“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.”
“And what’s the correct answer this time?” asked King.
Darren spread his arms, just as he’d seen dozens of other people— including many working scientists, rather than hobbyists like him—do today on other talk shows when asked the same question. “I haven’t the slightest idea.”
Everybody had hoped that other messages would continue to come from the Tailiens. Just as they had gone on to send the math problems after receiving no reply to the anatomy diagrams, humanity hoped that they would continue sending questions or information before a reply was sent.
But the Tailiens didn’t. They seemed to be intent on waiting for a response to the DNA puzzle.
And, finally, the United Nations decided that one should indeed be sent. By this point, Darren was pretty much out of the spotlight—and glad of it. The United Nations secretary-general himself was coming to Las Vegas to initiate the blinking of the city’s lights. That was fine with Darren; he wasn’t sure that the UN scientists had come up with the right answer, and he didn’t want sending an incorrect reply to be on his head.
The answer the UN had decided to go with was number one: the DNA that was similar, but not identical, to the sample string. There were various rationales offered for supposing that it was the correct response. Some said it was obvious: the aliens were moving us beyond questions of absolute truth, the kind of clear right or wrong that went with mathematical expressions; this new message was designed to test our ability to think in terms of similarity, of soft relationships. Although none of the three choices matched the sample string, the first one was the most similar.
Another interpretation was that it was a test of our knowledge of evolution. Did new species (the blank space to the right of the sample string) emerge by gradual changes (answer one, with its single nucleotide difference); by complete genetic redesign (answer two, with its totally dissimilar DNA); or out of nothing—that is, through creationist processes?
Some of the fundamentalists at the UN argued that the third answer was therefore the proper one: the aliens were testing our righteousness before deciding whether to admit us to the galactic club. But others argued that everything the aliens had presented so far was scientific—mathematics, anatomical charts, DNA—and that the scientific answer was the only one to give: new species arose by incremental changes from old ones.
Regardless of whether it was a question about inexact relationships or about the principles of evolution, answer one would be the correct response. And so the lights of Las Vegas were turned off one last time in a single, knowing wink at the heavens.
Palm-Up-Middle-Fingers-Splayed happened to be in the communications room when the response was received from the third planet. Of course, regardless of what answer they’d chosen, it would begin with one stretch of darkness, so Palm-Up-Middle-Fingers-Splayed waited … and waited … and waited for a second and third.