It is a conclusion based on mountains of evidence. Assumptions are claims made without proof. We have the proof.
No, it isn't. It is based on phylogenies. I discuss this very topic in this thread:
http://www.christianforums.com/threads/evolution-is-not-evidenced-simply-by-similarity.7943258/
We conclude it did, based on mountains of evidence. We don't assume.
Our descendants will always be humans, just as our common ancestor with other mammals was a mammal, and we are still mammals. What can happen is that the variation of human species will increase over time, just as the variation in mammal species increased over time.
It is based on mountains of evidence which you seem to avoid like the plague.
Chihuahuas were not always Chihuahuas.
We can test it, and we have tested it. I explain the evidence in the following thread:
http://www.christianforums.com/threads/the-new-retrovirus-thread.7942101/
Just with ERVs, we have over 200,000 pieces of proof.
Are you going to continue the evidence that exists?