” behave. These ideals are portrayed throughout the novel, and they support the claim that when humans – even seemingly innocent children – are left to our own devices, we naturally retreat to evilness and barbarism. Hope this helps!