Hypothesis

Aging is not merely a byproduct of declining selection pressure; it is an actively maintained program that releases mitokines to modulate the physiology of neighboring individuals, thereby favoring kin survival under resource‑limited conditions.

Mechanistic reasoning

1. Mitochondrial stress triggers mitokine release – In models ranging from yeast to mammals, mitochondrial dysfunction elicits a conserved secretory response (e.g., FGF21, GDF15) that acts systemically to adjust metabolism and stress resistance [6].
2. Mitokines act as kin‑directed signals – When secreted, these factors can be taken up by nearby cells, lowering their anabolic drive (e.g., reducing TOR activity) and increasing stress‑tolerance pathways. This creates a transient phenotypeshift that conserves nutrients for genetically related individuals who share the same microenvironment.
3. Feedback to the sender – The mitokine‑producing cell experiences a mild, hormetic benefit (enhanced autophagy, improved proteostasis) that extends its own lifespan just enough to complete reproductive output, after which the signal intensifies, accelerating somatic decline.
4. Population‑level effect – In heterogeneous groups, a subpopulation programmed for shorter lifespan secretes higher mitokine levels, suppressing reproduction and growth in neighbors. The net effect shifts the age structure toward younger, more fecund kin, echoing group‑level selection without requiring true altruism.

Testable predictions

• Prediction 1: In Caenorhabditis elegans, overexpressing the mitokine FGF21‑like protein specifically in the intestine of long‑lived daf‑2 mutants will decrease brood size and increase stress resistance of adjacent wild‑type worms sharing the same plate.
• Prediction 2: Knocking down the mitokine receptor (e.g., FGFR‑homolog) in neighboring wild‑type worms will abolish the observed lifespan extension and stress‑resistance gains seen when near daf‑2 mutants.
• Prediction 3: In budding yeast, deleting the gene encoding the mitochondrial retrograde signal (RTG2) will reduce the competitive disadvantage of long‑lived mutants observed in mixed‑culture assays [1]; adding exogenous mitokine‑conditioned medium will restore the disadvantage.

Experimental approach

1. Generate strains with tissue‑specific, inducible mitokine overexpression or CRISPR‑based knock‑down.
2. Co‑culture engineered sender strains with fluorescently labeled wild‑type receivers under graded food concentrations.
3. Measure receiver reproduction (egg lay or budding rate), lifespan, and markers of stress resistance (e.g., HSP‑16::GFP, superoxide dismutase activity).
4. Use RNA‑seq to verify TOR pathway downregulation and autophagy activation in receivers.
5. Perform rescue experiments by adding purified mitokine or neutralizing antibodies.

Falsifiability

If manipulating mitokine secretion in senders fails to consistently alter the reproductive output or stress phenotype of genetically neighboring receivers across multiple species and environmental conditions, the hypothesis that aging functions as a kin‑selected, signal‑driven program is falsified. Conversely, reproducible, receptor‑dependent effects would support the notion that evolution has retained aging as a regulated, population‑level trait rather than a simple decay [2, 7, 8].

References

• Yeast competition shows long‑lived mutants are outcompeted by wild type [1]
• Antagonistic pleiotropy underpins early‑life fitness trade‑offs [2]
• Human genetic links between early reproduction and accelerated aging [3]
• Germline‑soma signaling limits C. elegans lifespan [4]
• Age‑specific genetic correlations demonstrate widespread antagonistic pleiotropy [5]
• Disposable soma theory and TOR‑driven damage accumulation [6]
• Comparative biology finds no group‑selection signatures for aging [7]
• Critical reviews find no robust evidence for group selection of aging [8]
• Minority view posits programmed aging with antagonistic pleiotropy contributions [9]