Professor Chris Stringer, Research Leader at the Natural History Museum and joint author of the paper, says: “In the context of Neanderthals and Homo sapiens, we need to regard speciation as a gradual process that occurred over more than 400,000 years. It is correct that the two interbred where they were not geographically separate, but over time differentiation continued to a point where the two were distinctly different species. When the Neanderthals died out around 40,000 years ago, the two species were in the final stage of the speciation process and were developing reproductive isolation from each other.”
If this "occurred over more than 400,000 years", then we're talking about a very gradual amount of speciation (baby steps taking 400K years). If the earth is 4 billion years old, IMHO that doesn't give much time for such slow speciation to evolve goo to human beings.
But on the other hand, the Cambrian Explosion had 50 to 100 new phyla (many of them going extinct) all of a sudden appear in the fossil record within a 400K year timeframe. It's like, natural selection is too slow to do the job. But God can make not just new species, but also new genus and even new phyla appear whenever He darn well feels like it.