Views of a Foetus in the Womb detail. In humans, ageing represents the accumulation of changes in a human being over time, encompassing physical, psychological, and social changes. Reaction time, gouverner Les Fins De Carrière À Distance: Outplacement Et Vieillissement Actif En Emploi PDF example, may slow with age, while knowledge of world events and wisdom may expand.
Human beings and members of other species, especially animals, necessarily experience ageing and mortality. Early life forms on Earth, starting at least 3. 7 billion years ago, were single-celled organisms. Enlarged ears and noses of old humans are sometimes blamed on continual cartilage growth, but the cause is more probably gravity. A number of characteristic ageing symptoms are experienced by a majority or by a significant proportion of humans during their lifetimes.
In the mid-20s, cognitive decline begins. After peaking in the mid-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 risk for developing presbyopia.
Around age 50, hair turns grey. Menopause typically occurs between 49 and 52 years of age. Many vertebrates such as fish, birds and amphibians do not suffer presbycusis in old age as they are able to regenerate their cochlear sensory cells, whereas mammals including humans have genetically lost this ability. By age 80, more than half of all Americans either have a cataract or have had cataract surgery. Atherosclerosis is classified as an ageing disease.
Recent evidence suggests that age-related risk of death plateaus after age 105. The maximum human lifespan is suggested to be 115 years « for the foreseeable future ». Dementia becomes more common with age. 75 and 84, and nearly half of those over 85 years of age have dementia.