Property can be seen from two different perspectives: (1) as a relation between a man and an object; (2) as an understanding between members of society. I covered (2) in previous posts. (1) can exist even for an isolated Crusoe. But why would Crusoe need “property” in his solitary state? Perhaps in order to make the following counterfactual true: “If another person, Smith, suddenly appeared nearby, then these are the objects that Smith would have to recognize as Crusoe’s own and abstain from stealing them.”
How then does Crusoe appropriate unowned resources? The labor theory of property is lacking; according to it, as before, Crusoe takes an unowned object, mixes it with something that cannot be owned, namely, an act of laboring, perhaps shaping matter into a form that pre-exists in his mind but which, since this form is ideal, he also cannot own in a meaningful sense, and somehow ends up owning the resulting good.
There is an easy solution, however. We can permit an isolated Crusoe to come to own anything he uses for an end that demands that he has exclusive control over it. Now the human body is not just that which lives but that by which one lives and by which one enjoys. As such, it is a capital good. A fishing spear is a detachable extension of body. The spear is more obviously an extension than a caught fish, and yet both are intermediate goods on their way to utility or pleasure. It would be senseless to own the spear with no hope of catching fish, or to own fish with no hope of cooking them, or having cooked fish without a chance to eat them to either sustain life or enjoy the food.
A futuristic bodily implant that enhances human powers may be impossible to extricate without killing the owner; on the other hand, we’ve all heard stories of a homeless guy who goes to sleep on a park bench and wakes up elsewhere without a kidney. So, which parts of the body are “detachable” varies with available technology.
Once Smith appears next to Crusoe, Smith would only need to ascertain which objects Crusoe has been using in pursuit of his happiness. If the consumption of these objects is rivalrous, then Smith would know exactly what Crusoe’s “properties” are and be obliged to restrain himself. Once Smith has settled on the island and is cooperating with Crusoe, that man obtains ownership over further unowned objects who has homesteaded them first.
What of labor? Well, that a man is pursuing an end is best realized by third parties by their watching him work on it, pay the costs of the means of attain the end. After all, the end is hidden in the heart. Crusoe’s laboring on X is evidence to Smith that Crusoe is using X for his own ends and has set his mind to maintain the exclusive control over it that he needs. But laboring as such does not cause anything to become one’s property.