Even before it was flat, and well before it was round, the earth was shaped like a giant staircase. It had long, flat steps that ended abruptly at tall, earthen walls, which took up again as a higher step in a gradual ascent.
Diagram of the Earth's Layers, by Ruth C. Rafferty
Used by permission
On each step there existed precisely one animal species, which were organized more or less by size. The first thousand or so steps had various microorganisms, insects on the next few thousand, then crustaceans, fish, birds, etc. on up until you get certain big cats, humans, bears, mammals of the sea, and so on. The human step was the 2,470,0856th step, one step above chimpanzees, and one step beneath ostriches.
The populations of each species were small, and either vegetarian or, in the case of sharks and tigers, cannibalistic. To each animal species, the particular step on which they existed was the whole world, and for a long time, no species was aware of the other species on steps above and below them.
Then one day, one of the humans on the human step discovered the edge, and noticed that far, far below was more earth. This was fascinating in and of itself, and it garnered the attention of a moderately sized group of the humans, who spent quite a bit of time studying the edge and the ground far below. Within a few months, the group at the edge founded The Society for the Study of the World Below, and met twice a week to see what they could see. But they couldn't see much, because the next step was a great distance away.
With the invention of the binoculars (which, in our round earth, were only reinvented in the 17th Century), it wasn't long before a member of The Society for the Study of the World Below first spotted a chimpanzee, whom they named Jim. With the discovery of Jim, The Society for the Study of the World Below was renamed, The Society for the Study of Non-Human Species, and membership grew at an astonishing rate. According to the records, 99.3% of the population of humans joined the Society following the discovery of Jim.
Soon better binoculars were manufactured, and more chimpanzees were spotted. One by one entire villages relocated to the edge, fan clubs for favorite chimpanzees were started by precocious youth, and the binocular business was booming. 99.3% of the humans spent nearly all of their time crowding around the edge observing the chimpanzees. Little else got done-- music, art, and literature came to a standstill, few inventions were made, and the growth rate of the population of humans began to decline for the first time since the origin of the species. With the discovery of the chimpanzees, the human species had entered the first dark age.
The Universe Creators, whoever they are, must have realized that the step-like world just wasn't working, because before long they flattened it out to one enormous plane. All animals were born into a world in which other animals lived, and the existence of other animals became a mundane fact of life.
Though the diversification of species is considered by most to be an improvement, there were still the obvious complications with a flat earth - rotational issues, seasonal problems, the erratic behavior of gravity, etc. - and just before the birth of Christopher Columbus, or maybe the vikings, or even perhaps indigenous Americans, the Creators of the Universe redesigned the earth as a sphere.
