Humans (9 page)

“It was an interesting time to do physics,” said Ponter. “Our people learned a great deal about the—the process by which the field…you must have a word for it?”

Arnold nodded. “The geodynamo.”

Ponter frowned; another
ee
phoneme. But he let Hak take care of supplying it as needed; it was only proper names that Ponter had his Companion repeat exactly as he spoke them. “Yes. We learned much about the geodynamo.”

“We’d love to hear what you know,” said Arnold.

Ponter was glad that Tukana was asleep; he’d probably given away too much information already. But this concept of trading data—it upset the scientist in him. All data should be freely exchanged. Still, he decided to shift the topic slightly. “Is Inco worried that the demand for nickel will abate during the period of collapse?” Nickel was widely used in compasses on both versions of Earth—and the deposit here in Sudbury was one of the world’s largest.

“What? Hmm, I hadn’t even thought about that,” said Arnold.

Ponter was confused. “Reuben said you were a geologist…?”

“Yes, I am,” said Arnold, “but I don’t work for Inco. I’m with Environment Canada. I flew here from Ottawa as soon as word came that contact with your world had been reestablished.”

“Ah,” said Ponter, still not understanding.

“My job is protecting the environment,” said Arnold.

“Is that not
everyone’s
job?” asked Ponter, being, he knew, a bit disingenuous.

But again the subtlety was lost on Arnold. “Yes, indeed,” he said. “Yes, indeed. But I wanted to find out what your people might know about environmental effects associated with magnetic-field collapses. I was hoping you might have some data from the fossil record—but to have complete studies of a recent collapse! That’s fabulous.”

“There were no appreciable environmental effects,” said Ponter. “Some migratory birds were confused, but that was about it.”

“I suppose they would be, at that,” said Arnold. “How did they adapt?”

“The affected birds have a powerfully magnetic substance in their brains…”

“Magnetite,” supplied Arnold. “Lodestone. Three iron atoms and four oxygens.”

“Yes,” said Ponter. “Other kinds of birds navigate by the stars, and some individuals of the species that use brain magnetite for determining direction turned out to be able to use the stars, too. It is ever the way in nature: variation within a population provides vigor when the environment changes, and most crucial capabilities have a backup system.”

“Fascinating,” said Arnold. “Fascinating. Tell me, though: how did you originally determine that Earth’s magnetic field does, in fact, periodically reverse? That’s a fairly new insight for us.”

“The alternation of the planet’s magnetic-field polarity is recorded at meteor-impact sites.”

“It is?” said Arnold, his one long eyebrow—how refreshing to see someone who looked normal, at least in that regard!—rising up his forehead.

“Yes,” said Ponter. “When an iron-nickel meteor slams into the Earth, the impact aligns the meteor’s magnetic field.”

Arnold frowned. “I suppose it would, at that. Just like hitting an iron bar with a hammer and turning it into a magnet.”

“Exactly,” said Ponter. “But if you did not learn of this from meteorites, how did your people come to know that Earth’s magnetic field periodically reverses?”

“Sea-floor spreading,” replied Arnold.

“What?” said Ponter

“Do you know about plate tectonics?” asked Arnold. “You know, continental drift?”

“The continents drift?” said Ponter, making his face agog. But then he held up a hand. “No, that time I
was
making a joke. Yes, my people know this. After all, the coastlines of Ranilass and Podlar clearly once were attached to each other.”

“You must mean South America and Africa,” said Arnold, nodding. He smiled ruefully. “Yes, you’d think it would be blindingly obvious to everyone, but it took decades for our people to accept the notion.”

“Why?”

Arnold spread his arms. “You’re a scientist; surely you understand. The old guard thought they knew how the world worked, and they weren’t about to give up their theories. As with so many paradigm shifts, it wasn’t really a case of convincing anyone to change their minds. Rather, it was waiting for the previous generation to pass on.”

Ponter tried to conceal his astonishment. What an extraordinary approach to science these Gliksins had!

“In any event,” continued Arnold, “we ultimately found proof for continental drift. At the middle of the oceans there are places where magma wells up from the mantle, forming new rock.”

“We surmised such things must exist,” said Ponter. “After all, since there are places where old rock is pushed down—”

“Subduction zones,” supplied Arnold.

“As you say,” said Ponter. “If there are places where old rocks go down, we knew there must be places where new rock comes up, although, of course, we have never seen them.”

“We’ve taken core samples from them,” said Arnold.

Ponter’s face went honestly agog this time. “In the middle of the oceans?”

“Yes, indeed,” said Arnold, clearly glad for once that his side was coming out ahead. “And if you look at rocks on both sides of the rifts from which magma is welling up, you see symmetrical patterns of magnetism—normal on either side of the rift, reversed equal distances to the left and right of the rift, normal again on either side but farther out, and so on.”

“Impressive,” said Ponter.

“We have our moments,” said Arnold. He grinned, and was clearly inviting Ponter to do the same.

“Sorry?” said Ponter.

“It’s a pun; a play on words. You know: ‘magnetic moment’—the product of the distance between a magnet’s poles and the strength of either pole.”

“Ah,” said Ponter. This Gliksin obsession with word play…he would never understand it.

Arnold looked disappointed. “Anyway,” he said, “I’m surprised that your magnetic field collapsed before ours did. I mean, I understand the Benoît model: that this universe split from your universe forty thousand years ago, at the dawn of consciousness. Fine. But I can’t see how anything your people or mine might have done in the last four hundred centuries could have possibly affected the geodynamo.”

“It
is
puzzling,” agreed Ponter.

Arnold clambered off his chair and rose to his feet. “Still, because of it, you’ve been able to satisfy my particular concern better than I would have thought possible.”

Ponter nodded. “I am glad. You should indeed—how would you phrase it?—you should sail effortlessly through the period of magnetic-field collapse.” He blinked. “After all, we certainly did.”

Mary tried to concentrate on her work, but her thoughts kept turning to Ponter—not surprisingly, she supposed, since Ponter’s DNA was precisely what she was working on.

Mary cringed every time she read a popular article that tried to explain why mitochondrial DNA is only inherited from the maternal line. The explanation usually given was that only the heads of sperm penetrate eggs, and only the midsections and tails of sperm contain mitochondria. But although it was true that mitochondria were indeed deployed that way in sperm, it wasn’t true that only the head made it into the ovum. Microscopy and DNA analyses both proved that mtDNA from the sperm’s midsection does end up in fertilized mammalian eggs. The truth was no one knew why the paternal mitochondrial DNA isn’t incorporated into the zygote the way maternal mitochondrial DNA is; for some reason it just disappears, and the explanation that it had never gotten in there in the first place was nice and pat, but absolutely not true.

Still, since there were thousands of mitochondria in each cell, and only one nucleus, it was much easier to recover mitochondrial rather than nuclear DNA from ancient specimens. No nuclear DNA had ever been extracted from any of the Neanderthal fossils known from Mary’s Earth, and so Mary had been concentrating on studying Ponter’s mitochondrial DNA, comparing and contrasting it with Gliksin mtDNA. But there didn’t seem to be any one sequence she could point to that was present in Ponter and the known fossil Neanderthal mitochondrial DNA, but in none of the Gliksins, or vice versa.

And so Mary at last turned her attention to Ponter’s nuclear DNA. She’d thought it would be even more difficult to find a difference there, and indeed, despite much searching, she hadn’t found any sequence of nucleotides that was reliably different between Neanderthals and
Homo sapiens sapiens;
all her primers matched strings on DNA from both kinds of humans.

Bored and frustrated, waiting for Ponter to be released from quarantine, waiting to renew their friendship, Mary decided to make a karyotype of Neanderthal DNA. That meant culturing some of Ponter’s cells to the point where they were about to divide (since that’s the only time that chromosomes become visible), then exposing them to colchicine to immobilize the chromosomes at that stage. Once that was done, Mary stained the cells—the word “chromosomes,” after all, meant “colored bodies,” referring to their tendency to easily pick up dye. She then sorted the chromosomes in descending order of size, which was the usual sequence for numbering them. Ponter was male, and so had both an X and a Y chromosome, and, just as in a male of Mary’s kind, the Y was only about one-third the size of the X.

Mary arrayed all the pairs, photographed them, and printed out the photo on an Epson inkjet printer. She then started labeling the pairs, beginning with the longest, and working her way to the shortest: 1, 2, 3…

It was straightforward work, the kind of exercise she’d put her cytogenetics students through each year. Her mind wandered a bit while she was doing it: she found herself thinking about Ponter and Adikor and mammoths and a world without agriculture and…

Damn!

She’d obviously screwed up somehow, since Ponter’s X and Y chromosomes were the twenty-fourth pair, not the twenty-third.

Unless…

My God, unless he actually had
three
chromosome 21s—in which case he, and presumably all his people, had what in her kind produced Down’s syndrome. That made some sense; those with Down’s had an array of facial morphologies that differed from other humans, and—

Good grief,
thought Mary,
could it be so simple?
Down’s sufferers did have an increased incidence of leukemia…and wasn’t that what Ponter said had killed his wife? Also, Down’s syndrome was associated with abnormal levels of thyroid hormones, and those were well-known to affect morphology—especially facial morphology. Could it be that Ponter’s people all had trisomy 21—one small change, manifesting itself slightly differently in them than it did in
Homo sapiens sapiens,
accounting for all the differences between the two kinds of humans?

But no. No, that didn’t make sense. Principal among Down’s effects, at least in
Homo sapiens sapiens,
was an
under
development of muscle tone; Ponter’s people had exactly the opposite condition.

And, besides, Mary had spread out an even number of chromosomes in front of her; Down’s syndrome resulted from an odd number. Unless she’d accidentally brought some chromosomes in from another cell, it appeared that Ponter did indeed have twenty-four pairs, and…

Oh, my God,
thought Mary.
Oh, my God
.

It was even
more
simple than she’d thought.

Yes, yes,
yes!

She had it!

She had the answer.

Homo sapiens sapiens
had twenty-three pairs of chromosomes. But their nearest relatives, at least on this Earth, were the two species of chimpanzees, and—

And both species of chimps had
twenty-four
pairs of chromosomes.

Genus
Pan
(the chimps) and Genus
Homo
(humans of all types, past and present) shared a common ancestor. Despite the popular fallacy that humans had evolved from apes, in fact, apes and humans were
cousins
. The common ancestor—the elusive missing link, not yet conclusively identified in the fossil record—had existed, according to studies of the genetic divergence between humans and apes, something like five million years ago in Africa.

Since chimps had twenty-four pairs of chromosomes and humans had twenty-three, it was anyone’s guess as to what number the common ancestor had possessed. If it had had twenty-three, well, then, sometime after the ape-human split, one chromosome must have become two in the chimp line. If, on the other hand, it had had twenty-four, then two chromosomes must have fused together somewhere along the
Homo
line.

Until today—until right now, until this very second—no one on Mary’s Earth had known for sure which scenario was correct. But now it was crystal clear: common chimps had twenty-four pairs of chromosomes; bonobos—the other kind of chimp—had twenty-four as well. And now Mary knew that Neanderthals also had an even two dozen. The consolidation of two chromosomes into one had happened long after the ape-human split; indeed, it had happened sometime after the
Homo
branch had bifurcated into the two lines she was now studying, only a couple of hundred thousand years ago.

That was why Ponter’s people still had the huge strength of apes, rather than the puniness of humans. That was why they had ape physiognomy, with browridges and no chins. Genetically, they
were
apelike, at least in chromosome count. And something about the fusing of two chromosomes—it was numbers two and three, Mary knew, from studies of primate genetics she’d read years before—had caused the morphological differences that gave rise to the adult human form.

Indeed, the particular cause of the differences was easy enough to identify: it was neoteny, the retention into adulthood of childhood characteristics. Baby apes, baby Neanderthals, and baby Gliksins all had similar skulls, with vertical, ridgeless foreheads, and no particular protrusion of the lower face. As the other kinds grew, their skull shapes changed. But Mary’s kind alone retained their childlike crania into adulthood.

But Ponter’s people
did
mature cranially. And the differing chromosome count might be the cause.

Mary pressed her two hands together in front of her face. She had done it! She had found what Jock Krieger wanted, and—

And…
my God
.

If the chromosome counts differed, then Neanderthals and her flavor of
Homo sapiens
weren’t just different races, or even just subspecies of the same species. They were fully separate species. No need to double up the “wisdom” part in
Homo sapiens sapiens
to distinguish Mary’s kind from Ponter’s, for Ponter’s people couldn’t possibly be
Homo sapiens neanderthalensis
. Rather, they were clearly their own specific tax on,
Homo neanderthalensis
. Mary could think of some paleoanthropologists who would be thrilled by this news—and others who would be extremely pissed off.

But…

But…

But Ponter belonged to another species! Mary had seen
Showboat
when it was on stage in Toronto; Cloris Leachman had played Parthy. She knew that miscegenation was once a big issue, but…

But miscegenation wasn’t the appropriate term for a human mating with something from outside her own species—not that Ponter and Mary had done that, of course.

No, the appropriate term was…

My God,
thought Mary.

Was bestiality.

But…

No, no.

Ponter wasn’t a beast. The man who had raped her—Mary’s conspecific, a member of
Homo sapiens
—had been a beast. But Ponter was no animal.

He was a gentleman.

A gentle man.

And, regardless of chromosome count, he was a human being—a human being she was very much looking forward to seeing again.