I suppose my previous post may have been misleading, as it was simply a thought experiment, hoping to illustrate some of the ridiculous aspects present even in great wisdom traditions. It is not my position of things. The spiritual progression I was referring to was our increasingly clear understanding of things, not the actual advancement of souls through "better and better" forms of life.
I don't think I believe in a spiritual evolution, or any hierarchy of plant vs animal vs human. Not to say I don't believe in biological evolution. But, well, biological evolution is not linear, for one thing. The bacteria in my colon is just as modern as I am, and they are not trying to evolve towards humanity. And spiritually, they are as much one with the Tao as am I. I don't think the trees, birds, and bacteria are the souls of humans that have fucked up and gotten all this karma stuck to them, nor do I think humans are higher spiritually than anything else.
My original question was, how could a tree devolve at all? It can't fight against its upward growth, can't stop its roots from searching downwards, can't stop its leaves falling in autumn. And how can it progress? It is already perfectly at one with its nature, and has no way to be otherwise. As for acting instinctually: I don't think instinct means unconsciousness. Animals are directly aware of the world, but they aren't self-aware, aren't actively choosing, aren't questioning their motives.
But, wouldn't some ability to choose or change be required to spiritually evolve? What other mechanism is there for spiritual growth? It seems to depend on awareness, self-consciousness, reflection, self-discipline and/or increasing understanding. We should be careful about judging other beings by human standards. A bird doesn't have self-knowledge or the ability to reflect on its actions. I don't consider this ignorance. Humans have these abilities, and I don't consider them as better or higher for it. It is just a different "inner nature," a different way to be.
(Now, gradations do exist. Apes, dolphins, elephants, and such do have some level of self-awareness, and the ability to reason. That itself is a fascinating question and perhaps useful for understanding the “human question,” but is a topic for another post.)
Often we say, we are not in harmony with the Tao. But this is not true. In reality, we are one with it, and could never be otherwise so long as we exist; there is no escaping it. Just as when we think about the past or future, totally wrapped up in it, those thoughts occur in the present moment. Somehow, the discord is part of the harmony. Seeing through the illusion that we are anything other than our nature, that is enlightenment.
This is why I don't think spiritual evolution is a helpful idea. All that is, is at one with the Tao. All this about progressing towards something is actually a hindrance. We're already there, it's just a matter of seeing it. This is why the Buddha was right: there's no need to be born into the Brahmin class, and this is why I don't think animals and plants or anything has to wait to be a human. Tao is always right there, waiting to be seen. The only “problem” anywhere, is that we humans are living in illusion. Animals (and plants and bacteria) aren't in illusion, because they are directly confronting reality as it is, not as they pretend it to be; so there is no need to "evolve" towards any spiritual state. They're there.
At most I'm willing to grant a sort of spiritual evolution that has nothing to do with progress or higher or lower states. One where the universe is toying with novelty, in finding new (not better) ways of looking at itself. Maybe a sort of ratcheting up into more complexity, as per Teilhard de Chardin's Omega Universe or Robert Pirsig's Metaphysic of Quality. So novelty arises. For us that means self-consciousness and reflection. But that doesn't mean all living things are going that way. It just means the universe ratcheted "up," and it stuck in humanity. From here it may ratchet some more. And who knows, maybe in some animal out there, it will ratchet in a still different direction, unknown to us.
Disclaimer: it's amazing how easy it is to sound like you know what you're talking about with these things, isn't it? Truth is, the "human question" continues to baffle me. We do seem unique, and I don't know what to think about it. At the same time, no one knows what it's like to be a tree or a bird, so it's all speculation in the end. For that matter, I don't understand what living in tune with the Tao while still having self-consciousness and reflection means, what that would look like. How to be human without this inner conflict and tension. I don't really even know what consciousness is, though I consider it the ground of being. This blog is just a way for me to work on hammering all these questions out, and is to be taken provisionally. Your comments often spur me on, forcing me to think deeper, or see different angles, so I appreciate that.