In tomorrow’s New York Times book section, Abraham Verghese reviews Jonathan Weiner’s new book, Long For This World. It’s about the science of ageing, dealing with its physiology, genetics, and evolution (there’s a NYT podcast/interview here). The book is apparently centered on gerontologist Aubrey de Grey.
It’s a positive review, which is good. As a science journalist, Weiner is up there with Carl Zimmer as someone who really grasps the science he’s writing about, though Weiner’s prose sometimes shades, as is common in science journalism, towards the purple.
I did a double take when I first read this excerpt:
Yet evolution has equipped us with bodies and instincts designed only to get us to a reproductive age and not beyond. “We get old because our ancestors died young,” Weiner writes. “We get old because old age had so little weight in the scales of evolution; because there were never enough Old Ones around to count for much in the scales.”
But then I realized that what Weiner means by “getting old” is not an increase in years, but the phenomenon of senescence—those changes in the body that occur with ageing. He’s apparently referring to two evolutionary theories of senescence: we fall apart because mutations that make us fall apart were never selected against in our ancestors, who had a limited life span (the “mutation accumulation” theory); and the idea that natural selection might have promoted the accumulation of mutations that trade off increased reproduction when you’re young with degeneration when you’re old (the “antagonistic pleiotropy” theory). In both cases a high mortality in ancestors (due to disease, accidents, malnutrition and the like) could favor the evolution of senescence in descendants.
I must say that it’s not much consolation to realize that the aches and pains that start afflicting us around age 35 are the byproducts of natural selection.
And here I thought it was the tequila and too many nachos…
It is sin of course, that it why the young earth looks so old and we age. Teehee.
“Abraham Verghese review’s”?
Oh wait, this is no longer about typos and grammar anymore, is it?
😉
Yes, if it’s in common use, it must be right, and of course unnecessary apostrophes are all over the place (see here).
Nevertheless, I’ve fixed it!
“I must say that it’s not much consolation to realize that the aches and pains that start afflicting us around age 35 are the byproducts of natural selection.”
Word!
Word?
I think you have to be at least 35 to recall this all purpose interjection…maybe that’s the point!
Well, I’m 57, so maybe you have to be American too, to get it? Since I’m still not getting it.
It’s slang. Equivalent expressions might be “Too right!” or “Indeed!” or “Harumph!”
Example:
“This cake is mad moist, yo.”
“Word.”
Ah, okay, get it now. Never heard of it, though, so I learned something new. Thanks!
Uhm … “mad moist”?
Oh, never mind.
To be nitpicky, re: “we fall apart because mutations that make us fall apart were never selected against in our ancestors”
That would imply that there was an earlier state where H sapiens et ux lived longer, which doesn’t seem to have ever been the case. Seems like it ought to be more like “we fall apart because elements that promote or fail to act against our falling apart were never selected against in our ancestors, since they only infrequently lived that long, and were anyway largely past reproductive capability”
I would say “we fall apart because mutations that make us MORE DURABLE were never selected FOR in our ancestors”.
From the immortal gene’s point of view, our bodies are expendable and the extra durability is not worth the extra cost.
“I must say that it’s not much consolation to realize that the aches and pains that start afflicting us around age 35 are the byproducts of natural selection.”
This may be giving up. Surely, it may be better to have some reasonable idea than to have no idea or have the wrong idea, like senescence as a result of original sin or satanic agency?
Or just the will of God.
Who, ironically, must have really liked Ernst Mayr…
(Yeah, I know, that “joke” really doesn’t work when we’re talking senescence vs. absolute age. I just couldn’t resist…)
Aubrey seems very modest when he claims that people could live ~ 1000 y if we beat senescence. If we were like electronic systems, without consistent aging but failure of components, failure rates of ~ 1/2000 y^-1 for twenty year olds would mean ~ 2000 y average.
[But I’ll have to read him thoroughly.]
OTOH if we beat genetics, we could all be 20 m long…
… but of course he would like to work on failure rates if the anti-senescence program gets going. Two hearths, anyone?
At that rate you’d have lost 1/3 after ~800 years, and would get to spend the remaining ~1200 as a vegetable.
And I don’t have a clue what it means to “beat genetics” in this context. It’s not a matter of getting rid of “bad genes”, unless you find the story about Michelangelo chipping away all the bits of rock that didn’t look like David to be plausible.
Analogously to electronics you have lost 1/3 of the population (in single failures such a hearth attacks). The whole point us that failure as opposed to wear doesn’t make us vegetable or otherwise sub-functional.
But sorry about the frugal context. I meant that there isn’t a single gene that needs fixing. It’s complex, as WEIT likes to remind us of.
It seems to me the more interesting question is why we live so damn long. Most people over 40 aren’t going to have any more children, and most people over 60 aren’t going to contribute much in the way of heavy work (like hunting with a spear).
I’ve heard of the “grandparenting theory (sort of like the gay uncle theory – someone to help with babysitting),” but I’m sure there are other hypothoses I’m unfamiliar with. My favorite uncle retired at 60 and lasted until a couple of months ago aat 93. I’m glad he did, but I see no obvious evolutionary benefit.
That’s just humans fighting nature so well. Even before modern medicine some people lived to be very old, but those were rare cases. Now that we can warm the globe in winter, warm the globe in summer (while cooling the house), import food, and treat or even eradicate numerous diseases, growing old is becoming more common for many humans. If you visit societies without all the modern comforts such as in Africa, Asia, and the nomands of the high northern latitudes, you see people generally don’t get half as old.
One observation I’ve seen recently is that there is a correlation between size and long life. That is one factor.
[And a correlation is seen between size and intelligence too. We have all the fun!]
My duh, see comment below: this may be true, but what I had seen was a recent report that brain size correlates with longevity.
Then why is Pat Robertson still alive?
Good point.
… oh, wait. What makes you think he and his brain is alive?
Very old individuals serve as repositories for knowledge – in in particular, knowledge of rare events. This is especially important in a culture lacking the written word (which was all human cultures until only very recently, and all animal societies even today). It’s the very old individual who’s going to remember which water hole never goes dry even in the worst drought, for instance. Perhaps that knowledge is of enough evolutionary benefit to act as a positive selection pressure in favor of a longer (abet not immortal) post-reproductive life?
Also, one perplexing factor, which may or may not be accounted for in grandparenting theories and similar, is that maximum age is rumored to be rather constant. I.e. the oldest greeks and romans could well have been comparable to our own. (But we have a much higher population to draw individuals from, so we populate the tail of the age distribution better, we have more extreme examples.)
Now this is only rumor AFAIU, but it would be interesting to follow up, and if correct see the consequences on respective theories. (I.e. do they predict that?)
Yeah, rumor … so not actually “a factor”. Sorry for the confusion!
Given some of the newer hypotheses, such as aging due to telomere length reduction, that would make sense.
(http://en.wikipedia.org/wiki/Hayflick_limit)
Also, the interval between the oldest Greeks & Romans & ourselves may not be very significant, speaking of evolutionary time…
“evolutionary time”
Granted. It was an illustration of how individuals are (rumored to be) old in historical time, despite social/biological adversity.
But Noah lived past 600 or something (I know it’s true – I read it in the Bible!)
Maybe we modern folks aren’t sacrificing enough goats.
Aubrey looks like a goat – and he is obviously willing to sacrifice himself for the research.
Why isn’t that enough? Stupid religion!
Aches, pains, and other deficiencies. Oh well, some people get diabetes when they’re much younger … stupid god. I still have coronary artery problems, Alzheimer’s disease and depression to look forward to. It reminds me of one of Noel Coward’s songs: There are bad times just around the corner, there are dark clouds hurtling through the skies …
B*gger you, Jerry Coyne, yet another book that I have bought (as the Kindle e-book)on your recommendation, and have added to my list of books to read. I’ll start it after I finish the book I’m currently reading Scott Sampson’s (non-recommended) “Dinosaur Odyssey: Fossil Threads in the Web of Life”, which is actually very good.
Well, that explains why we degenerate in later years.
But what about our slow growth rate in comparison to other animals? Is there a reigning theory concerning that, or are there multiple?
Interesting, but I can think of record old reptiles and mussels that grow slow. References, please.
Well, sure. But mussels and reptiles are cold-blooded and generally do not expend so much energy as mammals.
In fact, the only mammals that can actually match us in age are whales (supposedly: it has been difficult to measure the age of a whale).
Something to do with that here: http://www.school-for-champions.com/animalhealth/animal_ages.htm
No, elephants also match us in age, as do other great apes (no surprise there) and several species of birds (mostly parrots). We’re unusual in living so long, but hardly unique.
But what’s the point? Our primordial lifestyle isn’t very low-stress, and we still had a lot of predators.
I think the graphs displaying the comparative ages of cats and dogs to humans gets my point across better.
I’m not sure the graph does (or rather, I’m not sure I understand what you’re deriving from it). We live much longer than cats and dogs, true – but we also live much longer than many larger animals (such as cattle and horses) and some small animals (parrots) are also quite long-lived, so body size isn’t the sole determinant. Neither is level of predation; we, like elephants, don’t face much, but parrots do, and they’re just as long-lived. Metabolic rate can’t be the major factor, either; while some reptiles (which have generally low metabolic rates) are long-lived, others are not. And birds have a higher metabolic rate than mammals do, but that doesn’t keep parrots from being long-lived. About the only thing we can say for sure is that at least for mammals and birds, extremely long life is correlated with high general intelligence – but is that the chicken or the egg? Both New World and Old World monkeys are extremely bright as animals go, but most species don’t have exceptionally long lifespans (certainly not as their cousins the great apes).
It’s quite a tangle!
Thanks, but that is data on senescence. I can’t beg the question.
And what dlnevins says. (Thanks!)
I’ve heard that, because of our large brains, we’re born in a much more neotenous stage than other mammals…
First, my duh! Above I claimed that body size may be a factor of longevity (and it may), but what I had seen was that brain size correlate with longevity:
“The authors of the study emphasise that the relation between a large brain and a longer life is not always one of cause and effect. “CBH points to this fact, that a larger encephalon favours a longer lifespan, but it is equally possible that a longer life favours the development of larger brains,” researchers assure. Thus, it is possible that a longer life works in favour of a delay in reproductive cycles and this would in turn allow progenitors to invest more resources and time in caring for their offspring. This also leads to the formation of stable social groups whose members, according to the Social Intelligence Hypothesis (SIH), must deal with more cognitive demands than animals living alone, and this would be the reason for larger brains.”
(It’s a large statistical sample of 500 species, so the data should be safe regardless of all those funny hypotheses.)
Second, it is to my satisfaction that swedish researchers have found that motor development is highly conserved in primates:
“time to the onset of walking counts from conception and not from birth, indicating that mechanisms underlying motor development constitute a functional continuum from pre- to postnatal life. […] Our findings do suggest, nevertheless, that a strong link between the timing of brain development and the timing of motor development may constitute the basis for a fundamental ontogenetic pattern of early life history shared by a wide range of placental mammals, some of which diverged in phylogenesis as long as 100 million years ago. This pattern, which therefore may be traced back before the evolution of primates, appears to be recognizable also in humans despite the fact that humans differ from other mammals in so many respects.”
So if this is the dominant characteristic, explaining the mechanism of gestation in our species, we are not exactly neotenous (retaining juvenile characteristics). We have a shortened (aborted) gestation to allow for a larger brain vs the female pelvis.
You’re right. I shouldn’t write so carelessly.
Interesting stuff, TL!
Thanks, DG!
No, I don’t think you wrote carelessly: I’ve heard the same claim. It may still be correct, but the result (which again is rather certain) points to a more complex situation.
If nothing else, the complexity shows that we are dealing with biology. 😮
Also, on second thought:
The conservation of motor development is likely the dominant mechanism, it predicts what we see. I believe it may inaugurate the reverse to neoteny: isn’t then the ability to recognize and respond to faces much accelerated in our development compared to other apes?
So in sum I guess the conclusion, if the research is good, is that brain size doesn’t contribute but retract from early neoteny. But contribute to our perception of it. [Cue cute baby faces.]
But as in Hollywood, we may beware of the return of The Brain (or other stuff) on Neoteny II (Later Neoteny)!? Again, it’s biology.
D’oh! The web link to motor development is highly conserved in primates. [A unifying model for timing of walking onset in
humans and other mammals
Martin Garwicza, Maria Christenssona, and Elia Psounib, PNAS. 2009.]
Interesting discussion of plantigrade vs. tardigrade development, too.
(Why do I always get a sophomoric laugh out of the term “functional biologist”?)
Which fact in any of itself tells you everything you need to know about the bizarre urban myth that ‘we only use 10% of our brains’. Human babies have such vast brains they not only frequently kill their mothers but have selected for premature birth so as to minimise this risk. If in knowledge of this fact you were to believe 90% of brain tissue was redundant or, like Aristotle, that it existed for some frivolous purpose such as cooling the blood you’d have to be insane.
Yet evolution has equipped us with bodies and instincts designed only to get us to a reproductive age and not beyond.
A man is able to contribute his sperm for much longer in his life than a woman is able to contribute her egg. So, why don’t men live longer than women?
While waiting on the WEIT experts: no, evolution works on differential reproduction (among other things), not reproductive age. That can well incorporate mechanisms like the grandparent hypothesis.
And AFAIU that hypothesis grants caretakers, likely females seeing the differential behavior, some evolutionary lever.
Also, there is a mechanistic explanation, which granted is iffy seeing the different X, Y trajectories: in principle the XX combination provides some functional backup, doesn’t it?
Okay, I expressed that badly, seeing that (in most cases?) one of the Xs in XX gets silenced. But AFAIU the picking is (somewhat) dependent on functionality. Thus the the advantage to XY (modulo the individual X,Y pathways).
D’oh! Advantage _over_ XY.
Well, duh! They nag us to death.
I am no specialist, but I guess that old age is just a byproduct of the fact that our bodies must decay slowly, so we won´t die all of a sudden, before generating and raising our offspring.
There’s no reason to expect that our bodies should last forever, since natural selection doesn’t require a very long life span.
There’s no reason either to expect them to decay quickly after reproductive age, since the potential duration of our lives has nothing to do with our reproductive capacity.
As natural selection doesn’t interfere with nothing besides the number of descendants we can produce and take care of, decay is just the natural wear and tear of the material.
So that’s a perfect statement of the ‘senescence is not selected against therefore it happens’ view. But consider another idea; there is a limited amount of resources to go around and if new, young creatures are all that evolution ‘cares about’ then it’s entirely possible for group selection effects (or if you don’t like Eliot Sober, the geneocentric proxy of group selection effects) to actively promote the senescence of agents after they’ve produced sufficient offspring. It would presumably be necessary for the fitness gained by having more offspring to be outstripped by the cost to those offspring by continuing to consume resources which (at least, intuitively, to me) suggests there would have to be some rudimentary senescence going on anyway (as Coyne mentioned, accidents and disease perhaps) but the odd thought is that under these circumstances evolutionary pressure would promote the senescence of the agents for the good of the offspring, ala Logan’s Run, and therefore in a weak sense aging/senescence might have evolved (or more strictly; been evolutionarily enhanced).
Torbjörn Larsson, OM said:
So, at age 89, my life-long resolve to selflessly extend the life span of Homo sapiens through a rigorous schedule of daily multiple masturbation has been in vain?
LOL!
But that is not a snap moment (unless you broke the twig).
You’ll have to ask if, say per the grandparent hypothesis, your behavior have made you a good grandparent.
Maybe you are going there, but I’m not touching that. (^_^’)
Gingerbaker IS my grandfather, and a damn poor one at that. Sure, Cream was great and Clapton was always useful for a quick fix, but Ginger – all that damn drumming. Listen, gramps, “Sunshine of your Love” does NOT make a good drum solo. It needs a guitar.
Now let me get some sleep.
I sincerely hope I’m wrong because this research is both interesting and important, but every time I read about this it _always_ involves de Grey. It seems as though he’s the only person in the field, and it also seems like he’s a raving lunatic with questional credibility.
These sorts of quotations are entirely typical:
“De Grey, you see, is not, as he is sometimes mistaken to be, a professor of genetics at Cambridge but a half-time research associate with a day job managing a genetics database.”
“He acquired his doctorate in biology by way of a hoary, little-used Cambridge shortcut: Without ever registering for graduate study, he submitted to the university a book he’d written on the mitochondria, the power plants of cells.”
http://www.popsci.com/scitech/article/2005-01/prophet-immortality
So my question is, who’s making the real progress, if any?