Sorry to break it to you guys, but live never would have evolved on a flat earth. For one, night and day would not occur. Second, the seasons would not occur. Third, there would be no gravity on earth. Fourth we have indeed taken pictures of the Earth (not needed to prove that Earth is a sphere) such as this:http://www.roumazeilles.net/news/en/wordpress/wp-content/uploads/earth_from_space.jpg.
Gravity comes from the incessant spinning of the Earth.