Advantages of Human PCs

Advantages of a Human Centered Milieu
Humans are diverse, unique, complex and ever-changing. No two humans are exactly alike and all humans are dynamically evolving organisms from the point of their birth to that of their death. What could be more interesting to role-play than a human?
The Original Game includes rules for playing humans and the fantasy races of dwarves, elves and hobbits/halflings - incidentally the same races that comprise good characters in the literature of Professor Tolkien whose Lord of the Rings was gaining enormous popularity during the early days of adventure gaming. The problem with role-playing those non-humans is they are archetypes - extreme versions of behavior seen among humans, plus a long beard, pointy ears or hairy feet.
The problem of archetypes is they limit the scope of diversity. Individuality among dwarves, elves and hobbits is severely limited. In order to act like a dwarf, elf or hobbit, the role-player must follow certain agreed upon characteristics of those fantasy races. By contrast, playing a human character opens the entire diversity of the human race for play. The dwarf, elf and hobbit character is frequently played as different from humans in shallow and insignificant ways that contrast with humans who are more interesting by nature. A human character is like us, but is different in personality, motives, morals, habits, beliefs, hopes, fears - really all that makes a character interesting, their character.
Fashion-ears, long beard and short stature, big nose, hairy feet and chubby physique can't really compete. The most interesting thing you can play is a human.
In a milieu where human characters are PCs and all other beings including the good professor's non-humans, are creatures to encounter, beings to give challenges to the PCs, the dwarves, elves and hobbits become more than funny looking humans - they become something of wonder, which is what they are in the source literature. They are the "other", alien, not like us, but perhaps beings we can cooperate with, learn from and grow to respect, even hold in awe. The milieu itself becomes richer for having restricted players to human characters and players can do what they do best - act like human beings.