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A distinction can be made between "proximal ageing" (age-based effects that come about because of factors in the recent past) and "distal ageing" (age-based differences that can be traced to a cause in a person's early life, such as childhood poliomyelitis). [54] Ageing is among the greatest known risk factors for most human diseases.
The categorisation of the past into discrete, quantified named blocks of time is called periodization. [1] This is a list of such named time periods as defined in various fields of study. These can be divided broadly into prehistorical periods and historical periods (when written records began to be kept).
Adult development encompasses the changes that occur in biological and psychological domains of human life from the end of adolescence until the end of one's life. Changes occur at the cellular level and are partially explained by biological theories of adult development and aging. [ 1 ]
Earliest development of bilateral symmetry, mesoderm, head (anterior cephalization) and various gut muscles (and thus peristalsis) and, in the Nephrozoa, nephridia (kidney precursors), coelom (or maybe pseudocoelom), distinct mouth and anus (evolution of through-gut), and possibly even nerve cords and blood vessels. [8]
He distinguishes four stages of human development, based on advances in the history of communication. [70] In the first stage, information is passed by genes. [70] In the second, when humans gain sentience, they can learn and pass information through by experience. [70] In the third, humans start using signs and develop logic. [70]
The age of an adult human is commonly measured in whole years since the day of birth. Fractional years, months, or even weeks may be used to describe the ages of children and infants for finer resolution. The time of day the birth occurred is not commonly considered. In some cultures, there are other ways to express age.
A fetus is a stage in the human development considered to begin nine weeks after fertilization. [4] [5] In biological terms, however, prenatal development is a continuum, with many defining features distinguishing an embryo from a fetus. A fetus is also characterized by the presence of all the major body organs, though they will not yet be ...
The development of the human mind is complex and a debated subject, and may take place in a continuous or discontinuous fashion. [4] Continuous development, like the height of a child, is measurable and quantitative, while discontinuous development is qualitative, like hair or skin color, where those traits fall only under a few specific phenotypes. [5]