what will happen if plants and animals do not change themselves according to the climate

if plants and animals do not change themselves according to climate they will die.for example if polar bear is not having thick fur then it will die in such a cold climate.as you see when we shear the sheep in winter then it dies because it cannot adapt it to such a cold climate.if a cactus plant does not reduce its leaves to spine then it will lose a lot of water and it will face water scarcity. so it will be very much difficult for plants and animals to survive if they do not change themselves according to climate.