THE train was full, as the guard kindly and politely explained, because it was the first off-peak service of the school half-term.

Aidan Semmens

THE train was full, as the guard kindly and politely explained, because it was the first off-peak service of the school half-term.

Which, as it happened, was precisely why we were on it. Bound - like half the young families in Suffolk, it seemed - for a capital day out.

I don't know which attraction you were bound for, but we were headed for the Natural History Museum. Us and about half the rest of the country, apparently.

Mind you, I'm not complaining. Though it coiled round and round on itself like a snoozing python, with a long straight tail all down Cromwell Road, the queue moved along swiftly enough.

And once inside the museum's great central hall, the journey and the wait were well worth it.

I'm not, in general, a great fan of Victorian mock-gothic architecture. But there is something grand - in an enjoyable sense - about that great space, with the sun shining through the high windows bringing a warm light to the stonework.

It reminds you simultaneously of a medieval cathedral and a main-line railway terminus. Two things not all that unlike, when you think about it. And both references are entirely appropriate.

The station is apt because in 19th-century Britain the railway had the same exciting sense of newness and discovery that scientific inquiry had. They were two of the great wonders of the age, along with the public spiritedness that caused such a museum to be built.

And the cathedral is apt because - well, this was the cathedral of the new science of evolution.

The science that put the “history” part into “natural history”. The science that told us where we, and all the living things around us, had come from.

And, like a cathedral, the great space centres on an amazing relic. A relic which naturally draws the eye and the awe wherever in the room you are.

It has to be big to dominate attention in such a huge space. And it is - 26 metres long and tall enough to tower over you as you stand under its monster neck or mighty tail.

The diplodocus was one of the largest animals ever to roam the earth and still, of course, one of the dinosaurs you remember from your own early schooldays. The fact that this colossal skeleton is actually a replica, a mere 104 years old, does not detract from its wondrousness.

The tyrannosaurus rex that turns its head to fix you with a beady eye and roar out a threat isn't the real thing either. Thank goodness. But it's a marvel of animatronics that the kids are sure to remember.

And there, looking down proudly and benignly from the turning of the stairway, is the great man himself. Or at least another replica. In the week of his 200th birthday, Charles Darwin presides in stone. Carved, not fossilised.

Darwin, of course, didn't get everything right. He knew that perfectly well himself.

No true scientist believes they've got everything right. It's one of the ways they differ from the dogmatic religionist.

He didn't discover (or, heaven help us, “invent”) evolution. What he did do was explain the way it works.

And unlike most scientific principles, natural selection is beautifully easy to understand. So much so that once it's been pointed out and explained (by David Attenborough, perhaps), it seems extraordinary that it wasn't always obvious.

Those who still persist in “denying” it today might as well deny the force of gravity. And maybe try stepping off a tall building to prove their point.

The evolution of evolutionary theory since Darwin is interesting in itself. And so is the parallel evolution of other ideas over the same period.

Many people suppose that evolution implies progress - things gradually getting better. It doesn't.

Merely that as things change over time, those better fitted to survival in their particular circumstances will survive. Those less well fitted won't.

Right and wrong don't really enter into it. Which is why it is theoretically possible (though not, I hope, likely) that rational inquiry and understanding will die out and creationist superstition flourish.

The environment in which these ideas must compete for survival is the minds of young people. Which is why institutions like the Natural History Museum are so vital.

Like Darwin, and like the thousands of eager youngsters who visit the museum each half-term, I find evolution hugely exciting. But there are things about it I regret.

Like every parent of all those kids, I was compelled to end a great day out by braving the museum gift shop.

And it left me sorry, once again, that this species had ever evolved into a creature of naked commercialism.