Ageing

Ageing, or aging as it’s known in American English, is the natural process of growing older, primarily observed in humans, certain animals, and fungi. It encompasses various physical, mental, and social changes that occur over time. While aspects like reaction time may decline with age, factors like memory and knowledge tend to improve. However, ageing also brings increased susceptibility to diseases such as cancer, Alzheimer’s, and cardiovascular issues. In a broader sense, ageing can refer to single cells within an organism which have ceased dividing, or to the population of a species

Current theories of ageing focus on either the accumulation of damage within biological systems or inherent internal processes that contribute to ageing. For instance, DNA oxidation is cited as a source of damage, while epigenetic maintenance like DNA methylation is implicated in programmed ageing. It’s important to note that programmed ageing isn’t the same as programmed cell death. Obesity is thought to hasten the ageing process, while calorie restriction has been shown to slow ageing and maintain health in non-primate animals, though its effects on primates, including humans, are still unclear.

Ageing versus immortality

Human beings, along with many other species including animals and fungi, experience ageing and eventual death. However, some organisms, like bacteria and certain plants such as strawberries and Hydra, possess traits that could be considered potentially immortal. These organisms reproduce asexually, preventing ageing, and can regenerate to avoid death due to old age.

The emergence of sexual reproduction roughly a billion years ago with the advent of fungal and animal kingdoms, and later seed-producing plants around 320 million years ago, introduced ageing and mortality to individual organisms. This reproductive strategy allowed genetic material to be passed on to offspring, making the parent organism dispensable for species survival. Recent findings challenging this notion include observations of distinguishable daughter cells in bacteria like E. coli, hinting at the possibility of “age classes” among bacteria.

Even within mortal species like humans, certain cells possess immortality potential. Cancer cells, for instance, lose their ability to die and can proliferate indefinitely in cell culture, as seen in the HeLa cell line. Additionally, specific stem cells such as germ cells (which produce eggs and sperm) exhibit immortality. Techniques like artificial cloning can rejuvenate adult cells to an embryonic state, allowing for the growth of tissues or organisms without the ageing process. Normal human cells however die after about 50 cell divisions in laboratory culture (the Hayflick Limit, discovered by Leonard Hayflick in 1961)

Ageing symptoms

A number of characteristic ageing symptoms are experienced by a majority or by a significant proportion of humans during their lifetimes.

• Teenagers lose the young child’s ability to hear high-frequency sounds above 20 kHz.
• Wrinkles develop mainly due to photoageing, particularly affecting sun-exposed areas (face).
• After peaking from the late teens to the late 20s, female fertility declines.
• After age 30 the mass of human body is decreased until 70 years and then shows damping oscillations.
• People over 35 years of age are at increasing risk for losing strength in the ciliary muscle of the eyes which leads to difficulty focusing on close objects, or presbyopia.Most people experience presbyopia by age 45–50.The cause is lens hardening by decreasing levels of alpha-crystallin, a process which may be sped up by higher temperatures.
• Around age 50, hair turns grey.Pattern hair loss by the age of 50 affects about 30–50% of males and a quarter of females.
• Menopause typically occurs between 44 and 58 years of age.
• In the 60–64 age cohort, the incidence of osteoarthritis rises to 53%. Only 20% however report disabling osteoarthritis at this age.

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