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categories: ["longevity", "foundations"]categories: ["longevity", "foundations"]tags: ["aging", "biogerontology", "mechanisms", "damage", "geroscience"]tags: ["aging", "biogerontology", "mechanisms", "damage", "geroscience"]summary: "The consensus taxonomy of cellular and molecular processes held to drive mammalian aging, set out as nine mechanisms in 2013 and expanded to twelve in 2023."summary: "The consensus taxonomy of cellular and molecular processes held to drive mammalian aging, set out as nine mechanisms in 2013 and expanded to twelve in 2023."updated: "2026-07-27"updated: "2026-10-29"humanEvidence: "No hallmark has been shown to satisfy the framework's third criterion in humans; the amelioration results come from worms, flies and mice, and the human data are observational and correlational."humanEvidence: "No hallmark has been shown to satisfy the framework's third criterion in humans; the amelioration results come from worms, flies and mice, and the human data are observational and correlational."issues: ["The mortality-doubling-time figure in the keyfacts block carries no source.", "The Outlook refers to prizes and consortia defining outcome measures without naming any."]issues: ["The mortality-doubling-time figure in the keyfacts block carries no source.", "The Outlook refers to prizes and consortia defining outcome measures without naming any."]------lines 39–50 → 39–5025 unchanged lines not shown
## Overview## Overview Human mortality rises close to exponentially with adult age; the annual probability of death roughly doubles every eight years, a regularity described by Benjamin Gompertz in 1825. Beneath that curve sit thousands of measurable changes — shorter telomeres, stiffer arteries, fewer functional stem cells, higher circulating interleukin-6, drifting DNA methylation. The hallmarks framework reduces that inventory to a set of processes that are general across tissues, conserved across mammals, and at least arguably actionable.Human mortality rises close to exponentially with adult age; the annual probability of death roughly doubles every eight years, a regularity described by Benjamin Gompertz in 1825. Beneath that curve sit thousands of measurable changes: shorter telomeres, stiffer arteries, fewer functional stem cells, higher circulating interleukin-6, drifting DNA methylation. The hallmarks framework reduces that inventory to a set of processes that are general across tissues, conserved across mammals, and at least arguably open to intervention. The framework does two jobs. It supplies a common vocabulary for a field that had spent decades arguing between rival single-cause theories. It also supplies a target list: most academic programmes and companies in the [[geroscience-hypothesis|geroscience]] sector map their work onto one or more hallmarks, and reviewers treat hallmark membership as prima facie evidence that a mechanism matters. That adoption is itself a fact about the field. The hallmarks are less a discovery than a coordination device that worked.The framework gives a common vocabulary to a field that had spent decades arguing between rival single-cause theories. It also gives the field a target list. Most academic programmes and companies in the [[geroscience-hypothesis|geroscience]] sector map their work onto one or more hallmarks, and reviewers treat hallmark membership as prima facie evidence that a mechanism matters. That adoption is itself a fact about the field: the hallmarks have succeeded less as a discovery than as a way of coordinating research. > [!note] Terminology> [!note] Terminology> "Hallmark" is borrowed from oncology, where Hanahan and Weinberg used it for capabilities a cell must acquire to become malignant.[^hanahan2000] The analogy is imperfect: cancer hallmarks describe what a tumour must do, while aging hallmarks describe what happens to an organism whether or not anything is required of it.> "Hallmark" is borrowed from oncology, where Hanahan and Weinberg used it for capabilities a cell must acquire to become malignant.[^hanahan2000] The analogy is imperfect. Cancer hallmarks describe what a tumour must do; aging hallmarks describe what happens to an organism, with no requirement that anything be achieved. ## Origins## Origins lines 62–111 → 62–11511 unchanged lines not shown
## What counts as a hallmark## What counts as a hallmark The 2013 paper set three criteria. A hallmark should manifest during normal aging; its experimental aggravation should accelerate aging; and its experimental amelioration should retard aging and extend healthy lifespan. The first criterion is easy — a great many things change with age. The second is harder but tractable, since almost any biological system can be broken in a way that produces a short-lived, sickly animal. The third carries nearly all the weight, and it is where the evidence thins.The 2013 paper set three criteria. A hallmark should manifest during normal aging; its experimental aggravation should accelerate aging; and its experimental amelioration should retard aging and extend healthy lifespan. The first criterion is easy to meet, because a great many things change with age. The second is harder but tractable, since almost any biological system can be broken in a way that produces a short-lived, sickly animal. The third carries nearly all the weight, and there the evidence thins. Nearly every amelioration result comes from short-lived laboratory organisms: *Caenorhabditis elegans*, *Drosophila*, and inbred or genetically heterogeneous mice. No hallmark has been shown to satisfy the third criterion in humans, for the simple reason that no intervention has been demonstrated to slow human aging. Establishing that would require either a multi-decade mortality trial or a surrogate endpoint that regulators accept, which is the problem the field of [[aging-biomarkers|aging biomarkers]] exists to solve.Nearly every amelioration result comes from short-lived laboratory organisms: *Caenorhabditis elegans*, *Drosophila*, and inbred or genetically heterogeneous mice. No hallmark has been shown to satisfy the third criterion in humans, because no intervention has been demonstrated to slow human aging. Showing that would take either a multi-decade mortality trial or a surrogate endpoint that regulators accept, the problem the field of [[aging-biomarkers|aging biomarkers]] exists to solve. A second difficulty is that accelerating aging and causing disease look alike from outside. Progeroid syndromes — Werner syndrome from *WRN* mutations, Hutchinson–Gilford progeria from the *LMNA* variant that produces progerin — recapitulate some features of aging and omit others. Patients with progeria develop severe atherosclerosis but not the cancer or dementia risk of ordinary old age. Whether such syndromes are accelerated aging or a distinct pathology that mimics it remains disputed.A second difficulty is that accelerating aging and causing disease look alike from outside. Progeroid syndromes, such as Werner syndrome from *WRN* mutations and Hutchinson-Gilford progeria from the *LMNA* variant that produces progerin, recapitulate some features of aging and omit others. Patients with progeria develop severe atherosclerosis but not the cancer or dementia risk of ordinary old age. Whether such syndromes are accelerated aging or a distinct pathology that mimics it remains disputed. ## The twelve hallmarks## The twelve hallmarks The 2013 paper sorted the hallmarks into three tiers by causal position, and the 2023 revision kept the scheme.The 2013 paper sorted the hallmarks into three tiers by causal position, and the 2023 revision kept the scheme. ```figure{"key": "hallmarks-nine-diagram", "caption": "The original nine hallmarks of the 2013 paper, redrawn in a 2018 review. The 2023 revision added disabled macroautophagy, chronic inflammation, and dysbiosis, bringing the list to twelve."}``` ### Primary hallmarks: damage### Primary hallmarks: damage These are unambiguously deleterious processes that accumulate. **Genomic instability** covers nuclear point mutations, structural variants, and somatic mosaicism, together with damage to mitochondrial DNA. **Telomere attrition** is treated separately because the [[telomeres-and-telomerase|end-replication problem]] gives it a distinct mechanism and a distinct relationship to cancer. **Epigenetic alterations** include DNA methylation drift, histone modification changes, and loss of heterochromatin, the changes that the [[epigenetic-clock|epigenetic clocks]] built by [[steve-horvath]] and others measure. **Loss of proteostasis** is the failure of the chaperone, proteasome and lysosomal machinery that keeps the [[proteostasis|proteome]] folded and turned over. **Disabled macroautophagy**, added in 2023, separates the [[autophagy|autophagic]] arm of that system into its own hallmark on the grounds that it declines with age across tissues and that genetically raising it extends lifespan in several model organisms — an epistatic and gain-of-function argument in animals, not a demonstration that autophagy can be restored in an aged human.These are processes that accumulate and are unambiguously harmful. **Genomic instability** covers nuclear point mutations, structural variants, and somatic mosaicism, together with damage to mitochondrial DNA. **Telomere attrition** is treated separately because the [[telomeres-and-telomerase|end-replication problem]] gives it a distinct mechanism and a distinct relationship to cancer. **Epigenetic alterations** include DNA methylation drift, histone modification changes, and loss of heterochromatin, the changes that the [[epigenetic-clock|epigenetic clocks]] built by [[steve-horvath]] and others measure. **Loss of proteostasis** is the failure of the chaperone, proteasome and lysosomal machinery that keeps the [[proteostasis|proteome]] folded and turned over. **Disabled macroautophagy**, added in 2023, separates the [[autophagy|autophagic]] arm of that system into its own hallmark on the grounds that it declines with age across tissues and that genetically raising it extends lifespan in several model organisms. That is an epistatic and gain-of-function argument in animals, not a demonstration that autophagy can be restored in an aged human. ### Antagonistic hallmarks: responses that turn harmful### Antagonistic hallmarks: responses that turn harmful These begin as protective and become damaging when chronic or excessive. **Deregulated nutrient sensing** covers the insulin/IGF-1 axis that [[cynthia-kenyon|Cynthia Kenyon's]] worm genetics opened up, along with mTOR, AMPK and the sirtuins — signalling that reports abundance and, when persistently activated, suppresses maintenance. It is the node that [[caloric-restriction|dietary restriction]], [[rapamycin]] and [[nad-precursors|NAD⁺ precursors]] all address from different directions. **[[mitochondrial-dysfunction|Mitochondrial dysfunction]]** describes falling respiratory capacity, altered dynamics and impaired quality control. **[[cellular-senescence|Cellular senescence]]** is a stable proliferative arrest that suppresses tumours in youth and, through the secretory phenotype of accumulated senescent cells, degrades tissue in age.These begin as protective and become damaging when chronic or excessive. **Deregulated nutrient sensing** covers the insulin/IGF-1 axis that [[cynthia-kenyon|Cynthia Kenyon's]] worm genetics opened up, along with mTOR, AMPK and the sirtuins: signalling that reports abundance and, when persistently activated, suppresses maintenance. It is the node that [[caloric-restriction|dietary restriction]], [[rapamycin]] and [[nad-precursors|NAD⁺ precursors]] all address from different directions. **[[mitochondrial-dysfunction|Mitochondrial dysfunction]]** describes falling respiratory capacity, altered dynamics and impaired quality control. **[[cellular-senescence|Cellular senescence]]** is a stable proliferative arrest that suppresses tumours in youth and, through the secretory phenotype of accumulated senescent cells, degrades tissue in age. ### Integrative hallmarks: the phenotype### Integrative hallmarks: the phenotype These are the level at which the organism visibly ages. **[[stem-cell-exhaustion|Stem cell exhaustion]]** is the decline of regenerative capacity in blood, muscle, gut and skin. **Altered intercellular communication** covers endocrine, neuronal and immune signalling changes, including the systemic factors studied in parabiosis. **Chronic inflammation**, added in 2023, formalizes [[inflammaging]] as its own hallmark rather than a subtype of communication failure. **Dysbiosis**, also added in 2023, is the least settled of the twelve; the human microbiome changes with age, but whether those changes cause anything is largely untested outside germ-free and gnotobiotic mice.At this level the organism visibly ages. **[[stem-cell-exhaustion|Stem cell exhaustion]]** is the decline of regenerative capacity in blood, muscle, gut and skin. **Altered intercellular communication** covers endocrine, neuronal and immune signalling changes, including the systemic factors studied in parabiosis. **Chronic inflammation**, added in 2023, formalizes [[inflammaging]] as its own hallmark rather than a subtype of communication failure. **Dysbiosis**, also added in 2023, is the least settled of the twelve; the human microbiome changes with age, but whether those changes cause anything is largely untested outside germ-free and gnotobiotic mice. ## Evidence and use## Evidence and use The strongest support for the framework is indirect: interventions aimed at individual hallmarks extend lifespan in mice, and several do so in genetically heterogeneous mice tested in parallel at multiple independent sites through the National Institute on Aging's Interventions Testing Program. That programme was designed to filter out the single-laboratory, single-strain results that had littered the earlier literature, and its positive findings — rapamycin most robustly, along with acarbose, 17-α-estradiol and canagliflozin, the latter two with effects reported only in males — act mostly on nutrient sensing and metabolic signalling. [[senolytics|Senolytic]] clearance of senescent cells improves physical function in aged mice, and transient expression of reprogramming factors reverses several molecular markers of age in mouse tissues, the approach pursued at scale by [[epigenetic-reprogramming|reprogramming]] companies.The strongest support for the framework is indirect: interventions aimed at individual hallmarks extend lifespan in mice, and several do so in genetically heterogeneous mice tested in parallel at multiple independent sites through the National Institute on Aging's Interventions Testing Program. That programme was designed to filter out the single-laboratory, single-strain results that had littered the earlier literature. Its positive findings act mostly on nutrient sensing and metabolic signalling: rapamycin most robustly, along with acarbose, 17-α-estradiol and canagliflozin, the latter two with effects reported only in males. [[senolytics|Senolytic]] clearance of senescent cells improves physical function in aged mice, and transient expression of reprogramming factors reverses several molecular markers of age in mouse tissues, the approach pursued at scale by [[epigenetic-reprogramming|reprogramming]] companies. None of this has yet produced a human result showing slowed aging rather than improved disease-specific endpoints. The human evidence is almost entirely observational and correlational: methylation-based age estimates predict mortality after adjustment for chronological age, senescent-cell markers rise in aged tissue, and inflammatory markers track frailty. Correlations of that kind are consistent with the hallmarks being causes and equally consistent with their being downstream readouts of something else. The framework is also used prescriptively in a way its authors did not license, as a checklist against which consumer testing panels and [[dietary-supplements|supplement formulations]] are marketed.None of this has yet produced a human result showing slowed aging rather than improved disease-specific endpoints. The human evidence is almost entirely observational and correlational: methylation-based age estimates predict mortality after adjustment for chronological age, senescent-cell markers rise in aged tissue, and inflammatory markers track frailty. Correlations of that kind fit the hallmarks being causes, and fit equally well with their being downstream readouts of something else. The framework is also used prescriptively in a way its authors did not license: as a checklist against which consumer testing panels and [[dietary-supplements|supplement formulations]] are marketed. > [!caution] Contested> [!caution] Contested> Hallmark membership is not a causal weighting. The framework says which processes belong on the list; it does not say which contribute most to mortality, in what order they act, or which would be worth intervening on first. Several authors argue this is the framework's central omission rather than a detail to be filled in later.> Membership of the list carries no causal weighting. The framework says which processes belong on the list, but not which contribute most to mortality, in what order they act, or which would be worth intervening on first. Several authors argue that this is the framework's central omission, not a detail to be filled in later. ## Criticism## Criticism The most sustained critique is that the hallmarks are a taxonomy presented as a theory. Gems and de Magalhães argue that the framework restates the damage-and-maintenance view of aging in new packaging while remaining agnostic on whether each hallmark is a cause, a consequence, or an adaptive response, and that this agnosticism makes it hard to falsify.[^gems2021] Because the hallmarks are heavily interdependent — senescent cells drive inflammation, inflammation impairs stem cell function, impaired stem cell function increases senescent burden — assigning causal priority from the list alone is not possible.The most sustained critique is that the hallmarks are a taxonomy presented as a theory. Gems and de Magalhães argue that the framework restates the damage-and-maintenance view of aging in new packaging while remaining agnostic on whether each hallmark is a cause, a consequence, or an adaptive response, and that this agnosticism makes it hard to falsify.[^gems2021] The hallmarks are also heavily interdependent. Senescent cells drive inflammation, inflammation impairs stem cell function, and impaired stem cell function increases senescent burden, so the list alone cannot assign causal priority. A related objection concerns list inflation. The inclusion criteria are permissive enough that many age-associated processes qualify, and candidate hallmarks have accumulated in the literature faster than the canonical list has been revised.[^schmauck2022] If the list grows whenever a new mechanism is characterized, it functions as an index of active research areas rather than a constraint on theory.A related objection concerns list inflation. The inclusion criteria are permissive enough that many age-associated processes qualify, and candidate hallmarks have accumulated in the literature faster than the canonical list has been revised.[^schmauck2022] A list that grows whenever a new mechanism is characterized works as an index of active research areas, not as a constraint on theory. Alternative frameworks reject the damage-centric premise. Blagosklonny's hyperfunction theory holds that aging is not damage accumulation but the continued, unregulated running of developmental growth programmes after they are needed, with mTOR as the principal driver.[^blago2006] On that account senescence and hypertrophy are the disease, and damage is downstream. A complex-systems view argues that aging emerges from the loss of homeostatic regulation across networks and is not decomposable into discrete mechanisms at all.[^cohen2022] [[sens-research-foundation|SENS]], the damage-repair programme associated with [[aubrey-de-grey]], predates the hallmarks and organizes aging into seven categories of accumulated damage on the argument that repair is more tractable than metabolic modulation.Alternative frameworks reject the damage-centric premise. Blagosklonny's hyperfunction theory holds that aging is the continued, unregulated running of developmental growth programmes after they are needed, with mTOR as the principal driver, and not damage accumulation.[^blago2006] On that account senescence and hypertrophy are the disease, and damage is downstream. A complex-systems view argues that aging emerges from the loss of homeostatic regulation across networks and is not decomposable into discrete mechanisms at all.[^cohen2022] [[sens-research-foundation|SENS]], the damage-repair programme associated with [[aubrey-de-grey]], predates the hallmarks and organizes aging into seven categories of accumulated damage on the argument that repair is more tractable than metabolic modulation. Finally, the framework is mouse-centric in ways that may not transfer. Laboratory mice have long telomeres and constitutive telomerase in many tissues, so telomere attrition means something different in mice than in humans. Species that violate the expected pattern — the [[negligible-senescence|negligibly senescent]] animals such as naked mole-rats and bowhead whales — are not well explained by any tiering of the twelve.Finally, the framework is mouse-centric in ways that may not transfer. Laboratory mice have long telomeres and constitutive telomerase in many tissues, so telomere attrition means something different in mice than in humans. Species that break the expected pattern, the [[negligible-senescence|negligibly senescent]] animals such as naked mole-rats and bowhead whales, are not well explained by any tiering of the twelve. ## Outlook## Outlook The open problem is converting a list into a ranking. Doing that requires measurements in humans that track the processes rather than their correlates, and interventions selective enough to move one hallmark without moving the others. Both are hard: most candidate drugs hit several hallmarks at once, and most candidate biomarkers are correlational. Prizes and consortia have begun to define outcome measures in terms of functional restoration across muscle, cognition and immunity rather than a molecular readout, precisely because the molecular readouts remain unvalidated as surrogates for [[healthspan]] or [[maximum-human-lifespan|lifespan]]. Until an intervention aimed at a named hallmark changes a hard human endpoint, the framework's central claim — that these processes are the causes of aging rather than its accompaniments — remains an organizing assumption rather than a demonstrated result. Arguments about [[biological-age]] reversal and [[longevity-escape-velocity]] are built on that assumption, and inherit its weakness.The open problem is turning the list into a ranking. Doing that requires measurements in humans that track the processes rather than their correlates, and interventions selective enough to move one hallmark without moving the others. Both are hard: most candidate drugs hit several hallmarks at once, and most candidate biomarkers are correlational. Prizes and consortia have begun to define outcome measures in terms of functional restoration across muscle, cognition and immunity instead of a molecular readout, because the molecular readouts remain unvalidated as surrogates for [[healthspan]] or [[maximum-human-lifespan|lifespan]]. The framework's central claim is that these processes cause aging and do not merely accompany it. Until an intervention aimed at a named hallmark changes a hard human endpoint, that claim remains an organizing assumption, not a demonstrated result. Arguments about [[biological-age]] reversal and [[longevity-escape-velocity]] are built on the same assumption and share its weakness. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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