COLLEAGUES said he tweeted more than any professor they knew, and Calestous Juma’s tweets covered a swarm of things. Income inequality, and a free-trade area for Africa, you might expect. Those were the subjects he taught at Harvard: getting poorer countries, especially in Africa, to grow and thrive was the obsession of his life. But he also tweeted about a wheelchair that could climb stairs, the increasing size of steaks, and the maximum number of goats seen eating up in a tree. He was extra-delighted to send out a New York Times editorial, from 1878, about Thomas Edison’s new “aerophone”: “Something ought to be done about Mr Edison, and there is a growing conviction that it had better be done with a hemp rope.”

Human beings always resisted change. He demonstrated this, on YouTube, by holding up a mug of coffee, opposed on safety grounds for around 200 years. Refrigeration had been fought against; margarine had been coloured pink, by law, so that consumers could reject it. Closer to his own life, in the remote litter of mud huts on Lake Victoria in Kenya where he had grown up one of 14 children, villagers had initially rejected the cassava cuttings his father had introduced, thinking the unknown tubers would breed demons. In fact, in that flood-prone corner, they ensured a stable food supply. Innovation in Africa, he had learned from that example, had to be “evolutionary”. Everyone—smallholders, herders, merchants—had to be involved and convinced it would work.

Progress would come, he was sure. But his many books and papers showed how far there was to go. In 2011 “The New Harvest” noted that 75% of Africa’s farmland, the mainspring of economic activity, was starved of nutrients. Only 4% of cropland was irrigated; fertiliser use was 10% of the world average. The crying need was for leadership, integration and innovation, in that order. Governments, scientists, entrepreneurs and farmers had to co-operate to improve crops and yields, build roads to get produce to markets, and generally invest. His favourite example was Bingu wa Mutharika, president of Malawi, who gave subsidies to farmers for improved seeds and fertiliser; yields rose so much that, in two years, Malawi was a net exporter of food. Why not do that everywhere?

He advised several African leaders, and found them receptive. In 2012, six of them were engineers—an encouraging fact for a man who had spent his boyhood Sundays mending villagers’ radios, and called that the only real job he had ever done. It was government ministries, and their turf wars, that frustrated him. His African Centre for Technology Studies, set up in Nairobi, was among the first on the continent to bring researchers and policymakers together. He had been softening up Kenya for a while: as a young teacher in Mombasa he so bombarded the Daily Nation with wit and ideas that he became its first science correspondent, and went on proselytising, just as perkily, from there. His own progress, from a school without water or power to Sussex University, the United Nations and Harvard, surely showed what his continent could do, with effort and a push.

Africa was a laggard, outstripped by everywhere else. But laggards had advantages, too. They could take what others had invented and run with it—leapfrogging, as he called it. The story of mobile phones in Africa greatly fuelled his optimism. Here was an invention people loved rather than feared, so that Kenya (with his help) became one of the first countries to use smartphones for money transfer, and herders in Somalia now exchanged and tracked their goats by painting them with their mobile numbers. He enjoyed starting lectures with a picture of those goats; though proper leapfrogging, he insisted, still needed power-lines and roads.

As with phones, so with agricultural technology. Africa, he wrote, contained 60% of the world’s available arable land. It also contained, in sharp contrast to monocultures elsewhere, a vast range of indigenous crops. Many of these, long adapted to arid conditions, could help feed the world despite climate change. Africa was a reservoir of biodiversity, and the next step was to ensure that the storing of seeds, and research into them, became the business of African governments, universities and farmers. Perhaps his most satisfying stint was as the first executive secretary of the UN convention on biodiversity of 1992—in effect an African safeguarder of that vast and endangered genetic library, still hardly catalogued and still largely unread.

What farmers need

Genetic modification held no fears for him. Modified seeds, resistant to drought and pests, were just what Africa needed. Gene research induced plants to release their secrets of success. If over-producing Europeans did not want this new tool, fine; but they had no right to limit farmers’ choices in Africa. When GMOs were restricted by the Cartagena protocol, signed in 2000, he left the UN in protest at its pessimism and “technological intolerance”.

There was plenty of that about, in the developed world as much as in Africa. His life was spent resisting it, grasping new inventions and initiatives joyously and with both hands. Lighthearted as he was, his constant message to Africa was also a stern one, and more succinct than most of his tweets: Innovate or perish.