You don't know that (that there were no original pair of humans), but I do as do many millions of others not influenced by religious mythology do. The theory of evolution is correct beyond reasonable doubt, and it allows us to understand that there was never a human born to a nonhuman.
Why? Because human is an imprecise predicate. There is no definition of human so precise that one can say that a mother and her offspring that differ by a single intergenerational mutation are not the same species.
Given that only a father can pass the Y sex chromosome to a male child and only the mother can transmit mitochondrial DNA, it logically follows that there must have been an initial man and an initial woman.
Your science is correct, but your logic is flawed. Thise facts don't support the conclusion you draw from them.
A single genetic alteration (microevolution) can only be inherited if there is an initial individual whose DNA has undergone a change.
Do you think that that supports your claims? If so, you are incorrect
Evolutionists entertain the illogical notion that whole populations can evolve without one individual of each sex experiencing transformation initially.
It seems that you're unfamiliar with the theory. Parents don't need to mutate to produce genetically original offspring. Meiotic reshuffling can do that.
And regarding mutation, only one parent need have a given mutation for it to be inherited by the next generation, not "one individual of each sex experiencing transformation initially."
Why are you arguing science you've never learned? You seem to know only what creationist sources teach. They are neither reliable nor honest. They are not interested in your scientific literacy, [just] maximizing pro-Christian voters and tithers.