Free Out at Night by Susan Arnout Smith

standing along the bottom. She was using the wall as a screen; it worked fine.
    “Basically a lot of our DNA is junk. It’s a matter of geography. Let’s say—a long time ago— we’ve got an Asian who lives someplace in the Pacific Rim. Let’s put him, for our purposes, in China.”
    She transferred a small figure to China and filled in the figure with slanting lines.
    “His family stays there for generations and over time, there are a few minute variations, some hiccups in his DNA that naturally occur randomly, and once they occur, they get passed down through generations. Those are called polymorphisms in the DNA, or SNPS, pronounced snips.”
    She waited as the scribbling subsided and the group was ready for her to go on.
    “Now let’s move a different guy to Cape Horn. He started out there and his family lives there for generations, long before recorded time. He’s called a sub-Saharan African.”
    She placed a second figure in the south of Africa and filled in the outline with gray pixels.
    “Same deal. Lives there eons and he has random snips that are passed down through his line and everybody in his part of the world has some of these same snips, but and here’s the key thing, the guy in Cape Horn probably never went to China, not even on vacation—we’re talking thousands of years ago, not now, jumping on a plane. So, the guys in Asia are going to have different snips than the sub-Saharan Africans living at Cape Horn.”
    She danced the third figure into what looked like the middle of France.
    “Here’s our third guy. He started out in what is now Europe. He has his own snips that go way back in time and that we still see coming up in his relatives alive today. He’s called Indo-European.”
    She filled the third figure in with dots and turned to the audience. “These snips insert themselves randomly and are then copied and passed down through generations. Different continents fostered different snips. We fast-forward to today.”
    She tapped the keypad again and figures appeared across the world, each a mix of slanting lines, gray pixels, dots; each figure different.
    “Nobody’s stayed in a neat little box, but we can pretty accurately trace percentages, how much percentage of a person comes from each of these subgroups. The most sophisticated tests involve one hundred and seventy-six of those snips, narrowing the ancestral pool pretty conclusively. Lights, please.”
    Zsloski blinked in the sudden light, looking confused and Grace amended it.
    “It means that after testing a sample, the most sophisticated tests can accurately say that a person is maybe—say—ninety-two percent Indo-European and eight percent sub-Saharan African.”
    “So we’d be looking for a white guy.”
    “In that example, Mike, yes; if you had this DNA sample at a crime scene, you’d be focusing on white suspects, because it would be genetically impossible for the perp to have come from a predominantly different subgroup. It stands to reason that it would serve to narrow the suspect pool in a reasonable way and save valuable time on the street.”
    “I got it.”
    “It’s not an exact science but I can tell you this, there’s a DNA printing outfit in Florida that’s a leader in this type of thing; they routinely do blind tests and nail it, every single time, just based on DNA. That means that if they analyze a sample that’s predominantly Indo-European, the features of the actual person will express in Caucasian features and skin tones, ditto if it’s Asian or African.”
    She clicked off the graphic.
    “Any questions?”
    FBI Special Agent Beth Loganis raised her hand; not really a hand, the merest flag of a manicured finger elevated for the briefest of seconds. She was about Grace’s age, early thirties, with the burnished look that always spoke of enriched preschool and normal childhoods with mothers who remembered to lay out lunch money and buy laundry soap. It was a look that, despite years of faking,