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We must start by referring to some astronomical accidents. First, the earth originated in, or settled into, an orbit at a distance from the sun such that, after it evolved its definitive atmosphere, temperatures permitted water to be present in the liquid state over most of the surface, most of the time. This must be a cosmic rarity but was vitally important to the origin of life as we know it. Second, the earth's axis of rotation turned out to be tipped away from normal to the plane of its revolution about the sun. This accident, of course, is responsible for the existence of seasons and thus greatly accentuated the diversity between regions in different latitudes. Another astronomical accident of some sort provided the earth with a moon which, after the oceans developed, was responsible for the existence of an intertidal zone where, eventually, organisms adapted to life in the sea could become tolerant of life out of water and so be prepared to colonize the land.

In 1939 the writer accumulated data bearing upon the relations of desert lizards to environmental conditions of radiant energy and high temperature.1 These data were analyzed with respect to what the writer considered a well-established and fairly obvious principle of animal ecology, namely: that animals might, through natural selection, become adapted in their coloration to the physical conditions of the environment. Recently, stimulated largely by the publication of Cott's "Adaptive Coloration in Animals" (Cott. '39). there has been a revival of interest in animal coloration, in which the relationship of coloration to climatic conditions has been largely overlooked. Despite the fact that Punnett ('15), Dobzhansky ('37), Shull ('36, '37), Hovanitz ('40) and others have called attention to the overemphasis f requently placed upon "protective coloration," the effect of Cott's book, whether intentional or not, has been to deny that the colors observed in animals may be adjusted to the physico-chemical environment. The current tendency seems to be to accept as habitat-adaptations only those cases where the coloration of the individual is directly induced by environmental conditions. In this category might be included those mammals which adopt a white winter coat as a direct response to reduced temperature. Other cases of environmentally induced coloration such as the classical cases described by Poulton ('87) of the effects of colored light on Lepidopterous larvae and pupae are generally described as adaptations entirely to predation factors.

Quantitative methods have long been increasing in importance in ecological studies and certain types of population data may be confidently handled with standard statistical procedures. When dealing with the distribution of living organisms in space, however, the assumption of normality of distribution is often so questionable as to cast doubt on the conclusions reached by means of statistical analysis. Some of the most persistent difficulties encountered in ecological field work stem from the fact that populations of living organisms are very rarely distributed at random over the space available to them. Nor is random distribution, implying that the individual organisms are scattered by chance, to be expected of most biological material. When plants reproduce either vegetatively or by means of seeds there is a tendency for the offspring to be concentrated in the neighborhood of the parent plant. The same is true of animals which produce their young in litters and especially of the many forms which deposit masses of eggs thus temporarily leading to a heavy concentration of individuals within a small area. Most animals furthermore show some tendency toward active congregation. Even the sexual attraction which brings pairs of animals together is a departure from the theoretical conditions necessary to produce a randomly distributed population, while the social instincts which induce the formation of flocks of birds, herds of mammals, and colonies of social insects depart so radically from random processes that no one would expect the density of ants or deer to exhibit any uniformity over a wide area. Both plants and animals also exhibit nonsocial, environmentally-induced congregation which is really an expression of sample heterogeneity. To a greater or less extent the investigator can circumvent intersample variability by selecting as homogeneous areas as possible for sampling, but there is always the possibility that the organisms under investigation were responding to local factors of which the investigator was unaware. Whatever the cause of the departures from randomness, the empirical distributions of organisms belong to the general type which Polya ('31) has termed "contagious distributions," the ecological implication being that the presence of one or more organisms within a sample unit influences the probability of other organisms occurring in the same sample. In most recorded distributions this contagious influence is positive in sign so that the organisms become concentrated into relatively few of the samples, leaving, by contrast with random distribution, an excess of unoccupied units and of densely occupied units, and a deficiency in the number of samples yielding isolated individuals or small numbers of individuals. There is, however, no reason for excepting from this classification those distributions which are "negatively contagious" I as a result of some type of disoperation or antagonism between individuals which causes the organisms to be spaced more regularly than would be expected to result from chance processes. Examples of negative contagiousness are furnished by certain bird colonies in which each nest occupies

Ecology as an autonomous science has existed about as long as genetics, but ecologists have been exceedingly timid about becoming involved in public affairs. Individually, they have lent support to conservation groups in protesting the destruction of natural areas and some of the more flagrant cases of environmental pollution. But only rarely have they shown signs of genuine outrage as many did over some of the programs of predator control in the West.

The part of Cole’s article included here outlines the relationship of Thompson’s work (1931, paper 20 above) to stable population theory. Omitted sections discuss the relationships between the rate of increase, numbers and spacing of offspring, and age structure, with their implications for species survival.

It is contended that there is little justification and no necessity for believing in the competitive exclusion principle as usually formulated. There is danger that a trite maxim like this may lead to the neglect of important evidence.

1955. The distribution of invertebrates on submerged aquatic plant surfaces in Muskee Lake, Colorado. Ecology, 36: 308-314. Scott, Will, Ralph Hile, and H. T. Spieth. 1928. A quantitative study of the bottom fauna of Lake Wawasee (Turkey Lake). Investigations of Indiana Lakes, 1 (1): 5-25. . 1938. The bottom fauna of Tippecanoe Lake. Investigations of Indiana Lakes and Streams, 1(4): 5-16. Wohlschlag, D. E. 1950. Vegetation and invertebrate life in a marl lake. Investigations of Indiana Lakes and Streams, 3(9): 321-372.

Under the intriguing title "Why do we sometimes get nonsense-correlations between time-series?" Yule (1926) brought to general attention some of the properties which impress us as sheer perversity when we attempt to analyze time-series by ordinary statistical methods. Biologists are among those who frequently find themselves concerned with data on fluctuations in time and it seems unfortunate that even modern statistical methods leave much to be desired for the analysis of such data (see, for example, the last 2 chapters of Kendall (1946) ). Although at least 70 years ago Swinton (1883) postulated a connection between locust outbreaks and sunspot numbers, the appearance of Yule's paper approximately coincided with a great upsurge of interest among zoologists in the possibility that animal populations might undergo periodic fluctuations in size. Literally hundreds of papers have been written on the subject analyzing the phenomenon, proposing explanations, or expostulating its importance. Under this virtual barrage of literature it was natural for biologists generally to discount the many conflicts of opinion among students of the subject and to accept the basic hypothesis that there must be some factor or factors either in the physical environment or within populations or ecosystems possessing a tendency to induce rhythmic population fluctuations. It seemed, therefore, an almost outrageous suggestion when Palmgren (1949) proposed to regard population cycles as random fluctuations. This hypothesis, however, had the merit of being susceptible to testing. The consequences of random fluctuation could be deduced and compared with population data in a much more direct way than was possible for any hypothetical remote connection between, for example, an empirical series of sunspot numbers and the population data. The hypothesis of random population fluctuations has the further advantage of being probably the simplest possible explanation for population cycles and in any logical study of the subject it seems that this possibility should be eliminated first before consideration is