Robert May (1936–2020)

Robert (Bob) May was the leading mathematical ecologist of his generation and one of the most influential individuals in UK science. A towering intellect, he combined an extraordinarily quick analytical brain with an ability to synthesize information.

May’s contributions were in three main areas: biodiversity, population dynamics and infectious-disease epidemiology. In each, he generated fundamental insights by creating analytical mathematical models that captured the essence of the biology. He helped to transform ecology from a descriptive discipline into a quantitative, analytical science.

From 1995 to 2000, May was chief scientific adviser to the UK government. With his direct style (he never shied away from blunt phrases), May established the role as a high-profile public post, unafraid to speak truth to power. May was forceful on many issues, including bovine spongiform encephalopathy (BSE), genetically modified crops, climate change, homeopathy and infectious diseases. Clarity of thinking and expression enabled him to present complex issues in an understandable way without sacrificing rigour. He developed the UK ‘Principles of scientific advice to government’, emphasizing three principles: transparency, seeking a wide range of views and fully acknowledging uncertainties. These are particularly relevant in the current pandemic, during which scientists have been called on to advise on policy to deal with a new and poorly understood threat.

May was born in Sydney, Australia, in 1936. He switched from studying chemical engineering at the University of Sydney to physics, attracted to its analytical nature. He completed his PhD in the field of superconductivity. In the 1950s, theoretical physicists were beginning to rely on computers to solve equations; May preferred pencil and paper.

In 1969, motivated by a group at Sydney concerned with social responsibility of scientists and influenced by the renowned ecologist Charles Birch, he became interested in the factors that would prevent collapse in ecosystems such as coral reefs. Two years later, May met Robert McArthur, then the world’s leading theoretical ecologist. Following McArthur’s untimely death, May moved to Princeton University in New Jersey to succeed him as Class of 1877 Professor of Zoology.

The prevailing view in the 1960s was that ecosystems with little biological diversity, such as agricultural monocultures, were more unstable because, for example, disease could spread rapidly through them. In his 1973 book Stability and Complexity in Model Ecosystems, May showed that communities of competing species become less stable as diversity increases, unless mechanisms that promote stability affect their interactions. The research his models stimulated has since demonstrated such mechanisms, for instance, plants extracting nutrients from the soil at different depths. This is highly relevant in current debates about the resilience of ecosystems to climate change and other disruptions.

Risk and uncertainty

May also became one of the pioneers of applying chaos theory to biology. Population ecologists seek to understand why the number of individuals in a population changes over generations. May showed that, for populations with discrete generations, the same model (a non-linear difference equation) could produce stability, cycles of increase and decrease, or chaotic fluctuations, depending on its parameters. The slightest change in initial conditions could lead to widely divergent patterns.