Primera especie en colonizar lugares que estaban sin habitar
The answer is; the skeletal system and the nervous system
The skeletal system (muscle and bone) give you rigidity and enable your legs to support your weight. The muscles also act on the bone as a fulcrum allowing it possible for them to contract and make motion possible.
The nervous system is important in the coordination of movement. The brain is the center for locomotor action. This ensures you are able to place one foot in front of the other in sequence and moving your arm in concert.
I believe the answer you are looking for has to do with cells, they are the basic building block of life and are the smallest life that can support itself.
