Ageing

Growing older is a big change.

It happens to people and animals. Some tiny living things do not age at all.

They can live for a very long time.

In people, our bodies change over time. We might get wrinkles on our skin. Our hair can turn grey.

Our eyes might have a hard time seeing close things.

Even as we age, our minds can grow. We get better at knowing many things. We learn more words and facts.

Some people live to be very old. One woman lived to be 122 years old. This is a very long life!

Growing older is a part of life for many.

Growing older is called ageing. It happens to humans, many animals, and fungi.

Most living things age and die. However, some species are potentially immortal. For example, animals called hydras can fix their bodies to avoid dying of old age.

Some plants make clones of themselves to live on.

In humans, ageing brings many changes. Our bodies change in many ways. We might get wrinkles from the sun. Our hair can turn grey by age 55.

Some people find it harder to hear high sounds. Others might have trouble seeing close objects. This happens when the lens in the eye gets hard.

Our minds change too. We often gain more knowledge and better words as we age. But, some people may face memory problems. This includes diseases like Alzheimer's. Scientists study why this happens. They look at damage to cells. They also look at programmed ageing. This is a set of steps inside the body. These steps might follow a biological timetable.

Ageing is the way living things become older over time. This happens to humans, many animals, and fungi.

While most creatures age and die, some are potentially immortal. For example, animals called hydras can fix their bodies to avoid dying of old age.

Some plants, like strawberries, grow runners to make clones of themselves. Even tiny bacteria can sometimes live forever by splitting into new cells. However, some bacteria like E. coli do show signs of ageing.

Scientists have two main ideas about how ageing works. One idea is called the damage concept. This says that tiny bits of damage build up inside a body over time. This damage can happen to our DNA. Another idea is called programmed ageing. This means the body follows an internal timetable to age.

This might be linked to how our genes work. Some researchers also study a tiny worm called C. elegans. It has a short life of only two to three weeks. This helps scientists study how genes affect how long things live.

Humans have studied these changes for a long time. In 1961, a scientist named Leonard Hayflick made a discovery. He found that normal human cells only divide about 50 times in a lab. This is known as the Hayflick limit.

We also know that humans have changed over millions of years. Sexual reproduction appeared about a billion years ago. This allowed living things to pass on genes to new individuals. Seed-producing plants appeared even later, about 320 million years ago. These big changes in history helped shape how life ages today.

Many different things happen to the human body as it ages. By age 55, hair often turns grey.

Many people also find it harder to see things up close by age 45 or 50. This happens because the lens in the eye gets hard. Some people may also develop cataracts, which make the eye lens cloudy. By age 80, more than half of Americans have had a cataract or surgery for one. Other changes include losing strength in muscles or having trouble hearing high sounds. Even our brains change, as the length of certain connections can decrease each decade.

Ageing affects our minds and our social lives too. Our memories and general knowledge often stay strong or even grow. However, some people may face memory loss or diseases like Alzheimer's. These can make it hard to think clearly. Ageing can also make it harder to communicate if hearing or vision fades. This can sometimes lead to feeling lonely or sad. Yet, some older adults find they have a better mood even as their health changes. It is a complex way that life moves forward.

Ageing is the biological process of becoming older over time. It refers to the accumulation of changes in humans, many animals, and fungi. In a broader sense, ageing can describe single cells that stop dividing or entire populations of a species. While many living things age and eventually die, some species are considered potentially immortal. For example, the genus Hydra has a regenerative ability that helps it avoid dying of old age.

Bacteria can also be potentially immortal through fission, which is when they split to create new cells. However, evidence shows that some single-celled organisms, such as the bacterium Escherichia coli and yeast, do experience ageing and death.

Scientists use two main theories to explain why ageing happens. The first is the damage concept. This theory suggests that the accumulation of damage, such as DNA oxidation, causes biological systems to fail. The second is the programmed ageing concept. This theory proposes that internal processes, like DNA methylation, inherently cause ageing through a biological timetable. It is important not to confuse programmed ageing with apoptosis, which is programmed cell death.

Researchers study these mechanisms by looking at how genes regulate maintenance, repair, and defense responses in an organism.

Evolution has played a major role in how ageing works. About one billion years ago, the emergence of the fungal and animal kingdoms introduced eukaryotic sexual reproduction. This allowed organisms to pass genetic material to new individuals. This meant the original organism could become disposable to ensure the survival of its species. Later, about 320 million years ago, seed-producing plants evolved. Even in modern medicine, we see the limits of cell life. In 1961, Leonard Hayflick discovered the Hayflick limit. He found that normal human cells in a laboratory culture only divide about 50 times before they stop.

Human ageing involves many distinct physical changes. As people age, they may experience presbyopia, which is difficulty focusing on close objects. This usually happens between ages 45 and 50 because the eye lens hardens. By age 55, hair often turns grey, and pattern hair loss affects 30% to 50% of males. Many people also experience presbycusis, or hearing loss, as they get older. While many vertebrates like birds can regenerate their hearing cells, mammals like humans have lost this ability.

Additionally, the incidence of osteoarthritis rises to 53% in the 60–64 age group, though only 20% report it as disabling.

The human body also undergoes significant structural and internal changes. After age 30, body mass typically decreases until age 70. Muscles may experience sarcopenia, which is the loss of muscle mass and strength. The cardiovascular system also changes through atherosclerosis, a condition that can lead to strokes or heart attacks. The heart may increase in left ventricular mass, which can eventually lead to heart failure. Vision can also be affected by macular degeneration, which impacts nearly 12% of people over age 80. This is caused by changes in the circulation of waste products and abnormal vessel growth near the retina.

Cognitive changes are another major part of the ageing process. While general knowledge and vocabulary often remain steady or increase, other types of intelligence may decline. After age 20, there is a 10% reduction each decade in the total length of the brain's myelinated axons. Some people may develop dementia, which becomes more common in older age groups. For example, nearly half of people over age 85 may live with dementia. This includes neurodegenerative diseases such as Alzheimer's, Parkinson's, and Lou Gehrig's disease. However, some studies show that older adults may paradoxically report improved moods despite declining physical health.

Ageing is a massive factor in global health and mortality. Of the roughly 150,000 people who die every day worldwide, about two-thirds die from age-related causes. In industrialized nations, this number reaches 90%. The maximum human lifespan is suggested to be around 115 years. The oldest reliably recorded person was Jeanne Calment, who lived to be 122. Scientists continue to use model organisms like the nematode C. elegans to study these patterns. Because C. elegans only lives for two to three weeks, it allows for easier genetic manipulation to understand how to extend lifespans.