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.
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.