The problem here is noting the differences between Darwin’s finches versus the stretch and improbability over time there are changes such as the natural selection of say, antibiotic-resistant bacteria, or Darwin’s finches, in which there is a speciation based on which of a population survive in a given niche, which narrows the gene pool of the population due to isolation or killing off of the others, resulting in one prevailing, but many leaps and forming new classes involves many more steps, and higher improbability. We haven’t found everything in fossils, either, so we need the best given explanation, which is that early life is largely archaebacteria similar to what we find in the Yellowstone hot springs that live off sulfur and extreme temperatures.
There isn't one, as far as I can tell. The fossil record cannot be reconciled with microevolution, as species exit the fossil record as they entered it. Macroevolution is the only logical alternative, but as yet, no one has proposed even a remotely probable mechanism.
Personally, I suspect divine intervention in various stages of Creation, such as the Cambrian explosion. But that's simply speculation.
For Christians, the God of Creation is the God of the Bible. Science and Revelation cannot contradict. When science seems to contradict Scripture, either the science is wrong, or our interpretation of Scripture is wrong.
Currently, as far as I can tell, we are a long way from a synthesis.