Judi’s Reviews > The New Encyclopaedia Britannica Set, Volumes 1-30 > Status Update

Aging, Human
Aging consists of the progressive changes that take place in a cell, an organ, or the total person with the passage of time. It is a process that goes on over the entire adult lifespan and is as much a part of living as are infancy, childhood, and adolescence, The science of gerontology (the study of aging) is concerned primarily with the changes that occur between the attainment of maturity and the...

THE CAUSES OF AGING
External environmental agents Ionizing radiations.
The shortening of life caused b ionizing radiation (e.g., X-rays) has been determined for many species, including mice, rats, hamsters, guinea pigs, and dogs. The occurrence of some disease, such as leukaemia, may increase disproportionate after irradiation, with the degree of increase influenced b age and sex.
The permanent nature of ...

Changes in tissue and cell morphology. There are numerous instances of tissue changes with age. The atrophy of tissues of moderate degree is usual. The shrinkage of the thymus is especially striking and important in view of its role in immunological defense. The diminution of cellular tissue and replacement by fatty or connective tissue is prominent in marrow and in skin, The the kidney, entire secretory...

The inheritance of longevity. The inheritance of longevity in animal populations such as fruit flies and mice is determined by comparing the life tables of numerous inbred populations and some of their hybrids. The longevity of sample populations has been measured for more than 40 inbred strains of mice. Two experiments concur in finding that about 30 percent of longevity variation in female mice is genetically...

Species differences in longevity and aging. That there are large differences in life-span between some species of animals has long been known, but only recently have the data become adequate for statistical analysis.
Maximum lire-span provides an estimate of the potential longevity of mammalian and avian species because of the sharp upper limit of the survival cures in life tables. Also, it. is superior to the...

Aging
Gerontology, the study of the aging process, developed from man's awareness of the inevitability of decline and death, an awareness that has long been a major influence in religions and philosophical systems and continues to shape man's intuitive conceptions about the nature and origin of aging. See the articles LIFE-SPAN and DEATH for related information.

GENERAL FEATURES
Gerontology is devoted to the ...

Defensive displays. In addition to territorial defense, aggressive behaviour may function to terminate some behaviour of a fellow animal. The crying of human infants effectively manipulates mother to remove sources of discomfort or fear; it is misleading to term it aggressive however. In the chimpanzee, screaming tantrums are known to allow infants to win disagreements with the mother and access to food,

Physiological effects on aggressive behaviour. It has long been known that the administration of male sex hormones (androgens) makes aggressive behaviour more likely in many male mammals and birds. It has no effect on aggressive behaviour in female rats and mice, apparently because of the general insensitivity of the female central nervous system to androgens. Male individuals castrated at birth are less ...

Facilitating stimuli. Startling and painful stimuli facilitate attach, which may be directed to objects not associated with the source of pain or startle. The effect has been shown in both rats and squirrel monkeys, following electric shock administered through a floor grid. A clear distinction has usually not been made between attack, defensive threat, and a mixture of the two; but both patterns are clearly ...

GENERAL FEATURES
Most modern theories of aggressive behaviour are based on laboratory experimentation, especially with mice and cats, and on field observations. Mammals show two basic aggressive patterns: attach and defensive threat. Direct evidence from brain-stimulation experiments in marsupials and eutherian (placental) mammals shows that each pattern is a closely coordinated series of events, obtainable in...