(1) In human evolution, due to climate change, forest areas have gradually become sparse and reduced, and open spaces have appeared among the trees. This has provided conditions for forest apes to move on the ground, and gradually evolved from trees to Transition from habitat life to terrestrial life on the ground.

(2) In the process of human evolution, after a long period of natural selection, physical characteristics have undergone major changes: the lower limbs are more suitable for walking upright, the brain size has gradually increased, and finally consciousness has emerged, giving rise to Learned the language. Engels once pointed out that walking upright was a "decisive step" in the transition from ape to human. The upright walking of ancient apes resulted in the division of labor between the front and rear limbs. Walking upright enabled ancient humans to free their forelimbs and use tools. The forelimbs are engaged in more and more activities, and the upper limbs are more dexterous. Walking upright frees up the forelimbs, makes and uses tools, extends the limbs, greatly enhances the ability to hunt and defend against enemies, and makes humans become more and more powerful. But they are not like modern people who have purposefully researched and invented various tools in order to improve production efficiency.

So the answer is: (1) arboreal; terrestrial; with the disappearance of the forest, the environment has changed;

(2) walking upright; hands (forelimbs); lower limbs; from Use simple tools to make your own.