Why do animals vary so much in life span?

[member 392791]

I was curious, why is it that dogs will live somewhere in the 10-20 year range, but humans make it to 80, and animals vary so much?

 

[mfb]

Why do you expect a similar lifespan for completely different animals, adapted to completely different conditions?

 

[phinds]

What factors do you think might affect aging?

 

[member 392791]

Well I suppose it would have something to do with the complexity of the organism. It seems larger animals live longer than smaller ones generally (whale vs. house fly). Still, why is the life cycle of a dog so relatively short? I want my doggy to live forever =(

 

[Ryan_m_b]

It seems larger animals live longer than smaller ones generally (whale vs. house fly).

Humans can live to 80 yet a horse only lives 20-30 years. Elephants can range from 75 to 105 times the mass of a human but they too only live around 80 years. Given this do you think there is something missing from your proposal about size and complexity? I'd suggest first looking up what the processes of ageing are and then trying to figure out why they might be different for different animals.

 

[mfb]

Significant differences can be found between different classes of animals - mammals tend to live long, but unicellular organisms can be immortal. The size-correlation is a side-effect: Many large animals (especially animals relevant for food, media coverage and so on) are mammals, many small ones are not.

 

[mishrashubham]

May I suggest the book "Cheating Time" by Roger Gosden. It's a nice non-technical book and makes for a good read. And the first few chapters are relevant to your question.

 

[spacester]

I remember hearing once that if you measure lifespan in heartbeats instead of years, most animals (or was it just mammals?) come in at about the same number, about 2*10^6 or something.

 

[Ryan_m_b]

I remember hearing once that if you measure lifespan in heartbeats instead of years, most animals (or was it just mammals?) come in at about the same number, about 2*10^6 or something.

Given an average human heartbeat of 60bpm that means a human life expectancy would be 3 weeks. This doesn't make any sense regardless of how many beats one proposes.

 

[mfb]

As not animals have a heart, it cannot be a similar number for all animals.

In addition, we should not compare the average lifespan - this is determined by the availability of food, predators, accidents and so on. The maximal lifespan is harder to evaluate, but better to compare.
There are several known correlations with various biological rates.

 

[Pythagorean]

Size, heart rate, and oxidative stress are the three wive's tales I always hear. (Acknowledging two of these have already been brought up in this thread).

 

[SW VandeCarr]

The fundamental determinant of the mean life span of a species in genetic. I don't think you can pin down individual traits consistently across species and genera that explain comparative life spans. Most research along these lines is in small rapidly reproducing organisms such as bacteria and insects.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1602065/

 

[tms]

I was curious, why is it that dogs will live somewhere in the 10-20 year range, but humans make it to 80, and animals vary so much?

The simple, but admittedly not very helpful, answer is evolution. Dogs who live to be 80 don't leave any more descendants than those who live to be 20.

 

[Evo]

This has come up before. And as someone mentioned, there seems to be a correlation with heart rate and life span. I can't find the refernce i used last time, but this has a table. Scroll down to Lifetime Heartbeats and Animal Size.

http://www.sjsu.edu/faculty/watkins/longevity.htm

Also here. It also has a table.

Heart beats represent energy expenditure. Life span is not determined by the number of heart beats, but the number of heart beats represents the amount of energy expended by mammals; it is a marker of our energy expenditure of cells, which still makes it useful.

http://www.medcan.com/articles/heart_beats_and_life_span_do_we_have_a_finite_number_of_heart_beats

 

[mfb]

This has come up before. And as someone mentioned, there seems to be a correlation with heart rate and life span. I can't find the refernce i used last time, but this has a table. Scroll down to Lifetime Heartbeats and Animal Size.

http://www.sjsu.edu/faculty/watkins/longevity.htm

It has a table, but I would not trust the graphs or mathematics there. It looks like a homework project with the target "we have to find some relations to get a good grade".

The life expectancy of humans is a bit special anyway.

 

[Evo]

It has a table, but I would not trust the graphs or mathematics there. It looks like a homework project with the target "we have to find some relations to get a good grade".

The life expectancy of humans is a bit special anyway.

Yeah, it's not the study I originally found a few years back. The second goes into more detail.

Here's a peer reviewed study published in The Journal of the American College of Cardiology.

Abstract

Among mammals, there is an inverse semilogarithmic relation between heart rate and life expectancy. The product of these variables, namely, the number of heart beats/lifetime, should provide a mathematical expression that defines for each species a predetermined number of heart beats in a lifetime. Plots of the calculated number of heart beats/lifetime among mammals against life expectancy and body weight (allometric scale of 0.5 x 10(6)) are, within an order of magnitude, remarkably constant and average 7.3 +/- 5.6 x 10(8) heart beats/lifetime. A study of universal biologic scaling and mortality suggests that the basal energy consumption/body atom per heart beat is the same in all animals (approximately 10(-8) O2 molecules/heart beat). These data yield a mean value of 10 x 10(8) heart beats/lifetime and suggest that life span is predetermined by basic energetics of living cells and that the apparent inverse relation between life span and heart rate reflects an epiphenomenon in which heart rate is a marker of metabolic rate. Thus, the question of whether human life can be extended by cardiac slowing remains moot and most likely will only be resolved by retrospective analyses of large populations, future animal studies and clinical trials using bradycardic therapy.

http://www.ncbi.nlm.nih.gov/pubmed/9316546

And I see more studies referenced on the page.

 

[Evo]

I found a free paper and it goes into the difficulties in determining the effects.

The transgenic manipulation studies are confounded by the problem that transgenic manipulations often also affect body size. This raises issues about how metabolic rate should be normalised (see discussions in Ramsey et al., 2000; Speakman et al., 2002) that are not yet resolved. How this normalisation is performed dramatically alters the conclusions that are drawn about the effects of metabolism. Some researchers therefore claim that the transgenic effects act via metabolism; others suggest there is an independence of the effects from metabolism. In other species, particularly mice, the measurements have simply not yet been made to indicate what is going on. This problem of normalising for effects of body size also besets the whole area of whether caloric restriction acts via a decrease in metabolism or not (reviewed in Ramsey, 2000). Comparisons across different strains of dogs and mice are much clearer in suggesting a positive association of metabolism and longevity, and this effect was also found in the single comparison made to date of individual variability within a strain of mice

http://jeb.biologists.org/content/208/9/1717.long

Paper was published http://www.ncbi.nlm.nih.gov/pubmed/15855403 in The Journal of Experimental Biology.

There are many peer reviewed papers that deal with the topic. There is no definitive answer AFAIK, but size and heart rate do seem to be a factor.

 

[epenguin]

The subject is called "allometry" and is a full-time study for some people, so you can find more about it by googling that word, e.g. http://en.wikipedia.org/wiki/Allometry

 

[Mute]

I saw a talk recently by Geoff West from the Santa Fe Institute which discussed the scaling of animal lifetimes with metabolic rate. Even some single celled organisms - heck, even some molecules - appeared to fit in with the power-law scaling of lifespan with metabolic rate.

Some of the topic is touched on in this TED talk of his: http://www.ted.com/talks/geoffrey_west_the_surprising_math_of_cities_and_corporations.html