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REVIEW 3 major objections 6 minor 3 references

Menopause averted a midlife energetic crisis with help from older dependent children and parents: A simulation study

T0 review · 3 major / 6 minor · reviewed 2026-08-03 · deepseek-v4-flash

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Pith's one-line read A simulation of forager family energy budgets finds that without menopause, short birth spacing, long child dependence, and long life could not have been sustained.

desk verdict Useful energetic accounting with a reproducible simulation, but the 'could not have evolved' headline overreaches what a deterministic energy-budget model can show. read the letter →

arxiv 2601.13442 v2 pith:AXICNSHB submitted 2026-01-19 q-bio.PE

Edward H. Hagen This is my paper · ORCID
classification q-bio.PE
keywords menopauseevolutionhunter-gathererenergeticslifehistorytheoryjuvenileforaginggrandmotherhypothesisinterbirthintervalenergybalancesimulationhumanlongevity
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

Menopause, on this account, is not a side effect of long life but a necessary part of the human life-history package. The paper simulates daily energy intake and use in a hunter-gatherer nuclear family—mother, father, and surviving children—using contemporary forager demographics, body sizes, and skill-acquisition speeds. Keeping reproduction going to the end of life pushes most simulated families into an energy deficit by the third or fourth birth, and they never climb out. Ending reproduction around age 38, while older children's foraging productivity rises and parents and young couples transfer food, turns the family balance positive in midlife. The author concludes that menopause is an integral energetic condition for the modern pattern of short interbirth intervals, long juvenile dependency, minimal reproductive skew, and long lifespans.

What carries the argument

The engine of the argument is an age- and sex-specific energy production function, productivity = adult peak productivity × strength(age)^α × skill(age)^(1−α), where α sets the weight of muscle strength (proxied by body weight) versus learned foraging skill, and skill follows a sigmoidal curve with fast, medium, or slow acquisition rates. This is embedded in a deterministic yearly simulation that sums consumption and production for the mother, father, and resident children, applying hunter-gatherer survivorship, three-year birth spacing, and either menopause at 38 or reproduction to age 80, over a grid of about 9,700 parameter combinations. The production function is what converts the broad

What would settle it

Re-run the simulation with juvenile productivity halved, or shift the 50%-skill age five years later, and ask whether any substantial region of parameter space keeps a no-menopause family above zero mean energy balance across the lifespan; if yes, the necessity claim fails. A field equivalent would be systematic measures of total daily juvenile foraging returns, including food eaten while foraging, across many societies, to check whether the age-return curve used here is overstated.

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Extended reading notes

Core claim

The author argues that menopause is an integral and necessary part of the modern human life-history package. In a simulation spanning nearly ten thousand parameter combinations for a hunter-gatherer nuclear family, keeping reproduction going until the end of life drives mean family energy balance below zero at the third or fourth birth in most of parameter space, and it stays negative for the rest of the lifespan. Ending reproduction around age 38, by contrast, lets maturing children's rising productivity and the eventual departure of grown children push the family out of deficit around the wife's mid-40s; on average, 80% of lifetime surplus is produced after menopause. The paper concludes t

Load-bearing premise

The result rests on the age schedule of production, especially the assumption that children's foraging productivity rises as quickly as contemporary forager datasets suggest and that adult productivity is a geometric mean of strength and skill; if ancestral juvenile returns were substantially lower, or if the skill curve is implemented as printed (it is singular at the age of 50% skill), the midlife deficit and its rescue by menopause could be artifacts of the production curv

Editorial extensions

If this is right

  • Menopause stops being a byproduct or evolutionary puzzle: in this model it is the energetic condition that makes the package of three-year birth intervals, two-decade dependency, and long life internally consistent.
  • Juvenile foraging matters: maturing children's own production is part of the rescue, so accounts of menopause must include children as producers, not only grandmothers as helpers.
  • The same midlife constraint appears under pooled communal energy budgets, so the conclusion does not depend on lifelong monogamous nuclear families.
  • Parental absence, not specifically father absence, is the relevant burden after a spouse dies; a widowed mother faces the same childcare crisis as a widowed father.
  • The simulated menopause age of 38 is not arbitrary: earlier menopause exits the deficit sooner but costs about two births, while later menopause delays recovery, bracketing a selective trade-off.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If the production schedule approximates ancestral conditions, the model predicts that the evolution of short birth intervals and long childhood should appear in the archaeological record together with evidence for substantial juvenile foraging and food sharing—not simply as a brain-size or longevity shift.
  • A sharp cross-population prediction follows: menopause age should correlate with the steepness of juvenile skill acquisition and with local food availability—later menopause where children learn fast or patches are rich, earlier where skills are slow or resources scarce.
  • The counterfactual no-menopause species is admittedly unrealistic; a full co-evolutionary model that lets interbirth intervals, juvenile mortality, or growth rates respond could find that menopause is one of several energetically equivalent solutions rather than uniquely necessary.
  • Because adult production is modeled as a geometric mean of strength and skill, the benefits of strict sex-specific specialization may be underestimated; re-running with additive division of labor could change the size of the deficit and the age at which it appears.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The paper presents a deterministic simulation of hunter-gatherer family energy balance (production minus consumption) over the female lifespan, comparing a menopause condition (age at last birth 38) with a no-menopause condition (births until age 80). The model varies skill acquisition rates, strength/skill weighting, productivity levels, marriage age gap, and uses published hunter-gatherer mortality, body size, and total energy expenditure data. The main finding is that, under the authors' parameter ranges, the no-menopause condition often produces a sustained midlife energy deficit, whereas stopping reproduction around age 38, combined with the rising productivity of maturing juveniles and transfers from older parents, allows families to escape this deficit. The paper concludes that menopause was a 'strictly necessary' component of the modern human life-history package. Code and data are provided. The central inference, however, moves from deterministic energy-balance accounting to an evolutionary-necessity claim that the simulation cannot support.

Significance. If confined to its actual scope—energetic feasibility under a fixed set of life-history and demographic assumptions—this is a useful and transparent quantitative exploration. The paper's strengths are its explicit energy accounting, the wide parameter sweep, the grounding in contemporary forager TEE, mortality, and foraging-skill data, and the public availability of the code. The comparative menopause/no-menopause simulations illustrate how cessation of reproduction relaxes a midlife energy constraint. However, the central claim that menopause 'could not have evolved' without such an energetic role is not established by the model: the simulation contains no fitness function, heritability, or selection, and the comparison is between two imposed birth schedules. The paper's value lies more in generating a falsifiable energetic constraint than in proving evolutionary necessity.

major comments (3)
  1. [§4 and §5] The claim that without menopause the modern human life-history pattern 'could not have evolved' is not supported by the simulation. The model fixes AFB, IBI, ALB, and reproductive skew; it contains no fitness function, heritability, or selection, and no life-history trait responds to energy balance. Indeed, §5 concedes that the simulations 'do not illuminate why the distinctive human life history pattern evolved.' Moreover, §3.4 reports that 3.6% of the restricted no-menopause parameter combinations produced positive energy balances (Figure S3). The existence of energetically viable no-menopause runs directly contradicts the modal claim of impossibility. I recommend replacing 'could not have evolved' with a feasibility statement, or adding an explicit evolutionary model that justifies the necessity inference.
  2. [Eq. 3, §2.4.1] Equation (3) as printed is invalid: the denominator is 1 − exp(−b1(age−age50)), which is singular at age = age50 and negative for age < age50, making skill negative before the 50% point. This is not a minor typo: the productivity schedule is load-bearing for the midlife-deficit result. If the intended function is the standard logistic sigmoid, 1/(1 + exp(−b1(age−age50))), it should be stated explicitly and used consistently. As printed, the equation cannot produce the curves in Figure 3D, so either the equation or the figure is wrong. This must be corrected and the simulations re-verified.
  3. [§3, restricted subset] The analysis is restricted post hoc to simulations with mean lifetime energy balance within 500 kcal of 0, motivated by the idea that surpluses would be transferred between families. This is a reasonable heuristic for identifying 'plausible' economies, but it creates a selection bias: the no-menopause condition is then populated by parameter sets that were matched to menopause runs, and the 3.6% of no-menopause runs that do reach positive balances are effectively outliers relative to the main narrative. Since the paper's necessity claim depends on the restricted subset, the sensitivity of the conclusion to this restriction criterion (e.g., different bandwidths, or requiring non-negative balance at every maternal age rather than on average) should be reported. Without such sensitivity analysis, the 'could not have evolved' conclusion is fragile.
minor comments (6)
  1. [Abstract and §4] The abstract uses 'strictly necessary' and the discussion 'could not have evolved,' while the concluding remarks soften to 'necessary to avert a midlife energetic crisis.' Please align terminology with the actual inferential strength.
  2. [§2.4] The text says women produced 'from to - of daily adult TEE' and men 'from to - of daily adult TEE'; the numbers are missing. Presumably this is a rendering issue, but it should be fixed.
  3. [§3.4] The sentence 'after menopause (age 32, 38, 44)' refers to the auxiliary simulations in Figure S6, but the main analysis uses only menopause age 38. The text should clarify that the main result is for age 38 and the other ages are sensitivity analyses.
  4. [Table 2] The parameter 'Age of menopause' with values 38 and 80 is confusing because 80 is the no-menopause condition. Label the rows as 'Menopause age (38) / no menopause (80)' for clarity.
  5. [§6] Typo in the heading: 'Acknowedgements' should be 'Acknowledgements.'
  6. [General] Please define precisely how 'mean energy balance' is computed (per day? per person? lifetime average?) and state the units in Figure 8 and Figure S1. This will help readers interpret the 500-kcal restriction.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the energy-balance comparison is a transparent deterministic counterfactual with independent empirical inputs; the 'could not have evolved' gloss is an overreach but not a definitional reduction.

full rationale

Walking the derivation chain, the paper's inputs are fixed empirically and the output is a deterministic family-level energy balance. Menopause is not derived or fitted; it is explicitly varied as ALB=38 vs ALB=80 (§2.1), and the No-menopause condition is defined as continued births until end of life. The main result—that ceasing reproduction reduces dependent-child consumption and helps resolve a midlife deficit—is therefore the intended counterfactual consequence, not a hidden renaming of an input. Independent external data are load-bearing throughout: TEE comes from the doubly-labeled-water regression of Bajunaid et al. (2025) and Pontzer et al. (2021); survivorship from UN model life tables via Gaddy et al. (2025); adult production ranges from Kraft et al. (2021); and juvenile/foraging ontogeny from Koster et al. (2020) and Pretelli et al. (2022). These give the energy-balance calculation quantitative content that is not an algebraic identity. The paper also reports that 3.6% of restricted No-menopause parameter combinations have positive energy balances (Figure S3), which would be impossible if the conclusion that menopause is necessary were forced by construction. The §4 statement that the modern human pattern 'could not have evolved' without menopause is an unsupported evolutionary extrapolation, and §5 itself concedes that the simulations 'do not illuminate why the distinctive human life history pattern evolved'; this is an inference-strength or scope limitation, not circularity. Equally, the singularity and negative-productivity behavior of Eq. 3 as printed at age=age50 is a modeling or implementation concern, not a circular step. Self-citations (Hagen & Barrett, 2009; Hagen et al., 2025) are incidental and are not used to justify the central result. No uniqueness theorem, no fitted parameter renamed as a prediction, and no ansatz smuggled in via self-citation appear. The derivation chain is therefore self-contained; the central claim has independent content from its empirical inputs.

Assumptions & free parameters 10 free parameters · 9 assumptions · 0 invented entities

The central claim rests on a stack of empirical inputs (TEE equations, mortality tables, production ranges) and modeling choices (Eqs. 1–3, dispersal at AFB, no energy-balance feedback). Most are reasonable proxies, but they are inputs, not consequences; the paper's 'necessity' conclusion inherits all of them.

free parameters (10)
  • TEE_prop_f = 0.4, 0.6, ..., 1.8 × adult TEE
    Female maximum productivity; range from Kraft et al. (2021) production data; strongly affects whether family can escape deficit.
  • TEE_prop_m = 1, 1.4, ..., 2.6 × adult TEE
    Male maximum productivity; same source; joint constraint with female value.
  • alpha_f / alpha_m = 0.25, 0.5, 0.75
    Weight of strength vs skill in Eq. 1; chosen by hand, not estimated.
  • b1_f / b1_m = 0.15, 0.25, 0.4
    Skill acquisition rates mapped to Slow/Medium/Fast; affect juvenile productivity onset.
  • age50_f / age50_m = 10, 15, 20
    Age at 50% skill; chosen with b1 to produce three ontogenies.
  • b2 = -0.15
    Old-age skill decline rate; fixed arbitrarily for both sexes.
  • b (strength decline) = -0.15
    Old-age strength decline rate; fixed arbitrarily.
  • Marriage age gap = 5, 10 years
    From Binford (2001); changes husband age/mortality exposure.
  • Age at menopause (ALB) = 38 (robustness 32, 44)
    Imposed at empirical median; the core comparison sets this input, so menopause is not an emergent outcome.
  • AFB and IBI = 20 y, 3 y
    From Davison & Gurven (2021); these set family size dynamics and the timing of the crisis.
assumptions (9)
  • domain assumption Productivity = strength^α × skill^(1−α) (Eq. 1)
    Modeling choice borrowed from Gurven & Kaplan/Koster/Schniter; no direct first-principles derivation.
  • domain assumption Skill follows a sigmoid in age with Fast/Medium/Slow parameters (Eq. 3)
    As printed, Eq. 3 is not a valid sigmoid (singular at age50); the intended curve is a stylized empirical fit.
  • domain assumption TEE regression of Bajunaid et al. (2025) applies to contemporary and ancestral hunter-gatherers
    Extrapolates a modern doubly-labeled-water model to foragers and deep time.
  • domain assumption No feedback from energy balance to survival, fertility, or IBI
    Step 12 in §2.6; families can run permanent deficits without consequences, which is what produces the 'crisis'.
  • domain assumption All adults reproduce; no reproductive skew
    Modeling simplification; ignores non-reproductive adults and helpers.
  • domain assumption Children disperse at AFB (age 20)
    Dispersal rule affects how long offspring contribute to the natal family.
  • domain assumption UN Model Life Tables with female e0=35, male e0=30 approximate hunter-gatherer mortality
    Used for survivorship; if ancestral mortality were higher, family composition and crisis timing change.
  • ad hoc to paper Counterfactual no-menopause condition: births continue until age 80
    Acknowledged as unrealistic in the Introduction; it defines the comparison and stacks the deck toward finding a menopause benefit.
  • domain assumption Families can subsist on surpluses from other life stages/families only implicitly
    Energy transfers between families are not simulated; the 500-kcal restriction is used as a proxy.

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Pith. "Pith review of Menopause averted a midlife energetic crisis with help from older dependent children and parents: A simulation study." pith.science (2026). https://pith.science/paper/AXICNSHB

@misc{pith2026260113442,
  author       = {Pith},
  title        = {Pith review of: Menopause averted a midlife energetic crisis with help from older dependent children and parents: A simulation study},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/AXICNSHB}},
  note         = {Machine review of arXiv:2601.13442}
}
read the original abstract

OBJECTIVES: The grandmother hypothesis proposes that ancestral women ceased reproduction midlife to instead provision their grandchildren. An alternative two-sex account proposes that the high energetic burden of caring for slow-developing offspring was met with biparental investment. Menopause evolved because the physiological costs of reproduction increased with age, yet productivity also increased with age, and the benefits of resource transfers by parents and grandparents of both sexes to adult children and their offspring eventually outweighed the diminishing benefits of continued reproduction (Kaplan et al., 2010). The father absent hypothesis proposes that the higher mortality rate of husbands would often have left wives without the resources to raise young children, selecting for early reproductive cessation (Kuhle, 2007). Juvenile production plays little role in the three hypotheses, yet subsequent studies have found it to be surprisingly high. MATERIALS AND METHODS: Simulations were conducted of hunter-gatherer energy consumption and production across the lifespan, taking account of age- and sex-specific survivorship, interbirth intervals, and varying rates of foraging skill acquisition typical of contemporary foragers. RESULTS: There is a pronounced midlife energy deficit that could be averted with the increasing production of maturing juveniles; midlife cessation of reproduction, which limited the number of mouths to feed; and energy transfers from older parents, and sometimes younger couples (e.g., brideservice). DISCUSSION: Menopause emerges as an integral and necessary component of the unique human pattern of relatively short interbirth intervals, a long period of juvenile dependency, and extensive food sharing, supporting and extending the two-sex and grandmother hypotheses.

Figures

Figures reproduced from arXiv: 2601.13442 by the authors.

Figure 1
Figure 1. Post-reproductive lifespans of humans, African great apes and other primates, and [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Energy production and consumption curves. A [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Age-specific productivity. A: Hadza children productivity. Each dot is one foraging trip by one child. Data from Crittenden et al. (2013) and Froehle et al. (2019). B: Tsimane female skill acquisition (male skill acquisition is similar). Figure from Schniter et al. (2015). C: Age-specific hunting skill. Data and code from Koster et al. (2020). D: Age-specific food acquisition skill for the three values of 𝑏1 in Equa… view at source ↗
Figures from the paper (5 more)
Figure 4
Figure 4. Figure 4: Survival curves. Ache data from Hill & Hurtado (1996). Hadza data from Jones (2016), ! [PITH_FULL_IMAGE:figures/full_fig_p007_4.png]
Figure 5
Figure 5. Figure 5: Weight by sex and age (top) and total energy expenditure (TEE) by age and sex (bottom). [PITH_FULL_IMAGE:figures/full_fig_p009_5.png]
Figure 6
Figure 6. Figure 6: Daily per capita adult energy production by contemporary hunter-gatherer females [PITH_FULL_IMAGE:figures/full_fig_p010_6.png]
Figure 7
Figure 7. Figure 7: Histogram of the mean differences in age at first marriage for husbands and wives in 177 [PITH_FULL_IMAGE:figures/full_fig_p012_7.png]
Figure 8
Figure 8. Figure 8: Simulation results from the restricted subset for the N [PITH_FULL_IMAGE:figures/full_fig_p016_8.png]

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Reference graph

Works this paper leans on

3 extracted references · 1 linked inside Pith

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    Do mammals have menopause?

    Antón, S. (2002). An ecomorphological model of the initial hominid dispersal from Africa. Journal of Human Evolution, 43(6), 773–785. https://doi.org/10.1006/jhev.2002.0602 Arnot, M. (2021). The evolutionary ecology of menopause. University College London. Bajunaid, R., Niu, C., Hambly, C., Liu, Z., Yamada, Y., Aleman-Mateo, H., … Speakman, J. R. (2025). ...

    arXiv 2002

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    J., & Gurven, M

    https://doi.org/10.3389/fsoc.2017.00011 Davison, R. J., & Gurven, M. D. (2021). Human uniqueness? Life history diversity among small- scale societies and chimpanzees. PLOS ONE, 16(2), e0239170. https://doi.org/10.1371/journal.pone. 0239170 Ellis, S., Franks, D. W., Nattrass, S., Cant, M. A., Bradley, D. L., Giles, D., … Croft, D. P. (2018). Postreproducti...

    arXiv 2017

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    S., Wilcox, N

    https://doi.org/10.3389/fpsyg.2011.00133 Schniter, E., Gurven, M., Kaplan, H. S., Wilcox, N. T., & Hooper, P. L. (2015). Skill ontogeny among Tsimane forager-horticulturalists. American Journal of Physical Anthropology, 158(1), 3–18. https:// doi.org/10.1002/ajpa.22757 Sievert, L. L. (2024). Evolutionary perspectives, comparative approaches, and the lived...

    arXiv 2011

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