Evolution: is it necessary to know how life ultimately began in order to study and debate the evidence that evolution has since occurred? [Spirituality & Religion]

If you think it is, why do you think so? Can you explain that reasoning for me?

I ask because i've encountered a creationist's position that the evidence for evolution can be ignored if we don't know how life began.
I point out that the theory of gravitation still allows us to study the interactions of matter without knowing how it came to be but this apt comparison appears to be ignored.

Since i've received no explanation from the parties involved, i'm coming to YOU!
So. Thoughts?🙂