Why do animals get cancer at a young age relative to humans?

I was thinking back about the pets I’ve lost and realized that almost all were from cancer. They may have only be 10 or 12-years old at the time. But we don’t see that kind of cancer incidence in humans. Although some kids do get cancer, it is pretty rare. So why do animals get cancer after 10 years but humans don’t?

Doesn’t that sort of play in to the ‘dog years’ thing? Most people also have a life span of more than 15 years as well.

Instead of thinking that they got cancer at a young age, maybe look at it from the angle that they get cancer at (estimating) about midlife or 2/3rds of their estimated lifespan. Sort of like humans.

10 - 12 years is not young for dog or cat. Most pets live to 14 -16 at the most.

I agree that 10-12 is at the end of their life, but why does 10 dog years produce cancer while 10 human years don’t?

Because a gene that causes terminal cancer at 10 years old in a dog doesn’t appreciably decrease their reproductive success (they’ve already, in principle, had all the puppies they are going to have) so it gets passed on. A gene that causes terminal cancer at 10 in a human is never passed on, because nearly all of the time a 10-year-old human has not reproduced.

From http://en.wikipedia.org/wiki/DNA_damage_theory_of_aging#Lifespan_in_different_mammalian_species

It would appear the DNA’s ability to repair itself only lasts so long. So a animal with a shorter lifespan will reach this point of exceeding the capacity sooner.

A 10- or 12-year-old dog or cat in the wild would be quite elderly, and has passed up multiple opportunities to die from starvation, predation, disease, childbirth complications, etc.

Not much different from our ancestors not so many generations back.

One of the reasons human cancer rates seemed to skyrocket starting in the late 19th century is simply because human lifespans in general nearly doubled during that time. Before that there were plenty of other things that killed you long before your body had a chance to develop cancer…

You have to stop thinking about absolute time and start thinking in terms of lifespan. Cancer in humans doesn’t take 60 years to develop. After a certain point in our lifetime things start to break down and go haywire. Elderly is elderly regardless if it took 10 years or 60 years to get there.

because a 10 year old dog is as “old” as a 60 year old human. animals with shorter lifespans than us age faster. most of the dogs my family’s had have been old (deaf, blind, and grayer than hell) by the time they’re 15 years old.

I see now. It’s like asking why a Yugo doesn’t last as long as a Mercedes. Everything is built with a certain lifespan. Once it starts to reach that age, systems start to fail, and that makes it easier for other failures to take hold (like cancer).

That was a nice analogy :slight_smile:

Pretty much entirely wrong about both Mercedeses, Yugos and organisms though.

There’s 2 hypotheses for the causes of human aging.

  1. The “wear out” hypothesis. Self repair in the human body isn’t perfect, so, eventually, stuff breaks.

  2. The “flaw in the software (genetic code)” hypothesis. Apparently, once a human reaches an arbitrary age, everything starts failing due to flaws in the code.

The fact that other mammals seem to develop the exact same infirmities that humans do (cataracts, cancer, etc) at a time that is chronologically much early provides very strong evidence for hypothesis 2.

Not so sure that such follows.

Aging is the result of accumulated cellular damage. Cancer is often the result of damage that leads to dysregulation of cellular proliferation and differentiation. These sorts of damage tend to accumulate at different rates dependent to no small degree on the individual’s metabolism. Generally speaking animals with faster metabolism accumulate more damage more quickly as a result of that faster rate hence both age and increase cancer risks pretty much in lock step. Slower metabolism (often but not always larger animals) accumulate less quickly. Within humans those with faster resting heart rates are likely to die younger.

IOW the “wear out” hypothesis has cells wearing out as a function of the rate of energy expended per unit mass and is consistent with aging and cancer both occuring more quickly in animals with faster metabolisms.

Of course the actual relationship is not completely correlated and other factors come into play, such as in pets inbreeding which allows genetic predispositions to accumulate as a consequence of aiming for other features (such as Goldens, Boxers, and other breeds having increased rates of breed specific sorts of cancers at earlier ages). So the code is important as well. Of course from evolution’s POV it may not be a flaw … but that is another discussion.

The human connection to the op is quite interesting.

Heart rate correlates with metabolic rate: in general a lower heart rate means less energy expenditure/lower metabolic rate.

Heart rate is a significant marker not only for cardiovascular and all-cause mortality but also specifically for future cancer death risk.

Despite the fact that the authors speculate that heart rate may be an epiphenomenon, the broad interspecies context suggests the metabolic rate explanation to have explanatory power.

Specific to the op: most pets live at a faster metabolic rate than do humans and thus age and are prone to cancer as function of that faster rate. That said it is also true that selective breeding has resulted in genetic differences between breeds independent of the metabolic rate factors, such for why big dogs may die younger possibly related to IGF-1 levels: selecting for size has resulted in very divergent IGF-1 (and related compounds, all integral to growth, metabolism and aging functions) in different breeds.

At Last!

One marker that says I’m NOT going to drop dead tomorrow!

Yea me!