Aging may not be as straightforward as we thought.
A research team looked at how aging varies across species; for example, some species grow weaker and more likely to perish with age while others become stronger and less likely, a University of Southern Denmark news release reported.
"Many people, including scientists, tend to think that [aging] is inevitable and occurs in all organisms on Earth as it does for humans: that every species becomes weaker with age and more likely to die. But that is not the case," evolutionary biologist and assistant professor Owen Jones from the Max-Planck Odense Center at the University of Southern Denmark , said in the news release.
The research team looked at the aging process of "11 mammals, 12 other vertebrates, 10 invertebrates, 12 plants and one algae" ranging from oak trees to lions.
"The diversity of mortality and fertility patterns in these organisms surprised us, and there is clearly a need for more research before we fully understand the evolutionary causes of ageing and become better able to address problems of [aging] in humans," Owen Jones said.
Research on the aging process of invertebrates, fungi, plants, and algae has been scarce.
Animals such as humans, killer whales, and even water fleas grow weaker and less vital with age. Species like the desert tortoise have a high mortality early in life, but the chances of death drop until the animal actually passes away.
The freshwater polyp Hydra magnipapillata has a constant low mortality rate its entire life; the rate is so low some even consider the creature immortal.
"Extrapolation from laboratory data show that even after [1,400] years five per cent of a hydra population kept in these conditions would still be alive," Owen Jones said.
Other organisms that show constant mortality rates throughout their lives include: "rhododendron (Rhododendron maximum), great tit (Parus major), hermit crab (Pagurus longicarpus), common lizard (Lacerta vivapara), collared flycatcher (Ficedula albicollis), viburnum plants (Viburnum furcatum ), oarweed (Laminaria digitata), red abalone (Haliotis rufescens), the plant armed saltbush (Atriplex acanthocarpa), red-legged frog (Rana aurora) and the coral red gorgonian (Paramuricea clavata)," the news release reported.
Fertility patterns also tend to vary in nature. Humans live for a relatively long time both before and after their concentrated fertility period; plant species such as the agave (Agave marmorata) and the rare mountain plants hypericum (Hypericum cumulicola) grow more fertile with age. The nematode is fertile early on in life, and abruptly loses its ability to reproduce.
"It makes no sense to consider ageing to be based on how old a species can become. Instead, it is more interesting to define ageing as being based on the shape of mortality trajectories: whether rates increase, decrease or remain constant with age," Owen Jones said.
