How does a Christian soul fit in with known facts?

We know from many sources of evidence that life started more than 4 billion years ago, and over the aeons evolution produced a huge range of different creatures. We also know that modern humans originated at least 200,000 years ago, and that for at least 50,000 years humans have had the same cognitive powers as current ones. The theory of evolution also tells us that there never was a "first couple". Instead, the genes that make us human spread through a population of almost-humans, and the change from almost-human to fully-human happened over a period of tens of thousands of years, with no clear speciation point. Among Christians, many accept evolution and the age of the earth as facts. However, most of them also agree that, somewhere along the line, we acquired a soul - which they argue is the final piece that makes us fully human. For example, Catholics believe that "after a long and gradual process of biological evolution, which produced hominins who were highly advanced mentally, there was a sudden transition, in which God raised some of them to the “spiritual” level, i.e. to the level of rationality and freedom" . I can see 2 possibilities here: either God implanted a soul in just one couple ("Adam and Eve"), or He gave souls to all humans alive at the time. Either way I see problems. If all people got souls, how do you explain the original sin, for which Jesus had to die on the cross? Did all those people commit the same sin? In that case, why was God complaining? He obviously built the same mistake into all people. If God built the same mistake into all people, He should not complain about it, and accept His mistake. Which leads me to the other alternative: if only one couple got a soul (or the soulless ones died out), and we are all descended from that one couple, how do you square that with DNA evidence? Our DNA shows no evidence at all of the human species ever having been restricted to just 1 couple. How do Christians reconcile the existence of the soul with the fact of evolution, and specifically the DNA evidence? **EDIT** I just realised there's a third alternative: God gave a soul to Adam & Eve only, and all the "soulless" ones survived as well. That explains who Adam's children had offspring with. However, it also means that the vast majority of people today are direct descendants of the soulless ones, and hence cannot have a soul. That is contrary to all Christian teaching.