I was in the garden today and found a dead blackbird chick on the lawn. It was a sad sight, most probably falling out of the nest and not surviving. This made me think about the notion of life, what it is, how easy it is to lose, and whether, if souls exist, you could argue that animals don't have them.
Let me be clear, I do not believe in the notion of a soul, unless (as many do without realising it) define a soul as consciousness. I look at this bird, and got a real sense of the loss of life. That whatever it is that life is, that I and my fellow humans possess, this bird once had and then lost. As such, it seemed that there was nothing that separated me and the dead bird other than degrees of complexity, and with that, degrees of complexity of consciousness. I could see no good reason to argue that this bird would not have a soul when humans would. The only reason this could be is if God arbitrarily assigned souls to humans and no other animals; that souls have nothing to do with the natural world whatsoever.
As with any such arguments invoking a God, anything is possible, no matter how implausible, and there needs to be no rhyme or reason. But if souls have any natural dimension to them, then it seems logical to me that all animals have them. However, this means that amoebas have souls too, and this seems to be stretching plausibility too. Therefore, it seems more obvious to me that souls do not exist at all. There seems to be a special pleading involved when invoking souls within humanity but declaring that they are uniquely human. If you see souls as a sort of 'life-force', then all animals have this, evidently.
Thus if souls exist, they exist in all animals unless arbitrarily assigned by God, or souls do not exist. I think souls do not exist.