Lord of the Flies, by William Golding, is a symbolic novel which is, as he says, "an attempt to trace the defects of society back to the defects of human nature." Each of the four primary characters in the novel represents one element of human nature; Ralph represents the physical man.
In the first chapter, Ralph realizes that there are no adults on the island, and "the delight of a realized ambition overcame him. In the middle of the scar he stood on his head." Soon after he jumps and leaps and swims. Throughout the entire novel, Ralph is the boy most aware of his body and
became conscious of the weight of clothes.... [Ralph] stood there naked, looking at the dazzling beach and the water. He was old enough, twelve years and a few months, to have lost the prominent tummy of childhood and not yet old enough for adolescence to have made him awkward. You could see now that he might make a boxer, as far as width and heaviness of shoulders went, but there was a mildness about his mouth and eyes that proclaimed no devil.
No other character in the novel gets so much attention given to his physicality.
Ralph discovers the conch but sees it only as a shell into which he can blow and make funny noises. After he blows it and the boys gather, Ralph is elected leader not because he has demonstrated any leadership but because he looks like a leader.
[T]here was a stillness about Ralph as he sat that marked him out: there was his size, and attractive appearance; and most obscurely, yet most powerfully, there was the conch. The being that had blown that, had sat waiting for them on the platform with the delicate thing balanced on his knees, was set apart.
Ralph is a climber of mountains, a builder of shelters, and a reluctant hunter. By the beginning of chapter seven, Ralph is one of the only boys who is still wearing most of his school uniform; in contrast, none of the other boys seem to give their clothes or bodies any attention at all.
Sitting, Ralph was aware of the heat for the ﬁrst time that day. He pulled distastefully at his grey shirt and wondered whether he might undertake the adventure of washing it. Sitting under what seemed an unusual heat, even for this island, Ralph planned his toilet. He would like to have a pair of scissors and cut this hair—he ﬂung the mass back—cut this ﬁlthy hair right back to half an inch. He would like to have a bath, a proper wallow with soap. He passed his tongue experimentally over his teeth and decided that a toothbrush would come in handy too. Then there were his nails—
When Ralph struggles to think, he bites his nails, which are now bloody.
Once Simon and Piggy are gone, Jack must kill Ralph, the last obstruction to Jack's complete control of the island. The entire last chapter is Ralph running and dodging and evading the tribe of savages; this final battle is purely physical. When the naval commander arrives, Ralph is the one who reacts, physically, to the man's presence with "great, shuddering spasms of grief that seemed to wrench his whole body."
Ralph is not the mind of man--that is Piggy. Ralph is not the soul of man--that is Simon. Ralph is not the base human nature of man--that is Jack. Ralph is the body of man.