I am convinced that both the notion of rights, and a *conscious* sense
of consideration of others' interests, are products of human evolution
that had the effect of ensuring the survival of the species. As such,
there is no valid philosophical reason either one *ought* to be extended
to animals. As both evolved as part of our - humans' - survival
"strategy", there is no compelling philosophical reason to extend them
to animals, *unless* doing so would enhance our survival. I don't
believe a compelling case can be made for either one - neither seeing
animals as rights holders, nor giving their interests equal
consideration to ours, would do a thing to enhance either the
probability or the quality of continued human existence.