Most animals have a maximum lifespan in the 10s of years. (Maximum life span - Wikipedia). I understand there are outliers but most seems to be in 10s of years. Also understand that most animals don’t get to live to the maximum lifespan.
The accuracy of the lifespan is not important to this question. Let’s say we have a median lifespan X for all the species of animals that exist in at a point of time.
How does X vary with the geological eras / periods ?
I’d think the variance of life span at any point in geologic time is going to be very big. I’d also think that since there are so many small and short-lived species, the median value for lifespan is going to be pretty small and relatively constant over time.
Are you interested in lifespans for larger creatures? I assume you’re not including plants.
Thank you Voyager. If it helps the discussion, let’s limit the animals to vertebrates.
I don’t think this question is very answerable except in the very broadest of terms. Are you asking for lifespans of individual animals? Of species? What do you consider to be “animals”, only vertebrates, or are you concidering all multicellular creatures that aren’t plants or fungi? For instance, you might could say that the median lifespan was much shorter in the Cambrian than today, but then you would be faced with the fact that to count the Cambrian you would have to count invertebrates, which would mean that you would also have to count invertebrates today, which have so many individuals and species that they would drag the median number so far down that it might not be very different from the Cambrian. (For instance, say today there are 10,000,000 species of animals, of which 9,800,000 live a year or less.)
Unless the actions of older individuals affect the lives of others in the species, or unless the individual remains able to foster young into its old age, I don’rt see how the lifespan plays into evolution at all.
Evolution is adaptive radiation moderated by natural and sexual selection, for the most part. If a new adaptation allows the creature to more successfully survive so that it can mate, or makes it more likely to mate, then it will be more likely to have offspring who will carry on the genes. If it continues to live after its effective breeding days are over, it won’t affect this pathway to survival, so the actual age of the individual becomes irrelevant.
The only exception I could see is if something that the individual does enables others of its group to survive – like if the creatures live together in a herd, and the oldsters take care of the young, or if they contribute to the defense of the group, or if they at least distract predators hounding the group and enable others to get away, or some such behavior that could contribute to the likelihood of the group surviving.
But if you had lone individuals past breeding age that don’t contribute to survival of a group, I can’t see how evolution would even affect their longevity.
Evolution affects all of nature, and that includes insects whose life spans may embrace a single season. I don’t see a cause/effect relationship there at all.
Okay, that narrows it down, but still in any given period there would have been vastly more vertebrates–both species and individuals–that are tiny than those that are huge. So for every giant sauropod living 100 years there might be millions of shrew-sized animals living one year.
I agree. The key factor in natural selection is passing on the genes that carry the trait to offspring.
So even if you have a species where you have individual animals who live past their breeding age and the species benefits from this, it isn’t a factor in natural selection unless it provides a relatively greater advantage to individuals who are still breeding and carry the same genes.
Disagree. With a collaborative/social species, older individuals are able to influence the survival of their descendants, and thus influence the longer term “success” of that genetic line.
Speaking as a grandparent, I think Homo Sapiens sapiens is a sound example of this. There are others not so close to home.
You clearly didn’t read my entire entry, because I said just that.
You have to know what you’re disagreeing with.
Maybe. But maybe it’s a negative on the survival of descendants. Once property rights are established and laws of inheritance take hold dying early may result in your offspring breeding earlier and more often.
Had I died 15 years ago when my children were reaching prime child bearing age leaving them the equivalent of five years salary they may have elected to have children earlier and I’d have four grandchildren instead of the two that I now have.
Of course, I may live long enough to have my grandchildren inherit and they may have more offspring, but if I live too long I’ll spend the nest egg and may actually become a burden on them, inhibiting their ability to reproduce.
Maybe once you get your children old enough to be sexually mature the best evolutionary strategy would be to die and get out of their way.
Most animals don’t usually live past their breeding age; female humans are one of the rare exceptions.
Other animals may have a bit of a fertility drop off as they age, but generally, they can keep on having babies until they die. Maybe less frequently, but sometimes the greater experience means they have the same or better success rate at rearing young compared to younger females.
Darren, thanks. The OP was about species wise median lifespan not individual lifespan.
Evolution occurs more quickly in species which have a short generation time. So smaller animals will evolve more quickly, since they have shorter lifespans.
Life span varies very roughly with size among vertebrates. Competition between vertebrates has likely been fairly evenly balanced ever since they arose, and there have been big versions of vertebrates almost since their beginning.
I don’t know how to guesstimate the lifespan when vertebrates were all aquatic, but I think X would be fairly stable through the eras, just dipping during extinction level events and the more dramatic climate changes.