Mortality and Aging Not the Same for All Species, Study Suggests

Humans age in a way not necessarily typical in the rest of nature, according to the results of a new study on aging habits of a range of species, which found that while some organisms, like humans, are strong in their youth and grow weaker as they age, the opposite is true for some species, while others seem to be unaffected by age at all.

The researchers, who studied aging in 46 species, including mammals, plants, algae and fungi, report unexpected diversity in aging patterns in a variety of species.

"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," said evolutionary biologist Owen Jones from the Max-Planck Odense Center at the University of Southern Denmark.

Jones and his colleagues report that while some species, such as humans, other mammals and birds, become weaker as they enter old age, other species, such as tortoises and some trees, grow stronger with age, and at least one freshwater polyp does not become stronger or weaker with age.

Writing in the journal Nature, Jones and is team, which includes researchers from Max Planck Institute for Demographic Research in Rostock, Germany, the University of Queensland in Australia, University of Amsterdam in Holland and elsewhere, describe their analysis of aging in a range of species, including 11 mammals, 12 other vertebrates, 10 invertebrates, 12 plants and a green algae.

"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 aging and become better able to address problems of aging in humans," Jones said.

Part of Jones desire of conducting the study stemmed from an abundance of research on the aging process in mammals and birds, but only sparse and incomplete data on aging in other groups of vertebrates and the majority of invertebrates.

While mortality increases with age for some species like humans, whales and even water fleas, it decreases for others, such as the desert tortoise or the white mangrove tree, which exhibit a high instance of mortality early in life that steadily declines with age.

The freshwater polyp Hydra magnipapillata, Jones and his team report, has constantly low mortality, seeming unaffected by age. In a laboratory setting, these polyps can be effectively immortal.

"Extrapolation from laboratory data show that even after 1,400 years, 5 percent of a hydra population kept in these conditions would still be alive," Jones noted.

Numerous organisms across a range of species seem to show little change in mortality with age, the researchers reported, noting the condition in such varied species as great tits, common lizards, red abalone, red-legged frogs, rhododendrons and many others.

The researchers conclude their report by stating that there is no strong correlation between the patterns of aging and the typical lifespan of a species. Organisms can have increasing mortality and still live a long time, or they can have declining mortality and still live a short time.

"It makes no sense to consider aging to be based on how old a species can become. Instead, it is more interesting to define aging as being based on the shape of mortality trajectories: whether rates increase, decrease or remain constant with age," Jones said.