Jonathan Kennedy, Pathogenesis: A History of the World in Eight Plagues (2023)

The first 90% of this book is scintillating, the final 10% perplexing and disappointing. Kennedy's work aims to update William McNeill's pioneering 1976 work on the interplay between people and germs, Plagues and Peoples. Five decades ago, we simply didn't know much about ancient plagues. In the intervening years, the revolutionary growth of biological knowledge, especially the sequencing of contemporary and ancient genomes, has put us on much more secure ground. Kennedy begins by making a plausible case for a revolution in our thinking about human history: just as Copernicus and Darwin (and perhaps Freud) decentered man, our increasing understanding of microbes should now do the same. Humans don't make history on their own (even in circumstances not of their choosing a la Marx) - humans and microbes (bacteria and viruses) together make history. After all, the number of bacteria in each of us is apparently about the same as the number of "our own" cells. These bacteria attack us occasionally, of course; they help us digest food; and they play a role apparently in modulating our moods. Their even more numerous cousins, viruses, have become incorporated in our DNA. Who am I, indeed! Kennedy doesn't spend much time on microbes' role in influencing out behavior (perhaps for the reasons David Reich gave - see previous post) and instead focuses on their role as agents of destruction. He makes plausible arguments that microbial diseases have played a much more decisive role in turning points in human history: the triumph of homo sapiens over other humans, such as Neanderthals, Denisovans, and the Hobbits of Flores; the displacement by early Indo-Europeans of neolithic farmers in Europe; the Europeans' preference for African slaves rather than European indentured servants. These first 90% of the book changes my picture of big history in major ways. Then we get to the last part of the book. Kennedy barely mentions the breakthrough due to the germ theory of disease, the development of antibacterial and antiviral drugs, and the exponential growth of biotech thanks to genetic manipulation. He discounts the role of medicine and rising living standards in improving health. Instead, he claims, improvements all due to political commitments to public health. I wish he had consulted Angus Deaton's magisterial The Great Escape. In his coverage of the last 150 years, Kennedy focuses on politics, especially baleful political decisions made by "neoliberal" leaders. Bizarrely, in a book about plagues, he switches from microbial to lifestyle diseases. In the end, he suggests, most people today live in "what must feel more like a dystopia" (226). All in all, this last section seemed like it was shaped by what I take to be Kennedy's political commitments. It's a perplexing ending to what otherwise is a thought-provoking, persuasive book.

David Reich, Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past (2018)

This is a fascinating look at the new science of ancient DNA by one of the field's pioneers. In the 1980s the female mitochondrial and male Y chromosomes were first sequenced, followed in 2001 by the entire genome. 2010 was the breakthrough year for ancient DNA when Svante Paabo and colleagues at the Max Planck Institute in Leipzig first sequenced ancient Neanderthal DNA. Five years later, Reich's lab at Harvard built on Paabo's work to "industrialize" the sequencing of ancient DNA: by now thousands of ancient individuals' DNA going back more than 50,000 years and including "modern humans," Neanderthals, and species newly discovered by these techniques, including Denisovans and Homo Floriensis ("Hobbits"), have been analyzed. Interestingly, Reich says that the sequencing of the whole genome has not yet shed much light on the genetic sources of behavior. Given the fact that usually dozens of genes contribute to individual behaviors, Reich admits, it may never do so. However, whole genome sequencing, including of ancient individuals, has made a major, indeed revolutionary, contribution to the understanding of the deep human past. Reich thinks this revolution is so fundamental that is best grasped not by comparison with the dedoding of DNA by Crick and Watson in 1953; rather, it's more like the invention of the microscope in the seventeenth century: a whole new world is coming into view, much of it at odds with previously held theories. The mixing of modern humans and Neanderthals turns out to be much more complex than previously thought. Several "ghost populations" - no longer extant but the source of some contemporary populations - can be identified. A much more detailed, and radically new, picture of the peopling of Europe, India, the Americas, and East Asia has become possible. For example, ancient DNA has settled the debate about the origin of the earliest Indo-Europeans - they came from the Pontic steppe, not Anatolia. As they spread to the west, they merged with neolithic farming population, who in turn had merged with indigenous hunter-gatherers. The precise contribution of these three source-populations to contemporary Europeans can be measured. Something similar happened in India, where Reich's techniques have allowed him to identify the emergence of numerous endogamous populations - castes - starting around 2,000 years ago. Four distinct waves settled the Americas, one of which, however, remains hard to pin down. As Reich repeatedly acknowleged, ancient DNA is a rapidly developing field. Many of the results he included in his 2018 book will now have been modified, overturned, or superceded.

Eric Kandel, In Search of Memory: The Emergence of a New Science of Mind (2006)

Kandel won the 2000 Nobel prize in physiology for his pioneering work on the neurobiology of memory. In this fascinating scientific autobiography, Kandel takes us from his early years in 1930s Vienna to his Nobel prize and beyond. Kandel explains the cellular and molecular science very lucidly, so that this layman only felt he got lost in the details a few times. Kandel's big contribution was to prove that short-term memory depends on chemical changes - increasing the flow of neurotransmitters at the synpapses between neurons - while long-term memory depends on structural changes - adding dendritic connections between neurons. The three key conditions Kandel examines here, inspired by early behaviorists such as Pavlov, are habituation, sensitization, and classical conditioning (all of which he, as usual, explains very clearly). In his 60s and 70s Kandel turned from this foundational work on implicit memory to the more complex topic of explicit memory, which depends on attention and, Kandel suggests, spatial awareness. Kandel also reflects on the skills, choices, collaborations, and serendipity that propelled him to the heights of the scientific world. Through his college years (at Harvard), Kandel was focused on historical questions, writing an honors thesis on different intellectuals' accounts of the Nazi menace that had chased Kandel's family from Europe. A college romance with the daughter of prominent Austrian-Jewish psychoanalysts piqued his interest in the mind and a possible career in psychiatry. However, early on this new path, under the influence of a different mentor, Kandel made a pivotal decision. Trying to pinpoint the biological substrates of the id, ego, and superego, as Kandel hoped to do, was too grandiose; instead, he should focus on the individual neuron. This "radical reductionism," as Kandel calls it, served him very well indeed! Beyond the science of memory and his account of his career, Kandel includes glimpses of him as a person: his lifelong interest in high culture and Bildung, his love-hate relationship with Vienna, which led him in later years, when he was raised to great prominence by his accomplishments, to pressure Austrian politicians and institutions finally to reckon with their country's past.