I agree with you (and, yes, I'm talking about micro-evolution).
I have made the point that, according to evolution, the first human woman would have had to have engaged in beastiality, since Adam supposedly didn't come along until thousands of years later.
And that point is wrong, but it appears you kind of know why.
There's also another reason why you are wrong: evolution doesn't suggest that a non-human suddenly gave birth to a fully fledged human. If you could follow our ancestors generation by generation, you would only see something less human-like giving birth to something slightly more human-like (goodness, I'm starting to sound like Dawkins

). "Eve" only ever had to pair up with her own species.
A rainbow is a good analogy: if you start at the red end and move along the spectrum in small steps you wouldn't be able to exactly pinpoint where red ends and orange begins. Neighbouring wavelenghts (successive generations) are similar enough to be considered the same colour (species or "kind" if you like), yet if you take enough small steps you will get to a point where you could no longer call the colour "red".
Ring species are really useful because they illustrate the continuum of speciation over space rather than time. So you can see this kind of rainbow without having to watch a population for a hundred thousand years.
(BTW, new species
can emerge in a single generation or very few generations by
hybridisation, but to my knowledge animals rarely do that. Plants are in many respects much less fussy than animals.)
They answer that by saying (if I get this story right), Eve's DNA, known as mtDNA, can be traced back further in time than Adam's DNA (Y-chromosome). [Evidently, mtDNA is easier to trace.]
Well, mtDNA can be traced further because women have less variation in the number of their children than men.
In any species where males compete for females and mate with more than one, some males will have a lot of offspring and many will have none, while females (in high demand) will usually have
some but never as many as the most successful males (let's face it, it takes rather less time and effort to father a child than to carry and raise it. And that also applies to eggs). Successful (or lucky) Y-chromosomes can spread much faster than mitochondria (and paternal lines are also more likely to die out).