When discussing animal rights with friends, we talked about Anthropocentrism, Biocentrism and Ecocentrism. We were wondering if there is a school of thought that is the opposite of Anthropocentrism, which thinks human are less significant (in terms of moral status or intrinsic value) than that of other animals or everything else?
Yes. In particular, the philosophy of the Australian moral philosopher Peter Singer takes this point of view in some cases. He does not argue that, for example, any given pidgeon has a higher 'value' than all human beings but instead that there is a sliding scale where it is possible in some cases for animals to have more worth than humans (essentially that there is nothing inherent in humans that makes us superior).
This has lead to much controversy - Following this principle there may be cases where you should prioritize saving a very gifted chimpanzee from a burning house rather than a heavily disabled human, and this has been interpreted by some people as a complete devaluation (I can't think of a better word right now) of disabled people in general.
EDIT: It really depends on what problems you are trying to cover, but if the above seems relevant to your interest then you might want to take a further look into the areas of (moral) utilitarianism, bioethics and discussions on the intrinsic value of animals/people.
It has in fact taken humanity a very long time to take the idea seriously that we might be the most important sort of being. And we have a hard time with it even now.
Almost uniformly, we have imagined forces above us, and we have imagined that those forces cannot be so alien that we cannot approach them. We have almost always had gods with personalities, conceived of as beings. Whenever we became more abstract and saw a single force above us, an ineffable monotheistic God, so that force might be too powerful for us to imagine correctly, we imagined intermediaries, avatars or messengers for this God.
So most of Christian history has considered God himself and Angels to be 'beings' and to be more important than individual human beings. Some notion of such a God maintains from Plato, and is elaborated in Medieval Scholasticism, and continued through Kant.
The other thread of religion that attempts to eschew multiple gods and/or personal messengers is typified by the Stoics, who saw all of Nature as a single force, and had no choice, ultimately but to relate to it as a being, that sought to teach them. This more abstract, yet still individual God, remained a 'being' through the arc of philosophy that produced them and flowed out of them, creating the God of Spinoza, Hegel or Whitehead.
This 'Big Guy' has become too abstract for much of our thinking. Coming full circle, people have turned back toward its source. This latter thread has produced the feeling behind the Gaia hypothesis of James Lovelock and the idea of the Universal Eschaton in Terrence McKenna's pastiche of attempted philosophies. These, along with a bunch of post-modern religions like Wicca, wish to revive the notion of lesser gods or more easily personified aspects of God as a basis for a more humane religious worldview. For them, the Earth (and perhaps the Universe), along with other natural forces, are organic beings more important than humans, to be served and worshiped.
Depending upon how you see it, this movement toward always knowing there is a being above us ranges through a variety of forms from Deism, if the personal relationship is one of distant mutual respect, to New Age, Angelology or NeoPaganism, if we are to strive for contact with the divine in various forms to be continuous and personal.
The overall sense of this has sometimes been captured in the notion of panhentheism (a portmanteau of Panentheism and Henotheism), a variant of pantheism that emphasizes that God, as everything, has parts and invests some sort of divine essence into the parts which we can interact with on a personal level. To the degree that pantheism is a monotheism, panhentheism is a polytheistic syncretism within it.