The first Mac I saw may have been one of the first in Britain, for it was at the house of my colleague WD Hamilton, shortly after he arrived from Michigan in 1984, and he may well have shipped it over. Bill showed it to his dinner guests one evening, and it stunned us. I immediately echoed Huxley's remark on closing The Origin of Species: "How extremely stupid not to have thought of that."

Nothing in my 20 years' intensive experience of programming and using computers had prepared me for the Mac. It wasn't an evolutionary advance on its predecessors; it was a macromutational leap into the future. It is that future we are now living in, whether we use a Mac or a virus-compatible PC. I later learned that the ingredients had been the subject of massive research and development at Xerox PARC. But Xerox never developed it commercially, and it didn't become widely known before the Mac.

The whole dinner party wanted one. Frustratingly for me, I had just acquired an earnestly competent but ploddingly conventional IBM-compatible, and this made it hard for me to justify buying a Mac. My colleagues had no such difficulty, and I found myself forsaking my IBM-compatible and borrowing a Mac whenever the owner wasn't looking. Suddenly, I realised this was ridiculous. With a feeling of joyous release, I donated the IBM-compatible to some good cause and bought a Mac. I've never looked back.

The key to the early Mac, and the thing that gave it its unique "look and feel" (later the subject of law suits) was its ROM Toolbox. A large toolbox of software routines was burned into the hardware of every Mac, to handle mouse movements and clicks, pulling down menus, resizing windows, scrolling up and down, setting up check boxes, "radio" buttons and action buttons, indeed everything that made Mac programs so unique in the early days and which we now take for granted.

Theoretically, third party developers could have ignored the Toolbox. After all, there was nothing like it in the other computers to which they were accustomed, which is why software for other computers was so variable and so hard to learn. But since the Toolbox was sitting in the Mac, and since it was so elegantly conceived and worked so well, it would have been insanely wasteful not to use it.

So Apple, by burning in this library of user-friendly routines, managed to make all Mac software, whether written by themselves or by others, look and feel the same. It was this, together with Apple's well-written guidelines for how to design user-friendly programs, that spawned the legendary belief - which was very nearly true - that Mac users never needed to open a manual.

A ll they had to do was ask themselves, what would be the neat, the elegant, the intuitively obvious Mac way of doing this? (In modern computers the Toolbox is no longer mostly in ROM, but the principle, once established, remains).

Before the Mac revolution, if you wanted to read a particular data file, you normally couldn't scroll your way through a list of candidates until you spotted it. You had to remember its name and type it in. Similarly, instead of scooting your mouse along the menu bar seeking a likely command, you'd most probably have to look the command up in the manual and literally type it in. Or, at best, you had to burrow your way deep into a complicated system of nested menus within menus within menus, getting hopelessly lost when you tried to back out again.

Nesting of this kind was one of the cardinal sins discouraged by Apple's guidelines for programmers. Above all, the Mac allowed its human users to do that most intuitively human of actions: point with the hand at a target, and physically move it where you want it.

Today, the Windows imitation has finally caught up, and you no longer have to be bonkers to prefer it. Ubiquity itself is a virtue, promising a richer supply of software, especially games and frivolous programs (ironic given that originally it was the Mac that had the hip Californian image, compared with IBM's crew cut and business suit).

Unfortunately, for exactly the same reason (and arguably other reasons too) ubiquity also appeals to the spiteful or deranged authors of viruses. In 2003, it was estimated that viruses are more than 600 times more likely to attack a Windows PC than a Mac.

But the virus menace is not the only reason for continuing to prefer the Mac. They are notoriously easier to set up. Having gone over to the Unix-based System X, today's Macs almost never crash. Even if one application does, you can always escape from it and find everything else running on, serenely unperturbed. The Unix base, too, gives Macs its own potential ubiquity.

Finally, and more elusively, there is the matter of style. Hard to define but, as Louis Armstrong said: "Man, if you gotta ask, you'll never know."

· Richard Dawkins's book A Devil's Chaplin has just come out in paperback

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