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An Animal Without an Observed Mortality Increase

Even the oldest animals on record are not dying of age-related diseases.

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Naked mole-rat tunnelingNaked mole-rat tunneling

The researchers of a previous controversial paper on the naked mole-rat’s impressive longevity have returned, publishing data in GeroScience that bolsters their original findings.

A darling of longevity

The naked mole-rat, an unusually long-lived rodent species that lives in large colonies, has long been a mystery of gerontology, and investigations into its biology have yielded some surprising findings. Despite their small size, these hairless, wrinkled rodents are uniquely resistant to cardiac dysfunction [1] and cancer [2].

Five years ago, these three researchers published a paper detailing the naked mole-rat’s general resistance to all age-related causes of mortality, reporting that this animal’s risk of death does not increase with age [3]. However, as a previous comment [4] and these researchers note, most of the animals in that study were relatively young.

Missing death records, which originated prior to these researchers’ analysis, may have introduced bias into the study. The researchers responded by re-analyzing their data with left-censorship, a statistical technique that labels data gathered from before a certain point, which also occurs in this study and many other long-term survival studies [5]. Right-censorship, a statistical technique that labels data after a certain point (for example, if an animal is transferred away or is simply still alive), is also used in this study.

The same colonies, half a decade later

These researchers have continued the same animal husbandry practices among the same populations of animals as they did in their original 2018 paper [3]. Data from a total of 7,536 animals is included in this analysis, with complete birth and death (or right-censorship) information being available for 6,949. All of these animals were microchipped in order to verify individual identity. Much of the original data had to be updated in some way, but vital data for 3,222 of the previous paper’s animals was consistent between these studies.

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One of the potential mortality-related factors that these researchers analyzed was colony size. Naked mole rats, like many insect species, are eusocial animals; in nature, they only leave to form new colonies of their own, and can never join other colonies because existing colonies act violently against intruders. Non-breeding animals in the smallest colonies had statistically greater mortality, particularly males, although this was not consistent from year to year. Larger animals also had a greater chance of survival. These differences are ascribed to social dynamics and violence rather than aging.

The researchers also analyzed mole rats from the Fukomys genus using the same statistical methods. These animals are somewhat similar to the naked mole-rat (Heterocephalus glaber), but they begin to die with age. Like with nearly other animal, their chances of death can be observed to increase over time. These species’ maximal lifespan is a bit over 20 years.

Naked mole rats, on the other hand, do not have this decreasing survival curve. While the animals do die over time, this rate seems to be unaffected by age. One animal died when it was nearly 31 years old, but the oldest animal that the researchers had at the time of data collection was just over 35 years old, and these researchers state that this is still not close to these animals’ median lifespan. These findings were confirmed whether or not they included data from the original 2018 paper.

Naked mole rat survival

We therefore maintain our original conclusion: that unlike every other species studied to date where mortality risk begins to increase long before median lifespan, naked mole-rat mortality hazard does not increase with age.

We still cannot know exactly how long a naked mole-rat lives on average under these researchers’ optimized animal husbandry practices. It may be that the naked mole rat does have a true median lifespan of 50, 60, or even beyond, when it dies of age-related diseases much later than other animals. Only time, or extremely advanced biological analysis, will tell. Meanwhile, researchers will continue to investigate this exceptionally long-lived animal and determine what of its abilities can be brought to human beings.

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Literature

[1] Can, E., Smith, M., Boukens, B. J., Coronel, R., Buffenstein, R., & Riegler, J. (2022). Naked mole-rats maintain cardiac function and body composition well into their fourth decade of life. Geroscience, 44(2), 731-746.

[2] Hadi, F., Smith, E. S. J., & Khaled, W. T. (2021). Naked mole-rats: Resistant to developing cancer or good at avoiding it?. The extraordinary biology of the naked mole-rat, 341-352.

[3] Ruby, J. G., Smith, M., & Buffenstein, R. (2018). Naked mole-rat mortality rates defy Gompertzian laws by not increasing with age. elife, 7, e31157.

[4] Dammann, P., Scherag, A., Zak, N., Szafranski, K., Holtze, S., Begall, S., … & Platzer, M. (2019). Comment on ‘Naked mole-rat mortality rates defy Gompertzian laws by not increasing with age’. Elife, 8, e45415.

[5] Ruby, J. G., Smith, M., & Buffenstein, R. (2019). Response to comment on ‘Naked mole-rat mortality rates defy Gompertzian laws by not increasing with age’. Elife, 8, e47047.

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About the author
Josh Conway

Josh Conway

Josh is a professional editor and is responsible for editing our articles before they become available to the public as well as moderating our Discord server. He is also a programmer, long-time supporter of anti-aging medicine, and avid player of the strange game called “real life.” Living in the center of the northern prairie, Josh enjoys long bike rides before the blizzards hit.