What does it mean to be “you”? It’s the kind of question you’d expect from a philosopher, maybe even a poet, but probably not from an immunologist. In Lousy Sex: Creating Self in an Infectious World, Gerald Callahan, an immunology professor at Colorado State University, takes that question and runs with it. Callahan tackles this through the sex lives of wood lice, how a bacterial infection impacted the genius of Beethoven, and the quiet resilience of his intersex friend. The result is a book that is part scientific essay, part memoir, and part meditation on what it means to exist as a “self” in this ever-evolving world of contradictions.
Take, for instance, the staggering proportion of bacterial cells we carry; the sheer mass of microbial life within us begs the question: how do we differentiate ourselves from our “microbial-selves”? Callahan is a master of comparisons; visualizing the bacterial mass on this planet in terms of the size of countries and airplanes makes these numbers tangible and, frankly, humbling. But these “fun facts” are not just used for their shock factor; he weaves this realization into a broader philosophical inquiry. The immune system, he argues, is not just a defense mechanism; it is the arbiter of identity, the biological machinery through which we define “I” versus “not I. For anyone who has ever read an immunology textbook, the concept of “self” versus “non-self” is quite simple – our immune system recognizes molecular markers on our own cells and attacks anything that doesn’t carry them. By layering philosophical reflection onto the biology, Callahan transforms a technical concept into a profound thought experiment, inviting readers to think beyond the boundaries of what we can measure.
The book is structured as a series of interconnected essays, organized loosely into three sections: origins, middles, and endings. Within each, Callahan oscillates between scientific exposition, autobiographical vignette, and narrative detour. It is an ambitious structure, and it doesn’t always land cleanly. The back-and-forth between a factual account of, say, geophagy (the practice of eating soil), and a personal anecdote can feel disorienting on a first read. The section on geophagy is full of genuinely surprising details, but it circles the same point for too long without clearly tethering itself to the overarching theme of “self.”
And yet, there is something to be said for this layered, occasionally meandering approach. The connections between Callahan’s stories are not always immediately obvious, and that may be by design. There is a sense that certain juxtapositions are meant to resonate on a level below the strictly logical. A second reading might well reveal patterns that the first obscured. In this way, the book mirrors its own thesis: identity is not a single, tidy thing. It is layered, chimeric, and sometimes contradictory.
The book truly shines in several standout passages, and I would read it again just for these. The chapters describing the sex of various animal species were truly captivating. For instance, clownfish change their sex in response to changes in social hierarchy, and turtles acquire sex because of changes in their environment. Callahan handles the broader implications of thinking about gender fluidity in nature with both scientific precision and genuine care. The story of his friend, Lisa May, born intersex through tetragametic chimerism (where two embryos fuse into one), and navigating life through identities imposed by others, is perhaps the most powerful section of the entire book. Callahan writes about her with such empathy that you cannot help but sit with the question she embodies: if biology does not give us a fixed self, then who decides who we are?
The passages on multiple sclerosis (MS) are deeply moving. Callahan draws on his mother’s experience with the disease to illustrate what happens when the immune system’s sense of self goes awry and the body begins to attack itself. It is a moment where the personal and the scientific converge powerfully, and immunologists will especially appreciate how viscerally it captures the consequences of immune dysregulation. The paragraphs that detail how, in MS, one loses not only a sense of their immunological self, but their personality, their social self, and their philosophical self, are genuinely heartbreaking.
Then there is the titular “lousy sex” chapter on wood lice and the Wolbachia bacterium, which I found mind-blowing. The bacterium is an intracellular parasite that can skew wood louse reproduction upon infection, causing the louse host to produce overwhelmingly female offspring. This is a mastermind strategy for the bacterium’s propagation, since the nefarious bacterium evolved to survive in the ample cell space of the females’ eggs and needs female hosts to propagate. It is the kind of story that makes you rethink what “control” even means in biology.
Similarly, given the neuropsychological impact of syphilis, the suggestion that the bacterium played some role in shaping some of Beethoven’s symphonies is the sort of provocative, slightly outrageous claim that Callahan handles well, presenting it not as fact, but as a thought worth entertaining.
Lousy Sex is not a perfect book. Its unconventional structure will frustrate readers who prefer a linear argument, and not every narrative detour earns its place. But it is a witty, stimulating, and surprisingly moving one. For immunologists, it offers a fresh lens on concepts as foundational as self versus non-self, autoimmunity, and thymic selection: ideas we think we know well. For everyone else, it offers a doorway into one of biology’s most fundamental questions, told through stories strange, sad, and wonderful enough to keep you turning pages.
Callahan writes with the precision of a scientist and the sensibility of a storyteller, justifying his cross-appointment at the Department of Microbiology, Immunology and Pathology, as well as the Department of English. Callahan passed away in 2020. That a book so deeply concerned with the fragility and persistence of selfhood should outlive its author feels, in a way, like one final illustration of his thesis. He would probably want you to read it anyway, if not for the deeply moving anecdotes, then perhaps for the “lousy sex,” Beethoven’s bacterium, and the gloriously weird biology of being our “self.”
Manjula Kamath
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