Why Do We Age? A 46-Species Comparison

2

Why we age is a tricky evolutionary question. A full set of DNA resides in each of our cells, after all, allowing most of them to replicate again and again and again. Why don’t all tissues regenerate forever? Wouldn’t that be evolutionary advantageous?

Since the early 1950s, evolutionary biologists have come up with a few explanations, all of which boil down to this: As we get older, our fertility declines and our probability of dying — by bus collision, sword fight, disease, whatever — increases. That combination means that the genetic underpinnings of aging, whatever they are, don’t reveal themselves until after we reproduce. To use the lingo of evolutionary biology, they’re not subject to selective pressure. And that means that senescence, as W.D. Hamilton wrote in 1966, “is an inevitable outcome of evolution.”

Except when it’s not.

Today in Nature, evolutionary biologist Owen Jones and his colleagues have published a first-of-its-kind comparison of the aging patterns of humans and 45 other species. For folks (myself included) who tend to have a people-centric view of biology, the paper is a crazy, fun ride. Sure, some species are like us, with fertility waning and mortality skyrocketing over time. But lots of species show different patterns — bizarrely different. Some organisms are the opposite of humans, becoming more likely to reproduce and less likely to die with each passing year. Others show a spike in both fertility and mortality in old age. Still others show no change in fertility or mortality over their entire lifespan.

Written By: Virginia Hughes
continue to source article at phenomena.nationalgeographic.com

2 COMMENTS

  1. As far, as I know, the cells of a Hydra are up to one third stem cells. This means, the Hydra carries one Third of it´s weight just in case it gets hurt. Obviously most animals can´t pay this price (more energy and more time to grow up, more energy to feed the bigger body, slower moving and more energy to move the bigger body) just to live longer (if not dieing by accident, illness or getting eaten). So, for example a mouse carrieing around 10 or 20% stem cells to hold it´s body longer in shape is in bigger danger of getting eaten bevore adulthood because it is slower moving and needs more time. And at the time it gets adult, the others without the stem cells will already have reproduced.

    • In reply to #1 by GerhardW:

      As far, as I know, the cells of a Hydra are up to one third stem cells. This means, the Hydra carries one Third of it´s weight just in case it gets hurt. Obviously most animals can´t pay this price (more energy and more time to grow up, more energy to feed the bigger body, slower moving and more ene…

      Yeah, I was recently reading Jared Diamond’s book The Rise and Fall of the Third Chimpanzee, and in that he suggests that ageing is part of a genetic trade-off between maintenance of a pre-existing, complex body and starting from scratch with a new body, depending on external conditions.

Leave a Reply