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Old 02-24-2020, 12:50 AM
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Are short lifespans inherently linked to domestication?


I was reading a comment about how sad it was that pets like cats and dogs have such a short lifespan in comparison to humans.

But I thought about it and it occurred to me that this might be an inherent part of the process of domestication.

A major portion of domestication is selective breeding. A human can breed through several generations of his animals in his own lifetime. But suppose that a cat or a dog (or a horse or a cow or a pig) had a lifespan that was similar to a human's; you'd have a situation where each generation of breeder could only work on a single generation of animals. No single human would ever see any noticeable progress in the species they were breeding or reap the reward for their work. Would humans put the effort into domesticating another species if they knew that the benefits wouldn't begin appearing until their great-great-great-great-great-grandchildren's time?
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Old 02-24-2020, 12:57 AM
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It doesn’t matter how long an animal lives, what matters is when it reaches breeding age.
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Old 02-24-2020, 01:17 AM
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Heck, humans can even take an interest in the breeding patterns of other humans. Someone who lives to be 80 might, for example:

-have a child at age 25
-when the parent is 50, their child is 25, and the parent intervenes with that child's choice of mate, promoting what the parent sees as a good match, discouraging what the parent sees as a bad match, and then the child produces a child of its own, which the now-grandparent can help with...
-when the grandparent is 75, their grandchild is 25, and the grandparent intervenes with that grandchild's choice of mate, promoting what the grandparent sees as a good match, discouraging what the grandparent sees as a bad match, and then the grandchild produces a child of its own, which the now-great-grandparent can help with...

So even a fairly long generation time can hold a human's interest.
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Old 02-24-2020, 01:19 AM
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It's well known that domestic animals (both pets & livestock) have a much longer lifespan than feral animals of the same species. For example, cats kept as house pets live 10-15 years, while feral cats average only 1/3 of that lifespan. Domestic horses live to age 25-35; wild horses live only 12-18 years. Etc.

But I believe this is due mainly to domesticated animals getting better food, shelter, & veterinary care, rather than genetic reasons. I don't believe himans have been breeding any domesticated species long enough to have effected a change in their genetic lifespan.
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Old 02-24-2020, 06:00 AM
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Some animals used for food have been bred to mature faster - such as broiler chickens. Whether or not that affects maximum lifespan is unknown because these animals are generally slaughtered and eaten long before they get old.

Breeding very large varieties of dog shortens the maximum lifespan - the really large breeds do not live as long as the toy varieties. In that case, "domestication" actually shortens lifespan.

A lot has to do what you're breeding for - if you selected domestic animals for longer lifespans you'd get longer-living animals. If you concentrated on some other trait it might have a side effect of shortening the lifespan.
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Old 02-24-2020, 06:12 AM
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I think the OP is not saying anything about the impact of domestication on lifespans. Instead, he is commenting on the impact of lifespans on domestication: longer lived species don't get domesticated because the logistics make it harder to apply selection pressure.
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Old 02-24-2020, 07:35 AM
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I think the OP is not saying anything about the impact of domestication on lifespans. Instead, he is commenting on the impact of lifespans on domestication: longer lived species don't get domesticated because the logistics make it harder to apply selection pressure.
You are correct. But with very few exception, such as the Galapagos tortoise, the vast majority of other animal species have much shorter lifespans than humans.
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Old 02-24-2020, 08:19 AM
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I think the OP is not saying anything about the impact of domestication on lifespans. Instead, he is commenting on the impact of lifespans on domestication: longer lived species don't get domesticated because the logistics make it harder to apply selection pressure.
There aren't many animals that live a long time that are suitable to domestication. Few animals have a life expectancy that matches humans and most can't be domesticated for some other reason. You can't domesticate sharks or bears - actually, most animals are totally unsuited to domestication no matter their lifespan.

The counterexamples are some pets, like parrots and koi, which can live a very long time but are domesticated.

The one example that might prove the OP right is the Indian elephant. They are widely used by humans, but aren't domesticated; most are taken from the wild. Elephants live a long time but just aren't economical to domesticate.

Obviously, the contrast between parrots and elephants is not lifespan, but the OTHER logistics of keeping animals.
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Old 02-24-2020, 08:20 AM
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I think the OP is not saying anything about the impact of domestication on lifespans. Instead, he is commenting on the impact of lifespans on domestication: longer lived species don't get domesticated because the logistics make it harder to apply selection pressure.
The question with that then comes down to what point do they slaughter (or whatever) the animal?

I mean, livestock with human lifespans wouldn't really be a big deal, as long as they mature in the same time frame as livestock animals currently do. The breeding would take longer, but the commercial value wouldn't be much different.

Most livestock until relatively recently were what are called 'landrace breeds', meaning that they're basically a breed that was bred local to an area through many, many generations of basically being kept by people, but not specifically bred as we know it today. So I suspect that the main difference would be that breeding would take longer, but that the commercial use wouldn't be any different.

Now if the time to maturity for livestock elongated to human-length along with the lifespan, then yeah, it wouldn't be very viable.
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Old 02-24-2020, 08:33 AM
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It doesn’t matter how long an animal lives, what matters is when it reaches breeding age.
Exactly. I don't think humans have made much effort to breed longer (or shorter) lifespans. But even if we had, it's difficult to breed for this.

If I want dogs with smoother fur, or bigger body size, I can evaluate a litter pretty much immediately, certainly within a couple of years. And breed the ones with the traits I like.

With longevity, we don't know until much later, after breeding age, which animals had the desired trait.

In fact this has some parallels to at least one of the main reasons we think organisms age. The longer after entering breeding age that a trait manifests harmful effects, the lower the selection pressure to remove that trait from the gene pool.
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Old 02-24-2020, 08:43 AM
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The counterexamples are some pets, like parrots and koi, which can live a very long time but are domesticated.
Technically... parrots are NOT domesticated. They are easily tamed wild animals. Each generation has to be re-tamed and they can go back to wild very easily.

That said - given a few more centuries we may very well have truly domesticated parrots, if anyone wants to bother. Or if there are any parrots left.
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Old 02-24-2020, 08:44 AM
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Don't wolves in captivity live about as long as domesticated dogs?
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Old 02-24-2020, 08:57 AM
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The truth is, very few animal species seem to be suitable to be domesticated, period. There's around a dozen or two out of I guess hundreds of thousands? I mean if you exclude exotic pets, and limit your list to animals which have been long bred in captivity and have become genetically distinct from the wild population from which they arose. Domestication, except for dogs, is a very recent concept in human history, I think sheep and goats, the earliest, were only 10,000 years ago.

Very few animals live out their 'natural' lifespan in the the wild. Most of these are too large or too armored to be easy prey and have some kind of reasonably unlimited food source, like elephants, lobsters, and some tortoises and sea turtles. Predators who must hunt agile prey starve quickly if they get old or injured, for example.
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Old 02-24-2020, 09:31 AM
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Would humans put the effort into domesticating another species if they knew that the benefits wouldn't begin appearing until their great-great-great-great-great-grandchildren's time?


Well, if you consider the history of forest management, some humans already do this. Growing oak trees that are sufficiently large for building construction purposes takes centuries.
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Old 02-24-2020, 09:43 AM
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Basically, humans live for a freakishly long time, at least as mammals go. When the average American woman dies, there are exactly zero nonhuman mammals left that were alive when she was born (when the average man dies, there might be one or two elephants still alive). And that's comparing average human lifespan to the absolute world-record maximum for other species: The human maximum is a good 60% or 70% longer than that.

Or to look at it another way, compare lifespans to metabolic rates: The vast majority of mammals have an absolute maximum world-record lifespan of about a billion heartbeats, plus or minus maybe 15%. The other great apes might be able to get two billion, at the outside. But humans reach our billionth heartbeat some time in our twenties, when we're still in our prime, or even a bit below our prime, and routinely live for three billion, with four billion or more not unheard-of.

In other words, domesticated animals live for a short time because, compared to humans, everything lives for a short time.
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Old 02-24-2020, 09:59 AM
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To quibble a little, some whale species live as long as humans. But yes, your point is well taken. I wasn't really trying to answer the question, I was just clarifying it; several people were answering an entirely different question and the thread seemed headed that way.
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Old 02-24-2020, 04:13 PM
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I think the OP is not saying anything about the impact of domestication on lifespans. Instead, he is commenting on the impact of lifespans on domestication: longer lived species don't get domesticated because the logistics make it harder to apply selection pressure.
Yes, this was what I was trying to say.
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Old 02-24-2020, 04:16 PM
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It doesn’t matter how long an animal lives, what matters is when it reaches breeding age.
Aren't breeding ages generally proportionate to lifespans?

I'm genuinely asking this. I don't know if there's a rule of thumb on this, like the billion heartbeat theory.
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Old 02-24-2020, 04:18 PM
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Heck, humans can even take an interest in the breeding patterns of other humans. Someone who lives to be 80 might, for example:

-have a child at age 25
-when the parent is 50, their child is 25, and the parent intervenes with that child's choice of mate, promoting what the parent sees as a good match, discouraging what the parent sees as a bad match, and then the child produces a child of its own, which the now-grandparent can help with...
-when the grandparent is 75, their grandchild is 25, and the grandparent intervenes with that grandchild's choice of mate, promoting what the grandparent sees as a good match, discouraging what the grandparent sees as a bad match, and then the grandchild produces a child of its own, which the now-great-grandparent can help with...

So even a fairly long generation time can hold a human's interest.
I think we can take it as a given that people are going to have a different perspective on their own breeding patterns than they've going to have on the breeding patterns of their animals.
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Old 02-24-2020, 04:27 PM
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Well, if you consider the history of forest management, some humans already do this. Growing oak trees that are sufficiently large for building construction purposes takes centuries.
I did consider this point when I was thinking about the topic. But I feel that forest management is a pretty fringe example of domestication. Do people really breed oaks in the sense that they're looking to modify the traits of the trees? Or are they simply acting to produce a future generation of trees like the ones they have now?

I think this is an important distinction because the time issue I'm talking about is based on the idea that breeders are trying to cause changes to occur in the overall population. That means they have to be able to see and compare different generations of the species they're breeding.

I know that fruit tree breeders are actively seeking to change the traits of their trees. But they're dealing with short breeding spans. Apple, cherry, peach, and pear trees will all begin producing fruit within around four years of being planted as seeds. So breeders can select seeds and work their way through several generations of trees in a human lifetime.
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Old 02-24-2020, 05:57 PM
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Aren't breeding ages generally proportionate to lifespans?

I'm genuinely asking this. I don't know if there's a rule of thumb on this, like the billion heartbeat theory.
Not really.

As an example: most parrots are fully mature and able to breed in 1-3 years, yet have lifespans comparable to human beings that take 12-18 years to mature physically (mentally is another question). Birds in general mature very quickly in a relatively long lifespan compared to mammals.

Then there are animals like salmon where "maximum age" and "breeding age" are pretty much the same (meaning the sorts of salmon that die after spawning once).

Even a lot of mammals mature quickly compared to entire lifespan when compared to humans.
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Old 02-25-2020, 07:35 AM
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I did consider this point when I was thinking about the topic. But I feel that forest management is a pretty fringe example of domestication. Do people really breed oaks in the sense that they're looking to modify the traits of the trees? Or are they simply acting to produce a future generation of trees like the ones they have now?


They're not breeding the way you are discussing above, I was merely addressing the issue of long-term projects, that span the lifetimes of several generations. With the example of oak trees, the generations that live in the years between planting and harvesting have to have a commitment that goes beyond their own immediate profit. You only make money when you cut down the tree, so every year, they would need to make the positive decision to not profit this year, so that someone else will profit even more decades down the line.

I see no reason why you couldn't find people to do the same with breeding animals, is the point.
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Old 02-25-2020, 12:06 PM
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They're not breeding the way you are discussing above, I was merely addressing the issue of long-term projects, that span the lifetimes of several generations. With the example of oak trees, the generations that live in the years between planting and harvesting have to have a commitment that goes beyond their own immediate profit. You only make money when you cut down the tree, so every year, they would need to make the positive decision to not profit this year, so that someone else will profit even more decades down the line.

I see no reason why you couldn't find people to do the same with breeding animals, is the point.
Just growing trees is a passive project, even if it takes a long time. You plant the acorn and wait for the tree to grow to a harvestable size.

Breeding, on the other hand, is an active process. You need to monitor the traits your breeding stock has and make choices about which ones will reproduce.
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Old 02-25-2020, 07:01 PM
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Well, if you consider the history of forest management, some humans already do this. Growing oak trees that are sufficiently large for building construction purposes takes centuries.
Well, that site is quite the rabbit hole.
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Old 02-25-2020, 08:14 PM
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Would humans put the effort into domesticating another species if they knew that the benefits wouldn't begin appearing until their great-great-great-great-great-grandchildren's time?
Not sure I agree with the premise.
The primary measure of domestication is temperament rather than genetics. The classic question: why has nobody succeeded in domesticating the zebra? If Bos taurus had the same temperament as Bison bison humans would be eating a whole lot more chicken and pork.

In the case of the horse, what determines it's value for domestication is being able to be broken in, which has a little but not much to do with genetics. Now sure, if you were wanting horses as a draught animal then breeding for size is a substantial aim for genetic improvement. However a horse bred to be the size of a bus which can't be accustomed to standing between the shafts it has no value to the cropper-farmer compared to a Shetland pony which will.

The value of sheep can be dominated by the value of the wool produced, which is why wethers (castrated males) may be kept as productive livestock their entire lives rather than being slaughtered from meat in their prime. The time limit to the productive value of sheep is their teeth, which fall out after 6-8 years in good conditions. There has been no genetic improvement in that character in millennia.

Similarly the value in agriculture of the mule, a typically placid, sterile hybrid, which patently has seem no genetic improvement.

The agronomic advantage of domesticated farm animals is that they stay on the farm. That phenotypic improvements can be achieved through selective breeding is a bonus.
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Old 02-25-2020, 10:42 PM
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The primary measure of domestication is temperament rather than genetics. The classic question: why has nobody succeeded in domesticating the zebra? If Bos taurus had the same temperament as Bison bison humans would be eating a whole lot more chicken and pork.
I think it's temperament due to genetics. Wild animals aren't naturally domesticated. They're bred for domestication just as they are for other traits.

I agree that not all species have the potential to be domesticated. Some species, like zebras, will never be domesticated even if you try to establish a breeding stock of them. Other species might be domesticable but offer no obvious benefits to justify the work of domesticating them.

So I'm not saying that lifespan alone if the determining factor. I'm arguing that an appropriate lifespan (or at least a breeding age if you prefer that term) is a necessary factor. A species which has the potential to be bred into a domesticated species with valuable traits will never be domesticated if it doesn't have the right lifespan.
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Old 02-29-2020, 12:49 AM
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Short-lived cats seem to have domesticated long-lived humans, not vice versa. Curious.

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Originally Posted by Little Nemo View Post
Aren't breeding ages generally proportionate to lifespans?
I searched on REPRODUCTION AND LIFESPAN but found no general rule, either of earliest or longest breeding ages. Maybe I missed something. The youngest verified human mother gave birth at age five years, seven months, and 21 days; the oldest was almost 67. Modern medicine could extend that range. The youngest known dad I can find became a father at age nine; the oldest, at 96. So humans can start VERY young and continue for a LONG time.
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