Humans are composed mostly of meat1) While this may seem obvious, it is an important fact to point out. No matter how much fancy armour a Human wears, he or she2) remains red and squishy on the inside. Some Humans forget this at their own risk.
This population makes up the majority of the less experienced contestants, who are still new to the Island and have not become infused with enough improbability yet to have transmuted into another type.3) Based in NewHome, Humans can be seen running amuck throughout the Island, yapping away with their shrill human voices in public places, swatting monsters in the jungle with their pointy metal sticks, and generally causing more chaos than they are worth. But, they are the Improbability Drive's favorite source of food, especially while still new to the Island, and the other populations tolerate Humans in part because otherwise the Drive would starve4) and also the other populations would die out.5) Likewise, the Island's most famous resident, the Watcher is a Human woman, which probably explains her lingering fascination with this unruly tribe.
Physically, Humans have few natural advantages. Their bodies offer average damage resistance and only average strength levels. They are, however, sometimes intelligent6), resourceful, energetic7), and often highly motivated. They are often armed with grenades to compensate for their relative lack of physical power or natural advantage. Overall, Humans are the most average of all races. The only thing that sets them apart are their free goodies, handed out by the Council Offices in their hometown.
Civilization on the Island, however modified by the influence of improbability, originated from the Human world outside and still reflects many of its rules and social conventions. Therefore, the events on the Island are still intelligible to the normal Human population in the world outside the improbability containment zone around the Island, a population that sees the events on the Island as a reality TV programme.
Whether the Human population will be successful in destroying the Drive once and for all, remains to be seen. But then, the Island is the site of the world's largest reality TV show.