‘No, it won’t get cold. It’s already cold.’ I was conscious of sounding awkward. ‘Is there some reason to delay?’

‘The city lights. The view’s amazing.’

‘Unfortunately it’s static. Once you’ve examined it, there’s no reason to look again. Like paintings.’

‘But it changes all the time. What about in the early morning? Or when it rains? What about coming up here just to sit?’

I had no answer that was likely to satisfy her. I had seen the view when I bought the apartment. It did not change much in different conditions. And the only times I just sat were when I was waiting for an appointment or if I was reflecting on a problem, in which case interesting surroundings would be a distraction.

I moved into the space beside Rosie and refilled her glass. She smiled. She was almost certainly wearing lipstick.

I attempt to produce a standard, repeatable meal, but obviously ingredients vary in their quality from week to week. Today’s seemed to be of unusually high standard. The lobster salad had never tasted so good.

I remembered the basic rule of asking a woman to talk about herself. Rosie had already raised the topic of dealing with difficult customers in a bar, so I asked her to elaborate. This was an excellent move. She had a number of hilarious stories, and I noted some interpersonal techniques for possible future use.

We finished the lobster. Then Rosie opened her bag and pulled out a pack of cigarettes! How can I convey my horror? Smoking is not only unhealthy in itself, and dangerous to others in the vicinity. It is a clear indication of an irrational approach to life. There was a good reason for it being the first item on my questionnaire.

Rosie must have noticed my shock. ‘Relax. We’re outside.’

There was no point in arguing. I would not be seeing her again after tonight. The lighter flamed and she held it to the cigarette between her artificially red lips.

‘Anyhow, I’ve got a genetics question,’ she said.

‘Proceed.’ I was back in the world I knew.

‘Someone told me you can tell if a person’s monogamous by the size of their testicles.’

The sexual aspects of biology regularly feature in the popular press, so this was not as stupid a statement as it might appear, although it embodied a typical misconception. It occurred to me that it could be some sort of code for a sexual advance, but I decided to play safe and respond to the question literally.

‘Ridiculous,’ I said.

Rosie seemed very pleased with my answer.

‘You’re a star,’ she said. ‘I’ve just won a bet.’

I proceeded to elaborate and noted that Rosie’s expression of satisfaction faded. I guessed that she had oversimplified her question and that my more detailed explanation was in fact what she had been told.

‘There may be some correlation at the individual level, but the rule applies to species. Homo sapiens are basically monogamous, but tactically unfaithful. Males benefit from impregnating as many females as possible, but are able to support only one set of offspring. Females seek maximum-quality genes for their children plus a male to support them.’

I was just settling into the familiar role of lecturer when Rosie interrupted.

‘What about the testicles?’

‘Bigger testicles produce more semen. Monogamous species require only sufficient for their mate. Humans need extra to take advantage of random opportunities and to attack the sperm of recent intruders.’

‘Nice,’ said Rosie.

‘Not really. The behaviour evolved in the ancestral environment. The modern world requires additional rules.’

‘Yeah,’ said Rosie. ‘Like being there for your kids.’

‘Correct. But instincts are incredibly powerful.’

‘Tell me about it,’ said Rosie.

I began to explain. ‘Instinct is an expression of –’

‘Rhetorical question,’ said Rosie. ‘I’ve lived it. My mother went gene shopping at her medical graduation party.’

‘These behaviours are unconscious. People don’t deliberately –’

‘I get that.’

I doubted it. Non-professionals frequently misinterpret the findings of evolutionary psychology. But the story was interesting.

‘You’re saying your mother engaged in unprotected sex outside her primary relationship?’

‘With some other student,’ replied Rosie. ‘While she was dating my’ – at this point Rosie raised her hands and made a downwards movement, twice, with the index and middle fingers of both hands – ‘father. My real dad’s a doctor. I just don’t know which one. Really, really pisses me off.’

I was fascinated by the hand movements and silent for a while as I tried to work them out. Were they a sign of distress at not knowing who her father was? If so, it was not one I was familiar with. And why had she chosen to punctuate her speech at that point … of course! Punctuation!

‘Quotation marks,’ I said aloud as the idea hit me.

‘What?’

‘You made quotation marks around “father” to draw attention to the fact that the word should not be interpreted in the usual way. Very clever.’

‘Well, there you go,’ she said. ‘And there I was thinking you were reflecting on my minor problem with my whole fucking life. And might have something intelligent to say.’

I corrected her. ‘It’s not a minor problem at all!’ I pointed my finger in the air to indicate an exclamation mark. ‘You should insist on being informed.’ I stabbed the same finger to indicate a full stop. This was quite fun.