Therefore only individuals can do things. Even when acting collectively, collaborating, they have to operate their own bodies for themselves. What we know human beings can accomplish, therefore, seems all out of proportion to the humble body's modest inherent capacities. Everything that human beings actually do upon this earth, then, every change they accomplish in their surroundings, each effect they produce on one another, results directly and exclusively from active use of muscle on the part of each separate individual. But some of the most minimal of bodily activities produce the maximum effects.
Physical cues produced by one individual heavily influence others' behavior.
Human individuals cannot alone much change their surroundings. They have each, by themselves, a negligible influence on nature. But the direct and indirect effects on other individuals of what they do can make their doings matter enormously in nature.