How would the book have been different if it were about a group of girls?Would they be more savage/less savage? Would they think about or organize things differently?
Whenever one proposes a question such as this, one must first consider the time frame in which the novel was written. So, it is to be expected that Golding would have chosen boys to be the characters in this novel since they would have been the future leaders of their country. Certainly, before World War II, very few women even worked outside the home; therefore, the attitudes of women about society were fairly subjective. Their concerns were primarily about what affected their families and towns/cities. And, schooling for young ladies had as it focus the development of the social graces and a liberal education that prepared girls to be the wives of doctors, lawyers, etc., since the liberation of women did not come about until the 1960s and the feminist movement.
With this in mind, "Lord of the Flies" would probably have had a markedly different exposition. Instead of the rational organizer such as Piggy, there may have been a matronly type who would have rounded up all the little boys first, tried to comfort them and feed them, and then been concerned about the "board meetings" and who would be the "CEO" as Ralph and Piggy are. Keeping the group together would be paramount to the girls of the 1950s as they were less independent and secure in themselves as some of the boys of that time. However, there would probably be more incidences of petty behavior such as vying for attention from others or credit for deeds because social prestige was important to women in that period.
Since it is a fact of Nature that the male of any species is inherently more aggressive, there probably would not have been the rapid descent into savagery that occurs with such characters as Jack and, especially, Roger.
This is a really interesting discussion question that gets into the nature vs. nurture argument. The novel, as I understand it, develops the idea that when these boys are separated completely from society, their thin veneer of being civilized drops away, and they revert to basic savagery, suggesting that in their savagery, man's basic nature is revealed.
So, following that line of thinking, what indeed would happen if a group of girls had been stranded on that island? Would their socially-imposed roles drop away? If so, would they they revert to their "natural" state, and if so, what would that be? Are females less aggressive than males by nature, or are they programmed to be submissive? Is every female submissive or aggressive in the same degree? (There were, after all, some pretty aggressive females in history.) Are all females maternal and nurturing? Finally, at what point does gender give way to basic human instinct?
I think that a group of girls in this situation would react very similarly to the boys' reactions. Some would be kinder and more sensitive than others; some would become dominant and cruel. Power struggles would ensue, and the pack mentality would develop eventually. This is disturbing--this is the same behavior I have observed in a few groups of teenage girls.