Modern evolutionary science, including the science of genetics is based on the hypothesis that most if not all things can be explained in a natural way through empirical research. A theist evolutionist will simply say that evolution is the way God works things. Suppose however that God is not like a watchmaker who creates a watch, winds it up, and leaves it to the empirical parts to do their jobs their after? Suppose God is constantly involved not merely in human history but in all things great and small. Suppose the designer constantly has his hand on the design, and makes changes and modifications? Suppose he designed human beings to be like other higher order creatures so that humans would feel some kinship with them, and take care of them, and be good governors of God’s creation? Evolution is a theory that leave God constantly out of the equation, or alternately simply says this is the natural mechanism God chose to accomplish things.
The same problems arise in applying this sort of information to the historical figures of Adam and Eve as arises in the neuro-scientific discussions about the mind and the brain, where the assumption is that human beings are psychosomatic wholes, and as such, when the body goes the whole person dies. There is no human spirit, human personality that survives death. Of course, no scientist has gone to the other side of death and done an empirical study of whether there might be spirits of the departed in heaven or elsewhere. The assumption again is— this world, this life, these natural processes, like evolution are all there is, and so a theory which explains some things, is globalized to explain everything, including ruling out ongoing divine action in the natural and human worlds, never mind ruling out the afterlife.
My point by drawing attention to these two differing attempts at discussing science and the Bible together is that science often has to extrapolate or theorize from the known to the unknown to come up with a purely materialistic and empirical explanation for things.