Thanks Agnes. Presumably the key statement in this paper is in the Discussion: "Both the present data and the existing literature support the conclusions that relatively few rhesus monkeys survive beyond the age of 25 years and that it is a rare monkey indeed which sees its fourth decade." Seems reasonable! But if anyone has other references, it would be great to have converging evidence from different biological systems.

Agnes, yes, that is perfect, although I've usually heard of it as 1:4, though I *have* heard of a 1:3 scaling before too. Thank you!

I have heard both 1:3 and 1:4 ratio for human to rhesus. My understanding is that the 1:4 ratio is based on the development of the visual system.

Boothe RG, Dobson V, Teller DY. Postnatal development of vision in human and nonhuman primates. Annu Rev Neurosci 1985; 8:495-545.

Thanks Jessica, much appreciated! It's pretty clear right from paragraph 3 that they're interested in exploring this 4:1 relationship, and their review does seem to support it.

This issue comes up a lot in peer review, for rodents as well as NHP. Though researchers try biological-based responses, lifestage approaches can help to just generalize for people who don't work with these models. I like to use age at puberty to anchor the 4:1 at early ages.

John P Capitanio Here is a reference that explains different ratios depending on life stages:

Article An overview of nonhuman primates in aging research

"Moreover, rhesus monkeys sexually mature around the ages of 2.5 – 3.5 years, they reach adult stature by 8 years of age, and females undergo menopause by about 25 years. Thus, the rate of aging ratio of human to monkey years can be summarized as follows: 1:4 from birth to sexual maturity, 1:3 during young adulthood, and 1:2 for females before menopause. In general, rhesus monkeys aged 15 – 22 years are deemed middle aged, while those over 30 years are considered old or elderly."

Thanks Negin. I like that the scaling varies with age in this model, but their estimates sound a bit high. At our facility, 19 is considered aged, and in fact, animals of this age appear more frail than one might expect of a middle-aged human.

I agree. I see various numbers in different resources. I guess even though people usually consider captive versus wild for variations in the aging process, one would need to consider differences in captive animals depending on the conditions as well.

Hi John and all. Just looking at this since need this info also. John do you think some of this is a difference between animal colonies vs those in the wild? Of course for most of the research the animal colonies would be the most relevant

Very interesting question, maybe it would be interesting also to compare with the age of the mouse, maybe, congratulations, very good question. (Rat's age versus human's age: what is the relationship?) Andreollo NA et al. Arq Bras Cir Dig. 2012 Jan-Mar;25(1):49-51. doi: 10.1590/s0102-67202012000100011. In adulthood, every month of the animal is approximately equivalent to 2.5 human years.

Hi Howard Fox, long time! I have a suspicion that this may be "lab culture" thing -- people use what their mentors use, perhaps. For rhesus, there seems to be a consensus that it's either 1:3 or 1:4, but most of what I"ve seen has been only captive animals. But it's a good point about the wild animals. I guess we'd have to ask if we consider ourselves "wild animals" for which the wild rhesus numbers might be best, or "captive animals" for which the captive data might be best. An interesting thought :-). In the end, for the paper we needed this for, I used the Tigges et al. ref that Agnes Lacreuse provided, and the 1:3 figure.

Thanks Carlos Ac Vasconcelos . I think it makes me even more nervous trying to scale rodent with humans. Rodent and human lifestyles are very, very different!

Yes it's true, more for a comparison not so much, for example the rhesus monkey to be seen to be less developed than chimpanzees, I liked your answer.