Re: longevity

J. R. Molloy (
Sun, 21 Nov 1999 15:09:25 -0800

Curt wrote,
>Sorry, I didn't phrase that right. If selection is weaker due to complicated
>the lifespan increase selection will be able to establish is shorter. If you
>hypothetical improvements with simple genetics and no disadvantages, maybe
>mice in the wild would end up with a lifespan of four years (I'm making up
>the numbers)
>If the mutations had complicated genetics, maybe the best selection would be
>to do is 3 years.

I see. So complicated genetics tends to resist a simple (genetically caused) extension in longevity. The more complicated the genetics (along with accompanying ecological complexities, of course), the less stable a genetically derived extension of longevity. Does that imply that Evolution selects for shorter life-spans under certain circumstances? I still find it difficult to fathom why a population that reproduces or completes its life cycle in half the time of a competing population does not garner an advantage for itself in that it can adapt to changing environmental conditions twice as fast.

For example: Suppose a catastrophic event destroys all human technology on Earth. Dogs and cats, with reproductive cycles seven times faster than human, could revert to their wild state, become feral, seven times faster than humans could revert to hunter-gatherer nomadic bush people. This would give the dogs and cats that got thrust into a primordial jungle an advantage over humans who could not so quickly revert to feral prehistoric conditions of living off the land.

>>>Of course longer lifespan may have costs. In the Rose lab, the long-lived
>>>strains take longer to develop and lay fewer eggs in the first part of life.
>> So, shorter life cycle strains would outperform long-lived strains?
>With these particular strains. Research has shown that some "short-lifespan"
>carry compensating advantages (for the genes, not necessarily the organism)
>others serve no purpose and have eluded selection. Theory suggests (although
>I'm not
>aware of any experimental tests) that genes with important and straightfoward
>"short-lifespan" effects essentially only come attached to compensating

Could a shorter reproductive cycle (producing more offspring in a given amount of time) constitute a compensating benefit?

>The best area of "natural" effects to look at, by this theory, are
>short-lifespan alleles
>which help the interests of the gene rather than the organism - mostly
>and sexual selection genes. It may well be possible to find genes that, say,
>the growth of secretory breast or prostate cells. Conking those genes will
>fertility (but we don't care much; we can deal with such problems) but
>they'll cut
>your chance of breast or prostate cancer. Since the genes are evolutionarily
>advantageous, they will exist even if easy to knock out and so be good targets
>for medicine.

So, Evolution wants organisms to reproduce, even if it means a greater risk of developing cancer (for the individual) to do so. That makes sense, since the species comes before the individual. Why doesn't it make sense for faster Evolution, via shorter life cycles, to render a biological advantage for a species? The mutability of bacteria and viruses gives them a powerful strategy against longer-lived species which cannot change as quickly, yes?

>We can also look at adaptations for our ancestral environement that are no
>appropriate. Genes for high LDL cholesterol and adult-onset diabetes seem to
>starvation defenses. Those should also be amenable to intervention, with no
>as long as we keep the supermarkets stocked.

I didn't know that. Thanks.

>Our best bet for the costless problems (whatever they are) is to look at
>things that
>would be hard for evolution to do, so gene knockouts, drug alterations and
>mutations are poor choices. We would want to bring in novel systems, from
>or from other organisms. An example (from Caleb Finch) would be whale
>mechanisms. Whales have a per-cell cancer chance that is orders of magnitude
>than yours. Presumably they have at least one additional layer of defense.
>If we
>could figure out what it was, we could take out a stem cell type, splice in
>the cancer
>defense, wipe out the cells in the body, and then insert the "improved"
>cells. Voila,
>90% reduction in leukemia. If we're really lucky, we might be able to
>improve cell
>senescence at the same time.

Very encouraging. Extropic genetic engineering trumps and transcends Evolution. --J. R.