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    • If it wasn't for cancer we wouldn't have evolved. If it wasn't for heart disease we also may not have survived as a species. If it wasn't for major diseases in general we wouldn't have come to be. Disease and death to the rescue! Could it be so? Could it be that if human like creatures lived too long we would have lost the evoutionary arms race and become extinct? I'd suggest that this is so.

      If a gene is inside the body of an organism that lives too long then that species and hence gene, would not be able to adapt (via evolution) fast enough to avoid extinction. Do I have proof? Not that I am yet aware of but then I'm not aware of much...I blame evolution for that too since evolution favours quick assessments.

    • Perhaps, but isn't that a bit Panglossian? Best of all possible worlds and all that? Seems to me a more fundamental question is, does human intelligence have long-term evolutionary value? As far as I can see, we've done well for now but the jury is still out.

      In any event, I'm not sure that what you're saying really holds up. The difference between our current lifespan and our lifespan when we first emerged as a species can't be much more than sixty years, which seems too little to have much impact on the results of natural selection on an evolutionary timescale. Perhaps increased longevity would have slowed the selection process some, but I don't know how much our success as a species is based on adaptations that have happened since homo sapiens began. Our capacity for language is probably the most important recent development, but I don't know that enough time has passed for that to have changed much.

      Or have I misunderstood your point?

    • Homo sapien sapien's adaptations have been fundamental in our success as a species among the numerous bipeds that habitated the world in the last 7 million years. Of course the jury is still out on what physical and/or behavioural adaptations had the most effect but certainly our ability to adapt has allowed us to out compete our fellow homo cousins. I also have to say that it's not clear whether or not living shorter lives helped us evolve faster but then that's the question I was asking. I don't see any strong evidence from your argument other than the fact that we don't live to be all that old to begin with which was my point. Under the right circumstances it's advantageous for children to have grandparents around to help look after and teach them but... I still think that keeping our generations shorter is advantageous and anything that lengthens this is probably not very advantageous. If we truly want to live longer then we could make it illegal to have kids before the age of 40 for example. That would create evolutionary pressure against cancer and other disease we get before we are 60 or so.

    • I'm still having a problem wrapping my head around this one--I probably just need more coffee. But let's see--it does seem correct that shorter generation times would increase the variation over a fixed amount of time. But I'm not sure that necessarily would be advantageous--I always thought that most mutations don't matter, but of those that do there are more bad ones than good ones. Perhaps that's incorrect. Still, getting back to the original post, I find it counter-intuitive that a disease that kills you gives an evolutionary advantage. Dunno.

    • The main thing to realize is that it's the timeframe of the disease killing you that is important. Anything that kills humans at a very young age is going to have a very strong evolutionary pressure to be wiped out. That's key. That's also why I said that if we want to increase our average lifespan we could make humans have kids at an older age. That would really increase the evolutionary pressure to eliminate diseases and other detrimental things until the time/age that we have had and raised our kids. Yes I know that there's many reasons why we wouldn't likely take this approach but it helps to illustrate the reason and age at which these diseases start to strike on mass. If a disease strikes us at say age 75 it really has no significant bearing on our evolution because we've already had kids and helped them get to child bearing age and therefore that problem is not really a problem at least for our species to survive.

      If too many of us live too long then overall resources will be reduced and there'd be less opportunities for younger humans to take their place. Younger humans with possible helpful mutations are needed to continue allowing humans to be better adapted to conditions.

      We are a very successful species and therefore most mutations are bad ones. Why would you want to change a good/successful design right? So bad mutations are generally going to be eliminated. Yes many mutations may not be significantly bad per se but if they have even a small deleterious effect they're likely to be eliminated over time. It's almost always only the 'good' or beneficial mutations that survive and help us adapt via evolution. What is good, will depend on what is needed in that habitat and those survival pressures. If we don't evolve fast enough because say we don't have enough beneficial mutations for nature to select from, then we could or would have become extinct.

      I hope my explanation helps clear up at least some of the confusion and makes my argument make more sense.