From June until October 1883 large parts of the Earth were shaded beneath dark clouds of smoke. More than half of the Indonesian island of Krakatau was thrown up into the atmosphere and tsunamis killed more than 36,000 people along the coast in Java and Sumatra, 40km away. The effects on climate and weather lasted for over a year and they were global.

The island actually increased in size with new volcanic ash up to 80m thick and in effect the whole area had been sterilised so that animal and plant life ceased. The following year someone saw a single spider and “a few blades of grass”, then more plants and a few birds and insects arrived from the island of Sebesi, 12kms away. Slowly, life started to return to something like it was before. Within fifty years the entire surface was re-colonised with forest but the changing succession, the sequence of changes to return to the stable flora and fauna, continued for several decades. Arguably it is still going on, well over a hundred years later. But a sudden event such as an explosion followed by a hundred years recovery was just one trivial catastrophe on a geological time-scale. For biological evolution it was a small turn of the screw, just one more environmental change. The eruption advanced interest in catastrophic events in nature and biologists learnt a lot. For example, when things moved onward more rapidly than was normal, it showed that there were major consequences for the environment of the region and for its biodiversity.

The immediate concerns of the scientists involved were to improve their understanding of volcanic activities so that one day they might be predictable. Others were able to use the new virgin territory to monitor the whole process of re-colonisation of the new island’s species. With his recent field experience in the Himalayas the Royal Society appointed Richard Strachey to chair a group to investigate these scientific aspects of the eruption. For evolutionary biologists the sudden event also raised interest in Frances Galton’s recently aired beliefs that sudden changes in the physical environment might cause evolutionary change. Darwin remained in favour of gradual change, not catastrophic: Galton was opening the argument again with a new theory and the volcanic event at Krakatau helped him keep the debate alive even though most of the biologists in The Royal Society remained highly sceptical.

Richard Strachey and his family – 1890s

To help understand catastrophism, Galton had raised the metaphor of a rough stone that would “tumble over into a new position of stability” an idea that first appeared publicly as an afterthought at the back of his earlier 1869 book Hereditary Genius.

Now he had good discussions with Richard Strachey about Krakatau so he brought the same metaphor into the main argument of his second important book about evolution published in1889, Natural Inheritance. Galton liked gadgets and so this time he made a wooden model of the rough stone, a few centimetres in diameter with 64 surfaces. He took it with him to demonstrate at his lectures all around the country and he called it his “polyhedron”: tipping the model to tumble onto one stable surface after another, each tumble taking it to a new position of stability until the next catastrophe.

Steve Gould called it “evolution by jerks”.

Similar thoughts were going on in the minds of a different kind of life scientists, those few new biologists beginning to measure inside reproductive cells. But cells were vulnerable to their own kind of catastrophe otherwise known as mutation, a phenomenon noticed by one of Darwin’s acquaintances, the horticulturist Hugo de Vries. This Dutchman bred varieties of evening primrose and in 1889 he observed that a larger version than normal had appeared in an instant during his breeding programme and it was stable, surviving from one generation to another. Although the Cambridge plant and animal breeder, William Bateson, suspected it to be a hybrid rather than a new species he agreed that its sudden appearance was important and should be investigated further as a possible example of a new mutant. There was also the difficulty for these breeders about what these words meant: species, variety, hybrid and mutant.

Were such instant new forms, de Vries and Galton wondered, compatible with the more gradual changes foreseen by Darwin? They noticed a lot of continuing support for change being cause by environmental changes, especially catastrophic ones rather than the familiar gradual trends. And there was still no sign of evidence to support any other kind of selection. There seemed to be a return to the idea of straight adaptation to a new environment, more like Lamarck’s continuous changes than Darwin’s selection of one or another.

Support for natural selection was reduced even more by a split between its two most fervent backers, Galton and Lankester, respectively the quantifier and the qualifier. Lankester’s limited powers in diplomacy were not going to help even though he understood both sides and tried to keep them together. For Galton, measuring seemed to be taking over from feeling, and instead Lankester stuck with the old methods to which slow hard work describing intricate new structures would eventually answer all the important questions. There was no new evidence to bring things together. Instead there was an unhappy set-back in 1895: the death of Thomas Huxley.  Lankester was devastated: “There has been no man or woman whom I have met on my journey through life, whom I have loved or regarded as I have him, and I feel that the world has shrunk and become a poor thing, now that his splendid spirit and delightful presence are gone from it. Ever since I was a little boy, he has been my ideal and my hero.”

The conflicts became obvious just after Huxley’s death but the foundations went back at least a decade and arguably much longer. Lankester began to notice the split showing up between his friends as their personalities and experiences took them in opposite directions. One group went outwards into space and time, keeping an open mind on how things worked; the other went inwards to the cell, looking for smaller and smaller units and expecting them to hold the key to it all. Lankester knew that studying evolutionary biology was one way to get down to the brass tacks about the meaning of life.