You are asking one of the most important questions of our day for Christians. As you point out, the answer has far-reaching biblical and theological implications. We at Reasons to Believe have been debating this question with the Biologos scientists and theologians for the past decade. Earlier this year a two views book was released by InterVarsity Press. The title of the book is Old-Earth or Evolutionary Creation? Discussing Origins with Reasons to Believe and Biologos. In 2015 Fazale Rana and I at Reasons to Believe released a second edition of our book Who Was Adam? where we lay out in detail our biblical and scientific model for human origins. In November of this year Zondervan will be releasing a four views book featuring the presidents of Answers in Genesis, Biologos, Discovery Institute, and Reasons to Believe. Much of that book addresses our differing views on human origins.
When Biologos writes that the ancestral population of humanity cannot possibly be the biblical two but must number at least ten thousand, they base that conclusion on theoretical genetics models that presume a common descent origin of humanity (that humans, Neanderthals, and chimpanzees are naturally descended from a common ancestor) and that certain shared features in the genomes of humans, Neanderthals, and chimpanzees are genetic scars (genes that are the result of natural mutations and serve no beneficial purpose). We at Reasons to Believe dispute both presumptions. We also point to research papers in the peer-reviewed scientific literature written by leading geneticists that conclude that genetics models are useless for determining ancestral populations. Furthermore, we cite conservation biology field experiments that demonstrate that a pair or small population of individuals in a mammal species always generates more genetic diversity that what current genetics models would predict. Therefore, these field experiments establish that Biologos’ conclusion that the ancestral population of humanity was at least ten thousand individuals must be an inflated upper limit.
Personally, I have observed the ancestral human population derived from genetics models decline over the past fifty years. Fifty years ago, geneticists were claiming an ancestral human population of about one million individuals. Thirty to forty years ago, that number declined to about one hundred thousand. Ten years ago, Biologos’ Francis Collins wrote that it was about ten thousand individuals. When my colleague Fazale Rana debated the Biologos geneticist Dennis Venema, Venema said the number was 1,200 individuals. When i had a public dialogue with the president of Biologos, Deborah Haarsma, she said the Biologos biologists could go as low as 132 individuals. I suggested in that dialogue that we should plot a graph and that the graph would indicate that geneticists will be done to the biblical two in less than two decades.
As for the claimed interbreeding between Neanderthals and humans, assuming the greater genetic similarity of Europeans, Asians, and Pacific Islanders to Neanderthals than compared to sub-Saharan Africans and Neanderthals indeed is a sign of interbreeding between Neanderthals and Europeans, Asians, and Pacific Islanders, the deduced level of interbreeding must be very small. It is so small that it is cited as evidence that ancient humans were engaging in beastiality at a much lower level than humans today. However, I am concerned that the eleven authors of the study claiming evidence for human-Neanderthal interbreeding were all Europeans, Asians, and Pacific Islanders. While the authors claimed they were careful to avoid contaminating the Neanderthal DNA, they could not guarantee no contamination occurred. Before I am convinced, i would like to see the study repeated on a new Neanderthal specimen where the only investigators in contact with the specimen are sub-Saharan Africans.
I agree with you that the biblical and theological implications are far from trivial. They strike at the very creeds of Christianity. I am deeply concerned when I hear my friends at Biologos write that our sin nature gradually evolved over a half million year time period, that the doctrine of original sin from a primordial human pair is a false doctrine, and that biblical inerrancy needs to be redefined as applying only to matters of faith, doctrine, and practice and not to science, history, and geography. In my most recent public dialogue with Deborah Haarsma she said that all the scholars at Biologos hold to some form of accommodationism (the belief that in inspiring the Holy Bible the Holy Spirit tolerated the errors and mistaken ideas of the human authors). In my opinion, accommodationism implies that human readers of the Bible never can be certain when a biblical text is the work of the fallible human author or the infallible Holy Spirit. In that case, the Bible ceases to be a reliable guide for humanity on any subject.