AGING Processes - Many? A Definition?

Steve Chambers steve at chambers.ak.planet.co.nz
Wed May 3 23:00:33 EST 1995


In <Pine.SOL.3.91.950422110448.24648A-100000 at corona> "Patrick O'Neil" <patrick at corona> writes:
>On Fri, 21 Apr 1995, Steve Chambers wrote:

>> In the hope of stimulating further debate, I'm going to play devil's
>> advocate.  The following might be seen as evidence against such a 
>> multiple process model of aging:

>> 1) It seems that homo sapiens' maximum lifespan may be double that of
>>    his most immediate ancestor.  Some might argue (notably Cutler) that 
>>    150,000 years is such a short period of evolutionary history that 
>>    advantagous mutations could only have influenced a FEW aging processes.

>What data is there to support a doubled lifespan for modern humans vs 
>their immediate ancestors?  

Patrick

I always enjoy your posts and I appreciate the fact that you are arguing 
in support of my earlier contentions.  However, the arguments I presented 
against a multiple process model for aging are very real and can't be 
dismissed so easily.

For point (1)
-----------------------------------------------------------------------------
Cutler RG 
Evolution of human longevity and the genetic complexity governing aging rate. 
Proc Natl Acad Sci U S A; 1975 Nov; 72(11); P 4664-8 

ABSTRACT
Genetic complexity of processes governing the aging rate of man was 
estimated by determining the maximum rate lifespan has evolved along 
the hominid ancestral-descendant sequence. Maximum lifespan potential 
was found to have increased approximately 2-fold over the past 3 million 
years, reaching a maximum rate of increase of 14 years per 100,000 years
about 100,000 years ago. It is estimated that about 0.6% of the total 
functional genes have received substitutions leading to one or more 
adaptive amino acid changes during this 100,000-year time-period. 
This suggests that aging is not the result of an expression of a large 
number of independently acting processes. Instead, primary aging processes
appear to exist where only a few genetic changes are necessary to decrease
uniformly the aging rate of many different physiological functions.
--------------------------------------------------------------------------

I've not sighted the paper, but I believe the methods used were:
(1) a phylogenetic analysis of the MLP of present living species and 
(2) an empirical equation using brain and body weight 
    estimates from fossils.

[snip]

>> 2) Calorie Restriction has a significant life-extending influence, and it
>>    influences MANY age-related changes.  The effect seems to be universal. 
>>    Some might offer this as evidence that there are only a FEW (and maybe
>>    only one) underlying aging processes.

>Not necessarily.  I would put forward the rather simple explanation of 
>this effect as being due to a reduction in the rate of metabolism.  

[snip]

This is not a new thought - but the jury's still out as to whether the 
life-prolonging effects of CR can be attributed to a generally reduced 
metabolism.  It's hard to square such a theory with CR's effects on 
glucose metabolism and the improvement in various immune functions.  
Several studies have also shown no change in BMR/kg body weight for
CR animals.

>> 3) Recent evidence (eg. Carey et al, 1992; Curtsinger et al, 1992)
>>    suggests that mortality rates may decline in late life of many species.
>>    Some might suggest that this argues against there being MANY aging
>>    processes.

>Hardly.  Those who make it to old age and are still functional might well 
>simply carry a slower developmental clock.  

Quite so - there is plainly some development-program-linked component
to aging.  But I can't see how it, per se, can provide a complete explanation
for a late-life reduction in mortality rates.  It could only do so if it
was controlled by very few gene loci with very few alleles.
 
But hey, I'm open to suggestions...

Steve

-- 
 ________________________ 
(I_lurk,_therefore_I_am!_\ ,,,                    Steve Chambers
                          (o o)   steve at chambers.ak.planet.co.nz
----------------------oOO--(_)--OOo-----------------------------
(c) Steve Chambers                     1995. All rights reserved 
----------------------------------------------------------------




More information about the Ageing mailing list