Paul did research and found that the pigmentation loci of mice were well-mapped and well-understood. He categorized his population by phenotype and found one mouse, a pale, dark-eyed cream that must have been a triple recessive: bb, dd, ee. But it wasn’t enough to just have them, to observe them, to run the Punnett squares. He wanted to do real science. Because real scientists used microscopes and electronic scales, Paul asked for these things for Christmas.

Mice, he quickly discovered, did not readily yield themselves to microscopy. They tended to climb down from the stand. The electronic scale, however, proved useful. He weighed every mouse and kept meticulous records. He considered developing his own inbred strain—a line with some combination of distinctive characteristics—but he wasn’t sure what characteristics to look for.

He was going over his notebook when he saw it. January-17. Not a date, but a mouse—the seventeenth mouse born in January. He went to the cage and opened the door. A flash of sandy fur, and he snatched it up by its tail—a brindle specimen with large ears. There was nothing really special about the mouse. It was made different from the other mice only by the mark in his notebook. Paul looked at the mark, looked at the number he’d written there. Of the more than ninety mice in his notebook, January-17 was, by two full grams, the largest mouse he’d ever weighed.

In school they taught him that through science you could decipher the truest meaning of God’s words. God wrote the language of life in four letters—A, T, C, and G. That’s not why Paul did it though, to get closer to God. He did it for the simplest reason, because he was curious.

It was early spring before his father asked him what he spent his time doing in the attic.

“Just messing around.”