Ecology refers to the study of natural systems, emphasizing the interdependence of one element in a system upon every other element. Darwin's and Wallace's theories of natural selection were originators of ecological theories. Darwin referred to the "web of life," indicating that in the struggle for existence every species must adapt to both the demands of the physical environment and every other species. Thus, as one species changed the others changed and produced systems in which each island had different life forms. In like manner, human ecology has a wholistic framework. Ecologists argue than one cannot understand one element in nature without considering its surroundings.According to Klausner (1971), "Adaptation is the most important dynamic concept in human ecology [p. 271." It is with regard to this quality that the writings of such diverse individuals as Webber, Darwin, Skinner, and many others are seen as containing a unifying element and becoming integrated into theories of human ecology. We will consider the ecology of aging in terms of the adaptation of man to his environment and his alteration of the environment as part of the process of human adaptation. The aging process itself can be seen as one of continual adaptation: adaptation both to the external M. Powell Lawton received his PhD in clinical psychology from Columbia University in 1952. He has worked in clinical practice and clinical research for the Veterans Administration and the Commonwealth of Pennsylvania. He is presently Director of Behavioral Research at the Philadelphia Geriatric Center. His major research interests are in social gerontology and ecological psychology. He is Secretary of the Gerontological Society, Past-President of the Division on Adult Development and Aging of the American Psychological Association, and Associate Editor for Social Gerontology for the Journal of Gerontology.

This sociometric study examines the friendship network among 270 residents of a city housing project with a high concentration of elderly tenants. The issues of propinquity of residence and similarity of age, race, and sex between chooser and chosen are examined in the context of a theory of social space. An inverse relationship is found between similarity of friends and proximity of residence. Friendships between people of different agss and races are found almost exclusively among those who live very close to one another.

The relationship between neighborhood characteristics and the well-being of elderly tenants was studied through a national area probability sample of 153 planned housing environments and over 3000 tenants in them. Six indices of tenants' psychological and social well-being were used as dependent variables in hierarchical multiple regressions where neighborhood characteristics were entered after personal factors were controlled. Neighborhood environmental factors accounted for a significant proportion of the residual variance in every index of well-being. In general, quiet neighborhoods in small or middle sized communities where the risk of crime was low were conductive to active and satisfying lives for older people. Well-being tended to be higher in segregated buildings even with other factors such as exposure to crime controlled. Although these residual effects were often small it was concluded that environmentally based interventions could significantly enhance wellbeing and in many instances have more widespread effectiveness than time-consuming attempts to change the individual.

The relationship between sponsorship, community size, building size (number of dwelling units) and height of building, on the one hand, and six indices of well-being of elderly tenants, on the other, was examined in a study of 2457 subjects from 154 federally-assisted housing projects. Control was exercised on a variety of personal variables prior to the examination of the environmental relationships to well-being. Private nonprofit sponsorship was associated with higher friendship scores and greater activity participation. Tenants in smaller communities had higher friendship scores, greater housing satisfaction, and greater activity participation. Housing satisfaction was greater in projects that were smaller in terms of total number of units but was not related to size when size was defined in terms of elderly-designated units. Thus, only marginal support for Barker's undermanning hypothesis was found. Greater height of building was associated with lower housing satisfaction and less neighborhood motility.

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