Let’s just agree that # of heartbeats is an artificial/irrelevant measure of lifespan. (it’s just fun statistics)
A better measure would be something like (assuming death from old age) the rate of decay of cellular repair, etc.
I’d have thought what you’re pointing out as having been overlooked was simply not dwelt upon because it goes without saying; We’re not “forgetting something important here,” it’s just the obvious conclusion.
Phobos responds to you by saying:
But I don’t think this is the case at all. I think it’s more accurate to say most animals live through a remarkably similar total number of heartbeats, with the exception of Homo sapiens, because we have an artificially extended lifespan.
I was also not aware Asimov had mentioned this phenomenon; It had been a wildly speculative theory of mine from childhood. I had always voraciously watched nature shows, Nova, etc., and had a decent understanding that most small animals had very fast heartbeats and most large animals had slower heartbeats. I also had a pretty good idea of the lifespans of many animals and one day wondered idly if there might be a correlation; a standard ratio. I also came across this theory as an adult, but I’m sure it wasn’t Asimov. It might have been Gould, or some other pop-biologist I was reading.
In any case, I’ve never seen hard evidence to prove that it’s so, but I don’t think it’s the kind of theory that requires hard evidence; after all it’s not a very hard theory. The correlation is there, and coincidence across so many species seems unlikely. I’d be hard pressed to imagine any evidence that would contradict the theory, so I’ll assume for now it’s true.
According to a comparative animal physiology text that I have (not with me at present unfortunately, but I did check it over last night), there are three related physioloigcal traits at work here: 1) metabolic rate is inversely proportional to body mass, 2) life span is proportional to body mass, 3) metabolic time is proportional to body mass (actually, by ‘body mass’, I really mean ‘body mass raised to the (1/4) power’). The text also mentioned the constant number of heart-beats thing (though there was no mention of Asimov anywhere - he may well have been stating what is well-known in physiology). Anyway, the basic conclusions (though somewhat obvious, if you ask me) the text made were that smaller animals have a higher metabolism and a shorter life-span than larger ones, and that smaller animals experience time differently than larger ones as a result (the text gave some examples, which in my dazed state right now I don’t remember).
That smaller (and thus shorter-life-spanned) animals experience time differently should not really be surprising. However, I wouldn’t go so far as to say that they actually get more out of a given time period than, say, humans (as per the OP). Critters like mayflies really don’t have much that they ‘wish’ to accomplish during their lifetimes: they eat and mate and die. It is difficult to determine whether they actually perceive time any differently; a second could still be a second to them, they just don’t need as many of them to lead a fly’s version of a ‘fulfilling life.’
The medical advances which have extended average human lifespan actually aren’t relevant to Asimov’s calculation, because all we’ve been able to do is prevent premature death. For all of our tinkering and experimentation, we’ve been able to make very little progress against old age. Consider that many of the Egyptian pharos are believed to have lived to be 80 years old, and one of the Psalms refers to the span of Man as “threescore years and ten”. It has never in recorded history been impossible for humans to live to be 70 or 80, or even longer, it’s just been extremely rare.
It is possible that there’s evolutionary pressure on humans and humans alone to live a long time; most animals have very little they need to do after their young are raised to maturity, but a human can take steps to ensure the sucess of his or her line throughout life, due to our enormous dependence on learned information, rather than instinct.
That still doesn’t make Homo sapiens’ exception to this irrelevant. No one would argue that the vast majority of humanity’s physiological evolution took place before the beginning of recorded history; some would even suggest that human evolution stopped when we became able to alter our environment rather than be altered by it.
For the sake of this discussion, I think the theory is that humankind’s lifespan say, a million years ago (completely WAG, as hominids are older than that), was probably closer to 30 or 40 years. Look how long teeth last without dental technology. That suggests to me that Homo sapiens was not “designed” to last any longer.
There is some truth in this, although obliquely. Homo sapiens’ evolution includes a tradeoff between brain size and neonate vulnerability. As the size of the species’ brain increased, it became more and more difficult for women to give birth to such bigheaded babies. So the gestation period decreased until a compromise was reached. Human babies are born more underdeveloped than those of most large mammals, but their brain continues to grow a bit after birth, and of course their parents are smarter and better able to care for a helpless infant for a longer period. Clumsily stated, but that’s the gist of the theory. Makes sense to me.
ok, if there’s actually a good correlation (I’d be interested to see the numbers), then maybe there’s something to it. Any idea if this correlation extends across biological class (mammal vs. reptile vs. bird)?