Blaine, an upper-middle-class, white high school student from a good home, compares his intelligence quotient (iq) score to that of his best friend, reese, who comes from an identical background. there is a 15-point difference in iq scores. based on what researchers have determined about the varying contributions of environment and heredity to intelligence, one can assume that the difference in the boys' scores is

due more to heredity than environment    

Explanation:

            Personality or intelligence quotient (IQ) is shaped by genes as well as by an individual's upbringing and surrounding environment. However, in recent time many scientists and researchers have succeeded to identify certain personality characteristics or attributes to some specific genes.

           There is a reaction range to intelligence quotient according to many experimenters and Hereditary plays both an upper and lower limit in the IQ and the environment determine where this limits of IQ lies within this.

                Thus in the context, a 15 point difference between Blaine and Reese is due to the heredity factor and not environment factor as they both come from identical background.

Hence the answer is --

due more to heredity than environment  

explanation:

may i ask what challenges?