Fair warning: this is a philosophical post.
Fruit flies are short-lived as adults. The eggs hatch, larvae crawl and grow, pupate, and therein metamorphose into adults. The adults live only a few days.
As an experiment, fruit flies were prevented from mating, and the longest-living were, eventually, allowed to mate. The experiment continued with their offspring. This was all reported in Nature, so you can check me on the facts. As I recall, after something like forty generations, the fruit flies were living a very long time – something like twenty times the normal adult life-span.
Then the flies, all longevity-bred, were allowed to live and breed freely. Within half a dozen generations or so, the average adult lifespan was back to the same as wild-type fruit flies.
The implications of this are manifold; I will content myself with just a few.
- Some combination of traits, already present in the flies’ genomes, was selected for by the pressure provided by the experiment. It is not conceivable that new mutations could be sufficient for this large a lifespan change in this short time frame. Instead, existing traits were reshuffled, and certain better combinations kept while others were discarded.
- W.D.Hamilton’s hypothesis, that one of the benefits of sex is the reshuffling of manifold varieties of genes already present, is hereby given some additional evidence.
- The extension of human lifespan, which we are seeing all around us, must also be selected for, or it will die out.
The fact that our increased lifespan is, to some large extent, technology based, does not weaken the above conclusion. We must select for the preservation of that technology, eh? Better health care, increased crop yield, nutritionally enhanced food (flour with vitamins, for example), and safer living conditions (heat, light, lack of wars, lack of predators), all contribute to our newly-increased lifespan.
Since we all seem to want to live almost forever (debilitating illness being the obvious counter-example) we should all be looking to safeguard the technology that assists us to live longer.
This means action against global warming. It means safeguarding energy supplies now, while developing renewable energy and materials. It means limiting population (the source of many wars) and eliminating famine and drought, (the source of some of the rest of the wars) and reducing poverty (the remaining major instigator of conflict).
Otherwise our increased longevity will be short-lived. Events will evolve against us, and the pressure will be to breed early and die crowded.