"Yes!" said Koen. "I can put this thing to use right now! I can go shopping."

Laura's pleasure evaporated. Her heart, now with neural firing rates increased, thudded. "Are you still thinking of going outside? Into the Zogreion?"

Tapping his fingers on the counter and assembling a shopping list, Koen failed to register her tone of horror. "I've been trapped in here for two weeks. Of course I want to go outside."

"Then I would be…happy to accompany you."

This hint, too, flew wide of its mark. Koen nodded eagerly. "Yeah! Great! It'll be like…"

A date? thought Laura, and stiffened.

"…back in Brasília."

She pushed her cup and saucer across the counter. Some social queues it was better for Koen not to pick up. "But the food in Brazil is normal. Well, some of it is, anyway. Human. What is there out there that we can even use? You can just order what you need from Yoshida."

Koen reached back and knocked on the door of a cabinet with his knuckle. "Do you know what's in here? A thousand different brands of ramen. We just ate most of my consignment from Earth, which means that until next week we have no fresh vegetables or fresh meat."

Laura's body reacted to the memory of the last fresh meat she'd eaten. The little Quotidian's eye had been the worst part. "Don't be selfish," she said, spurred by this disgust.

Koen furrowed his brows. "But I'll be cooking for you."

"Yes, of course. Sorry." She shook her head, which was tingling unpleasantly. Koen made his coffee strong.

"Once the paperwork goes through and I get control of the general consignment, I still wouldn't be able to import enough tomatoes and chickens to feed the embassy."

Laura rounded the corner of the counter, as if to block Koen from leaving. She didn't want to plead, but it was better to do that than go back on her offer to go outside with Koen. And she really didn't want to go outside. "What if we can start a garden? Talk to Yoshida."

He gave an easy smile, which Laura found distracting. "This isn't The Martian. We're in the middle of a city. We can just find local sources. Come on!"

He stepped as if to rush out of the kitchen, but Laura was still blocking him. Suddenly, they were standing very close together.

Laura took a deep breath through her nose, and was struck by Koen's smell.

Histocompatibility arises here as another interesting and pertinent subject. The major histocompatibility complex is a cluster of genes on chromosome 6 (in humans), which codes for molecules on the outer surfaces of cells marking them as safely part of the body and not foreign invaders.

Viruses, bacteria, and other parasites succeed if they can mimic human histocompatibility molecules and escape detection by the immune system. That means that a population of humans with only one kind of histocompatibility molecule will quickly find itself ill. The more different kinds of histocompatibility molecules there are sticking out of people's cells, the harder it is for a particular germ to evolve to mimic them.1

Now, where does sex figure in? Improved immunity is only one of the advantages bestowed by genetic diversity, and the major histocompatibility complex, because it contains so many genes, works as a good proxy for an individual animal's total genetic mix.2 The molecules it codes for (of a sort called "peptides") eventually break off their cells, mix with the blood, and escape the body along in saliva, sweat, and urine. This last we shall pass over, but sweat is, as most humans are aware, smelly.

If you discover this narrative on Amazon, be aware that it has been stolen. Please report the violation.

What humans are mostly unaware of, however, is that this smell carries information about the genetic diversity of the other humans around them. Since more diversity is good when it comes to immune response, people who can detect the histocompatibility molecules of others and compare them to their own will have an advantage when it comes to mate selection. The logic boils down to this: find someone whose sweat smells very different from your own and marry them.3

Koen and Laura belonged to populations that had shared comparatively little genetic material for the last 45 thousand years.4 They had significantly different major histocompatibility complexes, and this was only one of the many reasons they were attracted to each other. This fact shouldn't have been news to either of them, but still, they were shocked.

Laura's thoughts ran along the lines of Oh, no! and I do not need this with a pause to spin off rationalizations along the lines of, If he was interested, he would have said so before now and These Western men are never interested in marriage anyway.

Well, the practical part of her mind said, you could use a condom.

Requisitioned how?? And anyway, we walk into the canteen together, all tousled and smug… Everyone will know!

Won't they be jealous?

I'll be out of a job forever! Do I want to retire from foreign service and become Koen's housewife?

Do I??

And anyway, where will we live? What language will we teach our children to speak? What will my parents think when I show them this tall, handsome, intelligent, kind man with his quiet sense of duty and humor? And wide shoulders.

"Take a cold shower," that's what they'd say.

While Laura's internal dialogue evolved from panic to romantic fantasy and back again, Koen was thinking, too.

I want to kiss her.

Is that the right thing to do? It is if she wants me to kiss her, but what if she doesn't?

What if she does? Look at those eyes, man! Look at lips, and the way her breasts push her shirt out.

He tried to get a hold of himself. This was unprofessional. They were co-workers and Laura depended on Koen to do his job and let him do hers.

Which, by the way, she will absolutely lose if she gets romantically involved with a colleague.

And anyway, if she really was interested in him, wouldn't she have said something before now?

Koen winced as if from a physical blow. Laura saw it and winced, too. They shied away from each other, snorting.

Sex between most animals is a complicated and frightening gamble. This is even more the case for animals that can talk. Koen and Laura's motivation systems were active, but their reward systems were stymied. Their emotional states wobbled between lust, rage, and manic joy.

"Let's go shopping!" shouted Koen, before anything worse could happen.

1 Manczinger M et al. (2019). "Pathogen diversity drives the evolution of generalist MHC-II alleles in human populations".

2 Yamazaki, K; et al. (1976) "Control of mating preferences in mice by genes in the major histocompatibility complex".

3 Wedekind, C; et al. (1995) "MHC-Dependent preferences in humans". And Santos, PS; et al. (2005) "New evidence that the MHC influences odor perception in humans: a study with 58 Southern Brazilian students."

4 Maca-Meyer N et al. (2001). "Major genomic mitochondrial lineages delineate early human expansions".