For readers outside of the UK - England still has a substantial rail network, with a reasonably good standard of catering in the restaurant car. The custom, at busy times, is for perfect strangers to share tables, and abandon their traditional British reserve. Sometimes these meals are lubricated by quantities of alcohol particularly when the train has broken down and you are all marooned.

I had been talking with Dr. Jones for about 45 minutes, in the relaxed way of those who are enjoying both the comfort of good food and sharing the adversity of imprisonment in a stranded train restaurant car.

We had ranged over the safe topics: the rail network itself and previous encounters with mechanical breakdowns. The mobile phones had gone silent, either because their batteries had been exhausted, or there was no one else who might be called for conversations to be safely shared with 20 other people in the carriage.

One of the fascinations of railway meals is that people will talk about their professional roles and interests and hobbies without having to pitch, to sell, or to establish a social position. Perhaps I came to the 'Glasses Subject' because of the girl with the wire frame ovals on the table across the gangway (rx with about -8 in one lens and something very low in the other).

Dr. Jones had described himself as a researcher in behavioural genetics. I had vaguely described myself as something to do with computer networks, telephony and the internet - we bemoaned the fact that both our specialisms were discussed in the public media in such a crass way - as my subject is very much 'non-people' we kept away from it . I was still glancing at the girl across the carriage and remarked on what genetics had to say about what facial characteristics people found attractive.

"Ah", said Dr Jones, "now you are talking about my great enthusiasm of the moment" (this guy was a real polymath) - "what do you find attractive then - in women - perhaps the girl wearing glasses", he suggested (he actually quoted William Blake, "what is it men, in women, do desire".) "The glasses", I blurted out - he glanced across the aisle - "no", I said, "yes, she�s very nice and attractive, but what I mean is, many people find glasses to be a particularly attractive thing."

"Yes", he said, "I was aware of that, from a professional point of view, not that I share it myself. Do you - is it something which you understand? I have never heard a rationale for it."

Having come out in this way - in such an unthreatening conversation - it was a challenge to explain and recount the range of opinions we have all expressed on this site. That eyewear added sophistication mystery and all the other reasons.

After what I could sense was someone listening professionally and patiently - he interrupted - "Yes, many of those things are probably true - but you have given me no causation - you have missed the key point - its not a fetish, which could be explained just by the need for stimulation by association with something obscure or forbidden."

This is what he told me:

The media often explains genetics as the survival of the strongest, the fittest, those people who express most strongly the characteristics of the majority. Had it been that simple we would have become extinct long ago - yes some people and some species elevate those with the strongest profile, the brightest plumage to be the objects of desire with whom to copulate, but thats not the whole story. If such behaviour were universal, the species would evolve itself into muscle-bound oblivion.

You must consider human behaviour in terms of the span of its evolution - primitive man may have existed 40,000 years ago - civilisation is maybe 4,000 to 6,000 years old. Much of our underlying behaviour is still reliant on the first 36,000 years.

Let me give you an example. When I was a child I was often afraid of the dark - I gradually overcame it and for years felt quite grown up. About 10 years ago I lived in a country village. One night in the Autumn I went out to fetch coal for the stove. As I bent over the bunker, the old fear of the dark suddenly welled up inside me, so much so that all I could do was run back to the house.

For months, each night I went out and tried to control and rationalise the fear. I realised that in the half light what I was seeing was just typical of a primitive settlement thousands of years ago. Bending over to reach the coal I was turning my back on the danger, something primitive man would be programmed to avoid at all costs. He could not risk dropping his guard against all those possible predators or human or animal. Then one night, as I steeled myself to retrieve the coal I looked down and saw the embers of a fire our gardener had left. Suddenly a feeling of safety and almost sexual warmth came over me - of course - fire - the solution to primitive mans fears.

Think of it - what you are seeing in someone who wears glasses is another species or at least another tribe - with different plumage - with different tribal dress - the glasses are both highlighting and hiding something which may be a valuable opportunity for - your genes to miscegenate. You unconsciously express the wish to extend the mix, not with the strongest, those who have all the 'perfect' characteristics, but with those who are advertising their differentness - those whose visible world may be quite different to your own.

Look at your life choices, I bet they all show a tendency towards deviation from the population norms. Your attraction to people with glasses is an expression of that primitive urge to extend the genetic mix - all the characteristics you describe are those which your rational mind ascribes to an attractive person but they are not the cause of that attraction.

Of course the reverse is true - someone who wears glasses may think themselves to be defective and un-attractive and therefore not likely to receive the adoring attentions of those members of the tribe to are turned on by the 'brightest and tallest' genetic programming.

It's thanks to you people who have the genetic wanderlust that mankind has evolved beyond the nasty brutish and muscle-bound.

Did it all make sense ?