(Oh great, my browser just ate the nearly-complete reply I had written. Let's go at this once more.)
Us, and though I'm not sure, I think the immateriality of purpose results from elevating purpose above other concepts. Identity, experience, and role are other concepts which could organize a life and its activities equally effectively -- just imagine the implications of the questions "Who am I?", "What should I experience?" or "What is my role?" -- but instead those concepts are subordinated to that of purpose. At present a human being has the blessing to ask what his purpose is, but he is not blessed to ask whether or not purpose itself should matter to him. The question "What is the meaning of life?" is a common preoccupation, but the question "Why should meaning be asked of life?" goes unexplored.
Purpose might be put higher in the hierarchy because we want to perform actions that make a meaningful difference, and purpose provides such meaning in directing what actions we should take. If we are transient and the world is not (or at least greatly outlasts us), then what the question "what is my purpose" answers affects something which will stay around for much longer than the question of "who am I" or "what should I experience" does; and because of that transient nature of ourselves, there is a sense of urgency: "I have to know what I should be doing so that what I am actually doing isn't wasted".
I don't know if that is really the right explanation, I'm just going by what seems to be right; in such matters as these there is no verification. For instance, it might be that it is actually we who persist and the universe that is transient, in which case purpose is not as paramount - true, action would affect others, but we would also change ourselves by asking the other questions. Or; our placement of purpose so highly might be a yearning, where, in a world where (almost) everything is possible, yet nothing is clear (or the "purposes" seem shallow - working for food has no greater order to it), one wants a purpose that both has force and is without a doubt, right.
You already know that the creation of hierarchy is a pernicious human weakness, and the same tendency appears here. Rather than respecting the metaphysics of the concepts, and deciding that no direct comparison of importance can be made between ontologically unlike things, concepts are grouped into hierarchies of importance, with what is lower in the hierarchy forcibly put in terms of what is at the top of the hierarchy. So questions of, say, experience (and the ethics thereof) are subordinated to questions of purpose, and "What should I experience?" is taken to mean "What purposes should my experiences serve?"
That might be part of the reason, though it doesn't seem, at the face of it, that animals would be spared. If they can think about the metaphysics of the concepts, they can also rearrange things in the wrong way; and if they can't, then they are forced to use the arrangement provided in some manner.
In the former case, the argument could be applied to them as well; however, we might say that humans (or, heh, as you say, to the extent that we're human), have a particular weakness to hierarchy that we shouldn't expect animals to share unless proven otherwise. If so, even if animals are biased in some way, they can show us a point of view where purpose isn't the be-all, since their bias would be different.
In the latter case, how do we know that the metaphysical priorities of the animal is arranged correctly? They may have a hierarchy of their own, or have other values; the difference is that they can't do anything about them. If we were to lose our capacity to choose purpose, or to weigh purpose against other concepts, we would still have the hierarchy, but now it would be unchangeable.
Re: Purpose
Us, and though I'm not sure, I think the immateriality of purpose results from elevating purpose above other concepts. Identity, experience, and role are other concepts which could organize a life and its activities equally effectively -- just imagine the implications of the questions "Who am I?", "What should I experience?" or "What is my role?" -- but instead those concepts are subordinated to that of purpose. At present a human being has the blessing to ask what his purpose is, but he is not blessed to ask whether or not purpose itself should matter to him. The question "What is the meaning of life?" is a common preoccupation, but the question "Why should meaning be asked of life?" goes unexplored.
Purpose might be put higher in the hierarchy because we want to perform actions that make a meaningful difference, and purpose provides such meaning in directing what actions we should take. If we are transient and the world is not (or at least greatly outlasts us), then what the question "what is my purpose" answers affects something which will stay around for much longer than the question of "who am I" or "what should I experience" does; and because of that transient nature of ourselves, there is a sense of urgency: "I have to know what I should be doing so that what I am actually doing isn't wasted".
I don't know if that is really the right explanation, I'm just going by what seems to be right; in such matters as these there is no verification. For instance, it might be that it is actually we who persist and the universe that is transient, in which case purpose is not as paramount - true, action would affect others, but we would also change ourselves by asking the other questions. Or; our placement of purpose so highly might be a yearning, where, in a world where (almost) everything is possible, yet nothing is clear (or the "purposes" seem shallow - working for food has no greater order to it), one wants a purpose that both has force and is without a doubt, right.
You already know that the creation of hierarchy is a pernicious human weakness, and the same tendency appears here. Rather than respecting the metaphysics of the concepts, and deciding that no direct comparison of importance can be made between ontologically unlike things, concepts are grouped into hierarchies of importance, with what is lower in the hierarchy forcibly put in terms of what is at the top of the hierarchy. So questions of, say, experience (and the ethics thereof) are subordinated to questions of purpose, and "What should I experience?" is taken to mean "What purposes should my experiences serve?"
That might be part of the reason, though it doesn't seem, at the face of it, that animals would be spared. If they can think about the metaphysics of the concepts, they can also rearrange things in the wrong way; and if they can't, then they are forced to use the arrangement provided in some manner.
In the former case, the argument could be applied to them as well; however, we might say that humans (or, heh, as you say, to the extent that we're human), have a particular weakness to hierarchy that we shouldn't expect animals to share unless proven otherwise. If so, even if animals are biased in some way, they can show us a point of view where purpose isn't the be-all, since their bias would be different.
In the latter case, how do we know that the metaphysical priorities of the animal is arranged correctly? They may have a hierarchy of their own, or have other values; the difference is that they can't do anything about them. If we were to lose our capacity to choose purpose, or to weigh purpose against other concepts, we would still have the hierarchy, but now it would be unchangeable.