Complex sentence: The original corn plant known as teosinte is still grown in Mexico and its size (ears of corn) has substantially increased due to efforts of American Indians, and scientific research and it is now the third leading grain crop in the world.
Split into simpler sentences: The original corn plant known as teosinte is still grown in Mexico and its size (ears of corn) has substantially increased due to efforts of American Indians and scientific research. It is now the third leading grain crop in the world.