Does the human spirit exist?

Am I right in saying that the spirit that animates the lower creation is the same in kind as that of man, the differences being accounted for by the organisation into which the spirit enters? 

In man, you will find the whole of creation. The spirit of the animal is in a low state of development limited by its organisation, and spirit is the grand animating power down through all forms to the meanest speck that exists. 

But in us, there is an inner spirit and our brain becomes the seat of intelligence, the organ through which the grand inner self works. 

We may find a little of our intelligence in this one, and that one of the lower creation, but nowhere will we get a brain equal to ours. 

In bodily form, we get nothing better than us. 

In other worlds, we may find beings with bodies of finer material, some so fine that they may be said to glide away into spirit, but still the form is human.