With the number of books, movies, and religions on the topic, it’s pretty safe to say that humans are basically obsessed with the idea of immortality. This might be connected to the fact that as we age, we essentially start to fall apart. Everything from our skin elasticity to vital organs begin to fail as we grow old. This is true for many other animals, but not all of them. Some organisms are able to live and reproduce for centuries on end with no diminished quality of life. How this phenomenon relates to overall lifespan is explained by lead author Owen Jones from the University of Southern Denmark in Nature.
For the study, 46 different species including 23 vertebrates, 10 invertebrates, 12 plants, and 1 algae were compared. The fertility and mortality patterns were examined, and conventional wisdom said that longer lives should lead to senescence; the physical decline experienced during aging.
The researchers found that there actually wasn’t a link. The organisms that experienced the greatest levels of senescence weren’t any more or less likely to have long lives. Among those that do not exhibit much senescence, lifespan length was fairly evenly split as well.
They did find, however, that mammals experience the most senescence with plants on the opposite end, hardly experiencing any ill effects from aging. The birds and invertebrates were evenly distributed between the two extremes. Because there is no predictable link between life span and senescence, this research challenges current evolutionary theories that state that senescence is to be expected because certain genetic diseases (like Huntington’s) don’t appear until later in life, after the organism has given birth. This is how potentially deleterious alleles and mutations are able to persist over time and evade natural selection.
Not everyone is convinced that this research throws a wrench in current theories just yet. The study mostly used lab animals, which do not face the same struggles as wild animals. Without understanding how these life cycles take place in the actual environment when dealing with issues like predators, diseases, and starvation, it is hard to make these conclusions. When using data from field studies, the cause of death was not always made clear, which questions the results of the study. The authors of the article defend their conclusion, claiming that organisms that hadn’t been affected by senescence would be better able to avoid those environmental pitfalls.
While this paper does present an interesting perspective that aging is not experienced equally by all organisms, more research will probably be required before environmental biologists seriously look at revising existing theories.