After the fox, a creature that resembled a cross between a groundhog and a midget deer emerged to patrol in its turn. The creature was so strange tha… - David Rains Wallace

Flatness implied infinite extension, or at least a limitedness less inherent than that of the spherical, where every movement forward leads one step closer to the starting point.
Perhaps human values have yet to assimilate the earth’s shape. Although every physical evidence suggests that endless forward movement, endless growth, is impossible on a sphere, civilization is trying to grow endlessly. Our economics and politics are based on endlessness, and even our ideas of organic evolution, which of all things should have transcended flat-earth thinking, have an essential two-dimensionality.

Central America’s highest value as a natural phenomenon may be not in its diversity and adaptations, priceless as those are, but in its powerful demonstration of life’s sphericality. Life would have been fundamentally different if it had evolved on a limitless flat substrate instead of a limited, spherical one. It’s hard to imaging what it would have been like, but one possibility is that it never would have evolved beyond the first unicellular organisms. If they had been able to expand their populations ad infinitum, they might never have undergone the competitive pressures that led to natural selection and increasingly complex organization. Civilization has come to see the sphere’s limitations as an obstacle, but this is unimaginative, like being angry at the curved horizon because it hides objects more than a few dozen kilometers away.

Like all evolutionary stories, it is really two—of how the land bridge evolved, and of how people discovered it. Evolution occurs in geological time but is perceived in historical time.