Old Whales and Young Gobies: Some Thoughts on the Evolution of Aging

"In a human-dominated world, old age may be a luxury few animals can afford."

Love the thought-provoking last sentence. I wonder if our activities are exerting massive selection pressures on animals to shorten their life histories? In the same way that fishing for or hunting larger 'prize' individuals shunts populations toward smaller sizes. Maybe in a human-dominated world, Antechinus has the right idea...

"Now that I know how painful it is to live long, I am ashamed to imagine what the pine must think of me."

— Murasaki Shikibu, The Tale of Genji

But how does an evolutionary biologist explain living many years after you can no longer reproduce? Especially those species that don't look after their grandchildren?

Ed [1]: Great point. The shrinking of fish through overfishing might well have an effect on aging. The fish are smaller because their life history is altered, causing them to reach sexual maturity before they had reached full size. So that shift might make them age faster as well. The one study I know of that's at all related to this found that in an experiment that created earlier maturity in fish, they lost their swimming speed faster, but they didn't die any sooner.

Scott M [#3]: Which species, other than humans, are you speaking of? Menopause is a peculiar thing in the natural world. Female chimpanzees and humans stop reproducing at about the same age, but female chimps then promptly fall apart. Fin whales have been documented bearing calves in their eighties. As for humans, some scientists argue that menopause evolved through a selection favoring helping raise grandchildren over trying to have more children of one's own.

Elephants are the other species known for living after menopause. Child-bearing is a stressful experience for females, and the older an individual becomes, the lower the chance of producing and raising healthy offspring. As Carl already intimated, in long-lived social species an elderly female may contribute more to the continuation of her genetic legacy by aiding in raising grandchildren than trying to produce more children. This idea is also supported by the fact that male humans, who experience a lot less physical stress in reproduction, generally remain fertile pretty much until death.

Re: menopause, a recent PNAS paper suggested that menopause evolved to allow women to avoid the heavy physical costs of bearing more children and focus on raising their existing ones. The study looked at Mormon women in Utah in the 19th century, and found that women with more children have lower survival rates (as did their children). And on average, women who died early left behind three fewer grandchildren than those who survived to look after their children, which supports Carl's explanation in comment #4.

OK, I like the links and comments on aging. But something does not add up here. Imagine you were a detective and you found a dead body - say someone without any obvious cause of death. And you fuond in this person's body an old bullet wound and the bullet was still there. And it was a really old bullet - say from the Revolutionary War. Would you conclude that the person was shot during the Revolutionary War? Obviously not. Just because this whale had an old harpoon piece does not mean they were lanced the year the harpoon was made. Maybe, just maybe, someone kept the old piece around and used it a few years later. In fact, I have heard of some groups that like to use old/sacred weopons as part of hunts. So - sure it is POSSIBLE that this whale was harpooned the year the piece was made. But not guaranteed.

Jonathan [7]: The historians identified a window of a few years in which the harpoon was probably used, based on the fact that the particular model was only made for a short period of time and were used up quickly. (How they know about the speed of use is not entirely clear to me.) But in an industrial operation like whaling was in nineteenth century New England, I doubt anyone was holding onto a "sacred" bomb lance.

I am still not buying it. The calculation one would have to make here is not as straightforward as the historians imply. Even if MOST of these were used up quickly, the ones that were not used up quickly would have a different probability of being seen today, since the whales harpooned later would be more likely to be alive today. Thus if by some rare chance 10 of these were still in use today, we would be much more likely to see these. Thus even if those 10 in use today only represented 1 x 10-10 of all the harpoons made at that time, if they were still being used, we would possibly see them. I realize it is unlikely that any have been used recently, but I can easily imagine some of them being used 20 years after they were made. And again, those used at that time would be much more likely to be found today, and thus the probability calculation needs to be adjusted.

The same issue comes up over and over again in various areas of paleontology for example. One needs to incorporate the probability of finding things in order to calculate a probability of a past event from a current observation.

The whale+harpoon detective work is really interesting, especially since my daughter and I heard the same story last summer while on a whale-watching trip out of Gloucester (highly recommended, btw). It must have been a different whale, obviously, but the marine biologist cited it in support of the notion that we know very little about how long whales live.

From an evolutionary biology perspective, is there any correlation between lifespan and external factors such as predators, environment, etc.? One is tempted to conclude that whales have it pretty good- water supports their skeletons, the temperature doesn't vary much, there's food everywhere, and other than the occasional jackass with an explosive-tipped harpoon, predators don't appear to be an issue. Provided that the species in question can reproduce throughout its lifespan, it seems likely that living longer would represent an evolutionary advantage...but does the existing data support this?

Given that the whale's estimated ages falls well within the boundaries of its estimated potential lifespan (unlike your example of a human being with a bullet common in the Revolutionary War), doesn't it seem most logical that the harpoon likely came from the era during which it was used? It seems almost painfully straightforward to me, but pehaps your're looking for a new CSI series on marine mammals.

OK fine - I was being excessivly difficult in the face of a perfectly good explanation. But none of the stories I saw expressed any doubt about the explanation and I think scientists get ourselves in immense trouble when we suggest our explanations are perfect.

So unbloglike to concede! But don't you think we also get ourselves in immense trouble when we express doubt (because there is ALWAYS some uncertainty) on rather certain findings (e.g., evolution, global warming)?

OK now you have gone too far. Dating a whales age from harpoons and "Evolution" or "Global Warming" are a bit different no? Yes, certainly, I think one needs to choose wording and battles carefully because certain people and groups will use disagreement to support their absurd (e.g., intelligent design) positions. But asking that the whale age estimates be made carefully - well tha ain't the same is it now. Now I do regret conceding in an unblog-like manner. What was I thinking?

Now it's my turn to concede. I was not suggesting that there was a similarity between a harpoon and evolution. Just merely that, among the scientific community, there is a knee-jerk skeptical reaction to nearly everything. In some cases, the quibbling (as we are doing here) is innocent and without consequence. In other cases, the rifts in the scientific community have resulted in nothing short of public shutdown and decisions based on politics or morality rather than the quibbled-over evidence. Certainly doubting one piece of evidence (e.g., the harpoon) does not compare to doubting research in which consilience occurs (e.g., evolution, global warming).

I think there is not only one reason why some animals evolved longvity. In the case of social animals like primates or elephants it makes sense, and also for animals which life under very hard circumstances with long periods without food. But on the other hand, a longer life can also evolve as a result of ecological welfare. Experiments with guppys which were introduced in waters without specific predators showed that they evolved during a short time significant increase in body size, age at sexual maturity, number of offspring and lifespan. It seems that similar things also often happened when animals colonized predator-free islands. Reproduction rate and lifespan seems also have an important relation. It is also interesting, that even very closely related species can have very different life-spans. Another interesting question is how the genetic diversity of species with a very long lifespan is different from animals with a moderate long life. What effects does it have if single specimens beget of bears new offspring for many decades, especially if sexual maturity is although reached comparably early and even young animals (at least females) can and do reproduce even at a young age. Fire salamanders (Salamandra salamandra) and slow-worms (Anguis fragilis) are both known the reach an age of about a half century. Both life in comparably cold regions and normally hibernate, but this is surely not the only reason why they can life that long. I once found a nearly world-record-sized slowworm (can be seen on a post by Darren Naish: http://scienceblogs.com/tetrapodzoology/2007/05/pompey_and_steepo_the_w… ) which was undoubtly already much older than I am. I would really like to know how many descendents this old male had. Slow-worms are highly affected by carnivores of all kinds, small to medium sized mammals, several birds and at early stages even big insects. So here?s a completely different case. Perhaps the fact that both slow-worms and fire salamanders are viviparous has a connection with their longevity.