Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: diverjohn on 06/11/2011 18:12:59

Title: Why do healthy animals not live as long as humans?
Post by: diverjohn on 06/11/2011 18:12:59
This question comes from a poem I heard on the radio this morning, asking why a horse that takes in fresh air, sunshine, fresh food, and gets lots of exercise, will not outlive a human who drinks gin, smokes cigars, experiences city traffic jams, and lacks meaningful exercise?
If humans lived as horses do (or if horses drank gin and beer while watching old TV shows) would our lifespans change at all?
Title: Why do healthy animals not live as long as humans?
Post by: RD on 06/11/2011 18:38:00
hearts are only good for about a billion beats, regardless of the size of the animal ...

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.sjsu.edu%2Ffaculty%2Fwatkins%2Fheartbeatswt.gif&hash=591e6f488cd9bc888187d2ada8e53566)
http://www.sjsu.edu/faculty/watkins/longevity.htm

At 400 beats per minute even a teetotal non-smoking hamster is probably not going to see its 5th birthday.


http://en.wikipedia.org/wiki/Heartbeat_hypothesis
Title: Why do healthy animals not live as long as humans?
Post by: Bored chemist on 06/11/2011 21:38:40
A horse doesn't benefit much if its grandparents are still alive to help raise it. That's not the case with humans.
There's a lot of evolutionary pressure for our grandparents to not die until we are (at least nearly) adults. It goes with the territory of having to learn a lot.
Title: Why do healthy animals not live as long as humans?
Post by: CliffordK on 07/11/2011 01:39:06
Quote from: RD on 06/11/2011 18:38:00
hearts are only good for about a billion beats, regardless of the size of the animal ...

There are exceptions to every rule.  While size of the organism (and also the heart size) does influence the longevity of the animal species, it is not the only influence.

NameLifespan (years)
Hdra (http://en.wikipedia.org/wiki/Hydra_%28genus%29)Possibly immortal (no senescence)
Turritopsis nutricula (Jellyfish) (http://en.wikipedia.org/wiki/Turritopsis_nutricula)Possibly immortal, reverts to an immature polyp stage after reaching sexual maturity
Various Mollusks, Corals, and ShellfishPossibly hundreds of years
Japanese Koi (captivity?)200+
Greenland Sharks200
Bowhead WhalesApprox 200
Galapagos Land Tortoise193
Giant Tortoise152
American Box Turtle123
Box Turtle123
Turkey Buzzard118
Swan 102
Tuataras100-200
Carp100
Macaws (captivity)80-100
Blue Whales80+ (estimate)
Amazon Parrot80
Parrot 80
Elephant70
Alligator68
Great Horned Owl68
Catfish60
Snapping Turtle57
American Alligator56
Eagle55
Eel55 (at least 1 eel in Sweeden is believed to be 150 years old)
Giant Salamander55
African Grey Parrot50
Camel50
Macaw50
Crocodile45
Donkey45
Hippopotamus45

Sources:
http://www.myuniversalfacts.com/2007/01/life-span-of-animals-how-long-do.html
http://en.wikipedia.org/wiki/Maximum_life_span

The longest lived species are both big and small, of all types.  Certainly other animals should be added to the list, and some of the estimates will be refined over time.

Lifespans are part of a delicate balance in nature.  A short period of time to reproductive maturity will spread genes into the gene pool quicker. 

Too few babies, and the species dies out.
Too many babies, and overpopulation results, leading to hardship for the species.

A long period after the end of the reproductive years may not benefit the species significantly.  And, at least with humans, there is a greater risk for certain birth defects in children born from older women.  Perhaps menopause is also related to a benefit for a woman to be able to raise children for 10 to 20 years beyond the end of her reproductive period.

Another thing that has been noted in humans, but would also be true with animals is that diseases that show up late in life often are not selected against.  So, a genetic predisposition to getting cancer in the 40's might be passed on before the defect is noted in the parents.
Title: Why do healthy animals not live as long as humans?
Post by: Don_1 on 07/11/2011 17:20:56
Just to expand on your tortoise entry, Clifford, Harriet, a Galapagos Giant tortoise taken captive by Darwin lived to estimated age of 175. Tu'i Malila, an Aldabra Giant tortoise taken captive by Capt. Cook, lived to the age of 188. Adawaita, another Aldabra and the pet of Clive of India is now accepted as the longest lived at the grand old age of 256.

A Mediterranean Spur-thighed tortoise, one of the smaller species, named Timothy, mascot of several Royal Navy ships, died in 2004 at the approximate age of 165. Having two of these species myself, now just 8 years old, I think there is a good chance they will outlive the children of my newborn granddaughter.
Title: Why do healthy animals not live as long as humans?
Post by: Airthumbs on 07/11/2011 21:25:32
Imagine being a Hydra, say you got to ten thousand yrs old, you would be pretty wise yes....  then comes along a fish and gulp, game over....  [:o]
Title: Why do healthy animals not live as long as humans?
Post by: CliffordK on 08/11/2011 04:44:09
Quote from: Airthumbs on 07/11/2011 21:25:32
Imagine being a Hydra, say you got to ten thousand yrs old, you would be pretty wise yes....  then comes along a fish and gulp, game over....  [:o]

I don't think the 10,000 yr old Hydra will rival Einstein for intelligence.   [xx(]

Senescence must have to do with reproduction and population control.  The hydra must have other limitations on their population (like the fish) that it isn't as important to naturally age and die.
Title: Why do healthy animals not live as long as humans?
Post by: wolfekeeper on 08/11/2011 15:41:53
The theory is that a species that has managed to reduce its death by accident, predation and disease so that it dies of old age will, over time, evolve into a longer lived species, with a slower reproduction rate. It's because individuals that have longevity will be able to reproduce for longer and have more descendents, and so genes for longevity are selected for.

OTOH if conditions then change, then genes that code for faster reproduction will be selected for, and the genes that enable surviving to a greater age will be no longer selected for, and so will randomly mutate until they no longer work.

So, a tortoise is very well protected and can hence live for centuries and ages very slowly.

Humans are presumably evolving to be longer lived now, since we've largely solved accident, predation and disease, but I suspect that medical science will sort it out first.