—Very well. What can you tell me about the living? I trust you have at least examined the survivors we flew here.

—I’ve done a full genome sequencing on all t…twenty-seven of them. They have really bad ge…genetics.

—How so?

—They all share a co…cocktail of genetic variations and mutations, most of which are bad for you. These people shouldn’t even exist.

—Because of poor genetics?

—Because of rrr…because of rare genetics. There shouldn’t be more than one person with all these anomalies.

—Please explain.

—There are little “errors” in everyone’s DNA. Most of them are SNPs—

—Pardon me, I know very little about genetics.

—They’re differences in only one base pair of nu…nucleotides, one pair of letters. Replace a T and an A with a G and a C, that t…type of thing. The vast majority of these differences are in noncoding areas between the ge…genes and no one really cares, or knows anything about them. Those that occur inside genes are usually more interesting, and we’re beginning to understand how…some of them work. Differences that are more common are called p…polymorphisms, those that occur in less than 1 percent of the population are called mutations. People shouldn’t share multiple mmm…mutations.

—And the survivors do?

—A lot of them. Enough so that the molecule in the alien agent doesn’t re…recognize any of the long DNA chains it’s looking for. This many people should definitely not share this mmmany mutations. It just doesn’t happen.

—It obviously does. How unlikely is it?

—Well, let me give you an example. All the people you s…sent me have a mutation in their TREM2 gene. One of the things TREM2 does is help re…regulate immune response to disease and injury in the brain. There are all sorts of mutations that can make TREM2 not function p…properly. These people all have the same one: variant R47H. That one is rare. It occurs in a little more than half a percent of the po…population in certain places like Iceland, and it’s even harder to find everywhere else. All of the survivors have the same TREM2 mutation, in both co…copies of the gene. That’s rare enough, I don’t even have frequencies for it.

—Is it debilitating?

—It’s been shown to increase the risk of developing Alzheimer’s, but most people with the mutation won’t get the d…the disease, so no. There is also a mutation in the BCR2 gene. It increases your risk of br…breast cancer.

—Do all the survivors have it?

—They do. Both copies of the gene.

—How uncommon is that mutation?

—It’s ha…hard to tell. It’s more frequent in certain ethnic groups, but overall, it’s found in less than half of one percent of the general population. You see w…what I’m getting at. Assuming the two mutations are unrelated, half a percent times half a percent means that out of a mi…million people, you should only find about twenty-five with both mutations. Of course, that’s not all the survivors have in common.

—Do all the mutations shared by the people you examined increase their risk of contracting a disease?

—No. Most of them will have no effect at all. They do have one g…good thing going for them. They have a variation in their PCSK9 gene that leads to lower bad cho…cholesterol. That one is found in about 3 percent of the po…pulation. If you do the math: There should be no more than three people with just these three mutations in the four million who were exposed to the gas in London.

The people I examined share hundreds of SNPs; fifty-seven rare gene mutations. You should not be able to find two people on Earth with so many rare t…traits in common, there aren’t nearly enough people. I’ll need blood from all the survivors to confirm, but I’m willing to bet they all have the same t…traits, even if it’s…impossible. It’s not a coincidence that these people survived.

—Could all the survivors be related? Having common ancestry would increase the likelihood of their genetic similarities if I am not mistaken.

—Some of them are. Of the t…twenty-seven people you flew here, six are related to one of the others, two brothers, one brother and sister, one mmm…mother and daughter. Beyond that, no. Sixteen are of British descent, one is from Denmark, one from Morocco. There are four people from India, one Ca…Canadian, two Frenchmen. The mother and daughter are Russian. These people are related the same way you and I are related. You’d have to g…go back a long long time to find a common ancestor.

—Do you believe that these people were spared on purpose?

—Yes. It has to be by design. Well, it doesn’t have to be, but it makes mmm…more sense that way.

—How so?

—In theory, it could be that the aliens just don’t know that these p…polymorphisms exist and that’s just a flaw in their weapon. But the molecule they built targets really long DNA ch…chains and, at least from what I understand about genetics, that’s a lot more complex to create, and t…totally unnecessary. They could have made a much simpler molecule that targets short DNA chains that everyone has. They could have used a poisonous gas. Making bo…botulinum toxin would be child’s play compared to this. With the same delivery system, there are a m…million things they could have used that wouldn’t have left anyone alive and are much easier to build. They went through a lot of t…trouble to make it the way it is.

—Assuming, for a moment, that these people do indeed share a common ancestry, could the molecule you described have been programmed to specifically spare their descendants?

—That’s an interesting idea. But no, it wouldn’t work. You can’t know what part of your genetics your ch…children will inherit.

—It cannot be a completely random process. Surely, some of it is predictable?

—Some of it is. There is a sss…small portion of your genetics that only comes from your father, and a small portion that only c…comes from your mother.

—Could that DNA—is it DNA?

—Yes.

—Could that DNA have been used to program the alien molecule?

—No. It w…wouldn’t work over long periods of time. How can I explain this? Imagine that you wanted to target the desce…all the descendants of a John Doe who lived a thou…thousand years ago. The only genetic material you can be certain John Doe passed on is his Y-chromosome DNA, that is the sss…sex chromosome. You could use the markers in that DNA but it is only passed on in a direct p…paternal line, from father to son, to son, to son. No women. If it were the p…progeny of a Jane Doe you wanted to save, you could use mitochondrial DNA. That is only passed on by the m…mother. You would get the opposite results, only women in a d…direct maternal line. That’s an infinitely small portion of one’s lineage and these direct lines tend to die out. All it needs is for one father to not have a son, or for a mother to not have a d…daughter. You can look at it the other way, you have sixteen great-great-g…grandparents, yet you share Y-chromosome DNA or mitochondrial DNA with only four of them.