The seasons are caused by the tilt of the earth's axis and revolution of the earth around the sun. If the earth's axis had not been tilted to the plane of its orbit then there would have been no seasons and humanity would have suffered. If Earth did not rotate on its axis, one side would always face the Sun while the other side would be away from the Sun. Thus, one side would become very hot and the other side would become very cold. Ultimately, life would not have been possible under such circumstances.