Imágenes de páginas
PDF
EPUB

PART I

THE WORLD WE LIVE IN

Chapter I

THE SOCIO-BIOLOGICAL VIEW OF HUMAN NATURE

Fundamental characteristics of living things

The romantic story of evolution has many plots, but perhaps the most interesting of them all tells of the unbroken web of life. All living things without exception are bound by living ties to the past, first of their own kind, and cher through them to yet other kinds, back-far back-until the record is lost in the misty dimness of time. When and where life first appeared on our planet this story does not say; did our earliest progenitors arise from the sea an eon or two ago, under the favoring ministrations of that equable environment, or were they spawned in the heavy airs of some more distant geological age? The past offers no settled answer. It is possible that life has had several distinct beginnings, either at one time or at different times, and dead matter may even now be exploding into life in some corner or other of the cosmos.

Be this as it may, the unfailing continuity of life becomes. most impressive when we trace the stream backwards from the present. The very fact that any one of us is alive today proves conclusively that in one instance there has never been a break in the chain. Indeed, the almost numberless matings between living creatures that fill the past make it extremely probable that we are all members of one great family, even if we do not all come from the same ultimate parents. Speaking broadly, then, we may expect the basic birthright of all life to be identical.

Let us examine this common inheritance by asking ourselves what description would apply equally to a man, a rosebush, an elephant, a worm, and a diphtheria germ. Biologists name the following properties or traits as characteristic of organisms or living things: 1

(1) Cellular organization. Plants and animals of every

kind are composed of highly complex organic compounds,* which form the constituents of "protoplasm." Protoplasm

[merged small][merged small][merged small][merged small][merged small][graphic]

FIG. 1. Various types of cells. A, nerve cell from human cortex; B, epithelial cell from trachea; C, connective tissue cell from rabbit; D, human ovum; E, epithelial cell from human epidermis; F, columnar epithelial cell; G, smooth muscle cell. (From Bailey, Text-book of Histology, 7 ed., N. Y., William Wood and Co., 1925, p. 5.)

differs in its specific constitution in different species, and even within the same species; but in all organisms it combines

*I. e., compounds whose indispensible component is carbon in association with oxygen, hydrogen, and nitrogen and also less frequently with other elements.

« AnteriorContinuar »