Tom (as he was known to everyone) Johnson died February 22, 2026, age 77. An underappreciated pioneer in the genetics of aging, perhaps his most significant scientific achievement was the discovery in 1988 that mutations in a single gene that he named age-1, could lengthen C. elegans life by up to 50% [1]. He later demonstrated that it did so by slowing the rate at which mortality increases with age [2]. At the time, few researchers in the field (including one of us, SNA) believed that altering only one gene could have such far-reaching effects on aging. It was only after Cynthia Kenyon discovered a second worm longevity gene, daf-2, some 5 years later [3] that skeptics were quieted, and when Gary Ruvkun determined that both genes were in the insulin/IGF signaling pathway [4], that the significance of Tom’s original finding was truly appreciated.

Tom was largely responsible for the surge of interest in nematode longevity genetics after a clever dissection of the heritability of longevity even in a controlled laboratory environment [5]. This publication may be considered the “Watson and Crick” of nematode longevity genetics. Subsequently, Tom and co-authors analyzed mortality rates of age-1 and other mutants that increased mean lifespans with less impact on the maximum [1, 2]. These findings influenced discussions of genetics in human lifespans.

Characteristic of Tom’s broad view of the field, he was the first to notice that all or nearly all long-lived worm mutants were also resistant to multiple stresses. This observation led to a collaboration with one of us (SNA) and George M. Martin to discover that the association of increased longevity and stress resistance was not just a worm phenomenon but was general across multiple species [6].

The stochasticity of aging came to be a major shared interest between Tom and Finch. After Kirkwood and Finch theorized at book length that there was an irreducible stochasticity of lifespan [7], Tom followed up with some mechanistic validation of the idea [8]. In Career Retrospective: Tom Johnson-Genetics, Genomics, Stress, Stochastic Variation, and Aging [9], the authors describe experiments showing that individual worm variation of gene expression predict lifespan, in this case for twofold variations of hsp-16.2 heat-shock protein. These exacting experiments laid the foundation for future biophysical analysis of these variations in receptor protein levels arising from Brownian motion of thermodynamics and showed how organisms still maintain physiological coherence. Characteristically modest is Tom’s statement in Acknowledgements: “I (T.E.J.) wish to acknowledge all the authors of this Retrospective, especially Alex Mendenhall, for their efforts. They have been responsible for putting it together. In addition, there are all the authors of the individual papers who did the work. They deserve the real credit”. True enough, but Tom gave the conceptual leadership.

Not all of Tom’s scientific contributions used C. elegans as a model. He had a parallel career in mouse biology. Much of that career was not related to the biology of aging, but some was. His two papers with recombinant inbred mouse strains in collaboration with Jim Nelson’s lab were instrumental in revealing that the magnitude and direction of life- and health-extending effects of murine dietary restriction depended on genetic background [10, 11], a finding of significance for humans thinking of radically restricting their own caloric intake.

He contributed to the field in many ways in addition to his groundbreaking genetic discoveries. He served many roles in the Gerontological Society of America and served on numerous editorial boards. He was Editor-in-Chief of Experimental Gerontology (2008–2011), chaired a Gordon Conference and co-organized (with Finch) a Keystone symposium on the Molecular Biology of Aging.

Tom had a special affiliation with the American Aging Association having served on its Board of Directors as early as 1991. He also served on AGE’s Executive Committee as its President and, in 2010, received its Denham Harman Research Award. Importantly, the mentees that his lab produced have gone on to have their own major impacts on the field.

Talking with Tom was always great fun. He introduced one of us (SNA) to worm biology and provided for decades a sounding board for ideas having to do with the evolutionary biology of aging, something that he took seriously when few in the field did. Finch interacted with Tom for five decades. They first met in the mid-1980s at Gordon Conferences and hit it off immediately. When Tom joined UC Irvine as tenure-track Assistant Professor, his lab and the Finch lab exchanged visits. They often discussed the Gompertz model of exponentially accelerated mortality during aging. Finch cited Tom’s age-1 mutant studies in his 1990 book [12], which was a broad comparative analysis of mortality rate acceleration across the tree of life. In 1990, Tom’s analysis of worm mortality rate kinetics and Finch’s analysis of human populations were published back-to-back in Science [2, 13].

His passing signals a great loss for geroscience and a personal loss for both of us.