This is my own speculative framework for reconciling the evidence for evolution with the biblical truth of an historical Adam and Eve. This is just a brief sketch of the position, I plan to greatly develop this view in a proper essay when I get the time.
First off, what does the science tell us about human origins? Anatomically modern homo sapien sapiens emerged approximately 150-200,000 years ago, the human population was never at any time less than a few thousand individuals, and there is such a thing as a chromosomal Adam and a mitochondrial Eve from whom all individuals are descended. As Dr. Craig has pointed out, there are indications these days that this "Adam" and "Eve" may have been contemporaneous. My framework operates on the presupposition of the truth of this premise but is not inextricably bound to it.
Now that we have the basic scientific premeses out of the way, we need to establish the basic theological framework upon which this model is based. The evolutionary creationism i hold to is grounded in the reformed doctrine, best elaborated in the Westminster confession, that God foreordains "whatsoever comes to pass". Extrapolated into the sciences, this would mean that nothing is truly "random" but may merely appear that way. Each and every "random" genetic variation and environmental contingency, the backbones of descent with modification by means of natural selection, have been predestined by the creator. So based on this theological framework, we can put forward a model of evolutionary creationism wherby God, by means of predestination and divine providence, brought about by natural processes the whole of the diversity of life on earth. This process was wholly guided by God in that each and every event, down to the most miniscule, was foreordained, and yet all was accomplished by means of natural processes which God himself authored and used as the means of his creative work. This model of evolutionary creationism is completely consistent with the scientific record, and will serve as the foundation for our forthcoming speculations concerning human origins.
Before we may properly put forth a model of human origins we must first establish a basic theological framework for understanding the relationship of God and man. The basic theological principle which we shall here employ is the principle of covenant relationship. God enters into relationship with man by means of covenants. Following the classical reformed tradition, we can understand the relationship of God with the first man, Adam, as a covenant of works whereby eternal life is promised on condition of perfect obedience, while death is solemnly threatened on condition of disobedience. This understanding of the first covenant between God and man is essential to understanding Paul's exposition of the gospel in the epistle to the Romans and, as such, is key to our Christian faith. Though Christians may differ on the precise nature of this first covenant, it should at least be clear that an historical Adam is necessary for such a covenant to have existed at all, and is further rendered necessary by Pauls covenantal comparison of Christ and Adam in the epistle to the Romans.
All of this being said, we must conclude that bible-believing Christians must affirm the existence of a literal Adam whom God entered into a covenant with. Note that this is not to say that the early chapters of Genesis are necessarily a literal chronological account of these primevil events. Now here we run into a real issue; how can the scientific evidence of evolution and population genetics be reconciled with the biblically necessary truth of a first man, Adam, from whom all modern humans are descended? Given that we have already described the basic scientific data that lays before us, as well as the necessary theological foundations, we may now construct a model of the historical Adam within the context of our modern scientific knowledge.
My first presupposition is that the nature of humanity is most fundamentally theological not biological. This is critically important to my argument, as i will argue that an anatomically modern homo sapien sapien is not necessarily human in the full and proper sense. Rather, what makes a human a human is the image of God. Now the bible declares that God is spirit, so it is logical to conclude that the image of God is none other than a spiritual nature. So we can define a human as a homo sapien sapien that possesses a spirit, or a spiritual nature. So a human is a composit of a biological nature and a spiritual nature, and if either is lacking it cannot be said to be truly or fully human. This is also, as an aside, why bodily resurrection is so central to the record of divine revelation. This physical/spiritual composite nature of man is the anthropological basis of my model.
Now we get into the gist of the model itself. I will grant the conclusions of evolutionary biology and population genetics that homo sapien sapiens evolved by means of descent with modification from a common primate anscestor. I will also grant that the homo sapien sapien population was never less than a few thousand individuals. So where does the historical Adam and Eve come in?
Taking an initial localized homo sapien sapien population of a few thousand, in the very distant past, it is conceivable that God, wishing to create man and enter into covenant with him, elected one male and one female out of this population to be the subjects of his covenant. This would be Adam and Eve. He chose these two individuals and supernaturally infused a spirit, or spiritual nature, within them. Thereby it can be properly said, as Genesis 1 declares, that he made them male and female in the image of God. Being made in the image of God, this pair is now truly human and fitting subjects for Gods covenant. All modern human beings are descended from this historical pair. Over the course of time, by Gods providence, those homo sapiens who did not descend from this pair were rendered extinct. I will further presuppose that this pair corresponds to chromosomal Adam and mitochondrial Eve, though this may not be strictly necessary for the validity of the model.
This model simultaneously and rationally affirms a literal Adam and Eve from whom all modern humans are descended, while also affirming the reality of human evolution and the base population models of population genetics. Nothing in this model should contradict any piece of genetic evidence, as all descendents of Adam and Eve would share genetic traits all the way down the evolutionary chain, while still in reality being descended from two individuals.
This is a rough sketch of my model, which i hope to refine and further develop. I would greatly appreciate thoughts and constructive criticism. Thank you.