What does evolution have to say about longevity of individuals?

Great Debates
1

I’ll admit up front that I am not up on all the refinements to the theory of evolution. My rudimentary understanding is that evolutionary theory basically states that the “success” of a species is determined by whether it can survive in its environment. Random mutations cause individual critters to change, and if that mutation allows a critter to survive long enough to pass on their genes through reproduction, those changes are passed along to the next generation and are considered “successful” adaptations. Over long periods of times, these changes can accumulate to produce entirely new species.

Assuming this is an accurate (if rough) explanation, I’m wondering what evolutionary theory has to say about longevity of the individual? In other words, if a critter has a mutation that allows it to survive long enough to reproduce but causes it to die soon thereafter, is this still considered a successful adaptation?

I’m thinking here of genetic diseases such as heart disease, cancer, osteoporosis, breast cancer, etc., that tend to affect people after they have lived long enough to reproduce. Is the existence of these diseases in humans an indication that we are not 100% successful according to evolutionary theories (i.e., that we may someday evolve to rid ourselves of these problems), or did evolution give up on us once we adapted well enough to pass on whatever genes we currently have in our current environment? Does evolution “care” if we live to be 100 or only 30, as long as the species is perpetuated?

Barry

2

There is no way selection can occur to ‘remove’ susceptibility to genetic diseases that effect people subsequent to the passing on of their genes. We will. I believe, always continue to pass on a genetic predisposition to geriatric diseases.

Evolution doesn’t care about longevity of individuals, only genes.

3

If long-lived individuals act as repositories of knowledge and history, as anthropological research has shown is the case in many primitive societies, their survival would increase the chances of survival of their genetically related individuals.

4

I have heard that mentioned as a possible explanation of the ‘development’ of the female menopause - to stop elderly women ‘wasting’ bodily resources on menstruating and to focus on further longevity. Long postmenopausal life spans are unique to humans and thus distinguish us from all other primates. Of course, individual survival to pass on information / ideas / knowledge will have no actual bearing on the specific genes previously passed on to their existing offspring. But there may be other good reasons, as you suggest.

Evolution of Menopause

Is this cite out of date? Is there now conclusive research / agreement as to the evolutionary reasoning behind human menopause? Sorry if this is a bit of a hi-jack.

5

I think the “grandma” theory is still current. Of course, it’s one of those theories that’s next to impossible to prove.

Keep in mind that it’s generally not useful to look at only one trait in terms of it’s evolutionary advantage. While multivariable analysis is always much harder to do, it’s much more relavent to the real world. Longevity may be a successful stratgy for some species, and completely unnecesary for others.

6

This primarily depends upon whether or not a species is more K-selected or more r-selected. K-selected species have long gestations, low reproductive rates, and long immature periods that require young to be cared for by adults (or near-adults). This optimizes survival in fairly harsh environments, where it can be difficult to get enough resources for enormous numbers of organisms and wherein an organism’s “genetic investment” benefits from being directly guarded.

r-selected organisms, on the other hand, dump out lots of offspring, have rapid maturation, and generally little to no adult stewardship of maturation. In an environment wherein the resources are plentiful and the major risk is, instead, predation, r-selection tends to be favored. Flood out the predators and some of the offspring will make it to adulthood. However, a species needs a lot of resources for this to work, or the “genetic investment” is wasted as the offspring compete each other into oblivion and extinction.

Humans are fairly K-selected.

And, Aro, evolution doesn’t care about anything at all. It’s completely impersonal. Likewise, as was hammered into my head over and over, natural selection, genetic drift, mate selection, and all other known forces that end up in evolution do NOT operate upon genes. They operate upon individuals. It is not a gene that doesn’t eat. It’s an individual. It’s not a gene that has spiffy feathers, it’s an individual.

Show me any natural mechanism of evolution that operates directly upon genes, utterly unmodified by the status of an organism as a whole. Genotypes only matter in evolution inasmuch as they lead to phenotypes.

7

Transposons. :slight_smile:

8

The bottom line remains that any “maladaptation” that does not interfere with breeding and passing on genes–e.g., geriatric issues–are less likely to be selected against.

If (in a literally impossible but purely hyptothetical thought exercise) all human beings were prevented from reproducing until they were say forty, and this mandatory age increased gradually over many generations, our species’s longevity would also increase.

9

This reminds me of an ongoing study at some university I saw a special on…

Wait, I remember now. It was a special that was trying to scientifically apply what we currently know about genetics and technology in order to try to imitate the abilities of some of our most beloved super heroes: Spiderman, Superman, etc…, in order to theorize if such abilities were possible. It was pure speculation.

They were talking about Wolverine’s longevity. For non-Marvel fans, Wolverine is approximately 120 years old, with incredible regeneration capabilities. It helps that an adamantium skeleton was fused to his, making him virtually indestructable as well.

As a side note, it makes sense that someone with advanced regeneration abilities would also have longevity. From what I understand, the aging process is mostly attributed to our DNA “wearing out” after so many replications, that minute mutations slowly tax our bodies: sagging skin, liver spots, weaker bones. But don’t flame me if I’m blatantly wrong, that’s just a layman speaking.

So, about this special. This university, I cannot remember which one, was taking these fruit flies, with a life span of single digit days. They were removing all of the eggs from all of the females, don’t ask me how, except for the last few eggs. The result? Mother nature extened the fruit flies’ life span so that the males would still be potent when the females finally did have eggs to fertilize, released. Then, once mated, the fruit flies would rapidly die off. Apparently, they deduced, nature tries to keep you around long enough to spawn, and once you have, nature kills you off.

At the time of the special, the scientists had tripled the life span of these fruit flies.

10

But in the relatively small hunter-gatherer societies (<60 Individuals each) in which the majority or our own species’ evolution occured, it wasn’t necessary for every individual to survive beyond reproduction (to be walking libraries and help with functions like childbirth, cooking, et al.). Only a small number would be required. 3-10 geriatrics in a 50 individual group should be plenty to give the group a survival advantage, any more and it would burden the rest of the group.

To the OP:

From a survival of the species standpoint, yes, any mutation that allows an individual to be more likely to survive and reproduce viable survivable offspring can be considered a successful adaptation. Hell, look at the Arthropods. I am sure with a little investigation in the kids section of a library or a google search you can come up with dozens of examples of species whose lifespan consists of hatch, eat, mate, die, and very little else.
To Chicago Faucet:

The aging process is about a lot more than mutation, though that does have some effect on it. There is also the vast collection of injuries and scar tissue throughout your body that you have to contend with. As well as the collection of toxins in your muscle tissues and internal orgins, which are difficult to remove. On top of that, the hormones that encourage increased immune system function and encourage the growth of new cells etc seam to taper off in most peoples early to mid twenties or thirties and continue to decrease as time goes on.

As a comic book geek; regeneration would to a great deal for the repair of the injuries, and if the comic book version wolverine has could be imbued in a person, would probably signifigantly increase life span (since his also does a lot to remove toxins, and scar tissue/plaque buildups/kill diseases).

Wolverine’s cool.

11

Except, as noted by Dogface, this cannot be generalized to all species. For some, it is advantegeous to mate early and die “young”, thereby increasing the number of offspring out there. For others, not so much. All this experiment has really shown is that the lifepsan of fruitflies may be linked with reproduction.

(As an aside, I am of the same school of thought as Dogface with respect to the primary locus of natural selection: individuals, not genes.)

One important point is that the survival of any individual is largely irrelevant in an evolutionary sense. Natural selection only requires that a statistical preponderance of individuals within a population with a given mutation survive in order for it to become fixed in a population, and thereby lead to adaptation (and speciation). Dumb luck may still result in otherwise “fit” individuals meeting an early end, nor are all “unfit” individuals automatically excluded from breeding. On average, however, those individuals with beneficial mutations will be more likely to pass those genes on, and those with deleterious ones will not.

12

Even better, many aphid (Eriosaoma) and adelgid (Adelges) species are capable of giving birth to live, pregnant females in successive generations throughout the summer months!

how’s that for female independence.

Back to the op…

I don’t think our lifespan capacity (genetics) has changed so much since the first humans (Homo sapien) came about. The real difference is the ability, with current technology, to thwart many obstacles which killed off our ancestors at an early age.

As far as us evolving to eliminate the genetic disorders we have… Not likely, evolution does not flow in any particular direction; it can’t predict the future, it simply reacts to the environment provided. We are ‘successful’ as long as we are able to move our genes to the next generation, what happens after that to us is superfluous…

Evolution has not ‘given up’ on us, it is a continuing process that may or may not be easily noticed within our short time sample.