Which would be inverse to the way metabolism scales according to Kleiber’s Law, that is, inverse to the way metabolism scales as mass to a 3/4 exponent?
Which would be inverse to the way metabolism scales according to Kleiber’s Law, that is, inverse to the way metabolism scales as mass to a 3/4 exponent?
So that the rate of metabolism scaled, times longevity scaling is invariant?
Has this hypothesis been proposed? Are there are articles on the scaling of mammalian longevity?
Hi there,
Well, it's interesting but unfortunately so many species fall out of this scaling. For instance, Brandt's bats have a life span of 41 years, and naked mole rats, which weight up to 80g at best, live up to 32 years.
Some studies suggest that it is the efficiency of DNA repairment, rather than metabolism, that defines the lifespan of mammals.
Here is a review :
Article Scaling of Maximal Lifespan in Mammals: A Review
Here another interesting piece of work on the topic, investigating the role of ecological/behavioral traits in longevity of mammals (and birds):
https://www.researchgate.net/publication/261752454
I bet Robert H Peters would have something to say about this:
Peters, Robert H. The ecological implications of body size. Vol. 2. Cambridge university press, 1986.
The finding of the insulin/IGF-1 pathway was made decades ago in C. elegans. In mammals, IGF-1 level is controlled by the growth hormone, leading to life extension, which has stimulated the discussion of the size and longevity relationship. In the discussion, since reducing growth hormone tends to extend mouse lifespans, the prediction may be small in size may be correlated with life extension. This is within the same species:
You could take a look at current understanding at:
Article Somatotropic Signaling: Trade-Offs Between Growth, Reproduct...
Article Healthy Aging: Is Smaller Better? - A Mini-Review
Article Growth hormone and aging
It is intriguing that dogs do not seem to be following but I cannot conform with papers.
This is a fascinating question that does not have an easy answer, because the classical scaling constraints seem to be based on physiology and energetics, such as metabolic rates, whereas lifespans seem to be hugely influenced by ecology and behavior, especially social behavior. The paper cited by Andriollo is interesting, because it tries to address this issue, but it combined birds and mammals and breaks them down into volant (Flying) and non volant, rather than by phylogeny birds and mammals.
I study both birds and mammals because my research questions deal with the evolution of monogamy and life history evolution rather than systematic issues. Mammals are an odd group, because some groupings (bats and primates) have unusually long life spans for the body size, whereas others (carnivores and artiodactyls) typically have very short lifespans. It is important to look at the scatter in these plots rather than the lines, because the scatter contains the real information and the lines are largely meaningless. Another important issue is whether you mean average or maximum lifespan.
As an example look at cats and dogs (all carnivores really). When we look at wild individuals average lifespan is quite short, but with domestic animals we tend to look at maximum lifespans because housepets tend to live longer lives and achieve maximum lifespans more often. Anyway, all cats and dogs (Wild and domestic) seem to have maximum lifespans less than 15 years, although a few individuals can make it to 20 or more in captivity. This is independent of size, housecats live as long or longer than lions or tigers, and foxes live as long as wolves. Domestic dogs are wolves and they all have wolf maximum lifespans.
A problem with dogs is the capricious, often cruel, breeding practices of humans. Small domestic dogs live longer than the largest breeds. This is because human breeders focus on the external appearance and ignore organ sizes. In large breeds like mastiffs and Great Danes, their bodies are larger than their organs can support so they have lifespans shorter than 10 years, whereas miniature dogs can live to 15 or more. All dogs have internal organs built to support a wolf sized body and wolf sized dogs (50-100 pounds) function well. Small dogs organs are larger than their body size requires and this allows them to lives, whereas large breeds simply wear out their organs too soon.
An odd thing with carnivores is that even the largest, like pinnipeds and bears rarely have maximum lifespans that exceed 15-20. An elephant seal that weighs 3 tons has basically the same maximum lifespan as a wolf that weighs 100 pounds. Mammal that live in large social groups, like bats and mole rats (and of course primates) have unusually long lifespans. Humans bias our thinking because if we were 100-200 pound carnivores or artiodactyls, we would have lifespans around 10-15 years. In reality we are barely reproductive at that age and our lifespans. are more comparable to those of whales and elephants, which are obviously much larger.
I could go on all day, but my answer is basically, no mammalian lifespans do not scale well to any equation because of the variety in their ways of life. One last thing to think about is that birds live much longer lifespans for their body masses than do mammals, in fact mammals as a group tend to have the shortest lifespans for their body mass of any group of animals. Finally don't look at average lifespan which is overly influenced by ecology (predation and food supply) but at maximum lifespans, which is what evolution works on.
I could not tell about the longevity scale for mammals as a function of mass.
However, there is a known longevity scale for the number of heartbeats per lifetime for animals as a function of weight in kg.
See, for example, Figure 2 in Geoffrey West, Scale: The Universal Laws of Life, Growth, and Death in Organisms, Cities, and Companies, Penguin Books; Reprint edition (May 15, 2018), p.3.
Heartbeats per lifetime sounds cool, but it does not explain the longevity of humans, other primates, and bats or naked mole rats. These species all must have many more heartbeats than species heavier than they are such as many ungulates, elephants, bears, etc. You have to look at the scatter in these figures, not simply the regression lines, which hide a lot of important information.
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