I last saw John Maynard Smith speak in public in May 2002, to a packed lecture theatre in the Arts buildings at Sussex University. A local outcry had arisen about race and science: a Sussex professor of computer science had posted material on his website arguing that racial feelings are innate. Maynard Smith was one of a number of speakers on the panel at the meeting which was called to discuss how the university should respond.

The occasion was a dispiriting one. Nobody actually called for the professor to be silenced, but many of the speakers seemed to feel that the professor's views should be suppressed one way or another; some called for his dismissal. John Maynard Smith's contribution was in a different register to all the others. He presented a clear and simple critique of the arguments made in the offending article. There was certainly no question that nature has selected tendencies that encourage individuals to favour close kin, he said, noting the "disturbing" evidence among humans that stepchildren suffer higher rates of abuse than do biological children. But he was sceptical that nature would select hostile feelings for people who look different from oneself. "If you do the sums," he said, using a favourite expression of his, genetic differences would not produce the effects the article had claimed. He added that there was no reason to believe that the gap in IQ scores between black and white Americans, to which the article had also referred, was genetic in origin. (JMS was not impressed by IQ theory, which revolves around the idea of a factor called g, referring to general intelligence - or by those he felt overstated its explanatory power, whom he called "g groupies".) And he insisted that even if something was natural, it was "nonsense" to say that it was inevitable.

It was hard to tell what impression his comments had made, for they were not taken up by other speakers. Many of those present would probably have been unaware how apt it was that Maynard Smith was there to speak on the subject; that he was not only Britain's senior evolutionary biologist, but nearly forty years previously had been among the first to appreciate new ideas about 'kin selection' which have since transformed evolutionary theory. Perhaps other speakers felt that he had said all that needed to be said on the science. But it seemed that for many, the truth or likelihood of the claims was not the point.

Two hours went by; Maynard Smith looked tired and strained. Yet when his turn came to make some final observations, he spoke with grace and generosity, praising some of the contributions and promising to think about them. The phrase 'elder statesman' comes readily to mind when one thinks about his place in evolutionary biology; and on this occasion he behaved as one. He left his audience with a good-humoured but trenchant statement of principle. There was, he said, a need to defend unpopular views, and added that if sociobiological professors were not to be allowed to speak, the University would have had to sack him.

By that stage my own feelings about the debate had given way to a growing unease that there was something more seriously amiss with JMS than the burden of the afternoon upon a man of 82. I went up to him afterwards and asked him how he was. "If you want to have a serious talk with me, you'd better make it quick," he said. He explained that he had been given a grave medical diagnosis. His time was being called.

It wasn't a surprise in itself - apart from his age, I had thought something was up for a while - but the degree of the shock was a surprise. Refusing to take the hint from the passing years, John Maynard Smith had carried on going into work every day, continuing his researches, taking his colleagues to the pub at lunchtime, inspiring his juniors with his kind and keen interest. Latterly I had shared a little of this, as I met him and interviewed him for a biographical book about evolutionism and England. He seemed to defy time not by maintaining the past, but by being utterly contemporary. When the news came it seemed unfair, despite the calendar, because it seemed as though he would die young.

I decided then that I would write about that wretched day, on which he had given up time that, just a week before, he had learned he might have little left of to give, to do what he saw as his duty; to do it so generously despite evident physical strain and although, as he told me subsequently, he had found the occasion depressing. I saw another reason to admire him: I believe the word is mensch.

I feared that I would be writing about it much sooner, but nearly two years have passed. Today, a few days after his death was announced, I'm glad that he was able to carry on going into the university; that he had many days on which he was able to defy his health; that the last time I saw him, he was cheerfully surrounded by papers and folders of ongoing work; that he continued working almost till he died; that he finished his book on animal signals (with David Harper, whose obituary of him appeared in the Guardian); that he still went birdwatching. I'm glad that in my book he is in the present tense, and that he saw the start of another Sussex spring.

Brighton, 23 April 2004.