And let's not forget the oldest power source of all: human labor.

Natural building tends to rely on human labor, more than technology.

It has value, which represents a quantity of human labor.

But nothing here at ground zero gets done without human labor.

Nothing else suggests what it took in human labor to make this grand estate.

But how can such a system be maintained and repaired without human labor?

States have needed people as workers because human labor has been the necessary foundation of power.

These requirements called for an efficient and disciplined use of human labor.

For this operation more human labour had to be employed than with the other lines.

The system, it has often been noted, requires an enormous amount of human labor, or, more important to local political leaders, jobs.