How long should we take to age and die?
Asked another way, how long does natural selection want us to live? Let’s examine the short life by talking about Pacific Salmon. As an Alaskan, I head to Chitina every summer where I’m allowed to dipnet for thirty Copper River Reds. Dipnetting involves standing on the banks of certain rivers at special times of year and netting salmon as they swim upriver. I always feel a little guilty. Some of them have scars from close calls with sea lions and sharks. They survived the open ocean and then I eat them before they can pass on their genes. If you aren’t familiar with the pacific salmon life cycle, they only get one chance. They grow up in the streams, go to the oceans to fatten up for a few years, return to the stream, where they spawn, and then die.
So what causes pacific salmon to die? It doesn’t help that they stop eating once they enter the rivers, and that their bodies, adjusted to seawater, don’t re-adjust to fresh water, but the biggest factor might be buried in their cells. Drastic hormonal changes during spawning shut down many of the fish’s metabolic activities and it’s immune system. It seems that spawning kills them, since castrated salmon live a lot longer. They use all their energy to fight upriver and then they die looking like torn rags thrashing through the water, diseased skin peeling like old wallpaper (lucky for us we eat them long before they get to that state). Are their deaths programmed into their cells in order to make way for the next generation?
Do hormonal changes after peak reproductive years in humans cause aging for us too? I’ll soon have a post about hormonal theories of aging, but think about the advantages of a death gene that kills the old for the sake of the young. In the case of the salmon, parents die and their carcasses feed the forest which provides cover and shade for the salmon fry growing up in the stream. Their parent’s deaths also mean that in two or three years, when the fry go out to the ocean they won’t be competing with their parents for food.
Looking forward, if the human lifespan continues to increase, will there be too much competition for resources as more people are born and fewer die?
Or will technology and ingenuity see us through no matter what?
Looking back, has all the time we spent without life-extending technology programmed us to die, to make way for the next generation? Does natural selection want us dead as soon as possible following our peak reproductive years? I’ll post more about that next Friday, but in the meantime, do you think we should have shorter life expectancies, as a sacrifice for the next generation? Or should we be less like salmon and more like sturgeon, surviving for centuries?