Identity Theft and other stories (collection)

“It was?” King’s eyebrows shot up toward his widow’s peak. “Who says so?”

“Lots of biologists—more and more each day. You know, the initial problem with Darwin’s theory of evolution was this: it was clear that the process of natural selection would take a long time to develop complex life forms—but there was no evidence that the Earth was particularly old; we didn’t have any proof that it was old until the discovery of radioactivity. Then, when we found that Earth was billions of years old, it seemed that there was plenty of time for evolution. But now we’ve run into another not-enough-time problem: the oldest known fossils are 4.0 billion years old, and they’re reasonably complex, which means if life were indigenous to Earth, the first self-replicating molecules would have appeared only a few hundred million years after the solar system was born, 4.5 billion years ago.”

“We’re going to get letters, I know it,” said King, “from people disputing those age claims. But go on.”

“Well, that early on, Earth was still being bombarded by meteors and comets; extinction-level events would have been common. Earth simply wouldn’t have presented a stable environment for life.”

“So you think life came here from outer space?”

“Almost certainly. Some biologists believe that it arose first on Mars— Mars was much drier than Earth, even back then. A comet or asteroid impact has a much greater destabilizing effect on the climate if it hits water than it does if it hits dry land. But the original DNA on Earth could have also come from outside the solar system—meaning, in fact, that these Tailiens might be our distant, distant relatives. All life in this part of the galaxy might share a common ancestor, if you go back far enough.”

“Fascinating,” said King. “Now, what about this latest message from the Tailiens? Can you take us through that?”

“Well, the top picture shows what looks to be a snippet of DNA, three codons long.”

“Codons?”

“Sorry. Words in the DNA language. We read the language a letter at a time: A, C, G, or T. And since A and T always bond together, and G always bonds with C, we can just read the letters off one half of the DNA ladder and know automatically what the letters down the other side will be.”

King nodded.

“Well,” continued Darren, “each group of three letters—ACG, say, or TAT—is a word specifying one amino acid, and amino acids are the building blocks of life. What we have in the first picture is a snippet of DNA consisting of nine letters, or three words. Next to that, there’s space for another snippet of DNA the same length, see? As if you were supposed to place one of the strings from the lower section up here beside this one.”

“And how do we choose which one should go there ?”

Darren frowned. “That’s a very good question, Larry.” It was cool getting to call him Larry. He looked at his cheat-sheet on the desktop. “The sequence in the top part of the message is CAC, TCA, and GTC, which codes, at least here on Earth, for the amino acids histidine, serine, and valine.”

“Okay,” said King.

“And the three possible replies are below. Two of them are strings of DNA. The first one—in answer box one—is a string of DNA very similar to the one above. It reads as CAC—the same as before; TTA—which is one nucleotide different from the string on the top, so it codes for, umm, let me see, for leucine instead of serine; and then there’s GTC again, which is valine, just as before.”

“So it differs by only one-ninth from the specimen at the top,” said Larry. “A close relative, you might say.”

Darren nodded. “Exactly. And that brings us to the second possible response. Like the first possible response, it consists of nine codons, but here the codons don’t match at all—the sequence is completely different from the one above. And, if you look carefully, you’ll see it’s not just frameshifted out of synch from the sample above; it really has nothing in common with it. Nor could it be a possible match for the other side of the DNA ladder, because it doesn’t have the same pattern of duplicated letters.”

“So that second string of DNA represents a distant relative—if it’s a relative at all,” said King. “Would that be right?”

“It’s as good a guess as any,” said Darren.

“And the third possible answer?” asked King.

“That’s the puzzler,” said Darren. “The third answer box is empty; blank. There’s nothing in it except three pixels in the upper right, which just indicate that it is the third possible answer.”

“Have we ever seen an empty box like that before in one of the Tailiens’ messages?” asked King.

“Yes,” said Darren. “It was in message four-dash-twelve, one of the math problems. They asked us what the correct answer to six divided by zero is. The possible answers they gave us were six, one, and a blank box.”

“And—wait a second, wait a second—you can’t divide by zero, can you?”

“That’s right; it’s a meaningless concept: how many times does nothing go into something? So, in that case, we chose the empty box as our answer.”