J. B. S. Haldane was primarily a geneticist, and his career overlapped with the rise of genetics as a field of study in the first half of the twentieth century. He demonstrated a whole series of things through his work. One was the mechanism of genetic linkage in mammals — that’s the way in which two genes that lie next to each other on a chromosome tend also to be inherited together.

He mapped the genes for hemophilia and colorblindness, and introduced a theory for how life began on Earth. His most important contribution, I think, was to reconcile two aspects of genetics that in the early part of the twentieth century seemed to be irreconcilable. While the gap between those two aspects persisted, people had been afraid that Charles Darwin’s theory of natural selection was doomed.

When we talk about his stature and his role in public life, he became as famous as Albert Einstein was in Britain at the time. This came about primarily because of his double duty as a writer and speaker.

As a writer, he would publish opinion pieces. He wrote about his life and his experiences in World War I and II. As a speaker, he gave talks and hundreds of people would turn up to hear him speak. He wasn’t a particularly magnetic speaker, but he did have the quality of simplifying science in a way that allowed people to understand it without dumbing it down and stripping it of nuance.

Arthur C. Clarke called J. B. S. the most brilliant scientific popularizer of his generation. If you go into the Haldane archives, you’ll see hundreds of letters from regular people with scientific questions, and he would try to answer them. You’ll see newspaper clippings in which the press sought him out for comment on some aspect of science or economics or government policy.

Haldane was a sturdy pillar of the Left in Britain at the time. For a while, he was a card-carrying communist to the extent that MI5 kept a file on him for the better part of two decades. All of this added up to a kind of public profile that was not merely that of a scientist, but also that of a political thinker or a public intellectual — something that we see less often these days.

I think that’s right. I would attribute a lot of this to his father, J. S. Haldane, who was also a scientist. J. S. studied respiration, and he was a professor of physiology at Oxford. Right from the beginning of his own career as a scientist, J. S. seemed to be the kind of man who thought science should improve the lot of people out there in the world: it shouldn’t be confined to an ivory tower or to academic journals. The purpose of doing science was to improve the conditions of regular people.

In his studies on respiration, for example, he used the same principles to examine why coal miners were dying underground, or how being on ships for an extended period of time affected people, or how naval divers could rise from the depths safely without succumbing to the bends. He would go into slums in Dundee and try to measure the air in the tenements and see if it was sensible for people to breathe and live there.

All of this scientific activism, if you will, was informed first of all by a robust background and schooling in the sciences. That was something that J. B. S. had as well. But it was also informed by experiments. J. S. experimented on himself: he would often go out into the field, into mines and into slums, and see what the effect of the air in those places was on his own body.

He took his son along on some of these experimental field trips while he was just a boy. On one occasion, they all went down into a mine and J. B. S. was asked to stand up straight and recite the funeral oration from Julius Caesar. He was a little boy at the time and his head barely grazed the ceiling of the mine shaft. He began speaking, and because the poisonous gases that knocked people out in these mines had risen to the top, he started to feel woozy and had to sit back down.

All of these experiences instilled in J. B. S. a couple of principles. One was the joy and surprise of doing robust science. But there was also the idea that scientists could and should have a social conscience. They should worry about how the working classes of the world could benefit from the kind of science that he and his father ended up doing.

I think he went to World War I still carrying scars from having been at Eton, the public school in Britain, which was famously a place for snobs and the children of snobs from the upper classes. J. B. S. went there just past the age of ten. He was a shy boy, and he was picked upon quite frequently. He witnessed a huge degree of class snobbery around him in the school.

After Eton, he went to Oxford to get a degree, but then he went to the trenches as a soldier. The trenches were a relatively democratic space, at least in the way he saw it. It’s true that several people from well-born and wealthy backgrounds had been commissioned as officers and they supervised many men from the working classes, just as they did back home. But in the trenches, the hierarchies became those of rank rather than those of social class.

If you were a private with a public-school education, you didn’t get any special treatment or undue privileges (or that was how he saw it anyway). In any case, when you’re all sitting around in a cramped trench or coming under fire from the enemy, it’s very difficult to hold onto the distinctions of class. For the first time, J. B. S. found himself to be popular and enjoyed a kind of camaraderie that he hadn’t experienced until then. I think that experience never left him, and it informed his views about the irrelevance of class distinctions that he was to carry for the rest of his life.

He subsequently went to India, where he was on sick leave, and spent a considerable amount of time there. He came back with a sense of the vanity and purposelessness of the imperial project. He said at one point to his mother in a letter that he couldn’t see how long this system could possibly continue. He saw the unfairness of a handful of Englishman ruling a country as vast as India.

It was something that happened back then, although J. B. S. may have belonged to the last generation of nonspecialists. I cannot think of any scientists who came after that and specialized in a particular field without having been schooled in one of the sciences at least, if not in that field itself.

Perhaps there was a kind of Victorian hangover of the gentleman-scientists that persisted into the twentieth century when J. B. S. was at university. His father was a trained scientist, but there were many other people in that era who were amateurs. These were invariably men of privilege and wealth who were able to pursue scientific experiments for the love of it. They often found out things that were useful and that aided the progress of science.

As you mentioned, J. B. S. never studied science at university and never had a science degree, but he had done so much as a boy. He had helped his father and then started working out some genetics problems on his own. He had a great facility with numbers in particular. When he came back from the war and was offered a position in biochemistry at Oxford, it wouldn’t have been out of the ordinary back then, although as I said, he may have been one of the last nonspecialists to have been offered such a position.

Haldane’s own interest came about because of experiments that he ran as a boy, with which his sister Naomi often helped. These were experiments with guinea pigs. The siblings kept them in hutches at their home in Oxford, on the side of a path that ran to the tennis courts, and they would track how the guinea pigs produced and what traits they passed on — the color of their coats, for example, or the length of their fur.

They were watching, as Gregor Mendel did, for dominant and recessive traits — what kind of traits a particular combination of parents produced in the children. Mendel was a monk in what is now Czechia, in the town of Brno. He predated J. B. S. and Naomi by decades, but his work had only been recently rediscovered with great excitement. Mendel ran experiments with peas in which he tracked how parents passed traits onto their offspring, and he built up a tabulated system of how that happened and what that corresponded to in terms of what we now know as genes.

The rediscovery of Mendel in the early 1900s also presented a problem that was developing in genetics at the time. This was what I alluded to earlier. The people who followed Mendel and his theories attributed changes in a species to mutations in the genes. Those changes could be large or small, but they were always what you might call discontinuous.

If a guinea pig was born with an extra toe, for instance, that would be a discontinuous change — it’s discrete. Darwinians thought that small, undetected variations would eventually accumulate over many generations in a population. Eventually they would lead to a kind of fitness for their environment that would help the species thrive. Darwin had famously written that nature doesn’t make jumps.

If you think about height in a population of people, height is a continuous quantity. If you graph it in terms of how tall people are, it’ll follow a natural, continuous bell curve, whereas the followers of Mendel could only ever see jumps. This gap in the theory between Mendel and Darwin threatened to undo the theory of evolution and natural selection altogether.

It was at this point in the 1920s and ’30s that Haldane along with a couple of other scientists helped to yoke the ideas of Mendel and Darwin together. They essentially rescued the idea of Darwinian natural selection. Without getting into the numbers of it, they showed through mathematics that natural selection was a powerful force, capable of selecting even small genetic changes and amplifying them in a population surprisingly quickly. To resurrect the power of natural selection was to validate Darwin’s theory of evolution.

In both the US and the UK at the time, you could see what were definitely eugenic policies. The UK wanted to isolate the feeble-minded, as they called them, and the US wanted to sterilize people it deemed unfit to reproduce. This included not just people who had physiological weaknesses but also those who belonged to what were considered inferior races. All of this was happening throughout the 1920s.

Haldane himself as a very young man carried the prejudices of his class. At one point he wrote about Australian aborigines and said, “I find it hard to believe that their descendants will produce a [James] Watt or [Thomas] Edison.” He wrote several things along those lines when he was very young. But as he grew older, when he was in his thirties, he started to poke holes in these so-called theories of eugenics.

Part of this was simply a question of the scientific invalidity of those theories. For example, scientists had found no way to know which human characteristics would best serve future evolution, and no way to selectively breed them in humans, so obviously there was a huge scientific fallacy at the heart of eugenics. Another such fallacy arose from the fact that in the world of biology, diversity in a population is actually a good thing. It contributes to the overall genetic fitness of a population, because it is only if you have diversity that you can sometimes produce traits that help the population as a whole through natural selection.

The notion of race often bedeviled Haldane and other scientists in that part of the twentieth century because people struggled to understand how such visible physical differences could matter so little. But Haldane soon realized that people’s capacities were shaped by their environment as well as their genes, and that ideas of superiority and inferiority were quite meaningless in comparing humans.

He came to the conclusion that the word “race” as it was used then was very imprecise. He said that the races of the past were not purer than those of today, which is a claim that champions of racial perfection always come back to. Instead of “race,” he started using the term “population group,” which is the more accurate scientific term. We continue to use it today for a distinct set of people or other organisms that display similar characteristics.

That was the scientific platform on which Haldane stood when it came to eugenics. But part of his opposition to the theory was also his developing political sense. The further he went to the left politically, the more he came to realize that theories of eugenics were bound up in right-wing notions of class and imperialism.

Haldane’s primary avenue toward being a public intellectual was his writing. The essay I would recommend first and foremost is called “On Being the Right Size.” It is a concise marvel of the kind of writing we are talking about. The essay is very accessible and deals with a fundamental notion: the question of why our organisms are the size they are and what impact that has on their characteristics.

I think Haldane took his father’s idea that science should enrich the lives of common people one step further. He decided that everybody should be able to appreciate science and understand its basics. For Haldane, a scientifically informed society would be a better (and politically wiser) society.

Another aspect of this was the fact that a lot of his writing, if not all of it, was political in some form or other. The political thrust might not be explicit, although it did become more explicit as the 1930s wore on and World War II started. But very often, there was a sort of political moral at the end of every story that he told.

Sometimes the connections to the science he had just discussed were tenuous. Sometimes those connections were very clear, as the eugenic ideas that we just talked about started to swirl around public debate in the second half of the 1930s, especially as the Nazis rose to power in Germany. He was a loud voice in debunking the theories of blood that the Nazis promoted and by extension the theory of any kind of racial purity.

Haldane was also willing to take sides in the great political battles of the time over socialism and communism. He started off as a socialist and became a communist at some point in opposition to the forces of fascism.

He went out to Spain during the Civil War three times, trying to help and always writing for audiences back home about the things that he was seeing. He wrote about the dehumanization that the fascists were perpetrating on the people he wanted to be allied with — the Left in Spain — and about the weapons that were being used and the imperialist themes running through these conflicts.

All of these points made it into pieces back home. They very often ran in the Daily Worker, which was the publication of the Communist Party of Great Britain [CPGB]. Using that profile for public advocacy in this particular case meant urging people to think about where their loyalties lay and urging them to shun the Right in any country — the Nazis in particular.

We’ve already touched upon how he grew up in a relatively egalitarian household, given the times and his background, and how he found the trenches in World War I to be a relatively democratic space and felt solidarity with people from the working classes. His first wife, Charlotte, had a lot to do with his decision to join. She was a communist herself: in fact, she had joined the party well before him and made no bones about her affiliations. I think that influenced him tremendously.

A trip to the Soviet Union in the late 1920s influenced him as well. It was an odd time at which he went because some of Joseph Stalin’s show trials had already started. But perhaps they hadn’t been publicized quite as much to somebody who was visiting from Britain, didn’t read any Russian, and was taken selectively to particular scientific institutions.

I think one thing that really drew him to the Communist Party was his perception that the Soviet Union was very serious about the role of science in public life and in the uplifting of citizens. He went to Soviet agricultural research institutes and marveled at the resources they had and the facilities they were given.

He was not the only one in Britain at that stage who felt this way. One of his colleagues, J. D. Bernal, did a comparison to see what percentage of GDP the Soviet Union spent on science in relation to Britain. It turned out the Soviet Union outspent Britain handily. For somebody like Haldane, this was evidence of a rational form of governance in which you harnessed the power of science to improve the lives of the people in your country.

As the 1930s wore on, he began to perceive communism as a bulwark against fascism. He wasn’t the only one to see it that way. By the end of the decade, he had traveled and written enough and possessed enough of a public profile that the CPGB felt he would be a great catch. Haldane thought that it would be an act of solidarity against the fascist forces to publicly align himself with the Communists.

It’s difficult to tell at this remove how seriously he took dialectical materialism. There is an anecdote that I included in my book: he was once sent a beautiful new calendar as a gift and he wrote back to the sender saying, “I have only one possible serious criticism of the calendar — it seems a pity to have to tear out the pages of such a beautiful and instructive production — however, I expect this criticism is undialectical.” It’s impossible to tell if he was joking or not!

I think he did persuade himself that dialectical materialism explained the known universe relatively well and he spoke about the subject quite often. In fact, he published an essay in 1937 called “A Dialectical Account of Evolution,” which strained through all kinds of torsions of interpretation to conclude that natural selection falls into the great dialectical triad of thesis, antithesis, and synthesis.

Of course, these categories felt artificially neat, even to him. He may have felt at some point that he was turning the entire structure of dialectical materialism into a convenient pigeonhole for cherry-picked facts. But at the core, I think he never leaned on these principles to do what he would call real science.

The real science was always kept distinct from these essays that he wrote, which were almost entirely a political exercise — an exercise in spreading the Marxist way of thinking and popularizing Marxism as a philosophy. He was investigating some of this stuff for himself and we won’t ever know whether he found it entirely satisfactory. But we do know that in all of his rigorous, published scientific papers, there is no mention of dialectical materialism at all.

Lysenko was a Soviet agronomist. He became one of Stalin’s favorite scientists and was eventually appointed president of the Lenin All-Union Academy of Agricultural Sciences. His interpretation of biology and genetics ran completely counter to everything that scientists in the West (or anywhere else in the world) had previously discovered or proved.

Lysenko believed, for example, that the way genes behave is not random and they don’t change by accident. The body in which the gene is carried has an influence upon the gene itself. If you change the environment around an organism like a stalk of wheat, you will change the genes in it and make it hardier or more productive for the second generation of wheat. He said, “We cannot wait for favors from nature — we must wrest them from her.”

This outlook seems to have been very much of a piece with the Soviet philosophy of taming the natural world to get as much from it as possible in order to improve the lot of the working classes. Lysenko sometimes directly contradicted the things that Haldane had worked on or that he stood for. He rubbished the idea that mathematics or statistics could tell you anything about the way that genes behaved. That was precisely what Haldane worked on for most of his life.

Anybody in the Soviet Union itself who disagreed with Lysenko was ostracized or worse. In the case of Haldane’s acquaintance, Nikolai Vavilov, he was sent off to prison where he would eventually die. Several other people were kicked out of the academic sciences in the Soviet Union, while others disappeared.

In parallel with this, there were disastrous agricultural experiments in the Soviet Union based on Lysenko’s advice, which all failed spectacularly. You have to remember that much of this was happening in the 1940s, by which time Stalinism was well and truly entrenched and people were frequently being sent to the Siberian Gulags.

Lysenko created a climate of fear in the Soviet sciences. No one would be willing to speak out against his highly erroneous theories. Again, that went completely against the grain of Haldane’s thinking. If he championed anything in the sciences, it was the ability to speak the truth about what you found and thought, and to approach science with the so-called scientific temper — a cold, hard, rational look at the facts without any fear of political prejudice.

For decades, there has been a real sense of bewilderment about the way Haldane responded to Lysenko. This is particularly because he famously went on the BBC in the late 1940s and took on three of his scientific colleagues, attempting to defend Lysenko’s scientific theories. For anyone who only had access to that kind of information, it would appear as if Haldane had either subscribed to Lysenkoism wholesale, which seems ridiculous, or had given in to pressure from the Communist Party to defend Lysenko.

The truth is more complex, and a lot of the archival material that I found speaks to this. I think Haldane chose for a year or two to defend Lysenko in print and on radio because he felt that it was an important moment in the history of communism and that by rejecting Lysenko, he would do the party more harm than good. He decided that he would lend his stature to the task of buttressing Lysenko’s reputation and theories for the sake of the greater cause, you might say.

However, in the background, he was writing to his colleagues in the CPGB all the time, arguing that the party had to distance itself from Lysenko. He had furious arguments with people in the party on this point. After the Lysenko episode, the reason that he distanced himself from the CPGB was in part because he had burned so many of these bridges. He was quite upset with the way in which his colleagues in the party refused to stand by him or think like rational scientists, which was his model of thinking.

I think he did change his broader perspective on how the Soviet Union worked as well. But there’s no evidence of him rethinking his view of Stalin in private. I didn’t find anything in letters or diaries that indicated he had changed his mind about Stalin himself.

Somewhat disgracefully, I think, toward the end of his life, he gave the following answer when somebody asked about his perception of Stalin: “I thought and think that he was a very great man who did a very good job and as I did not denounce him then, I am not going to do so now.” I struggled for a long time to make sense of this and to figure out if it was one last show of public loyalty toward communism or the cause of the Left, or whether it was just an example of stubbornness and unwillingness to accept that he had made a mistake.

By the time he said this, the details of Stalin’s massacres, starvations, and penal colonies were well known, and yet it seemed as if he wanted to keep ammunition out of the hands of the critics of the Soviet Union. That might have been the last thing he ever said or wrote about Stalin. But I think disillusionment with the Soviet Union did set in, and one result of that was his move to India in the final phase of his life.

We know that he quit the CPGB at some point after the Lysenko affair, although we don’t know exactly when. He refused to confirm his departure to reporters who asked him about it. But I think it’s clear that he was disillusioned with the way that the party had behaved around Lysenko. Perhaps he felt that he couldn’t continue to be a public figure in British life while speaking up for the party and the cause.

There were other reasons, too. University College London, where he was a professor at the time, was in quite straightened circumstances after the war. Some of the buildings had been demolished, and they had so few resources that Haldane himself had to buy teaspoons for the staff room where his lab was based.

At this point, an offer came from a university in India promising the kind of resources, students, and pace of work that he was seeking now that he was quite old. His own finances in Britain were also quite straitened: he was paying alimony, and he was often in the red. His bank statements are still in the National Archives, so you can look them up and see that he was in the red month after month. This was frequently because he was paying for lab equipment and other expenses related to work out of his own pocket because the university wasn’t able to cover the costs.

He had got married for a second time and the university in India offered his wife Helen a position there as well, which was something that he wanted. He had been to India before, and he liked the country. He admired Jawaharlal Nehru, who was the Indian prime minister at the time. India might also have offered Haldane an alternative socialist model to the Soviet Union, a model in which the country was democratic but there was a strong welfare state.

Nehru himself was a huge advocate of science and technology and its role in public life, which was something that Haldane championed. Politically, he was very attracted to the Nehruvian idea of India, and it must have been a welcome relief from having to defend the Stalinist ideal of the Soviet Union.

I’m not sure that they consciously looked to Haldane, or at least I have found no evidence thus far that they did. They were very popular, lucid writers about science for the general public. But I think the uniqueness of Haldane lay in his willingness to stake out a political position almost every time he wrote about science.

I have read a lot of Stephen Jay Gould, and of course you could make the argument that all writing about science (or indeed anything) is political, and therefore that politics is implicit in every piece of work that you do. But what Haldane did, which writers like Sagan or Gould perhaps didn’t, was to relate science (or anything else he was writing about) to the political issues of his age.

It was a form of writing that was extremely partisan, in a good way. We might expect that approach today from political scientists, but not from biologists, physicists, or chemists. That culture faded as the twentieth century progressed. C. P. Snow famously wrote about this tendency for the sciences and the humanities to exist in different worlds, not speaking to one another.

It’s difficult to generalize because it was a different time. The fact that Haldane didn’t formally study science at university helped him to be a broader writer who could combine science with ideas about how society and politics worked. That formative background enabled him to become the kind of person that he was.

Scientists today begin specializing from a very early stage in their lives and careers. There are children in high school who start interning with scientists for the eventual career that they want to have fifteen years later once they have finished their PhDs. Of course, that greater degree of specialization is a symptom of how science has developed. There’s so much more to master in a particular field that you need to start studying it earlier in order to be able to make meaningful contributions.

It’s not that scientists today can look at Haldane’s life and aspire to mimic every aspect of it. Some of the exigencies of modern science and the modern era definitely weigh upon them. But having said that, when I was writing my epilogue, it was around the time that Donald Trump had been elected in the US and the March for Science was starting to take off in cities around the world. I remember thinking to myself that it was a shining example of scientists raising a public voice in a way that had only happened sporadically earlier.

It might have happened with climate scientists like James Hansen, for example, being loud and vociferous when arguing about the dangers of climate change. But it hadn’t happened in the realm of politics that confronts everyday life and society. I think Haldane made it a specialty of his own to speak to precisely those situations.

We should also remember the insistence of Haldane (and his father) that science shouldn’t transpire entirely in laboratories, ivory towers, or academic journals. They insisted that scientists should reach out to ordinary people and try to communicate important aspects of science in accessible terms, but also that they should constantly think about how science could relate to the problems of the working classes and the problems of society.

That is linked to the point about raising your voice in a political space — those two things go hand in hand. Haldane realized that science doesn’t exist in a vacuum. Science is always impacted by politics, so it should push back against politics as well.