Meanwhile, a steady trickle of pensioners who puff a little marijuana to relieve their arthritis (and it is said to be especially good for multiple sclerosis) are rounding off their hitherto blameless lives before the beak. Some citizens might rather feel that the police and judiciary should be doing better things. Others might conclude that our attitude to marijuana is grotesque beyond all reason; and, more broadly, that we should re-think our attitude to all psychotropic drugs from first principles. After all, for at least some of the time our early primate ancestors must have been stoned out of their heads - just as is evident, most afternoons, in modern, leaf-eating monkeys.
For we, Homo sapiens, are an evolved species, like every other. We carry the inheritance of physiology and proclivities that adapted our ancestors to the open woods of Pliocene Africa, and to the forest before that. That these proclivities are inherited does not make them good; but it does mean they must be taken into account.
Among other things, our ancestors had to come to terms with whatever was there to be eaten; and in very early days, between about 80 million and 3 million years ago when their corner of Africa became too dry for trees, they ate the produce of forests, as most wild primates do today: fruits, seeds, and leaves. Most edible components of trees contain "secondary metabolites" that are designed to repel predators. Many of those repellents home in on the predators' nervous system. In short, through most of their long history, our evolving brains were constantly assaulted by psychotropic biochemicals.
Whatever our brains (or guts, or muscles, or whatever) are exposed to over time, they adjust to; that is what "adaptation" means. Sometimes adjustment simply means "coping with" - as we cope, up to a point, with pathogenic bacteria. But sometimes - often - the coping grades into need. Thus the world's earliest creatures were poisoned by the first whiffs of atmospheric oxygen, yet most of their descendants now depend upon it. By the same token, we have inherited a need for vitamins; a random bunch of esoteric chemicals that just happened to be around, which our ancestors pressed into their own service.
It is eminently reasonable to suggest that our brains need the psychotropic agents they evolved alongside, just as our bodies need vitamins. But because our diet is now based on crops that are bred to be free from secondary metabolites, we are now deprived of them. To be sure, we suffer specific illness when we are deprived of vitamins (rickets, spina bifida, xerophthalmia) but nothing comparable, apparently, for lack of marijuana or cocaine. But who has tried to find out? In truth, the whole sorry spectrum of depression, anxiety, obsession and the rest are the commonest afflictions of our age. Perhaps we are all suffering from what might reasonably be called (and I claim the term as copyright) "pharmacological impoverishment".
The notion that most of us most of the time are drug-deprived has endless connotations. People think weird thoughts when they are drugged or drunk, do they not? But how do we judge what is weird? Perhaps it's our Wesley- clean minds that are odd. Aldous Huxley knocked at Blake's "doors of perception" with mescaline. Prophets sought revelation in the desert, their brains buzzed by wild plants and starvation. In vino veritas. Perhaps our best chance of finding out what is true and important in this world is the sum of our perceptions, in all psychological states. Perhaps that is going too far; yet it surely is arbitrary to suppose that our thoughts and feelings should be trusted most when our brains are deprived of the things they grew up with.
Consider, too, more practically, how the whole picture would alter if our attitude changed: how most of the perceived "problems" would disappear. Those that have to do with the pharmacology of the drugs themselves, the over-dependence and side-effects, could be enormously reduced. The problems that have to do with criminality - small-time adulteration and beatings- up, and big-time perversion of entire economies - could be virtually eliminated.
On the pharmacological front, consider what the modern pharmaceutical industry might achieve if it set out to accentuate the positive aspects of the world's major drugs and eliminate the negative. In some cases, a few tweaks of the molecules might make all the difference.
Others would need more, but the rewards would certainly justify the effort. Perhaps the ambience is wrong; perhaps SmithKline Beecham should link up with Arthur Bell of Perth, distillers of the world's finest blended whisky. There would still be difficulties, just as there are with whisky itself, but the problems of whisky are much less than they would be if people were obliged to drink poteen.
And who would buy overpriced rubbish from dangerous people on the streets when quality was guaranteed for the price of an imported lager? If you write articles like this, you invite letters from enraged citizenry, and much more poignantly from the parents of unhappy children. But such parents and their families stand most to gain from a rethink. Quality-controlled drugs, sold in a civilised atmosphere, would still cause problems - but they would be a lot more tractable than now, and they would not be those of uncontrollable dose, adulteration and dirty needles.
In short, drugs are more fundamental to us than we have allowed ourselves to believe, and our attitudes towards them should be far more in sympathy with our own biology. Such a change of heart and of policy would not make the world a perfect place but it would make it a lot safer and, perhaps in many other ways as well, a great deal more agreeable. To be sure, respectable citizens would not be worse off. The real losers would be the drugs mafia. The sinister thought occurs to me that this is why the laws are the way they are.
The writer's latest book on human evolution, 'The Day Before Yesterday', will shortly be available in paperback from Pimlico.